Lack of an effect of age on beta-adrenoceptor-mediated lipolysis in isolated human adipocytes.
We examined the effect of age on the beta-adrenoceptor response in adipocytes that contain both beta 1- and beta 2-adrenoceptors. Twelve healthy young and 12 old subjects on a 150 mEq/24 h sodium diet underwent gluteal fat biopsies. Isolated adipocytes from all the subjects were stimulated with increasing concentrations of isoproterenol for glycerol release. In 13 of the subjects (7 young and 6 old), we also performed beta-adrenoceptor binding studies on adipocyte membranes. In addition in eight subjects (four young and four old), we also utilized a competitive binding assay to calculate the percent of beta-adrenoceptors that were of the beta 1 subtype. Our data showed that old subjects, when treated under identical conditions as the young subjects prior to fat biopsy, did not demonstrate any differences in the beta-adrenoceptor stimulated lipolysis. The Vmax of lipolysis was 10.6 +/- 1.4 nmoles glycerol/mg lipid/2 h in the young group and 9.9 +/- 1.1 in the old group. The concentrations of isoproterenol that resulted in Vmax and 1/2 Vmax were also the same in the two age groups. The addition of 8-cyclopentyl-1,3-dimethylxanthine (CPT), a specific A1-adenosine receptor antagonist, resulted in mild but equivalent enhancement of glycerol release in both age groups. The beta-adrenoceptor numbers and affinities from adipocyte membranes did not demonstrate age-related differences either (Bmax 106 +/- 17 fmol/mg of protein in the young, and 137 +/- 27 in the old; Kd 79.6 +/- 21.3 pM in the young and 81.9 +/- 16.6 in the old). The percent of beta 1-adrenoceptors on the adipocyte membranes was also similar in the two age groups (35.2 +/- 2.6% in the young; 37.1 +/- 4.5% in the old). In conclusion, we could not demonstrate any differences in the beta-adrenoceptor responses from peripheral adipocytes that contain both beta 1- and beta 2-adrenoceptors, in a group of healthy elderly and young subjects who were subjected to identical dietary and orthostatic conditions prior to the biopsy. These data suggest that neither beta 1- nor beta 2-adrenoceptor responses in human adipocytes show significant changes due to aging.
Department of Medicine, University of Colorado Health Sciences Center, Denver, USA. John.Gerber@UCHSC.edu
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Gerber
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Detmar-Hanna
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Zahniser
D017667:Adipocytes / Q000378:metabolism*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism*; D001706:Biopsy; D002081:Buttocks; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005990:Glycerol / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes; D020120:Iodocyanopindolol / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008066:Lipolysis / Q000502:physiology*; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism; D058915:Purinergic P1 Receptor Antagonists; D019275:Radiopharmaceuticals; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D018342:Receptors, Adrenergic, beta-1 / Q000378:metabolism; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism; D012982:Sodium, Dietary / Q000008:administration & dosage; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D007457:Iodine Radioisotopes; D058915:Purinergic P1 Receptor Antagonists; D019275:Radiopharmaceuticals; D011943:Receptors, Adrenergic, beta; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D012982:Sodium, Dietary; C053907:8-cyclopentyl-1,3-dimethylxanthine; D020120:Iodocyanopindolol; D013806:Theophylline; D007545:Isoproterenol; D005990:Glycerol