1. Plasma noradrenaline and adrenaline responses to graded exercise, reflecting sympathoneural and adrenal activity, were compared with β-adrenoreceptor-mediated renin and heart-rate responses in 33 patients with essential hypertension and either high (n = 13), normal (n = 15) or low (n = 5) renin—sodium index. β-adrenoreceptor responsiveness, was assessed using the chronotropic dose of isoprenaline which increased heart rate by 25 beats/min (CD25).
2. No significant differences in adrenaline were found among the renin subgroups either at rest or during equi-effective exercise stimulation, though values in the older low-renin patients tended to be lower.
3. Plasma noradrenaline at rest or exercise was similar in the renin subgroups. This contrasted with the normal exercise tachycardia and hyper-responsive renin in the high renin patients and the blunted exercise tachycardia and reduced renin response in the normal and low renin patients.
4. The CD25 of isoprenaline was 2·5 ± 2·2 sd μg/m2 in the high, 3·1 ± 4·4 in the normal and 4·5 ± 5·9 in the low renin group.
5. Older age and a longer history of hypertension may be associated with a transition from a high to a low and hyporesponsive renin—angiotensin system, with diminishing β-adrenoreceptor sensitivity. In the presence of deficient β-adrenoreceptors, a normal or slightly elevated sympathetic nerve activity may act predominantly via α-adrenoreceptor-mediated vasoconstriction, enhanced by structural vessel changes.