Changes in function of cardiac receptors mediating the effects of the autonomic nervous system in the muscular dystrophy (MDX) mouse.

Adrenergic and muscarinic receptor mediated effects on the force of contraction and heart rate were studied in the isolated left atria and right atria from dystrophin-deficient mdx mice and age matched C57BL/10ScSn (C57) mice, respectively. The pD(2) and pA(2) values of (-)-isoprenaline and CGP 20712A, respectively, were not different in left atria and right atria from mdx and C57 mice. (-)-Phenylephrine produced a small positive inotropic effect on mdx left atria that could be antagonized by prazosin, whereas in C57 left atria no positive inotropic response was seen. In contrast, the positive chronotropic effect of (-)-phenylephrine was reduced in right atria from mdx compared to C57 right atria (P<0.05). The potency and efficacy to carbachol in the presence of (-)-isoprenaline were higher in right atria from mdx compared to C57 mice (P<0.05), although in left atria only a greater efficacy was evident in mdx mice. In left atria, basal force of contraction and maximum Ca(2+)-induced increases in force of contraction were lower from mdx compared to C57 mice (P<0. 001 and P<0.05, respectively). In conclusion, marked changes were demonstrated in the function of alpha1-adrenoceptors and muscarinic receptors, but not in beta1-adrenoceptors in left and right atria from mdx mice.