THE NORADRENERGIC INNERVATION OF THE KIDNEY IN OLD WISTAR RATS

Age-related changes of the sympathetic (noradrenergic) innervation of the kidney were studied in young (3 months) and old (25 months) female Wistar rats by means- of high-pressure liquid chromatography (HPLC) with electrochemical detection and catecholamine histofluorescence techniques. Body and kidney weights were significantly increased in old rats. Renal noradrenaline levels were slightly but not significantly decreased in aged animals. The density of fluorescent catecholaminergic nerve fibres was significantly decreased in old rats, primarily within branches of renal artery (at the hilum) and within interlobular and cortical radial arteries. However, in old rats the number of axonal varicosities corresponding to the site of neurotransmitter release was slightly increased in interlobular and cortical radial arteries but not in hilar branches of the renal artery. The number of cortical tubules supplied with a catecholaminergic innervation remarkably decreased with age. These findings are indicative of age-dependent changes of the intrarenal noradrenergic innervation in Wistar rats. The lack of correspondence between the results obtained using HPLC and catecholamine histofluorescence techniques underscore the importance of evaluating the age-related changes of autonomic innervation using more than one methodology.