Acute and Chronic Effects of Hypothalamic Lesions on the Release of FSH, LH and Prolactin in Intact and Castrated Rats

Plasma gonadotropins and prolactin were measured by radioimmunoassay before and after placement of direct current or radiofrequency lesions in the hypothalamus in intact and castrated rats of either sex. Following median eminence lesions, there was a rapid increase in the levels of plasma prolactin, LH and FSH. In general the response was greatest for LH, slightly less for prolactin and minimal for FSH. In the case of FSH and LH, this was followed by a decline to subnormal levels. The decline was much more pronounced in castrate than in intact animals. It is concluded that median eminence lesions may initially lead to release of stored releasing factors from the damaged tissues and that this is followed by a profound decrease in release of gonadotropins which is more pronounced for LH than for FSH. The initial rise in prolactin may be caused by release of prolactin—releasing factor. The maintained secretion of prolactin is presumably caused by withdrawal of tonic inhibitory hypothalamic influences. The elevation in prolactin in females following these lesions was more pronounced than in males. Suprachiasmatic lesions of the type that induce constant estrus led to elevated levels of FSH, LH and prolactin in animals with intact ovaries. The elevated levels of prolactin were presumably caused by estrogen from the ovarian follicles since they declined following spaying. Plasma gonadotropins did not rise as rapidly after spaying in these animals and declined when suprachiasmatic lesions were placed in chronically spayed animals which suggests that part of the negative feedback action of gonadal steroids is mediated by this region. Although acute changes in hormone levels were observed after lesions in certain other hypothalamic areas, there were no consistent chronic changes following these lesions. (Endocrinology91: 643, 1972)