Decrease in muscarinic cholinergic response of the rat heart following treatment with 6-hydroxydopa.

Pretreatment with 6-hydroxydopa (6-OHDOPA) at birth produced a decrease in the number of [3H]quinuclidinyl benzilate ([3H]QNB) binding sites in adult rat heart homogenates. The treatment caused hyposensitivity to acetylcholine (ACh) but did not alter the maximal negative inotropic action of ACh in isolated atria of the rat. These results suggest that 6-OHDOPA affects the negative inotropic response to ACh by modifying the receptor number or through an effect on a step between receptor activation and biological response.