Somatic afferent stimulation-plasma corticosterone, luteinizing hormone (LH), and testosterone responses in aged male rats under anesthetization.

Our previous studies have demonstrated that somatic sensory stimulation can produce increases in secretions of corticosterone, luteinizing hormone (LH), and testosterone in young male Wistar rats of 13-22 weeks old even after emotional factors are eliminated by pentobarbital-anesthetizing of the subjects. In the present study, we examined the effects of somatic sensory stimulation on plasma corticosterone, LH, and testosterone using aged male Wistar rats (24-27 months old) under the same anesthetizing condition as employed in our previous studies. We compared the reflex responses in aged rats with those previously measured in young rats. Nociceptive mechanical stimulation of both hindpaws by pinching for 10 min significantly increased plasma corticosterone levels in aged rats. The magnitude and time-course of this response were equivalent to those in young rats. On the other hand, neither plasma LH nor testosterone levels were changed by nociceptive mechanical stimulation of the hindpaws of aged rats. This is in sharp contrast to the increase in both plasma LH and testosterone caused by the stimulation of young rats. These results 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; however, LH secretion from the anterior pituitary and testosterone secretion from the testes to nociceptive somatic sensory stimulation are subject to dysfunction with aging.