Biphasic effects of the beta-adrenoceptor agonist, BRL 37344, on glucose utilization in rat isolated skeletal muscle.

1. The effects of the selective beta 3-adrenoceptor agonist, BRL 37344 (BRL) on glucose uptake and phosphorylation (i.e. glucose utilization; GU) and glycogen synthesis in rat isolated soleus and extensor digitorium longus (EDL) muscle preparations in vitro were investigated by use of 2-deoxy-[3H]-glucose (GU) and [U-14C]-glucose (glycogen synthesis). 2. Low concentrations of BRL (10(-11)-10(-9) M) significantly increased GU, with maximal increases of 30% in soleus and 24% in EDL at 10(-11) M. Neither the selective beta 1-adrenoceptor antagonist, atenolol (10(-8)-10(-6) M), nor the selective beta 2-adrenoceptor antagonist, ICI 118551 (10(-8)-10(-6) M) had any effect on the stimulation of GU induced by 10(-11) M BRL. 3. High concentrations of BRL (10(-6)-10(-5) M) caused significant inhibition (up to 30%) of GU in both soleus and EDL muscles. The inhibition of 10(-6) M BRL was blocked completely by 10(-6) and 10(-7) M ICI 118551 in soleus, and by 10(-6)-10(-8) M ICI 118551 in EDL; atenolol (10(-8)-10(6) M) had no effect. 4. Another selective beta 3-adrenoceptor agonist, CL 316,243, also caused a significant stimulation of muscle GU, with maximal increases of 43% at 10(-9) M in soleus and 45% at 10(-10) M in EDL. The stimulation of GU declined with further increases in the concentration of CL 316,243, but no inhibition of GU was seen, even at the highest concentration (10(-5) M) tested. 5. BRL at 10(-5) M inhibited completely insulin-stimulated glycogen synthesis in both soleus and EDL, but this inhibitory effect of BRL was abolished by 10(-6) M ICI 118551. BRL at 10(-11) M (with or without 10(-6) M ICI 118551) had no effect on insulin-stimulated glycogen synthesis. 6. It is concluded that: (i) low (< nM) concentrations of BRL stimulate GU via an atypical beta-adrenoceptor that is resistant to conventional beta 1-adrenoceptor and beta 2-adrenoceptor antagonists; (ii) the stimulation of GU is negated by the activation of beta 2-adrenoceptors that occurs at higher (> nM) concentrations of BRL; (iii) inhibition of GU via beta 2-adrenoceptor activation is associated with inhibition of glycogen synthesis, possibly due to activation of glycogenolysis; (iv) the opposing effects of beta 2-adrenoceptor and atypical beta-adrenoceptor activation on GU suggest that in skeletal muscle these adrenoceptors are linked to different post-receptor pathways.     

Characterization of rat liver beta-adrenoceptors during perinatal development as determined by [125I]-iodopindolol radioligand binding assays.

1. The subtype specificity of beta-adrenoceptors in foetal (20 days post coitum) rat liver membrane preparations has been determined by use of [125I]-iodopindolol binding assays and the characteristics of radioligand binding have been resolved. 2. The kinetics of radioligand association and dissociation (in the presence of 5 x 10(-4) M isoprenaline) showed an association rate constant of 1.5 x 10(7) M-1 S-1 and dissociation rate constant of 9.1 x 10(-4) S-1, corresponding to a dissociation constant for [125I]-iodopindolol of 60.7 pM. A similar dissociation constant (75 pM) was determined by saturation binding assays. 3. The rank order of potency for displacement of [125I]-iodopindolol binding was consistent with binding to a predominantly beta 2-adrenoceptor population (i.e. ICI 118551 greater than isoprenaline greater than adrenaline greater than noradrenaline greater than atenolol). Computer analysis of displacement curves in the presence of a beta 1-subtype selective agent (atenolol) or a beta 2-subtype selective agent (ICI 118551) revealed the presence of beta 2- and beta 1-adrenoceptor subtypes in a ratio of about 80:20%. 4. Saturation binding assays by use of [125I]-iodopindolol were carried out at different perinatal ages to determine total beta-adrenoceptor concentrations and beta 2-subtype (in the presence of 5 x 10(-7) M atenolol) adrenoceptor concentrations. Competition binding assays with atenolol confirmed that at all ages apparent beta 2-adrenoceptor binding accounted for 84-95% of the total beta-adrenoceptor binding. The total beta- and beta 2-adrenoceptor binding capacity increased by 2.3 fold from 20 days post coitum to birth, and then decreased postnatally at 1 and 2 days post partum. The dissociation constant for [125I]-iodopindolol binding did not show any change with age. 5. The change in beta 2-adrenoceptor concentration with age is discussed in relation to the changing beta-adrenoceptor-mediated responsiveness of glucose production by rat liver during perinatal development.     

Identification and characterisation of beta-adrenoceptors in guinea-pig skeletal muscle

(-)-[125I]Iodocyanopindolol (ICYP) was used to characterise beta-adrenoceptors in skeletal muscle of the guinea-pig. The binding if ICYP to soleus and gastrocnemius muscles was saturable and reversible with KD values of 10.7 +/- 1.1 and 11.6 +/- 1.4 pM and Bmax values of 84.0 +/- 5.7 and 59.9 +/- 8.6 fmol/mg protein for gastrocnemius and soleus muscles respectively. Hofstee plots for the selective beta 1-adrenoceptor antagonists atenolol and metoprolol and for the selective beta 2-adrenoceptor antagonist ICI 118551 were linear in both skeletal muscles suggesting the presence of homogenous populations of beta-adrenoceptors. Furthermore, from the Ki values for atenolol (8381 +/- 2063 nM), metoprolol (585 +/- 80 nM) and ICI 118551 (0.39 +/- 0.05 nM) in gastrocnemius and ICI 118551 (0.47 +/- 0.09 nM) in soleus muscle, it is concluded that the beta-adrenoceptors in skeletal muscle of the guinea-pig are predominantly if not exclusively of the beta 2-subtype.     

Regulation of beta-adrenoceptors by catecholamines in the rabbit skeletal muscle

(-)-[125I]Cyanopindolol (ICYP) was used to characterise beta-adrenoceptors in the gastrocnemius muscle of the rabbit. The binding of ICYP was saturable. The KI value for the selective beta 2-adrenoceptor antagonist, ICI 118551, was 0.16 +/- 0.01 nM (mean +/- S.E.M) and for the selective beta 1-adrenoceptor antagonist, metoprolol, was 300.1 +/- 33.3 nM. Hofstee plots for both antagonists were linear indicating the presence of homogeneous beta 2-adrenoceptors in the skeletal muscle of the rabbit. In gastrocnemius muscles obtained from rabbits chronically pretreated in vivo with vehicle (0.1% ascorbic acid), adrenaline (40-50 nmol.kg-1.h-1) or noradrenaline (80-100 nmol.kg-1.h-1) via osmotic mini-pumps implanted for 10 days, the Bmax values were 44 +/- 3, 25 +/- 4 (P less than 0.05) and 41 +/- 7 (fmol.mg-1 protein) and KD values were 7.3 +/- 0.9, 6.3 +/- 0.8 and 9.3 +/- 2.5 (pM), respectively. Thus pretreatment with the circulating hormone adrenaline but not noradrenaline down-regulated the number of skeletal muscle beta 2-adrenoceptors but did not influence the affinity.     

Mechanism of action of apomorphine on rat gastric secretion

The effects of apomorphine on the volume of gastric secretion and its content of H+, K+, Na+ and Cl- were determined in conscious rats having gastric cannulas. Apomorphine dose-dependently (0.25-0.5 mg/kg s.c.) decreased the volume of gastric secretion, its acid concentration and, at the highest dose, Cl- concentration. However, Na+ and K+ concentrations were unchanged. The alpha 1- and alpha 2-adrenoceptor antagonists prazosin (0.25-0.5 mg/kg i.p.) and yohimbine (5-10 mg/kg i.p.), the beta 1- and beta 2-adrenoceptor antagonist propranolol (5 mg/kg i.p.), the beta 2-adrenoceptor antagonist ICI 118551 (1 mg/kg i.p.) and the dopamine receptor antagonists haloperidol (0.25-2.5 mg/kg i.p.), metoclopramide (2.5-10 mg/kg i.p.) or domperidone (2.5 mg/kg i.p.), administered alone, had little or no effect on the volume, H+, Na+ or Cl- concentrations of gastric secretion. Propranolol prevented the action of apomorphine to reduce the volume of gastric secretion but failed to modify the reductions in H+ and Cl- concentrations. The action of propranolol was mimicked by ICI 118551 but not by the beta 1-adrenoceptor antagonist atenolol. Yohimbine, prazosin or domperidone had little or no effect on the actions of apomorphine. Haloperidol (0.5 mg/kg i.p.) and metoclopramide (10 mg/kg i.p.) antagonised apomorphine's action to reduce H+ and Cl- concentrations but significantly enhanced the action of apomorphine to reduce the volume of gastric secretion. The results suggest that the ability of apomorphine to reduce the volume of gastric secretion is mediated via beta 2-adrenoceptors whilst acid concentration is reduced via an action on neuroleptic sensitive receptors.     

Modulation of noradrenergic transmission in the rat isolated portal vein: role of prejunctional alpha 2-adrenoceptors and beta-adrenoceptors.

1. The effect of several adrenoceptor agonists and antagonists on the spontaneous and stimulus-evoked release of [3H]noradrenaline was studied in rat isolated portal vein. 2. Yohimbine (10(-6)M) increased the stimulus-evoked [3H]noradrenaline efflux. Adrenaline alone (3 x 10(-6)M) was without effect, while it increased the resting efflux when added together with yohimbine. 3. Propranolol alone was without effect on the release of [3H]noradrenaline. When added (2 x 10(-6)M) at the same time as yohimbine, it reduced the stimulation-induced 3H efflux. When added before adrenaline and yohimbine, propranolol (10(-5)M) reduced both spontaneous and stimulus-evoked release of [3H]noradrenaline. 4. The effect of several beta-blocking drugs was measured on the enhancing effect of yohimbine on the stimulation-evoked 3H efflux. The beta 1-adrenoceptor blocking drugs: atenolol (5 x 10(-6) and 10(-5) M), metoprolol (5 x 10(-6) and 10(-5) M), like the more selective bisoprolol (2 x 10(-6) and 4 x 10(-6) M) inhibited yohimbine activity. Likewise, propranolol (2 x 10(-6) and 5 x 10(-6)M) and the beta 2-adrenoceptor blocker ICI 118551 exhibited an antagonistic effect. 5. These results indicate the possibility for noradrenaline to activate presynaptic beta-adrenoceptors in rat portal vein. They show an interaction between the presynpatic alpha 2- and beta-adrenoceptor mediated systems in the release of noradrenaline. They suggest the presence and the activity of facilitatory beta 1-adrenoceptors.     

Selective stimulation of glucagon secretion by beta 2-adrenoceptors in isolated islets of Langerhans of the rat.

1. In rat isolated islets of Langerhans the selective beta 2-adrenoceptor agonist, clenbuterol (1 to 20 microM), significantly increased the level of adenosine 3':5'-cyclic monophosphate (cyclic AMP) within 2 min of incubation. 2. The cyclic AMP response to clenbuterol was inhibited in the presence of the selective beta 2 adrenoceptor antagonist, ICI 118551 (0.1 or 10 microM) but remained unchanged when the beta 1-antagonist, atenolol (0.1 microM) was administered. 3. Despite causing an elevation in cyclic AMP, clenbuterol (up to 20 microM) failed to influence insulin secretion at any glucose concentration tested, even in the presence of a phosphodiesterase inhibitor. 4. By contrast, clenbuterol elicited a dose-dependent rise in the rate of glucagon secretion; the maximal agonist-induced increase in secretion was two fold, a response equivalent to that observed with 20 mM L-arginine. 5. ICI 118551 significantly inhibited the rise in glucagon secretion induced by clenbuterol (up to 20 microM). 6. The results indicate that the rat islet A cell population is equipped with functional beta 2-adrenoceptors which influence glucagon secretion via the second messenger cyclic AMP, but that the B cells are deficient in functional beta-receptors.     

Mediation of the positive chronotropic effect of CGP 12177 and cyanopindolol in the pithed rat by atypical beta-adrenoceptors, different from beta 3-adrenoceptors.

1. The influence of beta 1-, beta 2-, and beta 3-adrenoceptor agonists and of CGP 12177 and cyanopindolol on heart rate and diastolic blood pressure was studied in the pithed rat. 2. The beta 1-adrenoceptor agonist, prenalterol, increased heart rate and the beta 2-adrenoceptor agonist, fenoterol, caused a fall in blood pressure. The effect of prenalterol was antagonized by the beta 1-adrenoceptor antagonist, CGP 20712 0.1 mumol kg-1 and the action of fenoterol was attenuated by the beta 2-adrenoceptor antagonist, ICI 118551 0.1 mumol kg-1. Both effects were markedly diminished by the non-selective beta-adrenoceptor antagonist, bupranolol 0.1 mumol kg-1. 3. The non-selective beta-adrenoceptor agonist, isoprenaline, three beta 3-agonists as well as CGP 12177 and cyanopindolol elicited a positive chronotropic effect, exhibiting the following pED delta 60 values (negative log values of the doses increasing heart rate by 60 beats min-1): isoprenaline 10.4, CGP 12177 8.3, cyanopindolol 7.2, BRL 37344 6.9, ZD 2079 5.2 and CL 316243 < 5. 4. CGP 20712 0.1 mumol kg-1, given together with ICI 118551 0.1 mumol kg-1, markedly attenuated the positive chronotropic effect of isoprenaline, BRL 37344, ZD 2079 and CL 316243 without affecting the increase in heart rate produced by CGP 12177 and cyanopindolol. 5. The positive chronotropic effect of CGP 12177 and cyanopindolol was attenuated by CGP 20712, 1 and 10 mumol kg-1 and bupranolol, 10 mumol kg-1 but was not affected by ICI 118551, 10 mumol kg-1. The effect of CGP 12177 was also not changed by BRL 37344 1 mumol kg-1, ZD 2079 10 mumol kg-1, CL 316243 10 mumol kg-1, the alpha 1-adrenoceptor antagonist, prazosin 1 mumol kg-1 and the 5-hydroxytryptamine 5-HT2A receptor antagonist, ketanserin 3 mumol kg-1. 6. CGP 12177 0.002 mumol kg-1 and cyanopindolol 0.003 mumol kg-1 shifted to the right the dose-response curve of prenalterol for its positive chronotropic effect. The -log values of the doses causing a twofold shift to the right were 9.6 and 9.5, respectively. 7. Isoprenaline 0.00001-0.001 mumol kg-1, BRL 37344 0.01-1 mumol kg-1 and CGP 12177 0.1 mumol kg-1 caused a fall in diastolic blood pressure which was markedly attenuated by combined administration of CGP 20712 and ICI 118551, 0.1 mumol kg-1 each. 8. CGP 12177 0.01 and 0.1 mumol kg-1 and cyanopindolol 1 mumol kg-1 elicited an increase in diastolic blood pressure. CGP 20712, ICI 118551, bupranolol and, in the case of CGP 12177, also BRL 37344, ZD 2079, CL 316243, prazosin and ketanserin did not influence this effect. 9. In conclusion, the positive chronotropic effect of CGP 12177 and cyanopindolol is not mediated via beta 1-, beta 2-, beta 3-, alpha 1-adrenoceptors or 5-HT2A receptors. This effect may involve atypical beta-adrenoceptors, similar or identical to those described by Kaumann (1989) in isolated heart preparations.     

The beta 1- and beta 2-adrenoceptor stimulatory effects of alprenolol, oxprenolol and pindolol: a study in the isolated right atrium and uterus of the rat.

The rat isolated right atrium (frequency response) and progesterone-treated rat uterus (relaxation) were used to examine the beta 1- and beta 2-adrenoceptor stimulatory effects of alprenolol, oxprenolol and pindolol. In addition, the beta 1-adrenoceptor stimulatory effect of practolol was studied in the right atrium. All the compounds studied caused a concentration-dependent increase in atrial frequency and relaxation of the uterus. The atrial response to pindolol was competitively inhibited by the beta 1-selective blocker pafenolol (10(-7) M), while the beta 2-selective blocker ICI 118551 (10(-8) M) was without effect. Pafenolol (10(-7) M) was also shown to inhibit the atrial frequency effect of alprenolol and oxprenolol. In the uterus, ICI 118551 (3 X 10(-9) M, 3 X 10(-8) M, 3 X 10(-7) M) blocked the pindolol effect with a pKB of 9.28. In addition, ICI 118551 (10(-8) M) competitively inhibited the relaxation of the uterus induced by alprenolol and oxprenolol. For alprenolol (right atrium and uterus), oxprenolol (right atrium), and pindolol (right atrium), the concentrations needed for half-maximal response were significantly greater than those required for occupation of half the receptors. This dissociation was most pronounced for pindolol in the right atrium. In this tissue, 80-85% of the beta 1-adrenoceptors had to be occupied by pindolol to initiate a tissue response corresponding to 50% of the maximal effect generated by the compound. The intrinsic activities of alprenolol, oxprenolol and pindolol (expressed as % of the maximal tissue response to isoprenaline) were significantly higher in the uterus than in the right atrium.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects and selectivity of beta-adrenoceptor agonists in rat myometrium and urinary bladder

Recent evidence supports a role for beta(3)-adrenoceptors in human non-pregnant and pregnant myometrium. The present study was designed to characterize the pharmacology of beta-adrenoceptors involved in the function of non-pregnant rat myometrium by comparison of the activity of several beta-adrenoceptor agonists and antagonists in isolated rat uterus and urinary bladder. Contractions of myometrial and detrusor strips were induced by adding 1 nM oxytocin and 15 mM KCl respectively. Cumulative concentration-response curves to the selective beta(3)-adrenoceptor agonists, CL 316243 and BRL 37344 and the selective beta(2)-adrenoceptor agonist ritodrine were obtained in the presence and absence of the selective beta(2)-adrenoceptor antagonist ICI 118551 and the non-selective beta-adrenoceptor antagonist bupranolol. Both BRL 37344 (pD(2)=6.79+/-0.09) and ritodrine (pD(2)=6.89+/-0.19) produced potent inhibition of oxytocin-induced contractions in myometrial strips; CL 316243 was inactive at concentrations up to 10 microM. Concentration effect curves to both BRL 37344 and ritodrine were shifted (10 to 30-fold) to the right in the presence of ICI 118551 (10 nM). BRL 37344 (pD(2)=8.51+/-0.21) and CL 316243 (pD(2)=8.61+/-0.24) produced potent inhibition of detrusor strips, while ritodrine was almost 100-fold less potent (pD(2)=5.83+/-0.17). The response to all agonists was significantly attenuated by pretreatment with bupranolol (10 microM), but only ritodrine was affected by ICI 118551 (1 microM). These results demonstrate that relaxation of rat myometrium is mediated by beta(2)-adrenoceptors while, consistent with previous reports, the beta(3)-subtype is primarily responsible for relaxation of rat detrusor.     

Effect of salmeterol on human nasal epithelial cell ciliary beating: inhibition of the ciliotoxin, pyocyanin.

1. Patients with airway infection by Pseudomonas aeruginosa have impaired mucociliary clearance. Pyocyanin is a phenazine pigment produced by P. aeruginosa which is present in the sputum of colonized patients, slows human ciliary beat frequency (CBF) in vitro and slows mucociliary transport in vivo in the guinea-pig. 2. We have investigated the effect of salmeterol, a long-acting beta 2-adrenoceptor agonist, on pyocyanin-induced slowing of human CBF in vitro. Salmeterol (2 x 10(-7) M) was found to reduce pyocycanin (20 micrograms ml-1)-induced slowing of CBF by 53% and the fall in intracellular adenosine 3':5'-cyclic monophosphate (cyclic AMP) by 26% and ATP by 29%. 3. Another beta 2-adrenoceptor agonist, isoprenaline (2 x 10(-7) M), also inhibited pyocyanin-induced slowing of CBF by 39%. 4. The effects of salmeterol (30 min preincubation) persisted after washing the cells. 5. Propranolol (10(-7) M) and the beta 2-specific antagonist, ICI 118551 (10(-6) M) blocked the protective effects of salmeterol completely, but atenolol (10(-6) M) was less effective. These results suggested that the effects of salmeterol on pyocyanin-induced effects were mediated primarily via the stimulation of beta 2-adrenoceptors. 6. Pyocyanin-induced ciliary slowing is associated with a substantial fall in intracellular cyclic AMP and ATP. Salmeterol reversed the effects of pyocyanin on cyclic AMP and ATP. 7. Mucociliary clearance is an important defence mechanism of the airways against bacterial infection. Salmeterol may benefit patients colonized by P. aeruginosa, not only by its bronchodilator action, but also by protecting epithelial cells from pyocyanin-induced slowing of CBF.     

Expression of beta 2-adrenoceptors mediating cyclic AMP accumulation in astroglial and neuronal cell lines derived from the rat CNS

The effect of isoprenaline on cyclic AMP accumulation has been investigated in the rat neuronal cell line B50 and the rat astrocytoma cell line C6. Noradrenaline and isoprenaline stimulated cyclic AMP accumulation in both cell lines. Isoprenaline (0.5 microM; EC50 = 0.1 microM) produced a rapid (T1/2 = 1.3 min) increase in [3H]cyclic AMP accumulation in B50 cells while the response to isoprenaline (0.1 microM; EC50 = 0.01 microM) in C6 cells was somewhat slower (T1/2 = 7.5 min). The response to 0.5 microM isoprenaline was antagonized by both propranolol (IC50 = 8.4 +/- 1.6 nM; N = 3) and the beta 2-selective antagonist ICI 118551 (IC50 = 2.1 +/- 0.2 nM; N = 6). However, no attenuation of the response to isoprenaline (0.5 microM) was observed at concentrations of the beta 1-adrenoceptor antagonist atenolol up to 10 microM (N = 3). In contrast, in C6 cells, which have previously been shown to possess beta 1-adrenoceptors, atenolol inhibited isoprenaline-induced (0.1 microM) cyclic AMP accumulation (IC50 = 2.0 +/- 0.5 microM; N = 6). Furthermore, the beta 2-selective antagonist ICI 118551 was much less potent in the C6 cell line (IC50 = 0.2 +/- 0.05 microM; N = 3) than in the B50 cells. In conclusion, the present data suggest that isoprenaline mediates cyclic AMP accumulation in the neuronal cell line via activation of beta 2-adrenoceptors, while in the astrocytoma cell line the cyclic AMP response is mediated by beta 1-adrenoceptors.     

Prenalterol is an agonist at beta 2- as well as at beta 1-adrenoceptors

Prenalterol exerted agonist activity in cat, but not guinea-pig, isolated atria, which contain predominantly beta 1-adrenoceptors. Prenalterol relaxed K+ -contracted rat uterus, but not histamine-contracted cat lung strips; both contain predominantly beta 2-adrenoceptors. The effect of prenalterol in rat uterus was antagonised by the selective beta 2-adrenoceptor antagonist ICI 118551 but not by the selective beta 1-adrenoceptor antagonist atenolol. Thus the ability of prenalterol to exert beta-adrenoceptor activity is tissue-dependent, rather than beta-adrenoceptor subtype-dependent.     

Beta-adrenoceptors and human skeletal muscle characterisation of receptor subtype and effect of age.

1. Rectus abdominis muscle biopsies were obtained from 28 patients undergoing abdominal surgery. In membranes prepared from these biopsies beta-adrenoceptor binding was examined. The apparent affinity (KD) and the density (Bmax) of the receptors for the radioligand (-)-[125I]cyanopindolol were 28.5 +/- 2.7 (pM) and 25.9 +/- 2.1 (fmol mg-1 protein) (mean +/- s.e. mean) respectively. In forceps biopsies from vastus lateralis muscle from four healthy volunteers the values for KD and Bmax were 22.5 +/- 4.4 (pM) and 16.4 +/- 2.2 (fmol mg-1 protein). The binding characteristics for the radioligand were similar in the biopsies from the two muscle sites. 2. Inhibition of the radioligand binding by the selective beta 2-adrenoceptor antagonist ICI 118551 (KI = 117 +/- 45 nM) and selective beta 1-adrenoceptor antagonist metoprolol (KI = 15229 +/- 5046 nM) suggests the dominance of beta 2-adrenoceptor subtype in human skeletal muscle. 3. There were no significant differences in the skeletal muscle beta-adrenoceptor densities or affinities between the young and older patients.     

Endothelium-dependent noradrenaline-induced relaxation of rat isolated cerebral arteries: pharmacological characterization of receptor subtypes involved.

1. The endothelium-dependence of catecholamine-induced relaxation of rat cerebral arteries was investigated in vitro. 2. In the basilar artery (BA), the maximal relaxant response was most pronounced with noradrenaline (NA), less with isoprenaline (Iso), and only very little with terbutaline. Methoxamine and the alpha 2-adrenoceptor selective agonists BHT 933 and clonidine, had no relaxant effect. 3. In BA, the relaxation by NA or Iso was markedly attenuated by N omega-nitro-L-arginine (L-NOARG) 10(-4) M. Short term perfusion of the vessels by Triton X 100 (1:1,000) suppressed the NA-induced relaxation. 4. The relaxation induced by NA or Iso was markedly reduced in presence of L-NOARG in the posterior, medial and anterior cerebral artery. 5. In BA, NA-induced relaxation was non-competitively inhibited by propranolol, atenolol, and the beta 1- and beta 2-adrenoceptor selective antagonists, CGP 20712 A and ICI 118551. 6. The relaxant NA-effect was not affected by prazosin but was non-competitively blocked by phentolamine. 7. The Iso-induced relaxation was competitively blocked by propranolol, whereas atenolol, CGP 20712 A and ICI 118551 caused a non-competitive inhibition. 8. The experiments indicate that the catecholamine-induced relaxation in rat isolated cerebral arteries depends upon the endothelium. They suggest that the NA-induced relaxation of BA is mediated by different alpha- and beta-adrenoceptors and that the Iso-induced relaxation is mediated by different beta-receptors. The findings would also be compatible with the idea of a receptor type which cannot be characterized by the pharmacological tools that we have used.     

Presynaptic beta-adrenoceptors in guinea pig papillary muscle: evidence for adrenaline-mediated positive feedback on noradrenergic transmission.

Guinea pig papillary muscles were preincubated in the presence of 5 x 10(-9) mol/L unlabeled noradrenaline or adrenaline then incubated with (3H)-noradrenaline and superfused. Electrical field stimulation with 180 pulses delivered at 1 or 3 Hz was used to induce overflow of radioactivity. Comparison of the effects of preexposure of the tissue to adrenaline or noradrenaline revealed that adrenaline incubation caused an enhancement of stimulation-evoked overflow of (3H)noradrenaline and a reduction of the effect of exogenously added isoprenaline. Furthermore, the selective beta 2-adrenoceptor antagonist ICI 118,551 (10(-7) mol/L), but not the selective beta 1-adrenoceptor antagonist ICI 89,406 (10(-7) mol/L), reduced electrically evoked overflow of (3H)noradrenaline in tissue preincubated with adrenaline but not in tissue preincubated with noradrenaline. The overflow-reducing effect of ICI 118.551 occurred at stimulation with 3 Hz but not at stimulation with 1 Hz. The present results support the hypothesis that noradrenergic transmission in guinea pig papillary muscle is facilitated via beta 2-adrenoceptors, and that adrenaline may serve as transmitter in this positive feedback mechanism after its incorporation into sympathetic nerves.     

Tocolytic activity of formoterol against premature delivery in mice

The tocolytic activity of formoterol (eformoterol), a long-acting potent beta(2)-adrenoceptor agonist, was assessed in pregnant mice, with determination of uterine effects on the 15th and 16th days of gestation. For examination in the lipopolysaccharide-induced premature delivery model, osmotic pumps filled with formoterol or saline solution were implanted subcutaneously under the back skin. The mice were sacrificed 18-20 h thereafter, and the numbers of fetuses in the uteri and the newborn were counted. The uteri, amniotic membranes and placenta were also rapidly removed for determination of IL-6 concentrations. Furthermore, the effect of formoterol on IL-6 secretion from mouse amnion cells was determined. Formoterol and ritodrine inhibited contraction responses of isolated mouse uteri and their intravenous administration resulted in lowered uterine motility. Lipopolysaccharide (30 microg mL(-1)/mouse) induced premature delivery, attributable to increased IL-6 secretion, and formoterol suppressed this. Doses of 5-500 microg/mouse thus reduced the number of prematurely delivered newborn, and 50 microg/mouse also depressed IL-6 secretion. On histopathologic analysis, the marked oedema and slight haemorrhage in the mouse cervix induced by lipopolysaccharide were reduced by administration of the beta(2)-adrenoceptor agonist. Neither formoterol (10(-7)-10(-5) M) nor ritodrine (10(-7)-10(-5) M) influenced spontaneous secretion of IL-6 in amnion cells. However, at 10(-7) and 10(-5) M, and 10(-6) and 10(-5) M, respectively, they inhibited lipopolysaccharide-induced IL-6 secretion and this inhibitory effect was competitively reversed by addition of ICI-118,551 (beta(2)-adrenoceptor antagonist), but not atenolol (beta(1)-adrenoceptor antagonist). These findings strongly suggest that formoterol can suppress premature delivery mediated by its actions on IL-6 secretion.     

Autoradiographic localization of beta-adrenoceptors in pig lung using [125I]-iodocyanopindolol.

The binding of the beta-adrenoceptor radioligand [125I]-iodocyanopindolol (I-CYP) has been studied in pig lung parenchyma and the distribution of binding sites visualised by light microscopic autoradiography. I-CYP binding was saturable (maximum binding capacity Bmax = 51 +/- 3 fmol mg-1 protein), involving sites with high affinity (dissociation constant KD = 73 +/- 10 pM). Specific I-CYP binding was displaceable both by beta-adrenoceptor agonists ((-)-isoprenaline greater than (-)-adrenaline greater than (+/-)-fenoterol greater than (-)-noradrenaline greater than (+)-isoprenaline greater than (+/-)-RO363) and antagonists ((+/-)-propranolol greater than ICI-118551 greater than atenolol), indicating a predominance of beta 2-adrenoceptors. Further analysis showed that displacement data for the beta 1-selective antagonist atenolol and the beta 2-selective antagonist ICI-118551 were fitted best to a 2 binding site model and that both beta 1- and beta 2-adrenoceptors were present in pig lung in the ratio 28:72 respectively. Autoradiographic grains were localized over tissue and were most dense over alveolar walls greater than vascular endothelium greater than vascular smooth muscle greater than bronchial smooth muscle = bronchial epithelium. Atenolol (10(-5) M) caused a 31% reduction in specific grain density over alveolar wall tissue, while a 10 fold lower concentration of ICI-118551 (10(-6) M) caused a 50% decrease. These results are consistent with binding data in pig lung parenchyma demonstrating a mixed population of beta-adrenoceptors with a predominance of the beta 2 subtype.(ABSTRACT TRUNCATED AT 250 WORDS)     

The comparative effects of ICI 118551 and propranolol on essential tremor.

1. The effects of the selective beta 2-adrenoceptor antagonist ICI 118551 on essential tremor, heart rate and blood pressure were compared with those of propranolol. 2. ICI 118551 (150 mg daily for 7 days) and propranolol (120 mg daily for 7 days) were about equally effective in reducing essential tremor (by about 40%) and were more effective than placebo. 3. When compared with the effect of placebo, propranolol reduced blood pressure and exercise heart rate whereas ICI 118551 had no significant effect on blood pressure and produced a small but significant reduction in exercise-induced tachycardia. 4. ICI 118551 may be useful in the management of essential tremor while having fewer cardiovascular side-effects than non-selective beta-adrenoceptor antagonists.     

Heterogenic contractile response of rat left ventricular myocytes to beta1-adrenoceptor stimulation

We measured the contractile response of left ventricular cardiac myocytes from female rats to selective beta(1)-adrenoceptor stimulation (isoprenaline, 10(-8) M and 10(-7) M in the presence of 10(-7) M ICI 118,551 a beta2-adrenoceptor inverse agonist). A heterogenic response to stimulation, inversely related to the extent of cell shortening prior to adrenergic stimulation, was observed. Challenge of cardiac myocytes with a selective beta1-antagonist, atenolol (10(-7) M), suggests the heterogenic response is not caused by basal beta1-adrenoceptor activity. Thus, basal myocyte contractility determines the response to beta1-adrenoceptor stimulation, this should be taken into account when experimental conditions are designed.