Reduced number of α- and β-adrenergic receptors in the myocardium of rats exposed to tobacco smoke

The concentration of α- and β-adrenergic receptors-as measured by specific ³H]WB-4101 and (−)-³H]-dihydroalprenolol binding-was diminished by 60% below control values in the hearts of hearts of rats exposed to tobacco smoke. These changes in receptor numbers took place almost immediately after tobacco smoke exposure and were rapidly reversible after termination of the exposure. The dissociation constant, K , for ³H]WB-4101 was identical in exposed (K_D = 0.34 ± 0.09 nM) and control (K_D = 0.35 ± 0.07 nM) hearts but was significantly different i in the case of (-)-³H] dihydroalprenolol binding (exposed, (K_D = 2.83 ± 0.30 nM vs control K_D = 5.22 ± 0.61 nM). For β-receptor binding there was no significant difference between exposed and control animals in the K_i values (−)-epinephrine, (−)-norepinephrine, (−)-alprenolol, (±)-propranolol or timolol. (−)-Isoproterenol, however, was found to bind with lower affinity in exposed compared with control hearts. For α-receptor binding there was no significant difference between control and ‘smoked’ animals in the K_i values for (−)-epinephrine, (−)-norepinephrine or phentolamine. The decrease in α- and β-adrenergic receptor concentration may be related to the phenomenon of receptor desensitization resulting from a release of catecholamines in rats exposed to tobacco smoke.