Coronary and peripheral vascular resistance in the anaesthetized diabetic sheep

To determine whether vascular resistance was altered in diabetes, the vascular resistance in both the peripheral arterial bed and the circumflex coronary artery was compared in six normal and five diabetic adult sheep, under pentobarbitone anaesthesia. Diabetes induced by alloxan significantly increased blood glucose (15.6 mmol/l, s.e.m. = 2.8, vs 5.5 mmol/l, s.e.m. = 0.6; P greater than 0.001) compared with controls. Systolic blood pressure was lower in diabetics (92 mmHg, s.e.m. = 12, vs 123 mmHg, s.e.m. = 5; P less than 0.025) as was diastolic blood pressure (73 mmHg, s.e.m. = 15, vs 104 mmHg, s.e.m. = 4; P greater than 0.05). Basal peripheral resistance was lower in diabetics than controls (36.0 mmHg.min/l, s.e.m. = 7.9, vs 42.3 mmHg.min/l, s.e.m. = 2.8), but not significantly so. Methoxamine markedly increased peripheral vascular resistance in both groups, but did not change coronary vascular resistance, due to autoregulation. The dose-response curves of peripheral or coronary arteries to methoxamine showed no significant difference between diabetic and control sheep. Dose-response curves for isoprenaline and noradrenaline infusion suggested there may be altered beta-receptor sensitivity in diabetes. In conclusion, there are marked differences in the vascular beds of diabetic and normal sheep under basal conditions. In contrast to previous studies, alpha-adrenoceptors are not different in diabetics, but further studies in unanaesthetized animals are indicated, as beta-receptor sensitivity may be altered in diabetes.