Adrenergic modulation of reactive hyperemia in rat gut.

The hypothesis was tested that peripheral, adrenergic nerves modulate reactive hyperemia (RH) in the intestinal circulation. In anesthetized rats, anterior mesenteric arterial occlusion for 30-120 s elicited subsequent RH responses, including 63-118% increases in the velocity of arterial blood flow, even greater increases in conductance, and durations of 64-139 s. The longer the period of arterial occlusion, the greater the magnitude of RH. Electrical stimulation of postganglionic, sympathetic nerves reduced RH responses in a frequency-dependent manner. RH responses were enhanced by pretreatment with hexamethonium and phenoxybenzamine and were diminished by pretreatment with propranolol. Propranolol also prevented the enhanced RH responses caused by hexamethonium and phenoxybenzamine. Reserpine prevented the enhanced RH responses to hexamethonium, but bilateral adrenalectomy did not. These findings support the hypothesis that peripheral sympathetic nerves modulate RH in rat gut, with alpha-adrenergic receptors restricting and beta-adrenergic receptors enhancing the hyperemia.