Figure 2. Influence of ageing on noradrenaline (NA) kinetics in the heart and hepatomesenteric circulation, and on secretion of adrenaline.

Cardiac noradrenaline spillover was higher in older men (upper left panel). This appeared to be due in part to reduced neuronal reuptake of noradrenaline, evident in reduced transcardiac extraction of plasma tritiated noradrenaline (upper right panel); removal of noradrenaline from plasma by the heart is largely by uptake into the cardiac sympathetic nerves. Noradrenaline spillover into the hepatomesenteric circulation was also higher in the older men (lower left panel), but unlike in the heart, this was most probably due exclusively to increased sympathetic nerve firing rates, as plasma tritiated noradrenaline extraction across the gut and liver (not shown) was normal. In contrast to the augmentation of sympathetic tone in the heart and hepatomesenteric circulation, adrenaline secretion rates were reduced in the older men (lower right panel). Mean +s.e.m. values are indicated in the histograms. *P < 0·05 vs. young men.