Effects of Castration and Gonadal Steroids on Serum Luteinizing Hormone and Prolactin in Old and Young Rats

Abstract

Changes in serum LH and prolactin concentrations in response to bilateral gonadectomy and gonadal steroid replacement were measured in mature young (4-6 months) and old (23-30 months) female and male Long-Evans rats. On day 13 after gonadectomy, female rats were injected with oestradiol benzoate (OB) and male rats with testosterone propionate (TP) for a period of 12 days. They were then permitted a recovery period of 6 weeks. Serum prolactin and LH concentrations were measured by radioimmunassay in single blood samples taken at various intervals before and after gonadectomy and during and after steroid treatment. Serum LH levels were about the same in intact young old female rats, but after ovariectomy LH rose several fold higher in young than in old remale rats. In male rats, after orchidetomy the increase in serum LH was greater in young than in old rats. Oestradiol benzoate and TP injections into female and male young and old rats produced variable effects on LH release. Serum prolactin concentrations were approximately six times higher in old intact than in young intact female rats, and after ovariectomy showed a much greater percentage reduction in old than in young female rats. Administration OB produced a greater absolute increase in serum prolactin in old than in young female rats. Serum prolactin values were about the same in old and young male rats, and the effects of castration and TP administration on serum prolactin were not markedly different in the two age groups. These results indicate that old female and male rats are less capable of releasing LH than young rats of both sexes, but old females release more prolactin than young females.

L-Dopa Effects on Serum LH and Prolactin in Old and Young Female Rats

“…The elevated pretreatment levels of serum prolactin concur with our previous findings of increased prolactin levels in the serum and pituitaries of aged rats [Clemens and M eites, 1971;Shaar et a!., 1975;R iegle and M eites, in press]. Al though the decreased sensitivity of the aged group 15 min after the 3-mg L-dopa injection is in agreement with our recent report in male rats (R iegle and M eites, submitted), the differences are not as dramatic and offer further evidence for sex differences in the effect of aging on neuroendocrine pituitary control in the rat.…”

Effect of Aromatizable Androgens and Estradiol on Prolactin Secretion in Prepuberal Male Rats

“…Castration slightly decreases [13,151 or has no effect on serum prolactin levels in male rats [7,111. Castration of prepuberal rats for 10 days did not alter serum prolactin levels in this study.…”

“…Increasing evidence has accumulated over the past several years indicating that testosterone can stimulate prolactin secretion in intact or castrated rats [6,7,13,141 and in juvenile rhesus monkeys [5]. Indirect evidence to this effect has also been obtained in man [4, 121.…”

Hypothalamic Luteinizing Hormone-Releasing Hormone(LHRH) and LH Secretion in Aging Female Rats.

“…After the cessation of the estrous cycle, the increase in plasma LH in response to ovariectomy is smaller in old female rats than in young ones (negative feedback effect) (Shaar et al, 1975;Huang et al, 1976;Takahashi et al, 1980). The positive feedback action of estrogen in ovariectomized rats on the LHRH level in mediobasal hypothalamus and LH secretion is attenuated in old rats (Steger et al, 1983;Wise, 1984).…”