Modulation of calcium mobilization in aortic rings of pregnant rats: Contribution of extracellular calcium and of voltage-operated calcium channels

Pregnancy is associated with decreased vascular responsiveness to vasopress or stimuli. We have tested the involvement of Ca2+ mobilization in myotropi c responses of aortic rings obtained from pregnant and virgin rats. Contrac tions of the rings to phenylephrine, in the absence of calcium in the bathi ng medium, were lower in tissues from virgin than from pregnant rats. Conce ntration-response curves to CaCl2 that were measured after stimulation by p henylephrine in the absence of Ca2+ were shifted to higher levels of contra ction. This was not observed when KCI was used to prestimulate the aorta. D -600; a phenylalkylamine calcium channel blocker, similarly inhibited these responses to CaCl2 in tissues from both pregnant and virgin animals. D-600 exerted a concentration-dependent inhibition of responses to phenylephrine and KCI. However, the calcium antagonist was less effective in aortic ring s of pregnant than of virgin mts. Basal Ca-45(2+) uptake was lower in aorti c rings from pregnant than from virgin rats, and Bay K 8644 was unable to r everse this difference. The time course of basal and stimulated (KCl) Ca-45 (2+) influx was lower in aorta of pregnant rats at all times studied. Moreo ver, when the intracellular calcium pools were emptied with phenylephrine, the refilling of these pools was delayed in aortic rings of pregnant rats. These results indicate an altered extracellular calcium mobilization of aor tic rings from pregnant ra ts. These changes may be due to a functional alt eration of the voltage-operated calcium channels during pregnancy.