[The effect of atrial natriuretic peptide on glucose tolerance and insulin level]

In previous studies, a pharmacological dose of human atrial natriuretic peptide (hANP) was found to increase serum insulin without influencing C-peptide levels. To examine whether blood glucose and insulin response to an oral or i.v. glucose load are influenced by raising hANP levels into the pathophysiological range, eight healthy, normal-weighted, male volunteers were studied. According to a randomized, double-blind study design, an oral glucose tolerance test (ogtt, 75 g) or an i.v. glucose tolerance test (ivgtt, 0.5 g/kg b.w.) were carried out. Beginning 30 minutes before glucose administration infusions of hANP 0.3 micrograms/min) or placebo were given for 180 minutes (ogtt) or 120 minutes (ivgtt). During the hANP-infusions maximal hANP levels were 72 +/- 11 pg/ml (normal less than 25 pg/ml). Responses of blood glucose and C-peptide levels to the glucose load remained unaffected by hANP in both studies. However, hANP increased mean insulin responses (given as area under the curve) by 11.5% in ogtt and by 15.9% in ivgtt (both p less than 0.05). Thus, elevated hANP levels within the pathophysiological range, as observed in chronic heart failure or in hypertension, lead to an increase in serum insulin. Unchanged C-peptide levels demonstrate that hANP does not interfere with insulin secretion, but exclusively inhibits insulin degradation in liver and/or kidney. Further studies are required to elucidate whether these findings play a part in the pathomechanisms of insulin resistance in patients with elevated hANP levels, e.g. in chronic heart failure or hypertension.