The roles of hepatic nerves in the reduction of food intake as a consequence of intraportal sodium propionate administration in sheep.

Like other mammals, ruminants can also control their food intake. One of the potential sites where feed-back signals arise is the liver. We have already shown in our previous study that intraportal administration of propionate depresses intake and that this action is dependent on an intact nerve supply to the liver because sectioning the hepatic plexus abolishes the effect of propionate. In the following work the relative importance and the possible roles of different hepatic nerves were investigated. Three-hour continuous infusions of sodium propionate or saline into the hepatic portal vein of sheep were carried out following applications of different surgical procedures and food intakes were measured. In experiment 1 bilateral splanchnotomies were sufficient to prevent the effect of propionate on food intake. The subsequent total hepatic denervations also resulted in the removal of the depressing effect of propionate. Experiment 2 was designed to compare the involvement of the splanchnic afferents from the liver and the hepatic vagal afferents. Intraportal propionate was demonstrated to depress feeding in the intact animal whereas splanchnic nerve blockade with local anaesthetic removed this effect. Paradoxically selective hepatic vagotomy also abolished this effect. It was concluded that there may be more than one pathway involved in transmitting information from the liver to the central nervous system. Possible implications of the results are discussed and attempts are made to explain the mechanism of action and compare different theories by other workers.