Vascular responses of isolated mesenteric resistance and basilar arteries from short- and long-term diabetic rats

Vascular dysfunctions, e.g. alterations in the reactivity of blood vessels to neurotransmitters and hormones, are a well-established complication of d iabetes mellitus. Whether these impairments are a consequence of direct pos tsynaptic deficits and/or indirect presynaptic deficits remains to be deter mined. To this end, we investigated the influence of the duration of diabet es on relaxation and contraction responses of isolated mesenteric resistanc e and equally-sized basilar arteries to postsynaptic activation by various vasoactive agents, using streptozotocin-induced diabetic rats and age-match ed controls. Relaxation responses to vasodilator agents were studied in KCl -precontracted arteries. The duration of diabetes (4 or 40 weeks) did not a ffect the vasodilator responses to sodium nitroprusside or salbutamol in ei ther artery. In mesenteric resistance vessels from short-term (4 weeks) and long-term (40 weeks) diabetic rats the vasoconstrictor responses to KCI, s erotonin and vasopressin were the same as those in non-diabetic rats; howev er, the sensitivity (ECS,) to noradrenaline was slightly but significantly enhanced after the long-term diabetic state. In contrast to the mesenteric arteries, noradrenaline did not cause contraction in basilar arteries taken from diabetic and control rats. Thus, there appear to be important differe nces in the reactivity to noradrenaline of the peripheral and cerebral vasc ulature. The basilar artery from shortterm and long-term diabetic rats did not show different responsiveness to vasopressin whereas to serotonin a sig nificant enhanced and decreased sensitivity (EC10 and EC50) was demonstrate d in short-term and long-term diabetes, respectively. Our findings indicate that postsynaptic impairments do not play a major role in the alterations of vasoreactivity to vasodilators, noradrenaline or vasopressin seen in exp erimental diabetes. However, the duration of the diabetic state may have se rious consequences for vasoreactivity of basilar arteries to serotonin and, therefore, warrants further investigations.