Characterization of beta-adrenergic binding sites on rodent Leydig cells.
A radioligand binding technique was used to study beta-adrenergic binding sites on rodent Leydig cells. Beta-Adrenergic binding sites were found on Leydig cells in both the rat and mouse. Binding of [3H]CGP-12177 [4-(3-t-butylamino-2-hydroxypropoxy)-[5,7-3H]benzimidazole-2-one] to purified rat Leydig cells was found to be saturable, temperature and time dependent, stereospecific, and readily reversible by the beta-adrenergic antagonist propranolol. Scatchard analysis revealed the presence of high-affinity sites with an apparent dissociation constant (Kd) of 0.79 +/- 0.22 nM and maximal binding capacity (Bmax) of 1716 +/- 245 sites per rat Leydig cell. Competition of various beta-adrenergic agonists and antagonists with [3H]CGP indicates an order of potency of L-isoproterenol greater than epinephrine = salbutamol greater than norepinephrine greater than D-isoproterenol and dl-propranolol = ICI 118,551 much greater than atenolol, respectively. These observations suggest that the binding sites are predominantly of the beta 2-receptor subtype. Incubation of freshly isolated rat Leydig cells with luteinizing hormone (100 ng/ml) caused consistent stimulation of androgen production, but only occasional stimulation by the beta-agonist isoproterenol (10 microM) was observed. However, these cells consistently responded to the beta-agonist after 3 h in primary cultures. These findings indicate that rodent Leydig cells possess beta-adrenergic binding sites and point out a possible dissociation between receptor recognition and physiologic response.
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D000319:Adrenergic beta-Antagonists / Q000378:metabolism; D000728:Androgens / Q000096:biosynthesis; D000818:Animals; D001667:Binding, Competitive; D002469:Cell Separation; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D007985:Leydig Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000494:pharmacology; D008297:Male; D051379:Mice; D011412:Propanolamines / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
D000319:Adrenergic beta-Antagonists; D000728:Androgens; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D007986:Luteinizing Hormone; D011433:Propranolol; D007545:Isoproterenol; C033394:CGP 12177