An examination of vascular reactivity during pregnancy in the chronic ewe model

The hind limb vascular responses to angiotensin II and phenylephrine, an alpha-adrenergic agonist, were determined in chronically instrumented pregnant (n = 7) and castrated (n = 6) ewes. On any one day, five doses of one or the other drug were administered directly into the arterial femoral circulation while the perfusion pressure and external iliac blood flow were monitored. The steady-state resistance change (baseline resistance - the resistance calculated during the 3 to 5 minutes of drug infusion) showed a reduction in vascular response to angiotensin II in the pregnant ewes compared to the controls, with no significant differences in response to phenylephrine. When the dynamic (within 40 seconds) rather than the steady-state changes were analyzed, a hyperreactivity to phenylephrine was present in the pregnant animals. These data are an illustration of the complex interactions that are present in the whole-body pressor responses to vasoactive stimuli during pregnancy.