Prolactin regulates maternal bile secretory function post partum.

The single-pass isolated perfused rat liver was used to assess bile secretory function in pregnancy and the post partum period and to evaluate the regulatory role of prolactin. Nonpregnant controls, post partum rats (48 hr post partum), pregnant rats (19-20 days of pregnancy) and pregnant rats treated with bromocriptine (3 mg/kg/day, s.c.) from day 20 of pregnancy until 48 hr post partum to block prolactin secretion were examined. In a separate set of experiments, ovariectomized rats were implanted with osmotic minipumps containing solvent alone or solvent plus varying concentrations of ovine prolactin (oPRL). Livers were isolated, [3H]taurocholate (TC) was infused at increasing concentrations and bile flow, bile acid secretory rate and hepatic clearance of TC from the perfusate were determined. Maximal bile flow (microliters/min/g liver) in response to infusion of TC was significantly higher in post partum rats (3.4 +/- 0.3) than in pregnant rats (1.4 +/- 0.3) and bromocriptine-treated post partum rats (1.7 +/- 0.3). The maximal bile acid secretory rate (SRm, nmol/min/g liver) in post partum rats was 276 +/- 19 and was significantly greater than SRm in pregnant (103 +/- 26) and bromocriptine-treated post partum rats (142 +/- 25). Hepatic clearance (ml/min) was significantly greater in post partum rats than in pregnant, control and bromocriptine-treated post partum rats at the highest TC concentration. Infusion of oPRL at doses of 100, 250 and 500 micrograms/day significantly increased maximal bile flow and SRm in a dose-dependent manner; these measures were increased to 4.38 +/- 0.21 microliters/min/g liver and 338.2 +/- 16.3 nmol/min/g liver, respectively, in rats treated with 500 micrograms/day oPRL.(ABSTRACT TRUNCATED AT 250 WORDS)