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Modulation of Calcium Mobilization in Aortic Rings of Pregnant Rats:Contribution of Extracellular Calcium and of Voltage-Operated Calcium Channels

^a Laboratoire de Recherche en Pharmacologie Périnatale, Hôpital Ste-Justine and Departments of Obstetrics and Gynecology and of Pharmacology, University of Montréal, Montréal, Québec, Canada H3T 1C5

Pregnancy is associated with decreased vascular responsiveness to vasopressor stimuli. We have tested the involvement of Ca²⁺ mobilization in myotropic responses of aortic rings obtained from pregnant and virgin rats. Contractions of the rings to phenylephrine, in the absence of calcium in the bathing medium, were lower in tissues from virgin than from pregnant rats. Concentration-response curves to CaCl₂ that were measured after stimulation by phenylephrine in the absence of Ca²⁺ were shifted to higher levels of contraction. This was not observed when KCl 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 KCl. However, the calcium antagonist was less effective in aortic rings of pregnant than of virgin rats. Basal ⁴⁵Ca²⁺ uptake was lower in aortic rings from pregnant than from virgin rats, and Bay K 8644 was unable to reverse this difference. The time course of basal and stimulated (KCl) ⁴⁵Ca²⁺ influx was lower in aorta of pregnant rats at all times studied. Moreover, 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 aortic rings from pregnant rats. These changes may be due to a functional alteration of the voltage-operated calcium channels during pregnancy.

¹ Correspondence: Jean St-Louis, Centre de Recherche, Hôp. Ste-Justine, 3175 ch. Côte Ste-Catherine, Montréal, PQ, Canada H3T 1C5. FAX: 514 345 4994; stlouisj{at}ere.umontreal.ca

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