AGI March 41/3

Nankervis, Craig A., and Philip T. Nowicki. Role of endothelin-1 in regulation of the postnatal intestinal circulation. Am. J. Physiol. Gastrointest. Liver Physiol. 278: G367– G375, 2000.—Newborn intestine is uniquely prone to vasoconstriction in response to a wide variety of perturbations. To test the hypothesis that endothelin (ET)-1 is an important factor in this process, we determined the effects of exogenous ET-1 administration and blockade of endogenous ET-1 in vivo and in vitro in 3and 35-day-old swine. Intramesenteric artery administration of exogenous ET-1 to vascularly isolated in vivo gut loops (1029 M/kg bolus) caused vasoconstriction and reduced gut O2 uptake similarly in these age groups. Selective blockade of ETA or ETB receptors with BQ-610 or BQ-788, respectively, in vascularly isolated in vivo gut loops had no effect on gut vascular resistance or O2 uptake in either age group; within in vitro gut loops, BQ-610 significantly increased vasoconstriction when perfusion pressure was reduced below baseline, but only in 3-day-old animals; i.e., it impaired the autoregulatory response to perfusion pressure reduction. Exogenous ET-1 significantly decreased capillary perfusion within in vitro gut loops, as evidenced by a decrease in capillary filtration coefficient, but only in 3-day-old animals; furthermore, blockade of endogenous ET-1 activity with BQ-610 significantly enhanced capillary filtration coefficient in 3-day-old animals and increased O2 extraction ratio. ET-1 did not depress intestinal metabolic rate, as evidenced by its effect on the O2 uptake-blood flow relationship; it did compromise tissue oxygenation because of its effects on intestinal O2 transport. ET-1 concentration in mesenteric venous effluent exceeded arterial concentration, but only in 3-day-old intestine, suggesting production of ET-1 by newborn intestine. We conclude that ET-1 exerts an age-dependent effect on intestinal hemodynamics in postnatal intestine, having a greater impact in 3than in 35-day-old intestine.