DIFFERENTIAL CONTROL OF PLACENTAL-LACTOGEN RELEASE AND PROGESTERONE PRODUCTION BY OVINE PLACENTAL TISSUE INVITRO

The hypothesis that placental secretion of progesterone (P4) and ovine placental lactogen (oPL) are controlled through different mechanisms was tested. Placental tissue was obtained at days 133–138 of pregnancy, and explant incubations were established using 200 mg tissue per flask in 5 ml O2-saturated DMEM containing 24 mM HEPES and lacking phenol red (pH7.4). Following a 30-min preincubation, and a 15-min control period, test substances were added and incubations continued, with periodic gassing, for 4 h at 37°C in a shaking water bath. Dopamine (DA), norepinephrine (NE) and epinephrine significantly stimulated P4 production (P<0.05). The enhancement of placental P4 production was mimicked by the addition of 8-bromo-cyclic adenosine monophosphate and forskolin (P<0.05). The response to catecholamines was abolished by the addition of propranolol (P<0.05) but not by phentolamine (P>0.05). Inclusion of a membrane-permeant substrate for P4 synthesis, 25-hydroxycholesterol, increased basal (P<0.05) but did not enhance agonist-induced P4 production (P>0.05). High performance liquid chromatographic analysis of placental tissue demonstrated the presence of DA (80.8±7.07 pg/mg) and NE (48.8±5.77 pg/mg), as well as catecholamine metabolites. Addition of 1,2-dioctanoyl-sn-glycerol (DAG) or phorbol 12-myristate-13-acetate (PMA) enhanced oPL secretion (P<0.05) without affecting P4 production. The response to DAG and PMA, representing the release of considerably more oPL than can be detected by extracting the tissue, was not influenced by treatment with cycloheximide (P>0.05) indicating that secretion of preformed oPL is regulated by the protein kinase C pathway. These results support the hypothesis that the secretion of oPL and the production of P4 are controlled by different mechanisms. © 1990, Baillière Tindall. All rights reserved.