Cyclic Adenosine-3′,5′-Monophosphate Stimulates the Acute Release of Placental Lactogen from Human Trophoblast Cells*

Abstract

CAMP has been shown to be a second messenger in the release of many hormones and other secretory products. To determine whether cAMP also plays a role in the mechanism of release of human placental lactogen (hPL), we examined the effects of (Bu)12cAMP, isobutyl methylxanthine, forskolin, and cholera toxin on the acute release of hPL from an enriched fraction of hPL-producing trophoblast cells. Statiic cultures of trophoblast cells exposed to (Bu)2cAMP (5 mM) for 2 h released 2.6 times as much hPL as control cells (P < 0.01) during the first 0.5 h of exposure. The increase in hPL release, was followed by a decreased rate of release during the subsequent 1.5 h. Perifused trophoblast cells (1.5 .times. 106) exposed to 5 mM cAMP for 20 min related 3.2 times as much hPL as control cells. The rate of hPL increased markedly during the first of 10 min of exposure, rapidly decreased toward control value during the remainder of the exposure period, and then declined to a subnormal rate for the next 30 min before returning to normal to control values. (Bu)2cAMP, however, had no acute effects on the release of human CG or the release of the cytosolic enzymes alkaline phosphatase and lactic dehydrogenase. The phosphodiesterase inhibitors theophylline (5 mM) and isobutyl methylxanthine (0.5 mm) and the adenylate cyclase activators forskolin (5 .mu.g/ml) and cholera toxin (25 .mu.g/ml) stimulated hPL release by 75-95%. These results strongly suggest that cAMP is a second messenger in the acute release of hPL.