The influence of the intrinsic sympathomimetic activity of beta-adrenoceptor antagonists on haemodynamic effects in anaesthetized dogs

1. The effects of propranolol, atenolol (ICI 66,082), practolol and pindolol on heart rate and maximal left ventricular dp/dt, atrioventricular conduction time, mean aortic flow and diastolic blood pressure during cardiac pacing were investigated over a wide dose range (0.025-4.0 mg/kg, i.v.) in dogs anaesthetized with pentobarbitone.2. Propranolol and atenolol produced similar reductions in haemodynamic parameters. Propranolol had no further effect in dogs pretreated with atenolol. 3. Practolol tended to cause smaller reductions in the haemodynamic parameters than either propranolol or atenolol. Subsequent administration of propranolol still had some depressant activity. 4. Pindolol produced a biphasic response, with depression of cardiac function at the low doses (0.025 and 0.1 mg/kg), but a reversal of effect as the dose was increased. 5. It is therefore concluded that, in anaesthetized dogs, the intrinsic activity of practolol and pindolol limits the fall in heart rate, cardiac conduction, aortic flow and maximal dp/dt observed with beta-adrenoceptor blockade. With pindolol, however, the influence of intrinsic activity is observed only in high doses related to beta-adrenoceptor blockade.

Comparison of sulfobromophthalein (BSP) and sulfobromophthalein glutathione (BSP-GSH) disposition under conditions of altered liver function and in the isolated perfused rat liver

Disposition of sulfobromophthalein (BSP) and sulfobromophthalein glutathione (BSP-GSH) was compared in control, phenobarbital, or alpha-naphthylisothiocyanate-(ANIT)-treated rats, and in the isolated perfused rat liver preparation. After dye administration, BSP-GSH was found to have a more rapid early plasma disappearance rate, a more rapid appearance in the liver, and a greater rate of biliary excretion both in vivo and in the isolated perfused liver, than that of BSP. In considering these observations, it is concluded that hepatic uptake as well as biliary excretion of BSP-GSH is faster than that of BSP. Comparing BSP and phenobarbital, augmentation or reduction in plasma dye concentration, mean plasma half-life (2 to 30 minutes), hepatic dye content, and bile dye concentration, were of the same order of magnitude for both dyes. However, with dye infusion of 3.6 mumoles per kilogram per minute, phenobarbital significantly enhanced the rate of biliary excretion of BSP but not BSP-GSH and ANIT treatment had a greater inhibitory effect on biliary excretion of BSP-GSH than BSP.

Effect of propranolol on blood pressure in normal and hypertensive rats

1. Propranolol has been given orally in a dose sufficient to achieve beta-blockade throughout the day in normal rats, renal hypertensive animals with and without contralateral nephrectomy, spontaneously hypertensive and deoxycorticosterone (DOCA) hypertensive rats. The drug was given either after hypertension had become fully established or during the phase of rising blood pressure.

2. With this treatment, heart rate was reduced by approximately 100 beats/min in all experimental groups.

3. In established hypertension, treatment with propranolol for 7–9 days was ineffective in lowering blood pressure in any of the models of experimental hypertension. It also had no effect on blood pressure in normal animals.

4. Chronic treatment with propranolol during the phase of rising blood pressure had no effect in renal hypertensive animals. In spontaneous hypertension, the rise in blood pressure was limited to 28 mmHg with propranolol treatment as compared with 58 mmHg in control animals. Likewise, in DOCA hypertension, the rise in pressure was limited to 18 mmHg as compared with 46 mmHg in control animals.