NITRIC-OXIDE REGULATION OF CORTICOTROPIN-RELEASING HORMONE-RELEASE FROM THE HUMAN PERFUSED PLACENTA IN-VITRO

We have investigated the regulatory role of nitric oxide (NO) in corti cotropin-releasing hormone (CRH) release from the human perfused place ntal lobule in vitro. The effects of the NO donor sodium nitroprusside , the NO synthase inhibitor-N-omega-nitro-L-arginine, and the NO subst rate L-arginine on human (h) placental CRH secretion have been studied . Single lobules of term placentae were bilaterally perfused with Kreb s solution (5 mL/min; 95% O-2-5% CO2; 37 C; pH 7.3). Fetal and materna l perfusates were collected at 4 C every 30 min for 3 h. CRH immunorea ctivity (CRH-IR) in perfusates was measured by RIA using the 41-residu e synthetic CRH as standard, I-125-labeled Tyr-hCRH as tracer, and a r abbit anti-CRH antibody Y2B0. The sensitivity of the assay was 0.13 pm ol/L. Under basal conditions, human perfused placentae in vitro contin uously secreted CRH-IR, which diluted in parallel to a synthetic hCRH- (1-41) standard curve. Size-exclusion chromatography of placental perf usates using a Sephadex G-50 column indicated that placental CRH-IR pr edominately coeluted with hCRH-(1-41) standard. Basal maternal perfusa te CRH-IR levels (27 +/- 4 pmol/L) released from perfused placental lo bules were nearly 10-fold greater than fetal perfusate CRH-LR levels ( 3.4 +/- 0.7 pmol/L; P < 0.05). Infusion of sodium nitroprusside (30-10 0 mu mol/L) into the maternal and fetal placental circulations inhibit ed CRH-IR release into maternal perfusate in a concentration-dependent manner, but did not inhibit CRH-IR release into the fetal perfusate. N-omega-nitro-L-arginine (100 mu mol/L) increased placental CRH-IR sec retion into fetal perfusate, and this effect was reversed by the infus ion of L-arginine (100 mu mol/L), which also reduced release below bas al levels. In contrast, maternal perfusate CRH-IR levels were not affe cted by N-omega-nitro-L-arginine or L-arginine. These results indicate that the human perfused placenta in vitro releases a substance of sim ilar mol wt and hCRH-IR. Moreover, modulators of the NO signaling path way differentially affect placental secretion of CRH-IR into the mater nal and fetal perfusates. These data are consistent with the involveme nt of NO in the regulation of placental CRH release during pregnancy.