HELLP-SYNDROME ALTERS HUMAN PLACENTAL VASCULAR RELAXATION TO PROGESTERONE

Background: We have recently described a dose-dependent, endothelium-i ndependent relaxation to progesterone in human placental arteries and veins. This receptor-operated, cAMP-mediated relaxation may be of valu e in maintaining adequate blood flow in the placental circulation. Obj ective: To investigate if HELLP syndrome alters this relaxation to pro gesterone. Study design: Isolated human placental arteries and veins f rom 7 pregnancies complicated by HELLP syndrome and 10 controls (uncom plicated term pregnancies), incubated in Krebs-bicarbonate under 5% O- 2/5% CO2/balance N-2 (P-O2 35-38 torr) and submaximally precontracted with 25-30 mM KCl, were exposed to cumulative doses of progesterone (0 .01-30 mu M), nitroglycerin (0.001-1 mu M), arachidonic acid 0.01-10 m u M), and forskolin (0.01-10 mu M) t test statistics were utilized. Re sults: HELLP syndrome reduced the relaxation to progesterone by 50-100 % in both arteries and veins compared with control (for example, relax ation to 10 mu M progesterone was reduced from 62 +/- 7 to 29 +/- 10% in arteries and from 65 +/- 8 to 31 +/- 7% in veins, n = 6-10, P < 0.0 5), while responses to other vasoactive agents such as arachidonic aci d, forskolin, and nitroglycerin were unchanged. Conclusion: Based on t hese results, HELLP syndrome significantly reduces the relaxation to p rogesterone in human placental arteries and veins. This alteration of the relaxation to progesterone may lead to an increase in placental va scular tone and possibly to a reduction of placental blood flow.