Effect of an obesogenic diet on circadian activity and serum hormones in old monkeys

Like women, old female rhesus macaques undergo menopause and show many of the same age-associated changes, including perturbed activity/rest cycles and altered circulating levels of many hormones. Previous studies showed that administration of an estrogen agonist increased activity in female monkeys, that hormone therapy (HT) increased activity in postmenopausal women and that obesity decreased activity in women. The present study sought to determine if postmenopausal activity and circulating hormone levels also respond to HT when monkeys are fed a high-fat, high-sugar Western style diet (WSD). Old female rhesus macaques were ovo-hysterectomized (OvH) to induce surgical menopause and fed a WSD for 2 years. Half of the animals received estradiol-17β (E), beginning immediately after OvH, while the other half received placebo. Animals in both groups showed an increase in body weight and a decrease in overall activity levels. These changes were associated with a rise in both daytime and nocturnal serum leptin concentrations, but there was no change in serum concentrations of either cortisol or dehydroepiandrosterone sulfate (DHEAS). These data suggest that 2 years of HT has little or no effect on locomotor activity or circadian hormone patterns in menopausal macaques fed an obesogenic diet.