Response of the circulation of pregnant sheep to angiotensin and norepinephrine before and after dexamethasone

We studied the vascular reactivity of the systemic and uterine circulations of six pregnant sheep. We placed catheters in a maternal carotid artery and a jugular vein, and then implanted an electromagnetic flow transducer around the uterine artery of the pregnant horn. After allowing 3 days for recovery from anesthesia and operation, we measured mean arterial blood pressure, heart rate, uterine blood flow, and calculated uterine vascular resistance, then separately infused angiotensin and norepinephrine in each ewe at the rate that produced a 20 torr pressor response. Dexamethasone, 0.2 mg. per kilogram of body weight, was then injected intravenously daily for 2 to 4 days. On the day following the final injection of dexamethasone, we separately infused angiotensin and norepinephrine at a rate that, before steroid treatment, produced a 20 torr pressor response. Administration of dexamethasone for 2 to 4 days did not change mean arterial blood pressure, heart rate, uterine blood flow, or uterine vascular resistance. Prior to steroid treatment, angiotensin increased blood pressure, decreased heart rate, but had no consistent effect on uterine blood flow or uterine vascular resistance; norepinephrine increased blood pressure without chenging heart rate, decreased uterine blood flow, and increased uterine vascular resistance. The changes produced by angiotensin and norepinephrine were the same after dexamethasone treatment. These studies indicate that dexamethasone does not influence systemic and uterine vascular reactivity during normal sheep pregnancy.