Pituitary portal vessel infusion of hypothalamic extract and release of LH, FSH and prolactin

Extracts of hypothalamic tissue (HE) or of cerebrocortical tissue were infused into stalk portal vessels of anesthetized male rats. The extract of cerebrocortical tissue, equal in weight to 1/2 of a hypothalamic fragment, had no effect on the release of LH, FSH, or prolactin. HE caused an increase in the levels of LH and FSH in arterial plasma and simultaneously a decrease in the level of prolactin. The responses to HE were related to the concentration of the extract. For example, in rats given HE equivalent to 1/12, 1/6 or 1/2 of a hypothalamic fragment per 30 min, the concentrations of LH in plasma at the end of the infusion period were 2.5, 4.5 and 6.9 times the control values, respectively. The corresponding levels of FSH were 1.6, 2.2 and 2.9, and of prolactin 0.73, 0.55 and 0.37. After the infusion of HE was terminated, the concentrations of LH and FSH in plasma fell and that of prolactin rose. The half-times of the disappearance functions of prolactin, LH and FSH in plasma of rats after hypophysectomy were 14.4, 28.9 and 123 min, respectively. The disappearance rates of prolactin during the infusion of HE and of FSH after the infusion (equivalent to 1/6 or 1/2 of a hypothalamic fragment) appeared to be slower than those seen in hypophysectomized animals. The disappearance rate of LH after the infusion of HE was the same as that seen in hypophysectomized rats.