The effects of drugs on the sensitivity of the rat anococcygeus muscle to agonists

Abstract

1 The effects of cocaine, 6-hydroxydopamine (6-OHDA), reserpine and 17-β-oestradiol on the sensitivity of the rat anococcygeus muscle to noradrenaline (NA), acetylcholine (ACh) and KCl were investigated. 2 Cocaine (10⁻⁵m) increased the sensitivity of the anococcygeus to NA (100-fold) but not to ACh or KCl. 3 6-OHDA treatment, whether discontinuous over 6 days or continuous for 12 days, also produced a specific increase in sensitivity to NA (50-fold). 4 Reserpine ((1 mg/kg)/day) produced a small increase in sensitivity of the muscle to NA and ACh but not to KCl, after 6 days and 12 days treatment. 5 17-β-Oestradiol (10_–⁵m) had no effect on the sensitivity of the anococcygeus to NA or ACh, but reduced the sensitivity to KCl and the possible mechanism of this effect is discussed. 6 Cocaine increased, while reserpine, 6-OHDA and 17-β-oestradiol decreased, the maximum response of the muscle to KCl. The response to KCl was shown to consist of at least three components; a direct action on the muscle, an effect due to release of NA, and an inhibitory action, probably due to release of the unknown inhibitory transmitter.