Regulation of colonic blood flow.

Intrinsic and extrinsic regulation of colonic blood flow is reviewed. The existence of intrinsic vascular control mechanisms is evidenced by pressure-flow (and oxygen uptake) autoregulation, reactive hyperemia, vascular responses to acute venous hypertension, and functional hyperemia in denervated colon preparations. Although myogenic factors have long been considered to be solely responsible for the intrinsic ability of the colon to regulate its blood flow, recent developments indicate that metabolic mechanisms may be of equal importance in this regard. Both parasympathetic and sympathetic nerves play an important role in regulating colonic blood flow. Although many hormones and circulating vasoactive substances alter colonic hemodynamics, their contribution toward the overall regulation of colonic blood flow remains uncertain.