The effect of ethanol on inhibitory and motor responses in the rat and rabbit anococcygeus and the bovine retractor penis muscles.

1 Ethanol (200 mM) reduced the response to inhibitory nerve stimulation in the rat and rabbit anococcygeus and the bovine retractor penis (BRP) muscles. Ethanol also reduced the response to the inhibitory extract from the BRP consistent with the inhibitory factor in these extracts playing some part in the response to inhibitory nerve stimulation. 2 Ethanol's effect on the response to other inhibitory stimuli was examined in the rabbit anococcygeus and the BRP. In the anococcygeus the response to carbachol was reduced, to bradykinin and isobutylmethylxanthine (IBMX) unaltered, and to isoprenaline and adenosine 5'-triphosphate (ATP) potentiated. In the BRP responses to IBMX and sodium nitroprusside were unaltered but in this tissue the response to isoprenaline was reduced. Ethanol's ability to reduce inhibitory responses is, therefore, selective and confined to inhibitory nerve stimulation, inhibitory extract, carbachol, and, in the BRP, isoprenaline. 3 Ethanol reduced the rate of development of inhibition even where the magnitude of the inhibitory response was unaltered. 4 In the rat anococcygeus, ethanol (200 mM) potentiated the response to motor nerve stimulation and to noradrenaline (NA) at low frequencies and low concentrations respectively. Higher ethanol concentrations (400 mM) reduced the response to both motor nerve stimulation and NA. The motor response to carbachol was also reduced. 5 Ethanol (200 mM) itself caused an easily reversible contraction in all three tissues. This was not due to the release of NA but was highly sensitive to the removal of external calcium from the medium. 6 A unified explanation of these varied effects of ethanol based on a reduction in membrane binding of calcium and a reduced efficiency of receptor coupling is suggested.