Occlusion of cremaster collateral circulation alters microvascular reactivity

Surgical preparation of the rat cremaster skeletal muscle for microvascular study usually involves occlusion of the deferential artery and vein which supply a collateral circulation to the tissue. This allows removal of the testis and ductus deferens, and permits direct observation of the cremaster microvasculature. We examined with intravital microscopy the effect of this occlusion on alpha-adrenergic and nonreceptor-mediated (KCl) constriction of large arterioles (1A, 136 microns i.d.) and venules (1V, 193 microns i.d.). The acutely denervated cremaster was suspended in a tissue bath containing propranolol to block beta-adrenergic receptors. alpha 1-adrenergic (norepinephrine (NE) + rauwolscine), alpha 2-adrenergic (NE + prazosin), and KCl (+ phentolamine) concentration-response curves were obtained for bath-added agonists before vs after occlusion of the deferential circulation. Occlusion had no effect on baseline 1A diameter but increased 1V diameter slightly. Arteriolar alpha 1- and alpha 2-adrenergic sensitivities were unaffected by occlusion, but venular sensitivities were reduced by the same amount (approximately fourfold) for both receptor types. Occlusion increased arteriolar sensitivity to KCl but had no effect of venular KCl sensitivity. These data indicate that occlusion of the deferential collateral circulation can produce significant and varied effects on alpha-adrenoceptor and nonreceptor-mediated constriction of cremaster large arteriolar and venular smooth muscle, and underscore the need to avoid collateral occlusion for certain studies of the cremaster microcirculation.