Influence of nutritional weaning on porcine adipocyte beta-adrenergic and adenosine A1 receptors.
Obese and crossbred (X-Bred) pigs were removed from sows at 14 d of age and given ad libitum access to a high-fat, milk-based diet. A subset of pigs fed this diet were killed at 28 and 49 d of age. At 28 d, another subset of pigs was given ad libitum access to a low-fat, grain-based diet and were killed at 31, 35, and 49 d of age (nutritionally weaned for 3, 7, and 21 d, respectively). Dorsal subcutaneous adipose tissue was obtained at death and adipocytes were prepared by incubation with collagenase. A portion of the cells was fixed with osmium to determine size and number; remaining cells were lysed in hypotonic media and centrifuged to yield a crude membrane fraction. The beta-adrenergic receptor (beta-AR) and A1 adenosine receptor (A1R) affinity and number were measured in the membranes by equilibrium saturation ligand binding. Obese pigs had a lower body weight than X-Bred pigs at all ages (P < .05). Obese pigs tended (P for volume > .1 but < .2) to have larger adipocytes than X-Bred pigs. The beta-AR affinity did not differ between obese and X-Bred pigs. There were fewer beta-AR per milligram of membrane protein in obese than in X-Bred pigs at 28 and 49 d of age when fed the high-fat, milk-based diet (P < .01). However, beta-AR number expressed per cell or unit cell surface area did not differ between genetic groups. As pigs of either genetic group continued to be fed the low-fat, grain-based diet, the beta-AR decreased when expressed per milligram of protein or unit cell surface area (P < .05) and tended to decrease when expressed per cell. Obese and X-Bred pigs fed the high-fat, milk-based diet had more beta-AR than respective pigs fed the low-fat, grain-based diet when data were expressed per milligram of protein (P < .01) but not when expressed per cell or unit surface area. The A1R were only detectable in 2 of 16 X-Bred litters but were more developed in adipocytes of obese pigs, being measurable in 8 of 14 litters. The A1R number, expressed per milligram of protein, was lower in obese pigs fed the milk-based diet than in those fed the grain-based diet (P < .05). These findings suggest the decreased beta-AR number after nutritional weaning, or the transition from a high-fat to low-fat diet, may contribute to fat accretion in pigs. Furthermore, the lower number of beta-AR in obese than in X-Bred pigs may contribute to the obesity.
Mersmann
H J
HJ
USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA. mersmann@bcm.tmc.edu
Carey
G B
GB
Smith
E O
EO
D017667:Adipocytes / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D000375:Aging / Q000378:metabolism / Q000502:physiology; D000704:Analysis of Variance; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001835:Body Weight / Q000502:physiology; D001947:Breeding; D004032:Diet / Q000662:veterinary; D004041:Dietary Fats / Q000494:pharmacology; D005260:Female; D050356:Lipid Metabolism; D008297:Male; D009765:Obesity / Q000378:metabolism / Q000503:physiopathology / Q000662:veterinary; D011817:Rabbits; D011943:Receptors, Adrenergic, beta / Q000032:analysis* / Q000378:metabolism; D018047:Receptors, Purinergic P1 / Q000032:analysis* / Q000378:metabolism; D013552:Swine / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013553:Swine Diseases / Q000378:metabolism / Q000503:physiopathology; D013556:Swine, Miniature; D014886:Weaning
D004041:Dietary Fats; D011943:Receptors, Adrenergic, beta; D018047:Receptors, Purinergic P1