Catecholamine-mediated reduction in uterine blood flow after nicotine infusion in the pregnant ewe.

The effect of nicotine on uterine blood flow, uterine vascular resistance, and plasma catecholamine concentration was studied in chronically catheterized pregnant sheep equipped with electromagnetic flow probes. The systemic administration of nicotine (14--32 micrograms/kg body wt per min) resulted in a 44% reduction in uterine blood flow (P less than 0.001) and a 203% increase in uterine vascular resistance. Both responses were inhibited by pretreatment with the alpha blocker, phentolamine. Arterial plasma concentrations of norepinephrine and epinephrine, measured by a single isotopic radioenzymatic assay, rose (from 117.9 +/- 6.7 to 201.8 +/- 13.3 pg/ml, P less than 0.001; and from 71.6 +/- 4.5 to 124.1 +/- 8.4 pg/ml, P less than 0.001, respectively) during nicotine infusion. The findings suggest that nicotine exerts a deleterious effect on uterine blood flow mediated through the release of catecholamines.