Neonatal chemical sympathectomy: Functional control of denervation of the vascular system and tissue noradrenaline level in the rat after 6-hydroxydopamine
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In adult rats, the degree of vascular sympathectomy following neonatal administration of 6-hydroxydopamine (6-OHDA) was assessed. Doses of 6-OHDA were 100 μg/g on days 1 (day of birth) and 2, and 250 μg/g on days 8 and 15. In treated rats, anaesthetized with pentobarbital, mean arterial blood pressure, heart rate and pressor response to tyramine were reduced, while pressor responses to noradrenaline, adrenaline, angiotensine II and arginine-vasopressin were markedly increased. The change of both the noradrenaline and tyramine response was also present in rats treated on days 1, 2 and 8, but absent in rats treated on days 1 and 2 only. Pressor responses to electrical stimulation of the sympathetic outflow of the spinal cord and of the posterior hypothalamus of treated rats were diminished and were practically absent after adrenalectomy. The 6-OHDA treatment caused gross depletion of NA from the spinal cord, and from peripheral organs and tissues except the adrenals. A reduced NA level in brain cortex was associated with an increase of that of the brain stem.
The 6-OHDA treatment schedule used in the present experiments results in a high degree of vascular sympathectomy. The use of a functional test appears to be a better control than measurement of tissue NA levels alone to determine the degree of vascular sympathectomy.
Key wordsNeonatal 6-Hydroxydopamine Control of Chemical Sympathectomy Sympathetic Outflow Stimulation Hypothalamic Stimulation Blood Pressure and Pressor Response
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