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 Co2+ and Ni2+.

Male Wistar rats were exposed to subtoxic doses of Co2+ or Ni2+, receiving Co(NO3)2 or NiSO4 with drinking water for 30 days. No significant differences in the body weight and no visible changes in the behaviour of the controls and experimental animals were established. Cumulative concentration-effect curves for carbachol were obtained in ileum and trachea isolated from control and Co(2+)- or Ni(2+)-treated rats. The effect of the Ca2+ antagonists on the carbachol-induced contractions was studied by adding increasing concentrations of verapamil or nitrendipine to the bath solution 20 min prior to carbachol. The results showed that exposure of rats to subtoxic doses of Co(NO3)2 or NiSO4 altered the contractile responses to carbachol. The changes in the pD2 values and the shift to the left of the concentration-effect curves suggest a higher sensitivity to carbachol in preparations from the ileum of Co(2+)- or Ni(2+)-exposed rats. The tracheal strips isolated from control and heavy metal-treated rats showed a less potent sensitiveness to carbachol as compared to the ileal segments. An opposite tendency for decreased cholinergic reactivity was observed in tracheal strips from Co(2+)- and Ni(2+)-treated animals. The inhibitory effect of the Ca(2+)-antagonists on the contractility of ileal preparations from Co(2+)-treated rats increased at all concentrations of verapamil and at the highest concentration of nitrendipine, but decreased at lower concentrations of nitrendipine. The effect of verapamil on the preparations from Ni(2+)-exposed rats was unchanged or even decreased at higher verapamil concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)