Naunyn-Schmiedeberg's archives of pharmacology
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Naunyn Schmiedebergs Arch. Pharmacol. · Oct 1991
Beta-adrenoceptors in the transplanted human heart: unaltered beta-adrenoceptor density, but increased proportion of beta 2-adrenoceptors with increasing posttransplant time.
To study whether in the (denervated) transplanted human heart beta-adrenoceptors are up-regulated we determined in right ventricular endomyocardial biopsies (weighing 2-7 mg) of 8 heart transplant recipients beta-adrenoceptor density and beta 1:beta 2-adrenoceptor ratio in weekly, later monthly intervals for 6-18 posttransplant months. beta-adrenoceptor density was assessed by 1-2 concentration (-)-[125I]-iodocyanopindolol (ICYP, 200 and 150 pmol/l) binding, the beta 1:beta 2-adrenoceptor ratio by a beta 1-adrenoceptor saturating concentration of the selective beta 1-adrenoceptor antagonist CGP 20712 A (500 nmol/l). In biopsies taken from the donor hearts immediately before transplantation beta-adrenoceptor density was 64.5 +/- 6.3 fmol ICYP bound/mg protein (n = 5), the beta 1:beta 2-adrenoceptor ratio 81.2 +/- 2.2:18.8 +/- 2.2%. beta-Adrenoceptor density did not change during the whole period investigated; it was in the first 9 posttransplant weeks 73.1 +/- 8.3 (n = 22) and after 4-18 months 74.2 +/- 7.6 fmol/mg protein (n = 16). ⋯ There is, however, a gradual decline in beta 1- and increase in beta 2-adrenoceptors with increasing posttransplant time. As noradrenaline acts in the human heart solely at beta 1-adrenoceptors, while adrenaline activates both beta 1- and beta 2-adrenoceptors with about the same potency, with increasing posttransplant time (and increasing proportion of beta 2-adrenoceptors) adrenaline may play an important role for regulation of contractility and/or heart rate in heart transplant recipients.