The effects of ritodrine on prostaglandin metabolite concentrations in the blood of pregnant baboons.

To investigate the relationship between beta sympathomimetic drugs and prostaglandins, we measured prostaglandin metabolites in the plasma of pregnant baboons that were given the drug ritodrine. Animals were at a mean gestation of 120 days, which is equivalent to 27 weeks in women. Ritodrine was infused i.v. at a rate of 23 micrograms/min or 80 micrograms/min for 4 h. Plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM), 11-deoxy-13,14-dihydro-15-keto-11,16-cyclo-prostaglandin E2 (PGEM-11), and 6-keto-prostaglandin-F1 alpha (6-keto-PGF1 alpha) were determined as indicators of the precursors, prostaglandin F2 alpha, prostaglandin E2, and prostacyclin (PGI2), respectively. At the 23 micrograms/min ritodrine infusion rate plasma levels of 6-keto-PGF1 alpha were decreased by 51% (+/- 15%) in the animals receiving the drug (p less than 0.005) whereas corresponding levels in control animals did not differ significantly from pre-infusion levels. At the 80 micrograms/min ritodrine infusion rate, the plasma levels of 6-keto-PGF1 alpha decreased by 66% (+/- 18%) compared with pre-infusion levels (p less than 0.001) but again the levels in control animals were not changed significantly. Plasma levels of PGFM and PGEM-11 in animals during ritodrine treatment did not differ significantly from baseline values.