Adenohypophysis has an inherent property for pulsatile prolactin secretion

Hypophysectomized male rats with adenohypophyses grafted under the kidney capsule (HG rat) for 3 weeks with or without estradiol implantation, were used to examine prolactin (PRL) secretion independent of hypothalamic influence. Changes in the circulating PRL concentration were monitored by taking blood samples every 2 min via an indwelling atrial cannula. The circulating PRL concentration did not remain at a constant level but fluctuated with time. When estradiol (100 microgram/kg) was administered to HG rats through the indwelling cannula the size of the PRL pulses was magnified. The ability of the grafted adenohypophyses to generate pulsatile changes in the plasma PRL indicates that the adenohypophysis possesses an inherent interlactotroph communication system to permit synchronized PRL secretion without the direct involvement of hypothalamic PRL-releasing factors or inhibiting factors.