Possible alteration of some cardiovascular and hormonal parameters after abrupt withdrawal of propranolol or guanfacine following chronic mono-or combined therapy in spontaneous hypertensive rats

ABSTRACT

Spontaneous hypertensive rats [SHR] were given either propranolol [P], guanfacine [G] or combined treatment for four weeks, followed by sudden withdrawal of either [P] or [G] for 6 days. Results showed a significant decrease of the systolic blood pressure, heart rate and plasma renin activity after [P], [G] or combined treatment with a significant rebound increase after withdrawal. Concerning plasma aldosterone concentration, a significant decrease of this parameter was detected only after [G] treatment with a rebound significant increase after withdrawal. As regards angiotensin converting enzyme activity, there was a significant decrease of this parameter after [P] treatment with a significant rebound increase after withdrawal. Total daily urinary catecholamine exhibited a significant increase after [P] treatment and even after its withdrawal but there was a significant decrease after propranolol withdrawal in the group treated with both drugs. There was also a significant decrease of this parameter after [G] or combined treatment with a rebound significant increase after withdrawal of [G]. A significant increase of serum potassium was apparent after [P] or combined treatment with a significant decrease after withdrawal. These results indicated that propranolol and guanfacine are effective antihypertensive agents, besides, when a drug is to be withdrawn from the combination regimen, it is the beta- blocker rather than guanfacine