VASCULAR REACTIVITY TO NORADRENALINE AND NEUROPEPTIDE-Y IN THE STREPTOZOTOCIN-INDUCED DIABETIC RAT

The study aimed to assess vascular reactivity to noradrenaline with an d without neuropeptide Y in diabetic rats, and to determine whether an y abnormality could be attributed to insulin deficiency or to hypergly caemia per se. The authors compared nondiabetic rats (n = 9) and rats with streptozotocin-induced diabetes that were either untreated (n = 1 0), or treated with insulin (n = 9) or food restriction (n = 8) to res tore near-normoglycaemia. After 4 weeks of diabetes, contractile respo nses to noradrenaline (0.24-48 mu mol L(-1)), without and with neurope ptide Y (0.1 mu mol L(-1)), were assessed using an isometric myograph in two mesenteric arteries from each rat. Vessels from untreated diabe tic rats were significantly more reactive to noradrenaline than the co ntrol vessels when tested without (P < 0.0001) but not with (P = NS) n europeptide Y. Diabetic rats rendered nearly normoglycaemic through fo od restriction showed dose-response curves that were very similar to t he untreated diabetic group (P = NS). By contrast, insulin-treated dia betic vessels showed reduced sensitivity to noradrenaline, with and wi thout neuropeptide Y, compared with both the diet-restricted and untre ated vessels (both P < 0.0001). The authors conclude that vascular sen sitivity to noradrenaline, without or with neuropeptide Y, is reduced over a wide dose range in vessels taken from rats treated in vivo with insulin; furthermore, vessels taken from diabetic rats not treated wi th insulin (hypoinsulinaemic) tended to be more reactive than either c ontrol vessels or those taken from the insulin-treated rats. The latte r group of rats were probably hyperinsulinaemic for much of the time; the results may therefore support the hypothesis that insulin acts as a vasodilator.