INS and Hyperglycemia: It should be noted that several studies have defined an inhibitory effect of acute direct/autocrine/paracrine dopamine on beta cell glucose stimulated insulin secretion (GSIS) in animals and man [38–41], with a potential role for gastrointestinal L-DOPA as an endogenous source for such physiological beta cell dopamine responses that may potentiate hyperglycemia [41].