Endocrine Abstracts

Men show an age-associated decline in 24-hour circulating testosterone levels, but the reason for this decline is unclear. To shed light on the possible cause we first established that male rhesus monkeys undergo a similar decline in testosterone with age. Testosterone from young adult (∼10 years) and old (∼26 years) unanaesthetized males was measured by RIA from blood samples collected remotely through a vascular catheter, every 30 minutes for 24 hours. In both yo...

Rhesus macaques, like humans, express two molecular forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II). Although the role of GnRH-I in the control of the reproductive axis is well-established, the physiological role of GnRH-II is less clear. Both forms of GnRH are highly expressed in the monkey hypothalamus and both forms are highly effective at stimulating LH and FSH release in vivo. However, estradiol appears to affect GnRH-I and GnRH-II gene expression diff...

A characteristic of aging in humans, as well as in nonhuman primates, is the disruption and attenuation of many biological rhythms. A desynchronization or dampening of cyclical neuroendocrine patterns, such as the circulating melatonin rhythm, may help to explain age-related disturbances in sleep and daytime alertness. Although the cause of age-associated disruptions of biological rhythms is largely unknown, it may be partially due to cumulative neuronal damage of relevant bra...