Article date: April 1980
By: R.E. BUCKINGHAM, T.C. HAMILTON in Volume 68, Issue 4, pages 667-676
The β‐adrenoceptor blocking drugs atenolol, metoprolol, practolol, propranolol, timolol and oxprenolol (as racemates) were administered acutely at three dose levels (0.01, 0.03 and 0.1 mmol/kg i.p. or s.c.) to spontaneously hypertensive rats with intact adrenal glands (SH‐rats) and following unilateral adrenalectomy and contralateral adrenal‐demedullation (SHAD‐rats). Changes in mean arterial pressure and heart rate were determined via an indwelling aortic catheter, with the animals placed in a quiet environment.
All drugs significantly lowered the blood pressure of SHAD‐rats, and these responses were not always associated with changes in basal heart rate.
With the exception of metoprolol and atenolol, the β‐adrenoceptor blocking drugs were less effective as anti‐hypertensives in SH‐ than in SHAD‐rats. Notably, timolol and oxprenolol lowered the blood pressure of SH‐rats at low doses only, whereas propranolol evoked a pressor response in this model.
Whilst (+)‐propranolol lowered the blood pressure of SHAD‐rats only at a dose which caused myocardial depression, the anti‐hypertensive response to (−)‐propranolol did not parallel changes in heart rate and was preceded by a pressor response.
The results imply that adrenal catecholamine release contributes towards masking the anti‐hypertensive effects of some β‐adrenoceptor antagonists in SH‐rats.
The β‐adrenoceptor blocking drugs atenolol, metoprolol, practolol, propranolol, timolol and oxprenolol (as racemates) were administered acutely at three dose levels (0.01, 0.03 and 0.1 mmol/kg i.p. or s.c.) to spontaneously hypertensive rats with intact adrenal glands (SH‐rats) and following unilateral adrenalectomy and contralateral adrenal‐demedullation (SHAD‐rats). Changes in mean arterial pressure and heart rate were determined via an indwelling aortic catheter, with the animals placed in a quiet environment.
All drugs significantly lowered the blood pressure of SHAD‐rats, and these responses were not always associated with changes in basal heart rate.
With the exception of metoprolol and atenolol, the β‐adrenoceptor blocking drugs were less effective as anti‐hypertensives in SH‐ than in SHAD‐rats. Notably, timolol and oxprenolol lowered the blood pressure of SH‐rats at low doses only, whereas propranolol evoked a pressor response in this model.
Whilst (+)‐propranolol lowered the blood pressure of SHAD‐rats only at a dose which caused myocardial depression, the anti‐hypertensive response to (−)‐propranolol did not parallel changes in heart rate and was preceded by a pressor response.
The results imply that adrenal catecholamine release contributes towards masking the anti‐hypertensive effects of some β‐adrenoceptor antagonists in SH‐rats.
DOI: 10.1111/j.1476-5381.1980.tb10859.x
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