Effects of subchronic exposure of rats to lead or zinc on alpha-adrenoceptor-mediated contractile responses in isolated vas deferens.

The effects of subchronic (30 days) drinking water exposure of rats to ZnSO4 or Pb(CH3COO)2 alone or in combination on the adrenergically-mediated contractile responses of isolated vas deferens were studied. The contractile effects of the alpha 1, alpha 2-adrenoceptor agonist noradrenaline (NA) and to the alpha 1-adrenoceptor agonist 1-phenylephrine (1-PhE) were decreased after zinc exposure, whereas after lead exposure or lead plus zinc exposure they were not changed. The contractile responses to field electrical stimulation (FES, 0.1 Hz, 1 msec, 80 V) were diminished in amplitude in all metal-treated preparations as compared to controls. The yohimbine-induced restoration of the clonidine inhibited contractions in response to FES was decreased in both lead- and zinc-treated preparations, the EC50 for yohimbine being 0.018 +/- 0.001 microM in control preparations, 0.073 +/- 0.019 microM in lead-treated preparations and 0.056 +/- 0.021 microM in zinc-treated preparations. The calcium-channel blocker verapamil was found to inhibit at low concentrations and to increase at higher concentrations the FES-induced contractile responses in preparations from zinc-exposed rats. The inhibitory effect of cumulatively applied nitrendipine on the FES-induced contractions was increased in both lead- and zinc-treated smooth muscles, but was not altered in the preparations from lead plus zinc-treated rats. Therefore, subchronic exposure to subtoxic doses of lead of zinc led to different changes in the adrenergically-mediated contractility of isolated vas deferens. The changes induced by zinc exposure were not observed after lead plus zinc exposure. All these findings might be of pharmacological, toxicological or clinical importance.