Vascular catecholamine sensitivity during pregnancy in the ewe.

Four pregnant and four castrated ewes were chronically instrumented for the measurement of external iliac blood flow to test the hypothesis that pregnancy alters alpha-adrenergic sensitivity in a major regional circulation. Complete dose-response curves were generated to methoxamine, phenylephrine, and norepinephrine. Pregnancy was associated with no change in methoxamine sensitivity, an increase in phenylephrine sensitivity, and a decrease in norepinephrine sensitivity. These differential changes in drug sensitivity suggest (1) the alpha 1-receptor population is functionally similar between the two groups of animals, (2) uptake 1 is inhibited, and (3) either catechol-O-methyltransferase activity is increased or the alpha 2- or beta-receptor population changes in this circulation during pregnancy. These data illustrate the complexity of the change in the adrenergic system during pregnancy.