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Gluconeogenesis from Lactate in Liver of Stress-Susceptible and Stress-Resistant Pigs^1,2,3,

Department of Animal Science, Iowa State University, Ames, Iowa 50011

In vitro rates of lactate conversion to glucose and oxidation to CO₂ were determined in livers of stress-susceptible (SS) and stress-resistant (SR) pigs because we hypothesized that livers of SS pigs had a lower capacity than livers of SR pigs to remove lactate from blood. Stress-susceptibility was determined by reaction to halothane at 7 weeks of age. At approximately 9 weeks of age, pigs were assigned to one of three experimental diets. Pigs weighing 95 kg were slaughtered immediately after stress, and liver samples were obtained. Incorporation of lactate into glucose in liver of SS pigs was 43% of that in SR pigs, while oxidation of lactate to CO₂ in liver of SS pigs was 38% of that in SR pigs. Addition of either vitamin C or vitamins C and E plus mangnesium oxide and collagen extract to a corn-soy diet did not alter lactate conversion to glucose, but depressed lactate oxidation to CO₂. No differences were detected in either activities of lactate dehydrogenase, NAD-malate dehydrogenase, phosphoenolpyruvate carboxykinase, fructose-1,6-diphosphatase, and glucose-6-phosphatase or concentration of glycogen in livers of SS and SR pigs. Our data indicate that livers of SS pigs possess a lower capacity to incorporate lactate into glucose and to oxidize lactate to CO₂; maximal activities of enzymes measured in this study are not the cause of these differences. Reduced capacity of lactate metabolism in livers of SS pigs seems a part of the etiology of the porcine stress syndrome.

KEY WORDS: • pigs • gluconeogenesis • liver • lactate • stress

¹ Journal Paper No. J-8816 of the Iowa Agriculture and Home Economics Station. Ames, Iowa. Project No. 2008.

² This study was presented at the annual meeting of the American Institute of Nutrition, Atlantic City. New Jersey. April, 1975. Federation Proc. 34, 920 (1975) (Abstr.).

³ Address reprint requests to: D. C. Beitz. Dept. Animal Science, Iowa State University, Ames, Iowa 50011.

Manuscript received 20 October 1975.