Pindolol is an antagonist of β1- and β2-adrenergic receptors (β1- and β2-ARs; Kis = 2.6 and 4.8 nM, respectively) and a partial agonist of the β3-AR, stimulating adenylyl cyclase in membranes of cells expressing the human receptor.[1],[2] It is also an antagonist of the serotonin 5-HT1A receptor (Ki = 81.1 nM for inhibition of 5-HT-stimulated GTPγS binding).[3] Pindolol inhibits isoproterenol-induced tachycardia in anesthetized cats (ED50 = 1.8 μg/kg).[4] It also decreases mean blood pressure in conscious spontaneously hypertensive rats when administered at a dose of 30 mg/kg per day, but concomitantly increases heart rate.[5] Formulations containing pindolol have been used in the treatment of hypertension.

Reference
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[3]. Krushinski, J.H., Jr., Schaus, J.M., Thompson, D.C., et al. Indoloxypropanolamine analogues as 5-HT1A receptor antagonists. Bioorg. Med. Chem. Lett. 17(20), 5600-5604 (2007).
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[5]. Antonaccio, M.J., High, J., DeForrest, J.M., et al. Antihypertensive effects of 12 beta adrenoceptor antagonists in conscious spontaneously hypertensive rats: Relationship to changes in plasma renin activity, heart rate and sympathetic nerve function. J. Pharmacol. Exp. Ther. 238(1), 378-387 (1986).