Light deprivation by bilateral orbital enucleation led to testicular and accessory sex organ regression in male hamsters within 12 weeks. Blinding also significantly depressed circulating levels of immunoreactive LH, FSH, and PRL. Twice daily injections of LRF did not prevent atrophy of the testes and accessory sex organs in blind animals even though they stimulated the release of both LH and FSH. Likewise, the restoration of normal plasma levels of PRL, due to the implantation of two pituitary homografts under the kidney capsule of blind hamsters only slightly stimulated testicular and accessory organ growth in the animals. However, twice daily LRF injections into lightdeprived hamsters bearing subcapsular pituitary transplants completely restored normal testicular and accessory sex organ sizes. The results suggest that LH, FSH, and PRL act to restore normal testicular function in hamsters suffering from pinealinduced gonadal atrophy due to light deprivation. The possibility that the pituitary homografts secreted hormones in addition to PRL which also assisted in maintaining gonadal size cannot be excluded. Since the LRF injections stimulated the release of both LH and FSH from the pituitary of blind hamsters, it appears that the pineal normally inhibits the secretion of the gonadotropins at a site above the anterior pituitary, i.e. within the brain.
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