Effect of aging on hypothalamic LH-releasing and prolactin inhibiting activities and pituitary responsiveness to LHRH in the male laboratory rat.
Hypothalamic content of LH releasing and prolactin inhibiting activities and pituitary responsiveness to LH releasing hormone was measured in young (4 mo.) and aged (26 mo.) Long-Evans rats by in vitro methods. Hypothalamic extracts (0.5 and 1.0 hypothalamic equivalents) from young and aged male rats were incubated with untreated hemisected rat pituitaries in medium 199. Doses of 0.5 and 1.0 hypothalamic equivalents (HE) from both age group stimulated LH secretion. The increase in pituitary LH release stimulated by 0.5 HE from aged male rats was about half that stimulated by 0.5 HE from the young male group (p less than .20). The increase in LH secretion stimulated by hypothalamic extracts of either age group was not associated with a change in pituitary LH content. Although 0.5 and 1.0 HE from young male rats and 1.0 HE from the aged group reduced incubated pituitary prolactin release, 0.5 HE from the aged males did not affect prolactin release. Treatment with hypothalamic extracts also resulted in increased pituitary prolactin concentrations. Pituitaries from young and aged male rats were incubated in medium 199 containing 0, 25, or 100 ng of LH releasing hormone. Although LH releasing hormone stimulated LH secretion in all groups, the increase in release of LH was less in the aged groups than from pituitaries from the young male rats. Pituitary LH content of the aged male group was only about 1/4 that of the young group.
D000375:Aging; D000818:Animals; D007031:Hypothalamus / Q000378:metabolism*; D008297:Male; D051381:Rats