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The adipocyte-derived hormone leptin plays a pivotal role in the regulation of body weight and energy homeostasis. Many studies have indicated that the circulating levels of leptin show a 24-h rhythm, but the exact cause and nature of this rhythm is still unclear. In the present study, we remotely collected blood samples every hour from young and old, male and female rhesus monkeys, and examined their 24-h plasma leptin profiles. In both the young males (10–11 years) and females (7–13 years), a clear 24-h plasma leptin rhythm was evident with a peak occurring ~4 h into the night and a nadir occurring ~1 h into the day (lights on from 0700 to 1900 h). A 24-h plasma leptin rhythm was also observed in the old males (23–30 years), even when they were maintained under constant lighting conditions (continuous dim illumination of ~100 lx). In marked contrast, plasma leptin concentrations were relatively constant across the day and night in old peri- and post-menopausal females (17–24 years), regardless of the lighting schedule. These data establish that rhesus monkeys, like humans, show a daily nocturnal rise in plasma leptin, and the magnitude of this rhythm undergoes a sex-specific aging-dependent attenuation. Furthermore, they suggest that the underlying endocrine mechanism may be driven in part by a circadian clock mechanism.
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Division of Neuroscience, Physiology and Pharmacology, Oregon National Primate Research Center, Beaverton, Oregon 97006, USA Departments of
Division of Neuroscience, Physiology and Pharmacology, Oregon National Primate Research Center, Beaverton, Oregon 97006, USA Departments of
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Division of Neuroscience, Physiology and Pharmacology, Oregon National Primate Research Center, Beaverton, Oregon 97006, USA Departments of
Division of Neuroscience, Physiology and Pharmacology, Oregon National Primate Research Center, Beaverton, Oregon 97006, USA Departments of
Search for other papers by Henryk F Urbanski in
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In temperate zones, day length changes markedly across the year, and in many mammals these photoperiodic variations are associated with physiological adaptations. However, the influence of this environmental variable on human behavior and physiology is less clear, and the potential underlying mechanisms are unknown. To address this issue, we examined the effect of changing photoperiods on adrenal gland function in ovariectomized female rhesus macaques (Macaca mulatta), both in terms of steroid hormone output and in terms of gene expression. The animals were sequentially exposed to the following lighting regimens, which were designed to simulate photoperiods associated with winter, spring/autumn and summer respectively: 8 h light:16 h darkness (short days), 12 h light:12 h darkness and 16 h light:8 h darkness (long days). Remote 24-h serial blood sampling failed to disclose any effect of photoperiod on mean or peak plasma levels of cortisol or dehydroepiandrosterone sulfate. However, there was a marked phase-advancement of both hormonal rhythms in short days, which was reflected as a similar phase-advancement of the daily motor activity rhythm. Gene microarray analysis of the adrenal gland transcriptome revealed photoperiod-induced differences in the expression of genes associated with homeostatic functions, including: development, lipid synthesis and metabolism, and immune function. Taken together, the results indicate that in primates, both circadian adrenal physiology and gene expression are influenced by seasonal changes in day length, which may have implications for adrenal-regulated physiology and behavior.
