Carazolol is a high-affinity, lipophilic, and non-selective ligand of the β-adrenergic receptors [1,2].

β-adrenergic receptors have been involved in mediating the physiological responses of the catecholamines, epinephrine and norepinephrine and modulating a myriad of physiological functions, such as relaxation of smooth muscle, chronotropic and inotropic cardiac responses, and lipolysis in adipose tissue. The β-adrenergic receptors exist in nearly all mammalian tissues. Until now, three β-adrenergic receptors have been identified, β1-, β2- and β3-adrenergic receptors [3].

In CHO cells expressing the human β3-adrenoceptor, the Ki value of carazolol was 2.0 ± 0.2 and the IC50 was 11.3 ± 1.2 nM. Carazolol exhibited an ECs0 of 25 nM and behaved as a full agonist (intrinsic activity = 0.97) towards the murine β3-adrenoceptor. In murine 3T3-F442A-derived adipocytes express the β3-adrenoceptor, carazolol stimulated lipolysis [1]. Carazolol bound to cortical β-receptors with a Kd value of 0.15 nM. Carazolol showed equal displacements constants when binding with calf cerebral cortex (which contained mainly β1 receptors) and calf cerebellum (which contained mainly β2 receptors), indicating that carazolol bound with equal affinity to β1 and β2 receptors [2].

References:
[1] Méjean A, Guillaume J L, Strosberg A D.  Carazolol: a potent, selective β3-adrenoceptor agonist[J]. European Journal of Pharmacology: Molecular Pharmacology, 1995, 291(3): 359-366.
[2] Innis R B, Corrêa F M A, Snyder S H.  Carazolol, an extremely potent β-adrenergic blocker: Binding to β-receptors in brain membranes [J]. Life sciences, 1979, 24(24): 2255-2264.
[3] Pellegrino S M, Lee N H, Fraser C M.  β-Adrenergic receptors[J]. Biomembranes: A Multi-Volume Treatise, 1996, 2: 245-279.