Relationship between atrial granularity and release of atrial natriuretic factor in rats with diabetes mellitus

We examined the effect of a 25% blood volume expansion on the release of atrial natriuretic factor (ANF) in conscious Wistar rats (13-15 wk old) injected 6 wk earlier with streptozotocin (55 mg/kg iv, diabetic) or saline (1 ml/kg iv, control). The diabetic rats demonstrated a significant (P less than 0.05) resting hypotension (132 +/- 2/91 +/- 1 mmHg, systolic/diastolic) and bradycardia (340 +/- 5 beats/min) compared with the controls (145 +/- 2/98 +/- 2 mmHg, 377 +/- 8 beats/min). Resting plasma immunoreactive (IR) ANF levels were significantly (P less than 0.05) elevated in the diabetic rats (control: 72 +/- 4 pg/ml; diabetic: 87 +/- 4), although resting right atrial pressures were not different (control: 6.0 +/- 0.8 cmH2O; diabetic: 5.2 +/- 0.6). Volume expansion with donor blood from similarly treated animals significantly (P less than 0.05) elevated IR ANF levels in both groups, but the increase in the saline-injected group (+527 +/- 80 pg/ml) was significantly (P less than 0.05) greater than that of the streptozotocin-injected group (+323 +/- 45 pg/ml). Both groups showed similar elevations in right atrial pressure (control: +1.8 +/- 0.3 cmH2O; diabetic: +1.6 +/- 0.4). Morphological examination of tissue taken from right atria demonstrated no difference in cardiocyte volume percent per unit of tissue but a significant (P less than 0.05) reduction in the relative frequency of occurrence of atrial granules in the diabetic group. The cause of the reduction in atrial granularity in these animals is as yet unknown.