PHYSIOLOGICAL-EFFECTS OF MACROCYCLE-1 ON THE RABBIT CORPUS CAVERNOSUM

When the penis is in the flaccid state, the corpus cavernosum smooth m uscle is under adrenergic control in order to maintain the sinusoids i n a contracted condition (primarily via alpha-adrenergic stimulation), Penile erection is mediated by relaxation of corporal smooth muscle t hrough a variety of direct and indirect mechanisms. Pharmacological ag ents that either inhibit alpha-adrenergic transmission or facilitate c orporal smooth muscle relaxation will be beneficial for penile erectio n, Preliminary studies on macrocycle 1, a novel bioactive agent, demon strated that this compound inhibits receptor-stimulated contraction wi thout significantly altering field-stimulated contraction. The current study was designed to determine the physiological effects of macrocyc le 1 on the response of the rabbit corpus cavernosum to various forms of stimulation. Sexually mature male New Zealand White rabbits were us ed in this study, The corpus cavernosum was dissected sharply from the removed penis and two longitudinal strips were prepared for isometric tension studies. Each strip was prestimulated with 200 mu mol/l pheny lephrine to produce a maximal contraction. The influences of macrocycl e 1 (15.6, 62.5, 250, 1,000 mu mol/l) on both the contractile response to phenylephrine and the relaxant effects of field stimulation. carba chol, ATP and nitroprusside were determined, The results demonstrated that although basal tension was not altered, the contractile response to phenylephrine was decreased by 5, 18, 47 and 57%, respectively, by the different concentrations of macrocycle 1. The degree of relaxation induced by field stimulation of various frequencies was significantly enhanced by macrocycle 1 in a concentration-dependent manner. Similar ly, the degrees of relaxation induced by bethanechol, ATP and nitropru sside were all significantly enhanced in a concentration-dependent man ner. The conclusion from this study is that macrocycle 1 significantly inhibits phenylephrine-stimulated contraction and significantly enhan ces field-stimulated and pharmacologically induced relaxation. Althoug h the mechanisms of action are not clear, its physiological effects on the rabbit corpus cavernosum implicate a potential for the treatment of erectile dysfunction.