INVITRO CONTRACTILE RESPONSE OF THE RABBIT CORPUS CAVERNOSA TO FIELD STIMULATION AND AUTONOMIC AGONISTS AND ANTAGONISTS - A QUALITATIVE STUDY

Field stimulation of rabbit corporus cavernosum tissue strips can result in relaxation, contraction, or a biphasic response depending on the frequency and the power utilized. In this study we characterized the autonomic components of this response by exposing corporal tissue strips to a variety of autonomic agonists and antagonists including phentolamine, isoproterenol, methoxamine, propranolol, bethanechol, atropine, and ATP. Low frequency electrical field stimulation produced a bi-phasic response characterized by an initial relaxation followed by a contraction. High frequencies (greater-than-or-equal-to 32 Hz) produced contraction only. All responses were abolished by tetrodotoxin, indicating that both the contractile and relaxant responses to field stimulation are mediated by complex neural mechanisms. The initial relaxation response involves a combination of mediators which include muscarinic cholinergic stimulation, purinergic, beta-adrenergic, and non-adrenergic, non-cholinergic (NANC) stimulation. The non-cholinergic contribution to corporal smooth muscle relaxation appeared to be approximately equal in significance to the cholinergically mediated relaxation. Beta adrenergic stimulation mediated a direct relaxation of the corporal smooth muscle. The contractile portion of the bi-phasic response was mediated by alpha-adrenergic stimulation. Additionally we have noted a rebound contraction following termination of field stimulation at all frequencies that is not affected by adrenergic or cholinergic blockade and may reflect the field-stimulated release of an endogenous smooth muscle contractile factor.