Developmental intestinal vascular responses to venous pressure elevation.

The response to venous pressure elevation is an important criterion for determining whether metabolic or myogenic mechanisms are involved in local vasoregulation. We studied the effects of venous pressure elevation on intestinal hemodynamics and oxygenation in 20 mixed-breed piglets, divided equally among 1-day-, 3-day-, 2-wk-, and 1-mo-old animals. A venous circuit was established between the superior mesenteric and jugular veins, which allowed measurement of superior mesenteric blood flow, venous pressure, capillary pressure, and arteriovenous oxygen difference at venous pressures between 0 and 20 mmHg. The resting intestinal oxygen uptake in 1-day-old piglets was significantly higher than in 2-wk-old and 1-mo-old piglets. The vascular response to venous pressure elevation in 1-day-old piglets was characterized by reductions in total and precapillary resistance and increased oxygen uptake, while older animals responded to venous pressure elevation with increases in total and precapillary vascular resistance and reductions in oxygen uptake. These results indicate that metabolic factors exert a dominant influence on the intestinal vasculature of the newborn, while myogenic factors predominate in older animals in response to venous pressure elevation.