Long-term non-invasive measurement of intraocular pressure in the rat eye

To study the optic neuropathy associated with glaucoma, a system for accurate, reliable, and non-invasive monitoring of intraocular pressure (IOP) is required. Of particular interest is the effect of sampling frequency on IOP. To address this issue, ten adult male brown Norway rats (group 1) were acclimatized to a 12-h/12-h light/dark cycle. On 20 days over a 30-day period, rats were anesthetized with short-acting isoflurane (Forane) inhalant anesthesia and IOP for each eye was determined by averaging 15 valid individual readings obtained with a TonoPen 2 tonometer. The last 12 measurement sessions were performed on a daily basis. To determine the minimum tolerable interval between IOP measurement sessions, a second group of 10 animals (group 2) was acclimatized in the same manner as group 1, and IOP was measured every 4 days over a period of 80 days. Next, IOP was measured every 4 days over a period of 28 days, and finally, every 2 days over a period of 19 days. For all group 1 measurements, there was no statistically significant difference between the right and left eye IOP, 14.75 +/- 1.08 (SEM) and 14.90 +/- 1.09 mm Hg, respectively. However, daily measurements produced a steady decrease in IOP and gradual weight loss. For group 2, overall mean right and left eye IOPs were 15.24 +/- 1.28 (SEM) and 15.12 +/- 1.26, respectively and were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)     

Circadian rhythm of insulin-induced hypoglycemia in man

Four healthy men were given an insulin tolerance test (0.1 IU/kg BW) six times in different days at the following clock hours: 0400 h, 0800h, 1200 h, 1600 h, 2000 h, and 2400 h, in random order. Four days separated two consecutive tests. The glucose disappearance rate (K value) was calculated for each test between 5 min and 25 min after iv injection of insulin. The statistical evaluation by Cosinor test showed a statistically significant circadian rhythm for the hypoglycemic action of exogenous insulin with a peak at 1030 h (95% condifence limits: 0830 to 1430 h).     

Circadian rhythm of breath hydrogen in young women

PURPOSE: The retention forces of a newly developed compomer cement (Dyract Cem), a glass ionomer cement (Ketac Cem Aplicap), and a resin cement (F21) were examined. MATERIAL AND METHODS: Cemented cast gold crowns were removed along the path of insertion with a Zwick universal testing device. The impact of both a cured and a noncured additional bonding layer that were applied to the inner surface of the crowns was examined across the Dyract Cem group. RESULTS: The mean adhesive strength was measured at 2.36 +/- 0.69 N/mm2 in the Ketac Cem group, at 0.60 +/- 0.28 N/mm2 in the F21 group, and at 1.85 +/- 0.94 N/mm2 in the Dyract Cem group, respectively. The application of an additional bonding layer to the inner surface of the crowns did not significantly improve the retentive strength of Dyract Cem; the respective mean strengths were observed at 1.46 +/-0.33 N/mm2 for the uncured and at 1.70 +/- 0.76 N/mm2 for the cured bonding layers. CONCLUSIONS: Dyract Cem and Ketac Cem showed significantly higher retentive strengths than F21 (p < 0.001, Wilcoxon test, 5% level). No significant difference was found in bond strength between Ketac Cem and Dyract Cem.     

Circadian rhythm of cutaneous hypersensitivity reactions in nocturnal asthma

Results of Gamma nail use in treatment for trochanteric fracture of the femur in 25 patients (15 females, 10 males) aged 45-91 years are presented. There were 12 type I, 9 type II, 3 type III and 1 type IV fracture according to Boyd-Griffin classification. Fracture healed 10-12 weeks after surgery in 24 cases; one patient died because of pulmonary embolism.     

Circadian rhythm of plasma corticosteroids in heroin dependent subjects

The circadian rhythm of corticosteroid secretion was investigated in six heroin dependent subjects by measuring plasma corticosteroids at 09.00 hours and 24.00 hours. All results were within the normal range and it seems unlikely that chronic heroin dependence affects the hypothalamic control of corticosteroid secretion.     

Circadian rhythm in susceptibility of mice to the anti-tumor drug carboplatin

The platinum-containing compounds has become a major chemical agent in the treatment of cancer. A circadian rhythm in the susceptibility of rodents and human being to cisplatin has been demonstrated, the maximal tolerance being found in the animal's active phase. Carboplatin is a second generation analog. Two studies were performed on mice with carboplatin under 12:12 light dark cycle to study its chronotoxicity and chronoeffectiveness. In study I, single intraperitoneal injection of 192mg/kg (LD50) carboplatin was given to four groups of mice at four different circadian stage. It was found that at 50% the overall mortality of mice, there was a mortality difference of 28% for mice receiving the drug at 9 a.m. to 71% for mice receiving drug at 9 p.m. It demonstrated that carboplatin was better tolerated in the animal's early sleep phase. In study II, S180 tumor-bearing mice were treated with 50mg/kg of carboplatin. The longest mean survival time and the lowest marrow toxicity occurred in the group which received the drug at the beginning of the sleep phase. It showed that the susceptibility of mice to carboplatin is circadian stage dependent. These data clearly demonstrate that, by timing the administration of drugs according to body rhythms, such as the host susceptibility-resistance rhythm to a drug, one can gain a therapeutic advantage over an approach which ignores such rhythms.     

Circadian rhythm in plasma concentrations of gamma-hydroxybutyric acid in alcoholics

Gamma-hydroxybutyric acid (GHB) was orally administered to six alcoholics at 09.00 and 23.00 h. The plasma concentrations of GHB show a clear circadian pattern, the area under the curve in the daytime experiments being 61% of that in the night experiments. The significance of alcohol dehydrogenase, the catabolic enzyme of GHB, for the difference is discussed. It is concluded that, although the activity of alcohol dehydrogenase in alcoholics is quantitatively disturbed, it remains subject to physiologic circadian activation.     

Circadian rhythm disorders, motivation and Alzheimer's disease

In Alzheimer's disease, when the breakdown of the sleep's circadian rythm is sudden, it reflects frequently a concomitant somatic or psychiatric disorder. If the trouble appears progressively, there is less pathological or disturbing behaviors in the beginning. Later, it is often associated with a loss of interest for the daily living activities (perte de motivation).     

Circadian rhythm of glomerular filtration rate in patients after kidney transplantation

Within 6 months of a kidney transplantation the graft can be regarded as an organ deprived of its innervation. We analysed whether the transplanted kidney has a diurnal rhythm of its glomerular filtration rate (GFR) similar to the GFR rhythm that has been demonstrated in normal individuals and in patients with nephrotic syndrome. GFR was measured by inulin clearances every 3 h during 1 day of bed-rest and identical food and fluid intake per 3 h in seven patients, 4-7 months after a successful kidney transplantation, and in 10 healthy volunteers. Similar to these healthy subjects, a normal circadian rhythm of GFR was detected in all but one patient with a maximum of 57 (range 45-82) ml/min in daytime, a minimum of 47 (range 36-70) ml/min during the night and a relative amplitude of 21 (range 10-41)%. The circadian rhythm of GFR was absent in the patient with the lowest value of GFR (39 ml/min). In conclusion, GFR has a circadian rhythm in patients studied within 6 months of a kidney transplantation, despite the absence of renal innervation.     

Circadian reactivity rhythm of rat gastric mucosa to restraint-cold stress and indomethacin: temporal variation in the protective effect of iloprost

In this study, the time-dependent ulcerogenic effects of restraint-cold stress and indomethacin on the gastric mucosa and the temporal variation in the protective effect of iloprost, a synthetic stable analog of prostacyclin, were investigated in rats synchronized to 12h light and 12h darkness, lights on at 08:00. The severity of gastric ulceration produced by either stress or indomethacin showed marked circadian variation; it was greatest at 11 HALO (hours after lights on) for restraint-cold stress and at 23 HALO for indomethacin. The severity of the induced ulcerogenesis was least at 7 HALO for both stimuli. The protective effect of iloprost against restraint-cold stress was most prominent at 15 HALO and 19 HALO with an approximately 80% protection score. On the other hand, pretreatment with iloprost reduced the indomethacin-induced mucosal injury only at 23 HALO. The circadian variation in the effect of iloprost and in the rhythmic modalities of these two experimental ulcer models are indicative of differences in their underlying mechanisms. In experimental models of ulceration, the circadian time of application of the ulcerogenic stimulus must be considered as an important experimental factor. Moreover, the protective effectiveness of antiulcer drugs can express time-dependent differences and must also be taken into account in investigative research.     

Circadian rhythm of the cyanobacterium Synechocystis sp. strain PCC 6803 in the dark

The cyanobacterium Synechocystis sp. strain PCC 6803 exhibited circadian rhythms in complete darkness. To monitor a circadian rhythm of the Synechocystis cells in darkness, we introduced a PdnaK1::luxAB gene fusion (S. Aoki, T. Kondo, and M. Ishiura, J. Bacteriol. 177:5606-5611, 1995), which was composed of a promoter region of the Synechocystis dnaK1 gene and a promoterless bacterial luciferase luxAB gene set, as a reporter into the chromosome of a dark-adapted Synechocystis strain. The resulting dnaK1-reporting strain showed bioluminescence rhythms with a period of 25 h (on agar medium supplemented with 5 mM glucose) for at least 7 days in darkness. The rhythms were reset by 12-h-light-12-h-dark cycles, and the period of the rhythms was temperature compensated for between 24 and 31 degrees C. These results indicate that light is not necessary for the oscillation of the circadian clock in Synechocystis.     

Circadian rhythm of heart rate variability is reversibly abolished in ischemic stroke

BACKGROUND AND PURPOSE: Acute brain infarction significantly decreases heart rate variability as a result of cardiovascular autonomic dysregulation. However, information regarding circadian rhythms of heart rate and heart rate variability is limited. METHODS: In this prospective study, we analyzed 24-hour circadian rhythm of heart rate and the time and frequency domain measures of heart rate variability in 24 patients with hemispheric brain infarction, 8 patients with medullary brainstem infarction, and 32 age- and sex-matched healthy control subjects. ECG data were obtained from the patients in the acute phase and at 6 months after the infarction. RESULTS: In the acute phase of stroke, all the components of heart rate variability, ie, standard deviation of RR intervals, total power, high-frequency power, low-frequency power, and very-low-frequency power, were similar at night (from midnight to 6 AM) and during the day (from 9 AM to 9 PM), indicating that the circadian oscillation of heart rate variability had been abolished. At 6 months after brain infarction, the circadian rhythm had returned and, as in the control subjects, the values at night were significantly higher than those in the daytime. The values in hemispheric and in brainstem infarction did not differ significantly from each other. CONCLUSIONS: These results suggest that circadian fluctuation of heart rate variability is reversibly abolished in the acute phase of ischemic stroke and that it returns during the subsequent 6 months. The loss of the relative vagal nocturnal dominance may contribute to the incidence of cardiac arrhythmias and other cardiovascular complications after acute stroke.     

Circadian rhythm of lymphocytes and their glucocorticoid receptors in HIV-infected homosexual men

Glucocorticoids (Gc) are known to modulate protein synthesis by immune cells through binding to a specific receptor (GcR). We outlined the circadian rhythm of plasma cortisol, ACTH, of the peripheral blood mononuclear cells (PBMC isolated by Ficoll-Hypaque technique), and of their subsets CD4, CD8 in 14 asymptomatic HIV+ homosexual men and in nine controls. We also estimated the GcR of the PBMC at 0700 and at 2300 hours, near the peak and nadir of the cortisol rhythm. In the HIV+ subjects, the PBMC circadian rhythm is abolished, an observation that confirms previous reports; in more than half of these patients, the GcR dissociation constant is larger than that of the controls. The circadian rhythms of plasma cortisol and ACTH levels do not differ from those of the controls. These changes may impair the function of the hypothalamic pituitary-adrenal axis in the HIV-infected subject.     

Individual variability in the diurnal intraocular pressure curve

BACKGROUND: Reduction of intraocular pressure (IOP) is a primary goal of most glaucoma treatments. However, because the IOP varies during the day, single measurements performed in an ophthalmologist's office do not necessarily provide information on the peak level and fluctuation of the IOP. METHODS: Home tonometry was performed to gain more information on the nature of the diurnal IOP curves and on their variability. One hundred seventy-six patients with open-angle glaucoma (OAG), 55 subjects with ocular hypertension (OHT), and 18 control individuals measured their IOP five times daily at home for 4 to 8 consecutive days using a self-tonometer. RESULTS: Well-defined diurnal IOP variations were observed in all three groups with a predominance of curves with morning or mid-day maxima. Erratic IOP curves without a diurnal rhythm were present in OHT (22%) and OAG (16%) patients but not in control subjects. Differences between the curves of the two eyes of an individual were frequent in OHT (33%) and OAG (36%) patients but not in control subjects (6%). Finally, the majority of OHT (72%) and OAG (66%) patients showed a difference in their diurnal curve patterns on repeat home tonometry performed months apart. CONCLUSION: The authors indicate that it is difficult to rely on one eye as a control for the other. They also indicate that changes in IOP observed in the office at different visits often may be due to a shift in the type of diurnal curve rather than to a true change in the mean IOP. Monitoring of the diurnal IOP may be necessary in some cases if the clinician relies, even partially, on the level of IOP when making a decision on patient management.     

Digital palpation of intraocular pressure

BACKGROUND AND OBJECTIVE: Previous studies investigating the accuracy of digital palpation through the eyelids to estimate intraocular pressure (IOP) have shown disappointing results. In this study, the accuracy of digital assessment of IOP by palpation of the bare cornea is investigated. MATERIALS AND METHODS: The IOP of a cadaveric eye model was varied from 5 to 40 mm Hg in increments of 5 mm Hg. Two examiners, one experienced and one inexperienced, digitally palpated the corneas and estimated IOP. The results were compared before and after a 1-hour training session. RESULTS: Prior to the training session, the experienced examiner guessed correctly 46% of the time and was correct within 5 mm Hg 100% of the time. The inexperienced examiner guessed correctly 21% of the time and was within 5 mm Hg 62% of the time. After the training session, the experienced examiner's score did not significantly (38% correct, 88% within 5 mm Hg, P = .05. CONCLUSIONS: Digital assessment of IOP by palpation of bare cornea is accurate when performed by experienced individuals. A minimal amount of training using the eye model may improve one's accuracy.     

Circadian rhythm of biosynthetic activity of the epiphysis in relatively wild and domesticated silver foxes

Circadian dynamics of biosynthetic activity in pineal glands of adult relatively wild and domesticated silver fox females was studied beyond the reproductive season using radioimmune and fluorometric methods. The level of melatonin, the principal pineal hormone; activities of enzymes controlling its biosynthesis; the level of its precursor and one of its metabolites, as well as those of neurotransmitters involved in the regulation of biosynthesis exhibited more or less pronounced circadian changes. The concentration of melatonin in the pineal gland at night was considerably higher in domesticated foxes than in relatively wild ones. The most likely reason for the elevated concentration of melatonin at night is its slow secretion from the pineal glands of domesticated foxes, because its concentration in plasma does not differ from that in relatively wild animals. The results obtained suggest that selection for domestic behavior has affected the adrenergic mechanism of regulation of pineal gland rhythms, as well as other functions of sympathetic divisions of the central nervous system.