Masked function of amino acid sensors on pancreatic hormone secretion in ventromedial hypothalamic (VMH) lesioned rats with marked hyperinsulinemia

SummaryIn neural regulation of the endocrine pancreas, there is much evidence to suggest that vagal efferents alter insulin and glucagon secretion, but less information on the effects of vagal afferents. In this study, we investigated the role and function of afferent fibers of the vagus nerve in normal and ventromedial hypothalamic (VMH) lesioned rats with marked hyperinsulinemia. In normal rats, hepatic vagotomy was associated with intraperitoneal (ip) arginine-induced enhancement of insulin and glucagon secretion without an accompanying change in blood glucose levels, ip leucine induced enhancement of insulin secretion accompanied by a decrease in blood glucose levels, and ip alanine-induced enhancement of glucagon secretion accompanied by an increase in blood glucose levels. In VMH lesioned rats with marked hyperinsulinemia, none of these amino acids caused significant changes in insulin and glucagon secretion. We conclude that amino acid sensors in normal rats inhibit excess release of pancreatic hormones induced directly by intake of amino acids, such as that in excess protein ingestion, and maintain blood glucose levels within the normal range. In contrast, in VMH lesioned rats with marked hyperinsulinemia, the function of the amino acid sensors is masked due to the marked hyperinsulinemia in these rats.