Reduced preabsorptive insulin response in aged rats: differential effects of amphetamine and arginine-vasopressin

The experiments presented here have been designed to investigated whether the age-related attenuation of the vagal reactivity to emotional stressors and its modulation by amphetamine (Amph) or arginine-vasopressin (AVP) can be generalized for other physiological response patterns. We therefore studied the vagal control of the endocrine pancreas during food intake. Young (3 months old) and aged (27 months old) male Wistar rats were provided with permanent cardiac catheters allowing free movement and repeated, stress-free blood sampling. The vagally mediated preabsorptive insulin response (PIR) in relation to food intake as seen in young rats was reduced in aged ones. Blood glucose increments were the same at both ages. Administration of Amph (0.5 mg/kg; s.c.) 30 min before, or AVP (10 micrograms/kg; s.c.) 60 min before presentation of a test meal led to an elevation of the magnitude of insulin secretion in young rats but reduced the response in aged rats. Moreover, the PIR was not reinstated in aged rats. Blood glucose increments were not influenced by the treatments. The results are interpreted in terms of age-related general reduction of parasympathetic reactivity. The differential effect of amphetamine and AVP treatment on the insulin response suggests that the central aminergic or peptidergic drive of vagal output to the endocrine pancreas is also age-related.