Analysis of Hypotensive Mechanisms of Pindolol, a β-Adrenoceptor Blocking Drugs in Rats

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Abstract
The hypotensive mechanisms of pindolol in anesthetized and conscious rats were investigated. Pindolol caused a fall in blood pressure in anesthetized, conscious and spinal rats; in conscious rats a higher dose of the drug was required to produce such a response. This hypotension with pindolol in anesthetized and conscious rats was markedly inhibited by pretreatment with the drug itself or other .beta.-adrenoceptor blocking drugs. A similar phenomenon also occurred when isoproterenol was injected i.v. in anesthetized and conscious rats. The relationship between the hypotensive actions of 4 .beta.-adrenoceptor blocking drugs in anesthetized rats and their intrinsic .beta.-sympathomimetic actions in isolated catecholamine-depleted tracheal preparations was determined. Order of hypotensive potencies was the same as that of their intrinsic .beta.-sympathomimetic action, i.e., pindolol > carteolol > bufetolol .**GRAPHIC**. propranolol (P < 0.05). The hypotension with pindolol appears to be mediated through a decrease in the peripheral vascular resistance due to an intrinsic .beta.-sympathomimetic action of the drug.

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