CHANGES IN THE CONTRACTILE RESPONSES TO CARBACHOL AND IN THE INHIBITORY EFFECTS OF VERAPAMIL AND NITRENDIPINE ON ISOLATED SMOOTH-MUSCLE PREPARATIONS FROM RATS SUBCHRONICALLY EXPOSED TO PB2+ AND ZN2+

Male Wistar rats were exposed to Pb2+ or Zn2+ and to Pb2+ +Zn2+, recei ving Pb(CH3COO)(2) or/and ZnSO4 with drinking water for 30 days. Cumul ative concentration-effect curves for carbachol were obtained in ileum and trachea isolated from control and heavy metal-treated rats. The e ffect of the Ca2+ channel blockers on the carbachol-induced contractio ns was studied by addition of increasing concentrations of verapamil o r nitrendipine to the bath solution 20 min. prior to carbachol. The re sults showed that exposure of rats to heavy metals in doses which did not change the body weight and behaviour, altered the contractile resp onses to carbachol. The sensitivity to carbachol was higher in prepara tions from the ileum of Zn2+-exposed rats as compared to controls, whi le a tendency towards decreasing this sensitivity was observed in ilea l preparations from Pb2+ treated animals. The concentration-effect cur ves for carbachol in ileal preparations from Pb2+ +Zn2+-treated rats d id not differ from those in the preparations from untreated rats. The inhibitory effect of the Ca2+ channel blockers on the contractility of ileal and tracheal preparations from treated rats was weaker as compa red to that in controls.