Changes in plasma cyclic AMP and cyclic GMP during spontaneous labor and labor induced by oxytocin, prostaglandin F2 alpha and prostaglandin E2

To investigate the response of cyclic nucleotides to the oxytocic agents administered for induction of labor, plasma concentrations of cyclic AMP (cAMP) and cyclic GMP (cGMP) were determined by radioimmunoassay during spontaneous labor and labor induced by oxytocin (OT), prostaglandin F2 alpha (PGF2 alpha), or PGE2 (PGE2). Subjects were 7 Japanese women in each labor group. Plasma cAMP levels significantly rose at the time of crowning of the fetal head in all 4 groups. They did not increase until that time in the 3 labor groups (spontaneous, OT-induced, and PGF2 alpha-induced labor groups). In the PGE2-induced labor group, plasma cAMP levels were significantly higher at labor onset (mean +/- SEM = 16.5 +/- 1.3 pg/ml) when compared to the pretreatment values (13.7 +/- 1.0 pg/ml), and increased thereafter gradually toward the time of crowning of the head (26.3 +/- 2.0 pg/ml). Plasma cGMP levels in the OT-induced group significantly rose after the onset of labor and remained at a high level until expulsion of the fetus. Plasma cGMP levels in the other groups did not change significantly throughout labor. These results suggest that cAMP may be involved in the labor process induced by PGE2, and that cGMP may be in that induced by OT.