THE INHIBITORY-ACTION OF LEAD ON MECHANICAL RESPONSES OF THE PROVENTRICULAR SMOOTH-MUSCLE IN THE CHICK

The purpose of the present experiments was to examine the mechanism of the proventricular dilatation caused by lead in the isolated vagus ne rve-proventricular smooth muscle preparation of the chick. Lead caused dose- and time-dependent inhibition of contractions induced by vagal stimulation, transmural stimulation and externally applied acetylcholi ne (ACh). Vagally evoked contraction was much more sensitive to the in hibitory action of lead than the contractile response to ACh. The lowe r the frequency of transmural stimulation, or the lower the concentrat ion of ACh was applied, the greater the inhibitory action of lead on t he evoked smooth muscle contraction. The results suggest that proventr icular impaction occurring in lead poisoning results from the pre- and post-synaptic inhibition of the vagus nerve-smooth muscle transmissio n.