Differential Effects of the Pineal Gland on LH-RH and FSH-RH Activity in the Medial Basal Hypothalamus of the Male Golden Hamster

Abstract

Crude neutralized acid extracts were made of medial basal hypothalamic (MBH) tissue obtained from adult male hamsters which had been either blinded, blinded and pinealec-tomized or left intact. After 11 weeks of treatment, the reproductive organs of the blind animals were markedly involuted compared to intact controls, an effect completely reversed by pinealectomy. The luteinizing hormone-releasing hormone (LH-RH) and follicle-stimulating hormone-releasing hormone (FSH-RH) activity of the extracts was assessed using an <i>in vitro</i> system in which LH and FSH release into the medium from hemipituitaries, derived from ovariectomized, estrogen-progesterone-treated female rats, was measured by radioimmuno-assay (RIA). LH and FSH release was responsive to synthetic LH-RH in a dose-related manner; however, in the latter case there were no statistically significant differences between the FSH responses to the various doses of LH-RH. The LH-RH activity of hypothalamic extracts from blind hamsters was depressed as compared with intact controls; however, this effect was not reversed by pinealectomy. The FSH-RH activity of hypothalamic extract from blind hamsters was virtually eliminated compared with that in hypothalami of intact controls. Unlike with LH-RH activity, pinealectomy completely reversed the effects of light deprivation on FSH-RH activity with levels returning to normal. These results indicate that the pineal gland of the male hamster is capable of influencing the hypothalamic levels of FSH-RH activity independent of LH-RH activity.