SUPERSENSITIVITY OF ISOLATED MESENTERIC ARTERIES TO NORADRENALINE IN THE LONG-TERM EXPERIMENTAL DIABETIC RAT

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Abstract
Noradrenaline[norepinephrine, NE]-induced vascular contractions in isolated rat mesenteric series were studied in short- and long-term experimental diabetic rats. The diabetic state was induced with streptozotocin (65 mg/kg, i.v.). Long-term diabetic rats were hypertensive when compared to age-matched control rats. Short-term diabetic rats appeared to be hypotensive when compared to age-matched control rats. Long-term diabetic mesenteric arteries were supersensitive to NE and developed more contractile force in response to NE when compared to age-matched control mesenteric arteries. Adrenoreceptor antagonism by phentolamine had no effect on the sensitivity of the mesenteric arteries (diabetic and control) for NE. There was an increase in the contractile force developed by these tissues in response to NE during .beta.-adrenoreceptor antagonism by propranolol. Adrenoreceptor antagonism produced a decrease in the sensitivity of both long-term diabetic and corresponding age-matched control mesenteric arteries. .alpha.-Adrenoreceptor antagonism had no effect on contractile force developed by long-term mesenteric arteries (diabetic and control) in response to NE. Long-term experimental diabetes apparently produced a supersensitivity of rat mesenteric arteries to NE. This phenomenon is dependent on the duration of the diabetic state. Supersensitivity of the mesenteric arteries to NE may indicate an increased arterial vascular resistance which may contribute to the observed hypertension.

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