Nutritional toxicology of mammals: regulated intake of plant secondary compounds

Many mammalian herbivores continually face the possibility of being poisoned by the natural toxins in the plants they consume. A recent key discovery in this area is that mammalian herbivores are capable of regulating the dose of plant secondary compounds (PSCs) ingested. The 'regulation model' describes the factors driving ingestion of PSCs by mammals and can be dissected into two separate hypotheses related to meal size and inter-meal interval (IMI). Testing these hypotheses independently yields a more thorough understanding of the underlying and potentially interconnected mechanisms. Three mechanisms could influence the size of meals that contain PSCs. These are the plasma concentration of PSCs, conditioned learning, and activation of bitter receptors in the intestine. Two mechanisms are proposed to govern the IMI. The first predicts that IMI is dependent on the concentration of PSC metabolites in the plasma; feeding will not resume until metabolite concentrations are acceptable for further ingestion of PSCs. The second hypothesis proposes that the intestinal bitter receptors modulate IMI through release of satiety compounds.