title: Comparison of the anti-hypertensive response to beta-adrenoceptor blocking drugs in intact and adrenal-demedullated spontaneously hypertensive rats.
abstract: 1 The beta-adrenoceptor blocking drugs atenolol, metoprolol, practolol, propranolol, timolol and oxrenolol (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. 2 All drugs significantly lowered the blood pressure of SHAD-rats, and these responses were not always associated with changes in basal heart rate. 3 With the exception of metoprolol and atenolol, the beta-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. 4 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. 5 The results imply that adrenal catecholamine release contributes towards masking the anti-hypertensive effects of some beta-adrenoceptor antagonists in SH-rats.
mesh_terms: D000313:Adrenal Medulla / Q000502:physiology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D000959:Antihypertensive Agents; D001794:Blood Pressure / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006973:Hypertension / Q000503:physiopathology*; D051381:Rats; D013997:Time Factors
chemical_list: D000319:Adrenergic beta-Antagonists; D000959:Antihypertensive Agents