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ARS Home » Plains Area » Houston, Texas » Children's Nutrition Research Center » Research » Publications at this Location » Publication #76036
Title: PORCINE ADIPOCYTE BETA-ADRENERGIC AND ADENOSINE A1 RECEPTORS AT WEANING.

Author
item Mersmann, Harry
item CAREY, GALE
item SMITH, E

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: We studied an important process that occurs in fat, in the pig when it is weaned. Our study focused on two types of receptors (cell sites): beta- adrenergic receptors, which control fat cell metabolism and fat tissue growth; and adenosine A1 receptors, which oppose beta-adrenergic receptor activity. Our Objective: to find out if there were any changes in the number and sensitivity of the receptors when pigs were weaned. We studied the piglet since it is an ideal model for the human infant. We performed our measurements in both normal crossbred and genetically obese piglets fed a milk-based diet and "weaned" to a grain-based diet. There were fewer beta-adrenergic receptors in obese than crossbred pigs on the milk-based diet. Both obese and crossbred pigs on the milk-based diet had more beta- adrenergic receptors than their counterparts on grain. The fact that there were fewer beta-adrenergic receptors after "weaning" may contribute to the increased formation of fat, and the decreased breakdown of fat, after weaning. The fact that there were fewer beta-adrenergic receptors in obese than crossbred pigs may contribute to the obesity. Adenosine A1 receptors were developed earlier in obese than crossbred pigs. These findings provide key data for further studies aimed at understanding fat tissue formation and the effects of diet and age.

Technical Abstract: Obese and crossbred (X-Bred) pigs were removed from the sow at 14d of age and given adlibitum access to milk-based diet. A subset of pigs fed this diet were killed at 28 and 49 d of age. The rest of the pigs were "weaned" at d 28 to a grain-based diet and were killed at 31,35, and 49d of age ("weaned" for 3,7, and 21 d, respectively). Dorsal subcutaneous adipose tissue was obtained at death and adipocytes were prepared by incubation with collagenase. Cells were treated with osmium to determine size and number. Cells were also lysed in hypotonic media and a crude membrane fraction was prepared by centrifugation. The Beta-adrenergic receptor and adenosine A1 receptor affinity (Kd) and number (Bmax) were measured by equilibrium saturation ligand binding. Obese pigs were smaller than X-Bred pigs. The KD was greater than (less sensitive) in obese than X-Bred pigs when fed the milk-based diet but less (more sensitive) in obese than X-Bred dpigs fed the milk-based diet. As pigs of either genetic group continued t be fed the grain-based diet (post "weaning"), the Bmax decreased. Both obese and X'Bred pigs fed the milk-based diet had more receptors than respective pigs fed the grain-based diet. The adenosine A1 receptors (A1-R were only detectable in two of 15 X-Bred pigs; no conclusions may be drawn regrading the effects of diet ("weaning") or age regarding these receptors. The A1-R were more developed in adipocytes of obese pigs; they were measurable in eight of 14 pigs. Both the Kd and the Bmax were lower in obese pigs fed the milk-based diet than those fed the grain-based diet.