This study was undertaken to determine whether immunoreactive atrial natriuretic peptide (irANP) concentrations in plasma and atrial tissue are altered in experimental diabetes mellitus (DM), and to compare the response of the DM and normal groups to exogenous administration of ANP. OM was induced by intraperitoneal injection of 45 mg/kg streptozotocin in male Sprague-Dawley rats. After three weeks of established OM (glucosuria and blood glucose> 250 mg/dl), plasma irANP levels were 149.6 ± 19.4 pg/ml in the OM group (n = 18) and 86.3 + 12.9 pg/ml in the normal group en = 12, P <0.01). Atrial tissue irANP levels were significantly lower in the OM group (38.1 ± 7.8 ng/mg, n = 7) than in the normal group (60.1 ± 1.3 ng/mg, n = 4, P < 0.02). In response to intravenous infusion of ANP (2.5 ug/kg prime, followed by 0.1 ug/kg/min for 30 minutes), urine flow rate and urine sodium and potassium excretion rates increased significantly in the normal group (n = 6, P < 0.05), while no significant responses were found in the OM group (n = 6). It is concluded that plasma levels of ANP are significantly elevated in streptozotocin-induced diabetes in rats, and that atrial tissue stores are significantly depleted in this diabetic model. In addition, the renal response to exogenously administered ANP appears to be diminished in streptozotocin-induced OM. / Master of Science