Beta-adrenergic receptor agonist infusion increases plasma prostaglandin F levels in pregnant sheep.

Recent evidence of a stimulatory effect of beta-adrenergic receptor agonists on prostaglandin production by human fetal membranes in vitro prompted us to investigate whether prostaglandins are increased during beta-agonist infusion in vivo. On days 120 to 125 of gestation, blood samples were drawn from the aorta and vena cava of five crossbred ewes at 15-minute intervals for 1 hour before, during, and for 1 hour after a 3-hour infusion of isoproterenol (0.16 microgram/kg/min) or normal saline solution. Plasma prostaglandin F2 alpha levels increased (177% +/- 13% SEM over baseline; p less than 0.002) in maternal aorta, while plasma 13,14-dihydro-15-keto prostaglandin F2 alpha levels increased in both aorta and vena cava (354% +/- 47% and 309% +/- 75% over baseline, respectively; p less than 0.002) during isoproterenol infusion but not during saline solution infusion. No change was seen in plasma prostaglandin E2 levels. The increase in plasma stimulatory prostaglandins in the pregnant ewe during beta-agonist infusion is compatible with the increased uterine activity observed after myometrial desensitization by continuous beta-agonist infusion.