ABSORPTION OF AMINO-ACIDS FROM THE INTESTINE AND THEIR NET FLUX ACROSS THE MESENTERIC-DRAINED AND PORTAL-DRAINED VISCERA OF LAMBS

Experiments were conducted to compare the rates of apparent absorption (disappearance) of individual essential amino acids (EAA) from the sm all intestine with their net fluxes across the mesenteric- (MDV) and p ortal- (PDV) drained viscera in sheep given a pelleted alfalfa diet at two levels of intake. Disappearances of individual EAA across the reg ion of the small intestine drained by the mesenteric arcade (jejunum t o ileum) were similar to those across the whole of the small intestine (duodenum to ileum). The net MDV flux of each EAA was similar to its rate of disappearance, but, with the exception of threonine on the low intake level, the net PDV flux was lower (P < .05). Increasing the in take of alfalfa from 800 to 1,200 g/d increased the rate of disappeara nce of individual EAA between the duodenum and ileum by .56 (range .43 to .65) and between the jejunum and ileum by .51 (range .45 to .60). The MDV and PDV blood flows increased by .35 and .39, respectively, an d, with the exception of valine, net fluxes of individual EAA increase d by .39 (range .20 to .50) across the MDV and by .44 (range .21 to .7 1) across the PDV. When net fluxes across the MDV and PDV were measure d simultaneously, the ratio of PDV: MDV flux for each EAA was less tha n (P < .05) unity (mean .61, range .55 to .69), even though all MDV bl ood enters the PDV, contributing approximately .45 of the total portal flow. This observation suggests that, in regions of the tract not dra ined by the MDV, extraction of arterial blood EAA for tissue and secre tory protein synthesis must exceed the release of protein degradation products into the venous drainage. The results are discussed in terms of endogenous protein secretions into the lumen of the tract anterior to the small intestine.