Showing papers on "Morning published in 1989"

Morning increase in onset of ischemic stroke.

Abstract: The time of onset of ischemic stroke was determined for 1,167 of 1,273 patients during the collection of data by four academic hospital centers between June 30, 1983, and June 30, 1986. More strokes occurred in awake patients from 10:00 AM to noon than during any other 2-hour interval. The incidence of stroke onset declined steadily during the remainder of the day and early evening. The onset of stroke is least likely to occur in the late evening, before midnight.

Diurnal variation of tissue-type plasminogen activator and its rapid inhibitor (PAI-1).

Abstract: Previous studies have shown that overall fibrinolytic activity in blood follows a diurnal rhythm with a peak in the morning and a trough in the evening. The purpose of this study was to determine which fibrinolytic factor(s) was responsible for this diurnal rhythm. Resting and postvenous occlusion tissue-type plasminogen activator (t-PA) activity, resting t-PA antigen, and resting plasminogen activator inhibitor 1 (PAI-1) activity were measured in the morning and evening in 33 healthy men (mean age, 31 years) and in 15 patients (mean age, 57 years) with previous myocardial infarction or unstable angina. PAI-1 activity and t-PA antigen were significantly higher (p less than 0.01) in the morning compared with the evening in controls and patients. In contrast, resting t-PA activity was significantly lower in the morning (p less than 0.01) in both groups and was inversely correlated with PAI-1 activity (r = -0.57, p less than 0.0001). Postvenous occlusion t-PA activity and t-PA capacity were not significantly different between morning and evening in either group. Because t-PA antigen levels and PAI-1 activity were highest in the morning, the variation in t-PA activity was probably not due to decreased secretion of t-PA but instead to changes in the secretion of PAI-1. Our findings indicate that diurnal variations in PAI-1 activity may reduce fibrinolytic activity in the morning in healthy individuals and in patients with coronary artery disease.

Increased morning incidence of myocardial infarction in the ISAM Study: absence with prior beta-adrenergic blockade. ISAM Study Group.

Abstract: The time of acute myocardial infarction was determined in all 1,741 patients of the ISAM (Intravenous Streptokinase in Acute Myocardial Infarction) Study, based on onset of clinical symptoms and evaluation of plasma CK-MB enzyme time-activity curves. The incidence of myocardial infarction was markedly increased between 6:00 AM and 12:00 noon compared with other times of day (p less than 0.001). Myocardial infarction occurred 3.8 times more frequently between 8:00 and 9:00 AM (hour of maximum incidence) than between 12:00 midnight and 1:00 AM (hour of minimum incidence). Time of myocardial infarction based on clinical and enzymatic methods correlated well (r = 0.95). Patients with higher or lower left ventricular ejection fraction, higher or lower degree of wall motion abnormalities and residual stenosis of the coronary arteries, and one-, two-, or three-vessel disease exhibited a similar circadian pattern, suggesting that the morning is a risk period for patients with mild as well as severe coronary artery disease. Only the group of patients receiving beta-adrenergic blocking therapy before the event did not show an increased morning incidence of myocardial infarction. This observation may contribute to an understanding of the mechanisms by which beta-blockers reduce the incidence of myocardial infarction. Further investigation of physiologic changes occurring during the morning period of increased risk of myocardial infarction may lead to better understanding of the disorder. Design and timing of cardioprotective medication may play a crucial role in improving prevention of acute myocardial infarction.

Diurnal variation in the Positive Affects

Abstract: We examined the circadian rhythm of two basic dimensions of mood—Positive Affect (PA) and Negative Affect (NA). Subjects were 196 college students in two studies who completed a mood rating form approximately seven times a day for 1 week. Significant diurnal variation was found to exist in overall Positive Affect, and in four component content areas, but not in Negative Affect. Specifically, all components of PA rose sharply from early morning until noon, remained relatively constant until 9 p.m., and then fell rapidly. The rise and fall of PA were quite robust across subjects, but the apparently static level of PA from noon to 9 p.m. was shown to result from averaging across marked individual differences in the time of peak PA. Various potential sources of these individual differences—“morningness-eveningness,” introversion-extraversion, and neuroticism/dysphoria—were investigated. Neither of the personality variables accounted for the significant variation in diurnal mood patterning, but clearly defined morning and evening types did show different patterns. Possible links between the mood pattern obtained and biologically based circadian rhythms, which have been postulated to be dysregulated in depression and mania, are discussed.

Differing circadian patterns of symptom onset in subgroups of patients with acute myocardial infarction.

Abstract: Circadian variation of the onset of acute myocardial infarction has been noted in many studies and may carry important pathophysiologic implications. However, only a few previous studies have attempted subgroup analyses. In 4,796 patients with documented acute myocardial infarction, the time of symptom onset was recorded. As in other studies, the peak of onset occurred in the morning from 6:01 AM to 12:00 noon, and 28% of the population (1.16 times the average percentage for the other time periods) experienced symptom onset in that period (p less than 0.001). There was a second, lower peak (25%) in the evening between 6:01 PM and 12:00 midnight, which was also observed in some previous studies. We sought to determine whether or not the presence of subgroups with specific clinical characteristics would exhibit different patterns and thereby contribute to these peaks in the overall population. In patients with a history of congestive heart failure (n = 606) or with non-Q wave infarction (n = 832), a pronounced peak (29%) occurred only in the evening. Two nearly equal peaks were observed in patients older than 70 years of age (n = 1,422), smokers (n = 2,057), diabetics (n = 767), women (n = 1,213), and patients taking beta-blocking drugs (n = 847). Finally, in patients with a previous myocardial infarction (n = 1,104), no peaks were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo release of luteinizing hormone releasing hormone increases with puberty in the female rhesus monkey.

Abstract: To determine the regulatory mechanism of the LHRH release associated with puberty, episodic release of LHRH from the stalk-median eminence was measured using a push-pull perfusion technique in conscious prepubertal and peripubertal female monkeys. After insertion of a push-pull cannula into the stalk-median eminence, a modified Krebs-Ringer phosphate buffer solution was infused through the push-cannula, and perfusates were collected through the pull-cannula at 200 microliters/10 min. LHRH in perfusates was determined by RIA. Two 6-h sampling sessions, in the morning (0600-1200 h; lights on 0600 h) and in the evening (1800-2400 h; lights off 1800 h) were performed in each animal. LHRH release patterns were analyzed in prepubertal (15.7 +/- 0.7 months of age; mean +/- SEM, n = 6) early pubertal (premenarcheal; 26.1 +/- 1.0 months, n = 7), and midpubertal (40.0 +/- 1.4 months, n = 6) monkeys. Results were as follows: 1) LHRH release was pulsatile in all age groups. While LHRH release in five of six prepubertal animals consisted of small (amplitude less than 2.5 pg/ml) pulses, in all peripubertal animals LHRH release was a mixture of small and large (amplitude greater than 2.5 pg/ml) pulses. 2) There was a significant developmental increase in mean LHRH release (P less than 0.02), and this was particularly apparent in the evening. Mean LHRH release in the early and midpubertal groups was higher than that in the prepubertal group (P less than 0.05 for morning and P less than 0.01 for evening). The mean release in the evening of the midpubertal group further increased over that of the early pubertal group (P less than 0.05). 3) Similarly, LHRH pulse amplitude increased developmentally (P less than 0.01). Pulse amplitudes in early and midpubertal groups were higher than those in the prepubertal group (P less than 0.05 for morning and P less than 0.02 for evening). Again the amplitude in the evening further increased from the early pubertal to the midpubertal period (P less than 0.05). 4) There was also a developmental increase in basal LHRH release (P less than 0.01). The evening values in the early pubertal and midpubertal groups were higher than those in the prepubertal group (P less than 0.05). 5) The interpulse interval decreased developmentally (P less than 0.001). Interpulse intervals in early and midpubertal groups were shorter than those in the prepubertal group (P less than 0.01 for morning and P less than 0.025 for evening).(ABSTRACT TRUNCATED AT 400 WORDS)

Propranolol and the morning increase in the frequency of sudden cardiac death (BHAT study)

Abstract: Sudden cardiac death (SCD) is a major problem confronting cardiology. We need to know more about the mechanisms responsible for its occurrence so that preventive measures may be designed. Recent evidence shows a morning increase in SCD,1,2 similar to the morning increase in myocardial infarction3,4 and transient myocardial ischemia.5 This suggests that increased sympathetic activity associated with assumption of the upright posture may be involved. Beta blockers have been shown to eliminate the morning increase in myocardial ischemia and infarction.3–5 Accordingly, we examined the timing of out-of-hospital SCD in the Beta Blocker Heart Attack Trial (BHAT) population to determine (1) if this morning increase was present in the placebo group and (2) whether it was eliminated by the use of β blockers.

Twenty-four-hour ambulatory blood pressure in shift workers.

Abstract: Blood pressure and heart rate of 15 male shift workers were measured every 15 minutes for 24 hours during three work shifts: morning, 4:00 AM to noon; afternoon, noon to 8:00 PM; and night, 8:00 PM to 4:00 AM. For each shift, 24-hour systolic and diastolic blood pressure showed a large "trough" (the low pressure span) and a continuous range of elevated pressure (the high pressure span). Fourier series were used to model the 24-hour blood pressure profiles. A careful examination of the residuals (measured minus predicted pressures) showed that four harmonics were necessary to describe the data accurately. The model enabled localization in each blood pressure profile of the high and low pressure spans that did not coincide with the subject's work and rest periods. The time and slope of blood pressure entering and leaving these spans could also be individually determined. Mean blood pressure during the high pressure span was the same for the three shifts, but mean blood pressure during the low pressure span was lower when the subject worked in the afternoon. During that shift, the systolic blood pressure slopes entering and leaving the low pressure span were steeper than during the two other shifts. The high pressure span was longest during the night shift and shortest during the afternoon shift. Therefore, a change in the working time profoundly perturbed the 24-hour blood pressure profile.(ABSTRACT TRUNCATED AT 250 WORDS)

Twenty-four-hour blood pressure is not dependent on endogenous circadian rhythm

Abstract: The effects of shifted working and sleeping phases on the diurnal blood pressure rhythm were investigated in 15 physically working industrial shift workers at a slowly rotated three-shift system. Ambulatory 24-h blood pressure monitoring was performed during the morning and night shifts. In the two

Diurnal variations in serum biochemical and haematological measurements.

Abstract: Twenty five biochemical and haematological measurements were determined on nonfasting blood and serum samples collected between 9 am and 7 pm from a representative group of 7685 British middle-aged men. Most measurements showed significant diurnal variations, but only for bilirubin, phosphate, and triglyceride did time of day account for more than 5% of the between subject variance. Serum bilirubin concentrations showed a pronounced downward trend in the afternoon, the mean value after 6 pm being 30% lower than the mean value in the morning. Mean serum triglyceride and phosphate concentrations increased steadily through the day. Mean concentrations of potassium, haemoglobin, and haematocrit and red cell count were higher in the morning, while urea and creatinine concentrations and white cell count had higher means in the afternoon. Glucose showed a pattern consistent with short term response to meals. The effects of these diurnal trends on routine use of biochemical tests needs careful consideration, and a greater understanding of their biological mechanisms is required.

Seasonal and diurnal body weight variations in titmice, based on analyses of individual birds

Abstract: ABsTRAcr.-The main aim of this study was to test different graphical models showing possible patterns of seasonal and diurnal body weight cycles in passerines as proposed by Lehikoinen (1987). About 13,300 weight records of five different European tit species (Great Tit Parus major, Blue Tit P. caeruleus, Coal Tit P. ater, Marsh Tit P. palustris, Willow Tit P. montanus) were collected in the period from August 1987 to April 1988 at two study areas in central Norway (61040' and 631 S'N). To get sufficient weight data at desirable times of the day (in the early morning, at noon, and in the evening), an electronic balance was used as a bird table. The data collected allowed an analysis of the weight cycles for individual birds. Most birds, regardless of species, followed the "winter fattening strategy," i.e., both the morning weight, noon weight, and evening weight increased during autumn, reached a midwinter peak (usually in December), and then declined. One dominant Great Tit male deviated from this pattern and decreased in weight from September onwards, apparently for reasons other than starvation or competition with other birds. This trend may be related to its high-ranking status in the social hierarchy. It is argued that the weight variations in titmice are controlled by the photoperiod and air temperature, with photoperiod as the prime factor.

Morning versus evening bright light treatment of late luteal phase dysphoric disorder

Abstract: Six women with late luteal phase dysphoric disorder had a significant reduction in depression ratings after treatment with evening, but not morning, bright light. Bright light may offer an alternative to the pharmacologic treatment of premenstrual mood disorders.

Dose-response effects of methylphenidate on academic performance and overt behavior in hyperactive children.

Abstract: In the present study, the effects of 0.3 mg/ kg and 1.0 mg/kg of methylphenidate on the overt behavior and academic functioning of 12 children with an established diagnosis of attention deficit disorder with hyperactivity were evaluated. A double-blind, placebo-control, within-subject (crossover) design was used, in which each child was tested four times in each drug condition. Drug conditions were alternated on a bidaily basis and each child received two different drug conditions each day. The academic tasks were designed for evaluation of the relationship between task complexity and dose. Whereas overt behavior improved with increasing dose, academic functioning was improved with methylphenidate, but did not vary with either dose or task complexity. Also, investigated were potential carryover effects of a morning dose of methylphenidate on performance in the afternoon. Behavioral and academic improvements produced by a dose of 0.3 mg/kg in the morning were no longer evident in the afternoon, but a morning dose of 1.0 mg/kg produced behavioral improvements that were clinically and statistically discernible in the afternoon, although the academic improvements had dissipated.

Fluctuation in grip and pinch strength among normal subjects.

Abstract: Grip and pinch strength testing are commonly used to evaluate hand strength for disability ratings and to assess responses to various forms of therapy. This study determined the variations in grip and pinch strength in normal individuals. Ninety-five healthy subjects--61 women and 34 men--were examined prospectively by use of a Jamar dynamometer and a Preston pinch gauge. Grip and pinch were measured in the morning and afternoon twice a week for 3 weeks, giving a total of 12 testing periods. Mean grip strength fluctuated between 5.1 and 8.4 kg, or between 19.2% and 23.7%. Mean lateral pinch strength fluctuated between 2.6 and 3.8 pounds, or between 13.8% and 17.6%. There were no differences between the morning and afternoon values. Grip and pinch strength fluctuate over time. Repeat testing is necessary to accurately assess hand strength. Grip and pinch strength do not vary from morning to afternoon.

Differential effects of a new central adrenergic agonist--modafinil--and D-amphetamine on sleep and early morning behaviour in young healthy volunteers.

Abstract: Modafinil (CRL 40476) is a recently developed central alpha adrenergic agonist with vigilance-promoting properties. In a double-blind, placebo-controlled sleep laboratory study, its single-dose effects on objectively and subjectively evaluated sleep, morning awakening, and early morning behaviour were investigated and compared with amphetamine. Ten young healthy volunteers of both sexes spent 12 nights in the sleep laboratory: one adaptation night, one baseline night, five drug nights (100 mg and 200 mg modafinil; 10 mg and 20 mg d-amphetamine; placebo) and five subsequent washout nights. The drugs were administered in one week intervals according to a Latin square design. Somnopolygraphic investigations were performed between 22h30 and 06h00. Subjects received the drug orally half an hour before bedtime. A self-rating scale for sleep and awakening quality and early morning behavior was completed subsequent to the morning toilet. Thereafter, noopsychic and thymopsychic variables were evaluated utilizing a psychometric test-battery. Statistical analyses of objective sleep variables demonstrated that modafinil causes no significant changes as compared to a placebo. Sleep initiation remained unchanged after all of the drugs, while sleep maintenance was impaired dose-dependently after d-amphetamine. Thus, total sleep time and sleep efficiency decreased significantly after 20 mg d-amphetamine as compared to the placebo and modafinil. In regard to sleep architecture a reduction of sleep stage 2 and rapid eye movement-sleep occurred under d-amphetamine while modafinil did not exhibit such an effect. Subjective sleep quality was significantly better after modafinil than after the reference compound. Subjective awakening quality and well-being in the morning did not show any significant findings. Furthermore, no differences were observed between the placebo and the other drugs concerning objective awakening quality (evaluated by psychometric tests). Critical flicker frequency increased significantly after 20 mg d-amphetamine as compared to the placebo. Pulse rate and evening and morning blood pressure remained unchanged. These data stress the necessity to differentiate between "vigility-increasing" properties of amphetamine and "vigilance-promoting" properties of modafinil.

Twenty-four-hour structure of sleepiness in morning and evening persons investigated by ultrashort sleep-wake cycle.

Abstract: "Morning" and "evening" persons, defined according to a modified version of the Horne and Ostberg questionnaire, performed the 7/13 min sleep-waking schedule under attempting sleep condition after sleeping for one night in the laboratory, and under the resisting sleep condition after one night of sleep deprivation. Morning types slept significantly more under the attempting sleep condition and showed an earlier rise in nocturnal sleepiness. After sleep deprivation, morning types had a more distinct sleep propensity pattern with well-defined midafternoon and nocturnal sleep gates. In this condition there was a significant interaction between type and time of day with respect to amount of sleep: morning types slept more during the night, and evening types slept more during the day. Based on their amounts of sleep, subjects were also divided into "sleepy" and "alert" types, which were independent from the chronotypology.

Circadian specificity in exercise training

Abstract: The purpose of this study was to determine whether metabolic and cardiorespiratory adaptations to exercise training are greater at the time of day of training than at another time. Twenty-seven subjects performed cycle ergometer tests in the morning (AM) and in the afternoon (PM) before and after a 6-wk period during which ten subjects trained regularly in the morning, seven subjects trained in the afternoon, and ten did not train. Training caused decreases in HR, VE, and rating of perceived exertion during submaximal exercise; a 7.7% increase (p less than 0.01) in VO2 max; and a 9.1% increase (p less than 0.01) in performance time. Adaptations (training effects) were independent of time of day of training for all variables except VO2 at the ventilatory threshold. Compared with each other, subjects who trained in the morning had relatively higher post-training thresholds in the morning, while subjects who trained in the afternoon had relatively higher values in the afternoon (p less than 0.05). This is evidence of circadian specificity in training and supports the notion of planning physical preparation to coincide with the time of day at which one's critical performance is scheduled.

Daytime napping and its effects on alertness and short-term memory performance in shiftworkers.

Abstract: Daytime napping and its effects on 145 female shiftworkers were studied by comparing the individual characteristics, alertness, and short-term memory performance of subjects who took or did not take naps. Of the subjects 56% (n = 82) took a nap before a night shift and 21% (n = 30) after a morning shift. After a morning shift, napping was more frequent among evening types and subjects living alone (not married). Before a night shift, daytime napping was not connected to individual characteristics, but the total sleep time of nappers during the preceding night was shorter than that of non-nappers. At 10.00 and at 04.00-08.00, at the end of the night shift, nappers were significantly more alert than subjects who had not taken naps. The length and timing of the daytime nap did not correlate to either alertness or performance during the following night. In a questionnaire, nappers before a night shift had less sleep disturbances than non-nappers.

Salivary testosterone levels in males from the Ituri Forest of Zaïre

Abstract: Morning and evening testosterone levels were measured in the saliva of Efe pygmies (N = 11) and Lese villagers (N = 18) living in the Ituri Forest of northeast Zaire and compared with levels in Boston controls (N = 10). With one exception, levels in the individual Zairois subjects fall within the normal ranges reported for Western clinical populations. Daily variation in the Zairois subjects (a.m./p.m. ratio = 1.32 for Efe, 1.22 for Lese) is also comparable to both the Boston controls (1.61) and values reported by other researchers for Western subjects. Average morning levels for the Zairois subjects (420 pmol/liter for Efe, 341 pmol/liter for Lese), however, fall significantly below the average for the Boston subjects (589 pmol/liter; Efe, P <0.05; Lese, P <0.01). A correlation between morning testosterone level and height is observed for the Lese sample (r=0.76, P <0.005). Similar correlations have not been reported for Western subjects. Possible roles of acute and chronic environmental conditions in generating these observations are noted. This study demonstrates the potential utility of salivary steroid assays for investigating questions related to male gonadal function under field conditions.

Morning increase of onset of myocardial infarction. Implications concerning triggering events.

Abstract: During the past 5 years it has been clearly established that there is a prominent morning increase in the frequency of onset of acute myocardial infarction. Similar increases have also been observed for the related conditions of sudden cardiac death, stroke and episodes of transient myocardial ischemia. The period from 6 a.m. to noon is also a time when a number of physiologic processes that could contribute to the onset of coronary thrombosis are intensified. Arterial pressure, which could lead to plaque rupture, rises; coronary tone increases; and platelet aggregability, which could contribute to a hypercoagulable state, increases. The immediate significance of these observations is the emphasis that should be placed on pharmacologic protection of patients during the morning hours. The primary longer-term significance of the recognition of the morning increase of onset of acute cardiovascular disease is the contribution it makes to the concept that onset of coronary thrombosis at any time of the day is frequently triggered by the activities of the patient. Investigation of this possibility may yield more information about the mechanism of disease onset and facilitate design of more effective preventive therapy.

Effect of Time of Day on Perceived Exertion at Work Rates above and below the Ventilatory Threshold

Abstract: The effect of time of day on ratings of perceived exertion (RPE) at various intensities of cycling exercise, both below and above the ventilatory threshold, was studied in 32 subjects, 18 to 35 years of age. The ventilatory threshold occurred at the same (p > .05) mean (± SD) work rate in the morning (110.6 ± 27.0 watts) and in the afternoon (111.9 ± 23.9 watts) and was perceived as equally strenuous (p > .05) in the morning (RPE = 13.8 ± 2.4) and in the afternoon (RPE = 13.6 ± 2.8). At intensities below the ventilatory threshold, RPE was the same (p > .05) in the morning and in the afternoon; above the ventilatory threshold, RPE was lower (p < .05) in the morning. We conclude that, during incremental submaximal cycling exercise above the ventilatory threshold, a particular work rate is perceived as less strenuous in the morning than in the afternoon. About 20% of this difference in RPE is explained by lower ventilatory demands in the morning.

Differential effects of the new central adrenergic agonist modafinil and d-amphetamine on sleep and early morning behaviour in elderlies.

Abstract: Modafinil (CRL 40476) is a new central alpha-adrenergic agonist with vigilance-promoting properties. In a double-blind, placebo-controlled sleep laboratory study its single-dose effects on sleep and early morning behaviour were investigated and compared with d-amphetamine. Ten elderly healthy volunteers (mean age: 68 years) spent 12 nights in the sleep laboratory: one adaptation night, one baseline night, five drug nights (100 mg and 200 mg modafinil; 10 mg and 20 mg d-amphetamine; placebo) and five subsequent washout nights. The drugs were administered orally in one week intervals at 10:00 p.m., and all-night somnopolygraphic investigations were performed between 10:30 p.m. and 6:00 a.m. A self-rating scale for sleep and awakening quality as well as psychometric tests were completed in the morning. d-amphetamine caused a dose-dependent impairment of sleep maintenance and sleep architecture, while modafinil did not. Thus, a significant reduction of total sleep time, REM-sleep and sleep stage 2 was seen after d-amphetamine when compared to placebo and 100 mg modafinil. Corresponding with these objective results, subjective sleep quality deteriorated significantly only after 20 mg d-amphetamine as compared to placebo. Morning investigations revealed an increase of CFF after 20 mg d-amphetamine. Pulse rate, evening and morning blood pressure remained unchanged. These findings suggest a different mode of action of the two compounds.

Influence of subchronic intake of melatonin at various times of the day on fatigue and hormonal levels: a placebo-controlled, double-blind trial.

Abstract: In a double-blind study, melatonin (50 mg) or placebo was administered daily to 25 subjects at 9 am or 7 pm for 1 week. Self-rated fatigue as evaluated by the Stanford Sleepiness Scale (SSS) was significantly increased during the 3 hours following melatonin intake in the morning, whereas, after administration in the evening, no difference between melatonin and placebo could be distinguished. Sleep onset latency slightly decreased in both melatonin groups without reaching statistical significance. No cumulative effects on sleep or behavior were observed. Twelve pituitary and peripheral hormones measured under baseline and partly (in the evening groups) under stimulated conditions before and after the trial did not change. The two most important conclusions are that: 1) the sedative potency of exogenous melatonin depends on the daily time of administration; and 2) the high pharmacological doses used for acute sedation do not seem to have cumulative effects after prolonged application.

Diurnal rhythms of cortisol, ACTH, and beta-endorphin levels in neonates and adults.

Abstract: To determine whether a diurnal rhythm exists in neonates admitted to neonatal intensive care units where there is continuous artificial lighting and periodic nursing and medical care, plasma cortisol, adrenocorticotropin (ACTH), and beta-endorphin concentrations were measured in two groups of infants and in adult human volunteers. As expected, a diurnal rhythm was seen in adults. A diurnal rhythm was also found for cortisol and endorphin levels in neonates (3 to 4 days postnatally) with minimal stress and in infants who were clinically severely stressed. There was not a significant difference between the morning and afternoon concentrations of ACTH in these infants, but the afternoon concentrations were lower than the morning's, as would be expected. We found that a diurnal rhythm does exist in neonates within the first few days of postnatal life and that the continuous lighting and medical and nursing interventions do not interfere with this rhythm.