| Abstract: | Cystic fibrosis (CF), a genetic disease characterized by abnormalities of exocrine gland and mucociliary function, has recently been shown to be associated with abnormal adrenergic and cholinergic physiologic responses in addition to decreased beta adrenergic-induced cyclic AMP generation in human leukocytes. In this study we have attempted to elucidate the nature of this hyporesponsiveness by assessing beta adrenergic receptor number and affinity (KD) in the intact neutrophil using the antagonist ligand [3H] dihydroalprenolol and cyclic AMP responses to isoproterenol in addition to histamine, and prostaglandin E1 in CF subjects, CF obligate heterozygotes (CFH), and normal control subjects. CF patients had significantly less (p less than 0.025) cyclic AMP stimulation above basals levels with isoproterenol (0.1 microM to 0.1 mM), compared with control values, but no consistent differences between groups were noted with histamine or PGE1. CF neutrophils had significantly fewer (p less than 0.005) beta adrenergic receptors per neutrophil (398.0 +/- 54.2 vs. 819.4 +/- 67.2) compared with control neutrophils, but the KD (0.740 +/- 0.11 vs. 0.630 +/- 0.05 nM) did not differ significantly (p greater than 0.05). There was no correlation between clinical severity and either cyclic AMP generation or dihydroalprenolol binding (r = 0.27 and 0.24, respectively, p greater than 0.05). The CFH group had approximately 50% of the cyclic AMP stimulation compared with controls, but the number (909.8 +/- 89.3) and KD (0.710 +/- 0.09 nM) of their beta adrenergic receptors were indistinguishable from control subjects. These findings suggest "down regulation" of the beta receptor in the CF patient. The cause of this remains unknown. Although the etiology of the decreased cyclic AMP responses in CFH was not due to decreased beta adrenergic receptors as assessed by antagonist ligand binding, further studies inthe CFH group to include agonist binding, receptor-adenylate cyclase coupling, intrinsic adenylate cyclase activity, and catecholamine metabolism may help determine the basic cause of beta adrenergic hyperesposiveness in both CFH and CF. |
