Age‐related changes in oxygen and nutrient uptake by hindquarters in newborn pigs during cold‐induced shivering

Abstract

SUMMARYNewborn pigs rely essentially on shivering thermogenesis in the cold. In order to understand the rapid postnatal enhancement of thermogenic capacities in piglets, the oxygen and nutrient uptake of hindquarters was measured in vivo in 1-(n = 6) and 5-day-old (n = 6) animals at thermal neutrality and during cold exposure. The hindquarters were considered to represent a skeletal muscle compartment. Indirect calorimetry and arterio-venous techniques were used. The cold challenge (23°C at 1 day old and 15°C at 5 days old for 90 min) induced a similar increase (+90 %) in regulatory heat production at both ages. Hindquarters blood flow was higher at 5 days than 1 day old at thermal neutrality (26 + 3 vs. 17 + 1 ml min-' (100 g hindquarters)-') and its increase in the cold was much more marked (+65 % at 5 days old vs. +25 % at 1 day old). Oxygen extraction by the hindquarters rose from 30-35 % at thermal neutrality to 65-70 % in the cold at both ages. The calculated contribution of skeletal muscle to total oxygen consumption averaged 34-40% at thermal neutrality and 50-64% in the cold and skeletal muscle was the major contributor to regulatory thermogenesis. Based on hindquarters glucose uptake and lactate release, carbohydrate appeared to be an important fuel for shivering. However, net uptake of fatty acids increased progressively during cold exposure at 5 days old. The enhancement in muscular blood supply and fatty acid utilization during shivering is probably related to the postnatal improvement in the thermoregulatory response of the piglet.

Mitochondrial and peroxisomal fatty acid oxidation capacities increase in the skeletal muscles of young pigs during early postnatal development but are not affected by cold stress

“…As shown previously [12], this is accompanied by a major rise in NEFA plasma levels, and a decline in the respiratory quotient reflecting the increased involvement of lipids as an energy source. This metabolic switch is likely to occur at the muscular level because, in these conditions, skeletal muscle is known to contribute 34-40% to whole-body oxygen consumption [6]. Indeed, we observed a marked increase in total fatty acid oxidation capacities expressed by g tissue wet weight between birth and five-days of life.…”

“…The cold-induced enhancement of NEFA plasma levels indicates that adequate mobilization of fat stores occurred. In similar cold conditions, we have also shown that, at this age, fatty acid uptake is stimulated in the skeletal muscle [6] thereby increasing fatty acid availability within the muscle cell. This mechanism was probably responsible for the enhancement of fatty acid utilization because very limited changes in fatty acid oxidation were noticed.…”

“…kidneys, liver and heart of young pigs [5], and our previous investigations on the in vivo metabolism [6], morphofunctional characteristics [18], mitochondrial metabolism [7] and CPT I activity [8] of skeletal muscle from young pigs.…”

“…At this age, heat production was measured in the respiratory chamber either in thermoneutral (TN, 30 o C, n = 6) or in cold (C, 15 o C) conditions during a 4-h period. These temperatures were chosen to take into account the downward shift of the lower critical temperature with age [12] and to achieve a similar increase in heat production at both ages [6]. An oral dose of fresh sow colostrum (30 g·kg -1 BW) was given to the newborn piglets before being put into the chamber to ensure that, at both ages, measurements were made on fed piglets.…”

“…Regarding skeletal muscle, the key thermogenic tissue of the piglet, direct demonstration of the postnatal enhancement of fatty acid oxidation is missing and the effects of muscle fiber type and cold stress are poorly documented. However, we have already shown that within the first five days of life, the in vivo hindquarter blood flow [6], mitochondrial protein mass and oxidative potential of skeletal muscles [7] are increasing. Furthermore, the inhibition of CPT I activity by malonyl-CoA was progressively relieved [8], which should favor fatty acid oxidation in the skeletal muscle.…”