1. The effect of exercise testing and beta-blockade on plasma
norepinephrine (PNE), and secretion of its metabolite 3-methoxy-4-hydroxyphenylethylene glycol (
MHPG), was assessed in 28 mild-to-moderate hypertensives before and after the administration of
dilevalol, a new beta-blocker with beta 2-agonism. 2. This double blind, placebo-controlled study consisted of two successive submaximal exercise tests before and after the administration of a single oral dose of
dilevalol (200 mg, 400 mg or 600 mg). Plasma
norepinephrine levels were determined at rest, at 100 watts step of exercise and at maximal effort (Emax). 3. During the control test, mean PNE levels increased from 1.73 +/- 0.52 nmol/L (resting value) to 8.01 +/- 4.01 nmol/L at Emax (P less than 0.01) as
MHPG levels increased from 11.18 +/- 1.33 nmol/L (rest) to 17.50 +/- 1.15 nmol/L (Emax, P less than 0.01). After
dilevalol, PNE increased significantly as compared to controls (P less than 0.05), from 2.32 +/- 0.99 to 12.42 +/- 5.97 nmol/L (P less than 0.01). PNE and
MHPG levels were correlated, both at rest and during exercise. PNE levels after beta-blockade were linearly related to the dose of beta-blocker administered.
MHPG levels were unaltered by the administration of
dilevalol, both before and after exercise. 4. The increase in
MHPG that occurs during bicycle exercise is largely generated from an increase in central nervous system noradrenergic activity. While
dilevalol increases the peripheral sympathetic nervous system, both at rest and during exercise (which is reflected by increases in PNE levels) the
drug does not alter resting central nervous system noradrenergic activity nor amplify the increase in central noradrenergic activity that occurs during exercise.