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Effects of Age and Adipocyte Size on Glucose and Palmitate Metabolism and Oxidation in Pigs¹

University of Minnesota, St. Paul 55108

Abstract

Thin adipose tissue slices prepared from middle subcutaneous (MSQ) adipose tissue of pigs weighing 57, 94 or 124 kg were incubated in vitro for 30 min in the absence of exogenous insulin with one of several substrate combinations: .75 mM [ 1-¹⁴ C] palmitate and 10 mM glucose; 10 mM [U-¹⁴C] glucose and .75 mM palmitate, or 10 mM [U-¹⁴C] glucose in the absence of palmitate. Esterification of palmitate in the presence of glucose declined (per cell) progressively with advancing animal age or obesity in adipocytes that were 20 to 63 or 63 to 102 µm in diameter. There was, however, a significant increase (per cell) in palmitate esterification by adipocytes 102 to 153 µm in diameter. Because of the increasing proportion of adipocytes in the 102 to 153 µm fraction, the esterification of palmitate per 10⁶ adipocytes (representing the entire distribution) increased significantly with increasing animal age or obesity. Associated with the enhanced rate of palmitate esterification was a markedly attenuated conversion of glucose to glyceride-fatty acids (GFA), for all cell-size fractions and over the entire distribution (per cell), when adipocytes from 124-kg pigs were compared with those from younger, leaner pigs. Conversion of glucose to glyceride-glycerol (GC) in the presence of palmitate was similar in adipocytes from 57- and 94-kg pigs for all three cell-size fractions; there was a significant decrease in GG synthesis per cell among all cell-size fractions from 124-kg pigs. The decrease in GG synthesis was less than the decease observed in the rate of de novo fatty acid synthesis from glucose. Palmitate oxidation increased sevenfold between 57 and 124 kg in the presence of glucose. Associated with the increase in palmitate oxidation was a significant decline in glucose oxidation by adipocytes incubated in the presence of palmitate. Incubation in the presence of palmitate inhibited the rate of de novo fatty acid synthesis from glucose in a similar fashion among the three cell-size fractions from pigs of different age or obesity. GG synthesis was significantly elevated when palmitate was present in the buffer compared to when it was absent.

¹ Paper no. 10958, Scientific Journal Ser., Minnesota Agr. Exp. Sta., St. Paul.

² Present address: Dept. of Dairy and Anim. Sci., The Pennsylvania State Univ., University Park 16802.

³ Dept. of Anim. Sci., Andrew Boss Lab. — Meat Sci., Univ. of Minnesota, St. Paul 55108.

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