Lead induction of crop dysfunction in pigeons through a direct action on neural or smooth muscle components of crop tissue.

Lead acetate solutions administered p.o. to pigeons produce crop stasis. Crop dysfunction may be an indirect effect on crop activity by a direct interaction with the cerebellum or some other site associated with lead-induced ataxia. Alternatively, crop stasis may be due to the direct interaction of lead with sites on the smooth muscle or neural elements in crop tissue. A behavioral test for ataxia was performed on pigeons given lead by crop intubation or i.m. injection. Blood lead concentrations were also monitored. Lead-induced ataxia was separable from lead-induced crop dysfunction depending on the route of lead administration, suggesting that lead-induced crop stasis is not secondary to toxicity at a site associated with ataxia. Intramuscular treatment produced crop stasis more readily than did crop intubation. This probably reflects different mechanisms of absorption and metabolism. A Tris-succinate medium was devised which accommodated the solubility characteristics of lead, permitting studies of crop tissue in vitro. Lead chloride added to crop tissue in tris-succinate medium caused a concentration-related reversible relaxation. Crop circular muscle was more sensitive to Pb++ than was longitudinal muscle, in agreement with the effects of other agonists. The EC30 of crop circular smooth muscle in plasma was 1000 microM PbCl2 compared to 3 microM in Tris-succinate medium. The results suggest that lead induces crop dysfunction by acting either directly on crop smooth muscle or on neural elements in crop tissue.