Prolactin stimulation of prolactin receptors in rat liver

Abstract

Hypophysectomy of the female rat results in a loss of prolactin receptors from the liver. Seventy percent of specific prolactin binding is lost within 24 hours; by 48 hours receptor levels are less than 5% of those found in livers from intact rats. A single dose of ovine prolactin to hypophysectomized rats causes a partial restoration of prolactin receptors between 12 and 18 hours after injection. As little as 0.5 mg prolactin significantly increases receptors, while doses above the 2 mg optimum are apparently less effective. These restored receptor sites are unaltered in their affinity for prolactin. Estradiol (E 2), progesterone, hydrocortisone, triiodothyronine (T 3) or E 2 plus T 3 could not mimic the prolactin effect. Neither combinations of prolactin with E 2 or T 3 nor repeated daily injections of prolactin alone increase receptors more than does a single prolactin injection. It appears that prolactin modulates the level of its own receptor in rat liver.