The Pineal and Its Hormones in the Control of Reproduction in Mammals*

Abstract

ONLY A LITTLE over a decade ago, any discussion of the function of the pineal gland included qualifying adjectives such as alleged, supposed, and putative. In the same vein, since it connoted a hormonal function, rather than referring to the pineal as a gland, the phrase pineal organ was usually employed to describe this portion of the epithalamus. However, this is no longer the case, at least in mammals. By the usual criteria in endocrinology, the pineal now fulfills all the qualifications of an organ of internal secretion. Several major discoveries revolutionized ideas concerning the function of the pineal gland. Certainly, as noted frequently in other reviews, the isolation and identification of N-acetyl-5-methoxytryptamine (melatonin), a pineal hormone, from bovine pineal tissue by Lerner et al. (1, 2) provided a strong impetus for subsequent investigations on this sometimes exasperating organ. At least as important as this discovery, however, were the observations that light and darkness govern both the biosynthetic activity (3, 4) and endocrine capability (5, 6) of the gland. These findings provided the scientific community with a heretofore unknown handle that could be used to exploit and elucidate the functions of the pineal. Indeed, it is my conviction that the one major factor that stymied pineal research until the mid-1960s was the lack of the basic knowledge that the endocrine output of the pineal gland is determined by the photoperiod to which the experimental subjects, be they animals or man, are exposed.