Circulation, Vol 80, 903-914, Copyright © 1989 by American Heart Association
AH van den Meiracker, AJ Man in't Veld, F Boomsma, DJ Fischberg, PB Molinoff and MA Schalekamp
In an attempt to further clarify the mechanism of the maintenance of the
antihypertensive effect of beta-adrenoceptor antagonists, the effects of
four antagonists with different ancillary properties (acebutolol, atenolol,
pindolol, and propranolol) on systemic and renal hemodynamics, body fluid
volumes, hormones, and lymphocyte beta- adrenoceptor density were studied
in four groups of 10 hypertensive patients. The patients were observed for
3 weeks during active treatment and for 2 weeks after withdrawal of
treatment. At the end of the 3-week treatment period, the four drugs had an
equal antihypertensive effect (fall in mean arterial pressure, 10-13%).
Although renin activity was suppressed (60-70%) by all four drugs, changes
in renin or pretreatment values of renin levels were not correlated with
the fall in blood pressure. The drugs had no effect on plasma catecholamine
concentrations or body fluid volumes. Despite similar antihypertensive
effects among the four drugs, the changes in flow and resistance underlying
the fall in blood pressure differed considerably. With pindolol, the fall
in blood pressure was associated with a fall in vascular resistance (26 +/-
6%), whereas with propranolol, it was predominantly associated with a fall
in cardiac output (11 +/- 7%). No significant changes in vascular
resistance or cardiac output occurred with atenolol or acebutolol. The
changes in renal blood flow and renal vascular resistance occurred in
parallel with the changes in cardiac output and systemic vascular
resistance. Plasma epinephrine concentration and pretreatment cardiac
chronotropic responsiveness to isoproterenol appeared to be inversely
correlated with lymphocyte beta-adrenoceptor density (Bmax) (r = -0.41 and
-0.43, respectively). With pindolol, Bmax decreased maximally by 39 +/- 6%,
and with propranolol, it increased by 51 +/- 17%. With both drugs,
significant changes in Bmax were already present 24 hours after treatment.
Furthermore, 1 week after withdrawal of treatment with pindolol, Bmax was
still down-regulated, and cardiac chronotropic responsiveness was still
decreased, whereas 1 week after withdrawal of propranolol, Bmax was still
up-regulated, and cardiac chronotropic responsiveness was still increased.
No changes in Bmax occurred with the beta 1-selective antagonists
acebutolol and atenolol. Thus, despite an equal antihypertensive effect,
the four beta-adrenoceptor antagonists appear to have dissimilar effects on
cardiac output, renal blood flow, and lymphocyte beta-adrenoceptors.
Changes in cardiac output, the circulating blood volume, or
angiotensin-mediated vasoconstriction are factors unlikely to be crucial
for the antihypertensive effect of beta-adrenoceptor antagonists.
Therefore, interference with vasoconstrictor nerve activity through
blockade of either central or peripheral prejunctional beta-adrenoceptors
could be an alternative explanation of their blood pressure-lowering
potential.
ARTICLES
Hemodynamic and beta-adrenergic receptor adaptations during long-term beta-adrenoceptor blockade. Studies with acebutolol, atenolol, pindolol, and propranolol in hypertensive patients
Department of Internal Medicine I, University Hospital Dijkzigt, Erasmus University, Rotterdam, The Netherlands.
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