Regulation Of Blood Flow And Microcirculation Resistance In Rabbit Bladder

Abstract

Human and animal studies have shown that filling, contraction and emptying produce cyclical changes in bladder blood flow. The mechanism of these hemodynamic changes remains unclear. We studied the regulation of bladder blood flow in the rabbit model. A total of 18 male New Zealand White rabbits were anesthetized. Arterial pressure, intravesical pressure, and dome and base blood flow were measured simultaneously in the empty bladder, at 25 and 50 ml. intravesical volume, and after draining. These measurements were recorded before and then after intravenous administration of atropine, phentolamine, propranolol, L-arginine or N-nitro-L-arginine. Changes in dome and base microcirculation resistance, and blood flow after treatment were compared with those recorded before treatment. In the empty bladder dome microcirculation resistance was greater than at the base and base blood flow was greater than at the dome. Filling increased dome microcirculation resistance, decreased dome blood flow and increased base blood flow without changing base microcirculation resistance. Emptying produced much greater reactive hyperemia at the dome than at the base. Atropine did not alter microcirculation resistance or blood flow. Phentolamine had no effect on dome or base microcirculation resistance, blood flow in the empty bladder or at 25 ml. intravesical volume but it decreased dome microcirculation resistance at 50 ml. intravesical volume. Propranolol caused dome contraction, increased dome microcirculation resistance and decreased dome blood flow in the empty bladder, and at 25 and 50 ml. intravesical volume. Propranolol increased base blood flow without changing base microcirculation resistance. N-nitro-L-arginine increased dome microcirculation resistance in the empty bladder and at 25 ml. intravesical volume but decreased dome blood flow in the empty bladder alone. N-nitro-L-arginine increased base microcirculation resistance and decreased base blood flow in the empty bladder and at 25 ml. intravesical volume but not at 50 ml. intravesical volume. L-arginine decreased dome and base microcirculation resistance, and increased blood flow in the empty bladder, and at 25 and 50 ml. intravesical volume. Reactive hyperemia decreased after N-nitro-L-arginine and increased after L-arginine. Our studies show large variations in bladder dome and base microcirculation resistance and blood flow. Bladder blood flow appears to be largely regulated locally by nitric oxide mediated changes in bladder microcirculation resistance. beta-adrenergic receptors may regulate bladder blood flow indirectly by modulating dome tension and shifting blood flow between the dome and base. Mechanical changes in bladder wall and vasculature shape may also contribute to changes in microcirculation resistance.