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The literature regarding whether or not there are diurnal differences in pain perception in men and women is equivocal. The purpose of this study was to examine the influence of time of day on experimentally induced pain threshold in men and women. A secondary purpose was to measure selected psychological and physiological responses. Pressure (3000 gm force) was applied to the middle digit of the left forefinger for 2-min with the Forgione-Barber pain stimulator. Twenty-nine volunteers (women = 14; men = 15) completed two randomly assigned sessions between 6.00-8.00 in the AM and PM. Selected psychological variables (STAI,POMS) and physiological variables (BP, HR, TEMP) were assessed before application of the pressure stimulus. Data were analyzed with a 2x2 ANOVA. Results indicated that men had significantly higher (p<.05) systolic blood pressure and pain thresholds than women however, there was not a significant time of day effect for pain threshold. Significant time of day effects (p<.05) were found for systolic blood pressure and tympanic temperature. Heart rate, and tympanic temperature were found to be significantly higher (p<.05) in women in comparison to men. It is concluded that pain threshold did not differ in the AM and PM. Furthermore, men were found to have higher pain thresholds compared to the women.

The hypothalamo-pituitary-adrenal axis appears to play an important role in regulating the circadian fluctuations of brain-gut peptides, as well as the cell cycle of the gastrointestinal mucosa. Since dexamethasone treatment tended to restore circadian fluctuations lost to adren-x, the influence of adrenal glucocorticoids in the coordination of the rhythms of regulatory peptides and cell cycle kinetics appears to be substantial.

Altered protein diets and circadian rhythms of gastrin and cholecystokinin (CCK) were investigated in 126 male and 126 female Sprague-Dawley rats acclimated for two weeks to a 12:12 hr light-dark cycle. Rats were divided equally and fed low-protein (8%), high-protein (64%) or normal protein (27%) diets for four weeks. All animals were fasted for 24 hr prior to blood collections. Blood samples were collected at 4-hr intervals for 24 hr for determination of plasma gastrin and CCK using specific radioimmunoassays. A significant rhythm for gastrin was detected in males on normal and low-protein diets (P less than 0.03) and in females on low-protein diets (P less than .02). A significant rhythm for CCK was detected (P less than 0.05) in rats of both sexes fed normal and high-protein diets. Mean plasma levels of both peptides were lower in females than males. In a separate study, food intake and body weight were monitored in male rats receiving the three diets over 21 days. Animals on the low-protein diet exhibited reduced food intake and body weight compared to rats fed the normal or high-protein diets.

Fluctuations in serum gastrin and plasma cholecystokinin (CCK) over a 24-hr period were examined in fasted and freely fed adult BALB/c mice and Sprague Dawley rats. Eighty-four mice and 84 rats were caged in groups of (six) each and placed in separate isolation chambers with light from 0600 to 1800 hr (CST) daily (LD 12:12). After standardization for 30 days, one-half of the animals were fasted 24 hr prior to circadian sampling, and the remainder were allowed continuous access to food. Animals were removed and killed by rapid cervical dislocation every 4 hr beginning at 0800 hr for seven time points. Blood was collected and serum gastrin and plasma CCK were measured by specific radioimmunoassays. The data document a circadian bioperiodicity for serum gastrin and plasma CCK. The parameters of the rhythms, evaluated by cosinor rhythmometric methods, are characterized by an acrophase that occurs in the dark period for both fed and fasted rodents and a mesor that is higher in fed than fasted animals. Circadian sampling time and nutritional status appear to be important in studies involving serum levels of gastrin and plasma CCK in rodents.

Voluntary drinking responses to an alternating three-bottle, two-choice paradigm to tap water or to 5% ethanol were measured in adult male Fisher (Fshr; N = 14) and spontaneously hypertensive (SP; N = 16) rats for 6-9 days. All animals were singly caged and housed separately in isolation chambers. The animals received light from 0600 to 1800 (CST) daily (LD 12:12) or remained in constant darkness (DD) at room temperature (23 degrees C). Food was freely available. Water and ethanol bottles were changed daily, and volumes of the respective fluids consumed by each rat were measured. A dim red light (approximately 0.5 lux) was used in handling animals in the dark. SP rats demonstrated significant (P less than 0.05) circadian drinking patterns of water and ethanol consumption under LD and DD lighting conditions. Fshr rats, however, exhibited a circadian pattern (P less than 0.02) only with regard to water consumption under an LD 12:12 lighting schedule; they did not exhibit circadian patterns of drinking water (P less than 0.054) in DD or ethanol in LD (P less than 0.24) or in DD (P less than 0.67) conditions. Volumes of ethanol consumption were also greater (P less than 0.05) in SP rats than in Fshr rats. It is concluded that differences exist in circadian drinking behaviors for both water and ethanol intake in two strains of rats. Perhaps variation in circadian patterns is an evolutionary mechanism that programs behavior over an appropriate time span for differences in physiological needs of nocturnal animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Lesions of the suprachiasmatic nuclei (SCN) have been reported to disrupt or abolish circadian rhythms of motor activity and body temperature as well as of several neuroendocrine functions. This study was undertaken to determine any effect the SCN may have on the prominent circadian rhythm characteristic of the mitotic index of the corneal epithelium. Singly caged adult mice of both sexes were fed ad libitum and standardized to 12 hours of light alternating with 12 hours of darkness. Animals were divided into experimental and control groups. Later they were killed in subgroups at the time intervals of 0800, 1200, 1000, 0000, 0400 hour. Mitotic counts were determined on both right and left corneas of all mice. The data were plotted separately for both groups and reflect colony variation. We conclude that major lesioning of the SCN or tis efferent projections disturbed but did not abolish the rhythm. In animals with unilateral lesions of the SCN, the mitotic index was consistently lower in the ipsilateral cornea. The mitotic index for animals with lesions which missed the SCN or its efferent projections did not differ from controls. The nuclei appear to function as pace-resetters and amplifiers of the rhythm studied.

Investigations into the role of the suprachiasmatic nuclei (SCN) in the coordination of circadian rhythms have presented differing results. Several reports have shown that ablation of the suprachiasmatic nuclei (SCNA) alters the phase and amplitude of rhythms but does not abolish them. The present study investigates the effect of SCNA on the rhythms in cell proliferation in various regions of the intestinal tract as measured by the incorporation of [3H]-thymidine into deoxyribonucleic acid, in the mitotic activity of the corneal epithelium, and in serum corticosterone levels. The study involved mice with verified lesions of the SCN (six to 13 mice per time point) and control groups of both sham-operated and unoperated mice (seven of each per time point). The mice were killed in groups that represented seven time points over a single 24 hr span (3 hr intervals with the 0800 hr sampled both at start and end of the series). The tissues examined were the tongue, esophagus, gastric stomach, and colon for DNA synthesis, the corneal epithelium for mitotic index, and blood serum for corticosterone level. The most consistent result of SCNA was a phase advance in the rhythms in cell proliferation in the tongue, esophagus, gastric stomach, colon, and corneal epithelium. A reduction in rhythm amplitude occurred in the tongue, esophagus, and corneal epithelium; however, there was an amplitude increase for the stomach, colon, and serum corticosterone. The mesor (rhythm-adjusted mean) was increased by SCNA in all tissues except the corneal epithelium. These findings further support the role of the suprachiasmatic nuclear area in the control of rhythms in cell proliferation and corticosterone production, by acting as a "phase-resetter" and as a modulator of rhythm amplitude.