Selective activation of sympathetic ganglia in young spontaneously hypertensive rats

Abstract

PROLONGED increase in peripheral sympathetic discharges producing vasoconstriction leads to enhanced synthesis of tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH) in terminal adrenergic neurones^1,2. This is mediated by an increased activity of the preganglionic cholinergic nerves¹. Young spontaneously hypertensive rats (SHR) have been used as a prehypertensive model of essential hypertension to investigate whether such peripheral sympathetic neuronal activation initiates the increase of blood pressure. Study of the prehypertensive stage gives more information on the initiation of the blood pressure elevation than study of hypertensive animals. Circulating levels of noradrenaline, and DBH activity (as measures of peripheral sympathetic nerve system activity were markedly elevated in young SHR (refs 3, 4), although contradictory results were reported for adrenomedullary activity^3–5. In young SHR, adrenal levels of DBH, TH and phenylethanolamine N-methyl-transferase (PNMT) activities were lowered³, whereas other investigators^4,5 found an elevation of adrenal DBH and PNMT activities. Transection of the splanchnic nerves markedly lowered blood pressure in young^5,6 and adult SHR (refs 5, 7), and also reduced adrenal venous output of adrenaline in conscious young SHR (ref. 5). All these findings suggest enhanced activity of the adrenal medulla and preganglionic cholinergic discharges to the adrenal medulla. We report here preganglionic nerve-dependent elevation of choline acetyltransferase (ChAc) and TH activities occurring specifically in the coeliac ganglia of young SHR.