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Lipid Mobilization by Obese and Lean Pigs Infused with the ß-Adrenergic Agonist Isoproterenol

U.S. Department of Agriculture^1,2,3,, Clay Center, NE 68933

Abstract

Generally obese and lean pigs in both the fed and fasted states were anesthetized and then acutely infused with increasing concentrations of the ß-adrenergic agonist isoproterenol. Plasma free fatty acid (FFA), blood glycerol, glucose and lactate, and heart rate were monitored during the infusion period. Data were reduced by estimating the parameters of the generalized logistic function (minimum, maximum, ED₅₀ and slope) and subsequently analyzed to compare the lean and obese genotypes within nutritional state. Lactate data could not be fitted to this function because the upper asymptote was not approached during the experiment. The minimum plasma concentration of FFA tended (P < .1) to be less in obese than in lean pigs. The maximum, ED₅₀ and slope for the responses of FFA were similar for obese and lean pigs in fed pigs and in fasted pigs. In fed pigs, the minimum glycerol concentration was greater in obese than in lean pigs, and the ED₅₀ for heart rate tended to be lower in lean than in obese pigs. All other estimated parameters for the variables were similar in fed obese and lean pigs. In fasted pigs, the maximum glucose concentration was greater in obese than in lean pigs. All other parameters for the variables were similar in fasted obese and lean pigs. The results suggest that there was no major defect in lipid mobilization in these obese pigs (only a lower minimum FFA concentration was detected) and that an increased maximum blood glucose concentration in the fasting state might contribute to the obesity.

¹ Roman L. Hruska, U.S. Meat Anim. Res. Center, ARS.

² The authors thank R. W. Chloupek and C. J. Smith for execution of these experiments, B. E. Larsen and S. V. Reece for the care of and assistance with animals and M. M. Bierman, D. A. George and J. R. Watts for secretarial assistance.

³ Mention of trade names, proprietary products or specific equipment does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products that also may be suitable.