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Genotype-dependent time course of lymphocyte beta 2-adrenergic receptor down-regulation
Heike Bruck1, Kirsten Leineweber, Anja Beilfuss
1Department of Pathophysiology and Nephrology, University of Essen Medical School, Germany.
Background:
Volunteers homozygous for Glu27 beta(2)-adrenergic receptor (beta(2)AR) polymorphism have delayed onset of agonist-induced desensitization of cardiac beta(2)AR responses.
Methods And Results:
To determine whether this can also be demonstrated for Glu27Glu beta(2)AR natively expressed in circulating lymphocytes, we assessed the effects of 2 weeks of oral treatment with 3 x 5 mg/d terbutaline on lymphocyte beta(2)AR density (determined by [-]-[iodine 125]iodocyanopindolol binding) and responsiveness (assessed as [-]-isoproterenol hydrochloride [INN, isoprenaline] [1 nmol/L to 1 micromol/L]-induced lymphocyte cyclic adenosine monophosphate increases) in 23 healthy volunteers (13 with wild-type beta(2)AR [group A], 5 homozygous for Glu27 with Gly16Gly or Arg16Gly [group B], and 5 homozygous for Gly16 with Gln27Gln or Gln27Glu [group C]). Before terbutaline treatment, lymphocyte beta(2)AR density and isoproterenol-induced lymphocyte cyclic adenosine monophosphate accumulation were not significantly different in the genotype groups; 2 weeks of terbutaline treatment significantly decreased lymphocyte beta(2)AR density and responsiveness in the 3 genotype groups to a nearly identical extent, and no differences were observed. In time-course studies, however, in groups A and C lymphocyte beta(2)AR showed significant (P <.05, repeated-measures ANOVA) down-regulation as early as 24 hours after the first terbutaline intake, whereas in group B significant (P <.05, repeated-measures ANOVA) beta(2)AR decreases were observed only 72 hours after the first terbutaline intake. Thus the time course of lymphocyte beta(2)AR down-regulation in group B was significantly (P <.01, 2-way ANOVA) different from that in groups A and C.
Conclusion:
The extent of lymphocyte beta(2)AR down-regulation after long-term terbutaline treatment in volunteers homozygous for the Gly16 or Glu27 beta(2)AR polymorphism was genotype-independent and was nearly identical to that in wild-type beta(2)AR volunteers. However, the onset of beta(2)AR down-regulation was delayed in volunteers homozygous for the Glu27 beta(2)AR polymorphism.