Central Oxytocin Stimulates Luteinizing Hormone Release in the Marmoset, a Primate which Fails to Show Lactationally-lnduced Infertility.

In several species, including humans, suckling is known to suppress pulsatile gonadotrophin secretion and substantially reduce fertility (1). During suckling high titres of oxytocin are present in both plasma (2, 3) and cerebrospinal fluid (CSF) (4) and there is some evidence that oxytocin is inhibitory to gonadotrophin secretion by an action on t h e central nervous system, (5, 6). The common marmoset, however, has a different physiological response and fails to show lactational infertility; ovarian cyclicity is resumed immediately post-partum (7). We have therefore examined the effect of centrally administered oxytocin on luteinizing hormone (LH) secretion in this species. We report that LH release was stimulated with a rapid:esponse and in a dose-dependent manner by oxytocin injected into t h e third cerebral ventricle. In contrast, oxytocin administered intravenously was without effect on LH secretion. These results clearly indicate, for the first time, a stimulatory role for oxytocin in LH secretion in the marmoset, a species which fails to demonstrate lactational infertility.