In vivo degradation and stimulating effect of phaseolin on nitrogen secretion in rats

In short-term feeding experiments, about 78% of the phaseolin administered to rats was degraded regardless of the amounts of phaseolin intubated. In contrast, the total N found in the feces increased rapidly and exceeded the original administered amounts. The bulk of N output was not immunologically related to the glycoprotein. The effects of phaseolin on the stimulation of endogenous N secretion in the small intestine were confirmed from the results of acute experiments. Phaseolin fragments, derived from the breakdown of the native protein, when reapplied intragastrically to rats, were broken down further and to a similar extent as the original glycoprotein and were even more potent related to stimulation of N secretion. It is suggested that this secretagogue biological activity of phaseolin and not its resistance to gut proteolysis, is the main reason for the poor nutritional value of this glycoprotein.