Involvement of the adrenergic system on the release of prolactin and lactogenesis at the end of pregnancy in the rat.

The part played by the adrenergic system on the release of prolactin and lactogenesis induced by prostaglandin F2 alpha and the antiprogesterone RU 486 was studied in pregnant rats. Two doses of prostaglandin F2 alpha (150 micrograms) administered at 08.00 and 12.00 h on day 19 of pregnancy induced, at 12.00 h on day 20 (24 h after administration), a significant increase in the serum concentration of prolactin, with a significant decrease in serum progesterone levels. These hormonal changes significantly augmented casein and lactose levels in the mammary gland. Treatment with RU 486 (2 mg/kg) at 08.00 h on day 19 augmented casein and lactose concentrations in the mammary gland at 12.00 h on day 20 without modifying serum concentrations of prolactin and progesterone. The adrenergic antagonists, propranolol (3 mg/kg), metoprolol (10 mg/kg), ICI 118,551 (200 micrograms/kg), idazoxan (100 micrograms/kg) and prazosin (10 mg/kg), were administered s.c. at 12.00 and 20.00 h on day 19 and 08.00 h on day 20 of pregnancy to intact rats or to rats previously treated with RU 486 or prostaglandin F2 alpha. These adrenergic antagonists did not modify serum prolactin or progesterone levels in intact or RU 486-treated rats, but serum prolactin levels in the prostaglandin F2 alpha-treated group were significantly reduced by treatment with propranolol, metoprolol or prazosin. In addition, propranolol and ICI 118,551 also decreased the casein and lactose concentrations in the mammary glands of RU 486- and prostaglandin F2 alpha-treated rats, while the other compounds had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)