Age-dependent changes of the sympathetic innervation of the rat kidney

The influence of aging on the sympathetic innervation of the kidney was studied in 3- (considered to be young), 12- (considered to be adult) and 24- (considered to be old) month-old male Sprague-Dawley rats by means of high pressure liquid chromatography with electrochemical detection, catecholamine histofluorescence and acetylcholinesterase (AChE) histochemistry. Body and kidney weights were significantly increased in adult in comparison with young rats. No further increase of either body or kidney weight was appreciated in old rats. Noradrenaline levels were increased by about 48% in adult rats and were decreased in old rats (by approx. 22% vs. young and 60% vs. adult). The density of perivascular noradrenergic fibres was significantly increased in adult rats and decreased in old animals. The percentage of kidney glomeruli supplied by AChE-positive nerve fibres is also remarkably increased in 12-month old rats and decreased in 24-month-old rats. The present data indicate that there is a striking increase in the expression of sympathetic innervation of rat kidney at 12 months of age followed by a significant decrease in the expression of innervation in old age. These changes are discussed in relation to the age-dependent impairment of renal function.