Hypothalamic neurohormonal agents and sexual maturation of immature female rats

Abstract

The possible role of four recognized hypothalamic constituents in activation and maturation of the hypophysial-reproductive organ complex of immature female albino rats was investigated. Normal and hypophysectomized rats and rats with bilateral destruction of an area extending from the ventromedial nucleus to mammillary body were studied. Animals were injected either with 70 milliunits of antidiuretic hormone (ADH), 70 milluniits of oxytocin, 25 µg of serotonin, or 2 µg of epinephrine every 5th day, from age 20 through 45 days, via a cannula permanently implanted in the 3rd ventricle of the brain. No response to ADH was observed. Oxytocin accelerated vaginal canalization and caused premature reproductive organ growth in normal recipients. Whereas lesioned untreated controls remained sexually retarded, vaginal opening and reproductive organ growth equivalent to 50-day-old sham-operated controls were induced in lesioned animals by oxytocin administration. Serotonin prevented maturation in normal controls, but was ineffective in lesioned animals. Hypophysectomized rats were unresponsive to any agent injected. The results imply that oxytocin may directly activate the hypophysis of immature female rats. Serotonin, on the other hand, inhibits the hypophysial-gonadal axis of these animals, but its effects probably are relayed via the hypothalamus.