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

Abstract
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 μg/min or 80 μg/min for 4 h. Plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F (PGFM), 11-deoxy-13,14-dihydro-15-keto-11,16-cyclo-prostaglandin E2 (PGEM-11), and 6-keto-prostaglandin-F (6-keto-PGF) were determined as indicators of the precursors, prostaglandin F, prostaglandin E2, and prostacyclin (PGI2), respectively. At the 23 μg/min ritodrine infusion rate plasma levels of 6-keto-PGF were decreased by 51% (± 15%) in the animals receiving the drug (p < 0.005) whereas corresponding levels in control animals did not differ significantly from pre-infusion levels. At the 80 μg/min ritodrine infusion rate, the plasma levels of 6-keto-PGF decreased by 66% (± 18%) compared with pre-infusion levels (p < 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.

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