ALTERATIONS IN THE OPIOID CONTROL OF LHRH RELEASE FROM HYPOTHALAMI ISOLATED FROM AGED MALE RATS

Several lines of evidence have suggested that the opioid control of go nadotropin secretion in the male rat is altered with aging. Because ne ural control of gonadotropins is mediated through luteinizing hormone releasing hormone (LHRH) secreting neurons, we examined the postulated changes in the opioid control of gonadotropins more directly by study ing isolated hypothalamic fragments in vitro. Hypothalami from young ( 75-90 days) and old (18-20 months) males were examined for their abili ty to release LHRH when incubated with increasing doses of naloxone in a semi-static culture system. Serum concentrations of testosterone an d luteinizing hormone (LH) in the donor animals were both significantl y lower in old male rats compared with young males. Basal secretion of LHRH was similar in Both age groups. Two-way repeated measures ANOVA indicated that naloxone stimulated a significant dose dependent increa se in the release of LHRH into the media. ANOVA also indicated a signi ficant effect of age. We conclude that the changes in the endogenous o pioid systems reported to occur with aging are, in fact, linked to dif ferences in LHRH secretion and thus to differences in the dynamic rela tionship between testosterone and LH in older male rats.