Pineal antigonadotrophic substances: polypeptides and indoles.

Two categories of compounds, polypeptides and indoles, are discussed in terms of their potential importance as pineal antigonadotrophic substances. One of the polypeptides has been structurally identified as arginine vasotocin. Arginine vasotocin and other peptides of unknown structural identity have been found to be strongly antigonadotrophic in experimental animals. Besides melatonin, the gonad-inhibiting ability of several other pineal indoles including serotonin, 5-hydroxytryptophol, 5-methoxytryptophol and N-acetylserotonin was considered. In addition to its gonad suppressing ability, in three species of rodents melatonin has been shown to negate the antigonadotrophic effects of the pineal gland, i.e., it acts as a counter antigonadotrophic factor. A theory is presented in which the indoles may interact with the polypeptides in the control and/or the synthesis of the latter compounds. A mechanism for the secretion of pineal polypeptides is also considered. It is concluded that it is premature to classify any pineal constituent, be it a polypeptide or an indole, as $\text{the}$ antigonadotrophic factor of the mammalian pineal gland.