Effects of intravenous isoxsuprine and ritodrine, with and without concomitant dexamethasone, on fetoplacental and pituitary hormones and cyclic adenosine monophosphate during late pregnancy.

Beta sympathomimetic drugs are used to inhibit preterm labor and glucocorticoids to accelerate fetal pulmonary maturation. A study was designed to investigate the hormonal effects of intravenous infusion of isoxsuprine 150 to 200 mcg. per minute or ritodrine 100 to 150 mcg. per minute in a series of 28 women at 28 to 40 weeks' gestation, with and without concomitant dexamethasone therapy. Serial serum samples taken before and during the six hours of infusion were assayed for cyclic adenosine-3,5-monophosphate (AMP), estradiol, estriol, progesterone, human placental lactogen (hPL), thyrotropin (TSH), follicle-stimulating hormone (FSH), and human growth hormone (gGH). Ritodrine was more potent than isoxsuprine in increasing the circulating levels of cyclic AMP. The levels of placental steroid hormones decreased slightly, as did the ratio of progesterone to estradiol. Human placental lactogen and pituitary hormones showed no consistent changes. Simultaneous administration of dexamethasone did not modify these results.