The relative contribution of the nervous system, hormones, and metabolites to the total insulin response during a meal in the rat.

An attempt was made to quantitatively determine the relative contribution of the nervous system, hormonal factors, and metabolites to the total peripheral plasma insulin response (integrated incremental area) during a ten-minute liquid meal in conscious freely moving rats. The neurally mediated insulin response, as measured in the gastric-fistula bearing sham-feeding rat, amounted to at least 26%. The possible contribution of neural mechanisms triggered by the gastric, intestinal, and postabsorptive phases of the meal were, however, not determined. Hormonal factors were found to contribute at least 30% to the total insulin response on the basis of the insulin response to real feeding in atropinized rats, in the absence of any increases of plasma glucose and with only small elevations of plasma alpha-amino nitrogen. A possible atropine-suppressible hormonal factor was not isolated in the present study. Finally, the relative contribution of rising plasma glucose as determined by intravenous glucose infusions was found to amount to no more than 20%; however, the contribution of rising plasma amino acids was not determined. Thus, 23% of the total insulin response could not be segregated, but it is thought that a good part of it can be attributed to synergistic mechanisms. Because of such interactions, the sum of the effects of the isolated factors is less than the effect of the combined factors.