Oxytocin receptors in the oviduct during the oestrous cycle of the ewe

The presence of oxytocin receptors in ovine oviduct has been investigated. High-affinity binding sites for [3H]oxytocin were detected in crude membrane fractions prepared from the oviducts of ewes killed during the oestrous period. The dissociation constant calculated for these sites in competition studies was 1.7 nmol/l. Similar dissociation constants were calculated for [Arg8]-vasopressin and the oxytocin-specific agonists [Gly7]-oxytocin and [Thr4, Gly7]-oxytocin, indicating that these sites represent oxytocin receptors. At least one additional site of lower affinity and undetermined identity was present. The relative concentration of oxytocin-binding sites in preparations of oviduct membranes were estimated in ewes killed at different stages of the oestrous cycle using a single concentration of [3H]oxytocin. Binding was low during the luteal phase of the cycle but increased to a maximum at oestrus (77.7 fmol/mg protein). Binding fell after ovulation, reaching what appeared to be basal concentrations by the early luteal stage of the cycle. Binding to oviductal membranes from prepubertal, anoestrous and pregnant ewes was also low, but in anoestrous animals which had been treated with progesterone and oestrogen it was similar to values measured in ewes at oestrus. These results are consistent with the existence of oviductal oxytocin receptors which are regulated by ovarian steroids. We conclude that oxytocin receptors are present in the oviduct of the ewe around the time of ovulation. The significance of oxytocin to events taking place in the oviduct at this time remains to be determined.     

Characterization and localization of oxytocin receptors in the uterus and oviduct of the non-pregnant ewe using an iodinated receptor antagonist.

Some of the binding characteristics of a novel oxytocin receptor ligand 125I-labelled [1-(beta-mercapto-beta, beta-cyclopentamethylene propionic acid), 2-(ortho-methyl)-Tyr2,Thr4,Orn8,Tyr9-NH2]-vasotocin ([125I]OTA) have been determined in the sheep uterus. The compound was subsequently used for the autoradiographic localization of oxytocin receptors in the uterus and oviduct of the ewe. Specific binding of [125I]OTA to crude membrane fractions of ovine endometrium was time-dependent and was unaffected by the addition of cations to incubation media. Endometrial membranes contained a single population of saturable, high-affinity binding sites for the iodinated ligand (dissociation constant (Kd) 0.23 +/- 0.08 nmol/l) and unlabelled oxytocin competed with [125I]OTA for binding sites with high affinity (Kd 1.29 +/- 0.4 nmol/l) in the presence of Mg2+ In contrast, unlabelled OTA was able to compete with high affinity (Kd 1.13 +/- 0.16 nmol/l) in the absence of cation. Competition studies with a number of oxytocin analogues and related peptides and the tissue distribution of [125I]OTA binding sites also indicated that [125I]OTA bound to the ovine oxytocin receptor. This was further validated by autoradiographic studies which showed specific labelling with [125I]OTA to be greater to uterus and oviduct obtained from ewes which had been killed within 2 days of oestrus than to similar tissue from ewes killed during the luteal phase. In both the ampullary and isthmic regions of the oviduct and the myometrium, [125I]OTA binding sites were confined to smooth muscle. Endometrial binding sites for [125I]OTA were consistently located on the luminal epithelium and epithelial cells lining secretory glands.(ABSTRACT TRUNCATED AT 250 WORDS)     

Control of the preovulatory gonadotropin surge in the ewe

The aims of this study were to determine the effect of ovariectomy on the release of LH and FSH during the preovulatory gonadotropin surge and to ascertain, by the use of sodium pentobarbitone (NaPb), if the secretion of these pituitary hormones requires continuous stimulation from the hypothalamus. Sheep were treated with NaPb for 2 h beginning 1) immediately before the gonadotropin surge, 2) during the ascending limb of the gonadotropin surge, and 3) during the descending limb of the gonadotropin surge. Ewes were ovariectomized (ovx) at each of the time periods listed above, and intact ewes included were at times 2 and 3. A group of intact ewes was given 100 microgram gonadotropin-releasing hormone (GnRH) in addition to NaPb at time 2, NaPb given during the ascending limb of the gonadotropin surge caused a transient fall in peripheral LH and FSH; however, the release of gonadotropins was reinitiated and the surge continued when the ewes recovered from anesthesia. Treatment with NaPb after the apex of the gonadotropin surge did not affect circulating levels of LH and FSH. Ewes given NaPb and ovx before the initiation of the gonadotropin surge released significantly less LH and FSH during the surge than the other treatment groups. The total amounts of LH and FSH released in intact and ovx ewes treated with NaPb after the surge was initiated were not different than those levels in the saline-treated controls. Intact ewes treated with 100 micrograms GnRH also released an amount of LH similar to that in the control group. We conclude that gonadotropin release from the pituitary gland requires the continual presence of GnRH during the ascending limb of the preovulatory gonadotropin surge, and that once the surge has been triggered, the ovaries do not appear to be required for further hypothalamic stimulation.     

Quantification of opioid-binding sites in the ewe hypothalamus

Opioid-binding sites were quantified in the ewe hypothalamus using [3H]diprenorphine ([3H]DIP) as the radioligand. [3H]DIP binding to hypothalamic membrane preparations was stereospecific, saturable with respect to [3H]DIP concentration, and linear with hypothalamic membrane protein content. Scatchard analysis revealed a single class of binding sites. There were no significant differences in binding site concentration or binding affinity in hypothalami from intact ewes during the breeding and non-breeding seasons, or from long-term ovariectomized ewes with and without oestradiol treatment during the breeding season. Thus, whilst ovarian steroid hormones are known to modify LH responses to opioids and their antagonists in the ewe in vivo, they do not appear to do this by modulating the numbers of hypothalamic opioid-binding sites.     

Estrogen receptors in the chick oviduct.

An estradiol binding component has been identified in the cytoplasmic fraction of the immature chick oviduct. The method used to resolve this receptor differed from the standard sucrose gradient centrifugation approach in that tritiated hormone was present throughout the sucrose gradient. This modification was necessary to preserve the hormone complex during centrifugation. Under these conditions, an similar to 8 S binding component was demonstrated which underwent dissociation to a similar to 5 S component in high ionic strength medium. Binding specificity determinations revealed that this receptor preferentially bound estrogens. Quantitative binding analysis showed that a limited class of binding sites was present with a dissociation constant (K-d) for estradiol of similar to 8.6 times 10-10M. These properties indicate that this binding component may function as a biologic receptor for estrogens in the oviduct.     

The photoneuroendocrine control of seasonal breeding in the ewe

The major environmental parameter controlling seasonal breeding in ewes is photoperiod. Short days stimulate, and long days inhibit breeding activity. One of the more intriguing enigmas of neuroendocrinology is the endocrine mechanism whereby a mere change in daylength initiates or prevents estrous cycles. Recent experiments have begun to solve this problem by demonstrating that in ewes, photoperiod governs response of the hypothalamo-pituitary axis to the negative feedback action of estradiol. In long days, estradiol is a potent inhibitor of gonadotropin secretion, whereas in short days it is relatively ineffective in this regard. These photoperiod-induced changes in estradiol feedback are proposed to permit or prevent estrous cycles by controlling the occurrence of a crucial step in the sequence of events leading to ovulation, namely a sustained, preovulatory rise in LH. Thus, estrous cycles cease in long days because an increase in estradiol negative feedback prevents the sustained rise in LH. In short days, estrous cycles resume because a decrease in estradiol feedback permits the sustained rise in LH required for ovulation. Even more puzzling, at present, than the mechanism of transduction of photoperiodic information into an endocrine event controlling seasonal breeding is the problem of transmission of photoperiodic information from the environment to the hypothalamo-pituitary axis. In sheep, early investigations of the transmission pathway have elicited provocative results, only some of which are similar to those obtained in other species. Among the questions which remain to be answered are: what is the location of the photoreceptors, and what, if any, are the roles of the suprachiasmatic nuclei and the pineal in photoperiodic control of seasonal breeding? These issues promise to provide a tantalizing challenge for future investigations into the photoneuroendocrine control of seasonal breeding.     

Endocrine control of uterine oxytocin receptors in the ewe

Specific binding of [3H]oxytocin to high affinity sites (hormone receptors) in membrane preparations from uterine tissues of the ewe has been determined at varying stages of the oestrous cycle and in pregnancy. Mean receptor concentrations in caruncular and intercaruncular endometrium and in myometrium were 14.2, 1.9 and 13.0 fmol/mg protein respectively between days 10 and 13 of the cycle. By the day of oestrus these values had increased to 749, 1085 and 179 fmol/mg protein. These increases in receptor concentrations coincided with luteolysis and falling plasma progesterone levels and followed the preovulatory decline in peripheral oxytocin and rise in ovarian venous oestradiol-17 beta. Receptor concentrations were low in all uterine tissues from pregnant animals between days 14 and 19 after oestrus. Analysis of binding parameters by Scatchard plot suggested a single population of receptor molecules in each of the tissues studied with apparent dissociation constants in the range 1.9-2.2 nmol/l. A number of naturally occurring neurohypophysial peptides inhibited binding of [3H]oxytocin to the receptor from ewes at oestrus; the cross-reactions of arginine vasopressin and vasotocin exceeded that of oxytocin. Use of a receptor binding assay to measure oxytocin in extracts of corpora lutea on days 4 and 10 after oestrus gave values similar to those obtained by radioimmunoassay, suggesting the absence of other receptor-active peptides in the corpus luteum. It is concluded that the oxytocin receptor is present in both components of the endometrium, as well as in the myometrium and that changes in uterine receptor concentrations before oestrus are consistent with receptor activation by steroid hormones.     

Jugular wave recognition breakthrough: X' descent vs the X descent and trough

Irrational nomenclature and concentrating on ascents and peaks of waves have made recognition of jugular waves an occult art. By agreeing to call atrial relaxation X: and the systolic fall in atrial pressure due to the descent of the base X', we can begin to teach the easy recognition of jugular contours. Next, it is necessary to realize that the artifacts seen on electronically derived jugular pulse tracings are not to be expected when observing the neck pulsations with the naked eye. Finally, it can be shown that the easiest way to recognize jugular waves is by timing only descents as being either systolic or diastolic according to their relation to either the patient's radial pulse or heart sounds. It is almost unknown that only a single systolic descent due to the descent of the base is usual in the normal adult jugular.     

Gastroscopy in immigrants of Turkish descent

Background and Aim:  Little data is known on morbidity and Helicobacter pylori in the upper part of the gastrointestinal tract in male and female patients of Turkish descent. A study was done in order to assess the presence of H. pylori in Turkish men and women in relation to the diagnostic yield of the endoscopy.
Methods:  All consecutive patients of Turkish descent were included in the present study. Detection of H. pylori was done with hematoxylin–eosin stain, an immunoperoxidase and Gram stain and culture.
Results:  In 16 years, 2427 procedures (10.4%) were done in Turkish patients. After exclusions, 842 endoscopies in Turkish women and 827 procedures in Turkish men remained. Peptic ulcer disease was diagnosed in 101 (6%) patients and reflux esophagitis in 97 patients (5.8%). Seven patients had cancer. In 749 patients (64%), no macroscopic abnormalities were seen. Turkish men suffered more often from reflux esophagitis (81% vs 19%, P  < 0.0001), hiatus hernia (58% vs 42%, P  < 0.0001) and peptic ulcer disease (74% vs 26%, P  < 0.0001). Women more often showed no abnormalities ( P  < 0.0001). There was no change in the yearly prevalence of reflux esophagitis and peptic ulcer disease in women, while the peptic ulcers decreased, and reflux esophagitis increased in men. Men were significantly more often H. pylori -positive ( P  = 0.03). There was a clear trend towards a decrease in H. pylori -positives.
Conclusion:  There are differences in the presence of ulcer disease and reflux esophagitis between Turkish men and women. Men are significantly more often H. pylori -positive. Prevalence of H. pylori infection in Turkish patients slowly decreases in the consecutive years in both men and women.     

Luteinizing hormone in testicular descent

A proper hypothalamus-pituitary-testis axis with normal androgen synthesis and action is a prerequisite for normal testicular descent. Various defects in this axis may result in cryptorchidism but endocrine abnormalities are rarely detected. Androgens regulate testicular descent but androgen action alone is not sufficient for normal testicular descent. The regulation of androgen production is influenced both by placental human chorionic gonadotropin (hCG) and pituitary luteinizing hormone (LH). There is evidence that the longer pregnancy continues, the more important role pituitary LH may have. Insulin-like hormone-3 (INSL3) is suggested to be the main regulator of gubernacular development and therefore an apparent regulator of testicular descent. INSL3 production is also related to LH, and reduced INSL3 action is a possible cause for cryptorchidism. Cryptorchid boys have normal testosterone levels with slightly but significantly elevated LH levels as compared to healthy boys. This high gonadotropin drive may compensate for mild Leydig cell dysfunction in cryptorchidism.