Non-stress levels of serum luteinizing hormone (LH), prolactin and corticosterone were determined at 3-hr intervals during controlled 24-hr light-dark cycles in adult male rats. Significant 24-hr periodicity was demonstrated for non-stress levels of serum LH, prolactin, and corticosterone; peak values for corticosterone, LH, and prolactin occurred at 5 PM, 8 PM and 11 PM respectively. In contrast, stress markedly reduced the amplitude in serum corticosterone and abolished the rhythm in serum LH concentrations; only serum prolactin showed significant periodicity following stress. These data suggest that circadian periodicity in serum levels of LH, prolactin, and corticosterone can be demonstrated for male rats provided adequate consideration is given to the effect of stress on adenohypophyseal function. {Endocrinology 90: 29, 1972) I T IS NOW apparent that a wide variety of factors influence the hypothalamo-pituitary-gonadal axis. Photoperiod (1), olfactory, tactile and auditory stimuli (2), as well as various environmental stimuli (2) and anesthesia (3) have all been reported to influence gonadal function. In addition, the existence of a 24-hr periodicity within the neural system regulating gonadotropin secretion is well documented (3). Although there exists considerable information regarding the effect of each of the above factors on reproductive function, data concerning the interaction of these factors on gonadotropin secretion is limited.The purpose of the present study was to characterize for male rats the rhythm phenomena in serum concentrations of luteinizing hormone (LH) and prolactin, to describe the temporal relations of LH and prolactin concentrations over a 24-hr period, and to determine the effect of stress on the circadian periodicity in basal or non-stress LH and prolactin concentrations.Animals used in this study were adult (340-380 g), male, Sprague-Dawley (Charles River, CD) rats, housed 2/cage under conditions of controlled lighting (fluorescent illumination from 4 AM to 6 PM) and temperature (24 ± 2 C) for at least 2 weeks. Seven days prior to each experiment, rats were transferred to individual cages and handled daily in order to familiarize animals with entry to animal quarters, cage opening and removal from cage. To further standardize conditions, the animal quarters were locked and not entered during the 18 hrs preceding the experiment. Additionally all treatment and collection procedures, assigned and carried out according to a randomized block design, were done outside the animal quarters. Purina Laboratory Chow and tap water were available ad libitum.The method used to assess non-stress and stress levels of LH, prolactin, and corticosterone was similar to that described by Zimmermann and Critchlow (4) for plasma corticosterone. Nonstress blood samples were obtained by removing rats individually from the animal quarters to an adjacent preparation room where they were rapidly decapitated ( < 20 sec following cage opening). Trunk blood was collected, centrifuged following clot formation...

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Circadian rhythms in DNA synthesis are described for the tongue epithelium, five different regions of the alimentary canal (gut)--esophagus, stomach, duodenum, jejunum and rectum--and bone marrow in a group of BDF1 male mice. A circadian rhythm is also described for the mitotic index in the corneal epithelium in the same mice. The data document for the first time in the same animals the dramatic variation in cell division encountered from one region of the gut to another. This variation is seen in the amplitudes of the rhythms as well as in the over-all 24-hour means. On the contrary, the phasings of the rhythms in the different regions of the gut are remarkably similar. In this study, where the mice were standardized to 12 hours of light (0600-1800) alternating with 12 hours of darkness, the peak of the DNA-synthesis rhythm occurred around the time of transition from dark to light, and the trough around the time of transition from light to dark. The implications of these findings, and those of others, to the study of cell kinetics and to cancer chemotherapy are discussed.