Effects of beta-receptor blockers in pharmacology EEG

d,l-sotalol enhances baroreflex sensitivity in conscious rats surviving acute myocardial infarction

The aim of the present study was to characterize the influence of D,L-sotalol on arterial baroreflex sensitivity (BRS) which is generally considered as an estimate of vagal activity and has prognostic value in patients after myocardial infarction (MI). Conscious rats were studied 3 days after left anterior descending coronary artery ligation (n= 5) or sham-operation (SH, n= 6). BRS was determined by linear regression analysis of the RR-interval (interval between heart beats) and mean arterial pressure changes evoked by i.v. bolus injections of methoxamine (inducing reflex bradycardia, RB) and nitroprusside (inducing reflex tachycardia, RT). In MI-rats heart rate and mean arterial pressure were not significantly different from values in SH-rats, left ventricular end-diastolic pressure was increased and contractility was depressed. The BRS (RB: MI: 0.48 +/- 0.04(*), SH: 0.79 +/- 0.08; RT: MI: 0.41 +/- 0.05(*), SH: 0.86 +/- 0.08 ms mmHg(-1)) ((*)P< 0.05 vs SH) was markedly reduced. d, l -Sotalol (1.5 mg kg(-1)i.v.) reduced heart rate (MI: -11 +/- 3 %(*), SH: -11 +/- 3 %(*)) and mean arterial pressure only moderately [MI: -6 +/- 4 %(n.s.), SH: -7 +/- 2 %(*)], while BRS depression in MI-rats was completely neutralized [RB: MI: 1.08 +/- 0.14(*), SH: 1.19 +/- 0.11(*); RT: MI: 0.84 +/- 0.08(*), SH: 0.88 +/- 0.12 (n.s.) ms mmHg(-1)] ((*)P< 0.05 vs pretreatment). The BRS is reduced in rats early after MI, indicating a depressed reflex vagal activity. Treatment with D,L-sotalol at a dose with little effect on heart rate and mean arterial pressure markedly enhances and, thus, restores BRS in MI-rats. These data suggest that D,L-sotalol has both peripheral and central effects leading to an increase of reflex vagal control of heart rate in rats.

Central effects of beta-adrenoceptor antagonists. II--Electroencephalogram and body sway

1. Effects of the beta-adrenoceptor antagonists, propranolol (40, 80 and 160 mg) and atenolol (50 and 100 mg) on the electroencephalogram and on body sway, were studied in 12 healthy male subjects. The study was double-blind, and included two placebos and an active control, oxazepam (15 mg). Medication was ingested at 11.00 h, and assessments were made before, and at 2 h and 4 h after ingestion. 2. All doses of both beta-adrenoceptor antagonists modified the electroencephalogram, and the changes reported were statistically significant at probability levels of less than 5%. The circadian rise in alpha activity was reduced by both beta-adrenoceptor antagonists as well as by oxazepam. Atenolol also decreased beta activity. 3. Body sway was modified by atenolol and oxazepam (P less than 0.05). The increase with oxazepam was most marked in the low frequency component (0.05-2.25 Hz) of the spectrum, while atenolol modified only the component of higher frequency (2.25-4.0 Hz). 4. These observations suggest that propranolol and atenolol have a sedative effect, and that hydrophilic antagonists are unlikely to be free of central activity. The changes in body sway could imply that peripheral mechanisms may be modified at least with atenolol.