[Effects of cutaneous mechanical stimulation on plasma corticosterone, luteinizing hormone (LH), and testosterone levels in anesthetized male rats].

Effects of cutaneous mechanical stimulation on plasma corticosterone, luteinizing hormone (LH), and testosterone levels were examined in young adult (13-22 weeks old) and aged (24-27 months old) male Wistar rats anesthetized with pentobarbital. Under the resting condition without somatic sensory stimulation, neither plasma corticosterone measured every 15 min between 1430 h and 1630 h nor plasma LH and testosterone measured every 30 min between 1400 h and 1730 h revealed any significant fluctuations. Nociceptive mechanical stimulation of both hindpaws by pinching for 10 min significantly increased plasma corticosterone, LH, and testosterone, in young adult rats. Plasma corticosterone was increased for one hour following the stimulation. On the other hand, plasma LH was increased 30 and 60 min after the cessation of stimulation, while plasma testosterone was increased 60-150 min after stimulation. However, innocuous mechanical stimulation of both hindlimbs by brushing for 10 min did not significantly change either plasma corticosterone, LH, or testosterone. These findings indicate that, nociceptive information from skin lead to the increased secretion of corticosterone from the adrenal cortex and the increased secretion of LH from the anterior pituitary, resulting in an increase in testosterone secretion from the testes into the plasma, after emotional factors are eliminated by anesthetizing the subjects. In aged rats, the same nociceptive mechanical stimulation by pinching significantly increased the plasma corticosterone levels. The magnitude and time-course of the response in aged rats were equivalent to those in young adult rats. On the other hand, in aged rats, neither plasma LH nor testosterone levels were changed by the same nociceptive mechanical stimulation. This is in sharp contrast to the increase in both plasma LH and testosterone caused by the stimulation of young adult rats. These findings indicate a functional dissociation induced by aging between the secretory responses of the anterior pituitary, testes on the one hand and the adrenal cortex on the other hand, to nociceptive somatic sensory stimulation. Aging does not alter corticosterone release from the adrenal cortex to nociceptive somatic sensory stimulation, but LH secretion from the anterior pituitary and testosterone secretion from the testes to nociceptive somatic sensory stimulation are subject to dysfunction with aging.