Enzymes of Glucose and Fatty Acid Metabolism of Liver, Kidney, Skeletal Muscle, Adipose Tissue and Mammary Gland of Lactating and Non-Lactating Sheep

Abstract

The effect of peak lactation on the activities of a number of enzymes of glucose and lipid metabolism of perirenal and subcutaneous adipose tissue, skeletal muscle, liver, kidney cortex and mammary parenchyma of sheep are described. Enzymes studied included hexokinase (glucose utilization), pyruvate carboxylase (gluconeogenesis), pyruvate dehydrogenase (glucose oxidation and production of acetyl CoA for fatty acid synthesis), acetyl CoA carboxylase (fatty acid synthesis) and glycerol-3-phosphate acyltransferase (fatty acid esterification). Major changes that were found include a decrease in activities of enzymes of fatty acid synthesis and esterification in adipose tissues, decreased activity of pyruvate dehydrogenase in muscle and adipose tissues and increased pyruvate carboxylase; there was no change in activities of enzyme of fatty acid esterification in liver. Activities of hexokinase, acetyl CoA carboxylase and glycerol-3-phosphate acyltransferase have been estimated per tissue; this shows the quantitative importance of limiting glucose utilization by muscle and of suppression of fatty acid synthesis in adipose tissue for efficient partitioning of nutrients for milk production.

Glucose-6-phosphate dehydrogenase and leptin are related to marbling differences among Limousin and Angus or Japanese Black × Angus steers1,2

“…To our knowledge, very little data are available concerning the lipogenic activities of muscles depending on their metabolic types. However, one study reported a 2-fold greater G3PDH activity in skeletal muscles than in s.c. adipose tissue in sheep (Vernon et al, 1987), which was also observed in our study. From these results, we conclude that in muscles from steers, G3PDH is not only involved in TAG synthesis but probably also in the glycerol phosphate shuttle (Estabrook and Sacktor, 1958).…”

“…To our knowledge, breedrelated leptin gene expression in muscles has never been reported before. Because leptin mRNA level in bovine is high in adipose tissue but barely detectable in muscle (Chelikani et al, 2003), and most of the lipogenic enzymes are more strongly expressed in adipose tissues than in muscles of ruminants (Howarth et al, 1968;Vernon et al, 1987;Belk et al, 1997), the greater G6PDH and MD activities and leptin mRNA level in LT from Angus vs. Limousin steers may result from a greater number of muscular adipocytes, from greater lipogenic activities of these cells, or both. To address this question, we assayed the same variables in the i.m.…”

“…Moreover, adipose sitespecific development results from nutrient partitioning between adipose and muscle cells as well as from their proportion in the muscle. However, little attention has been paid to the lipid uptake and metabolism in whole muscles (Vernon et al, 1987;Belk et al, 1997;Kazala et al, 2003).…”

Variations du volume des adipocytes et de la note d'état corporel chez la brebis Rasa aragonesa pendant la lactation et après le tarissement

“…Les variations du gras sous-cutané peuvent être estimées in vivo à partir de la note d'état corporel (Russel et al, 1969), ou par les modifications de la taille des adipocytes sous-cutanés (Thornton et aL, 1983 (Vernon et al, 1981(Vernon et al, , 1987Vernon & Taylor, 1986 …”

Changes in cell number and size and in lipogenic enzyme activity in adipose tissues during growth and fattening of Lacha (Manech) lambs

“…These (Hood, 1982;Rule et al, 1987;Vernon et al, 1987;Gagliostro and Chilliard, 1991 In ruminants, the increase of acetate concentration or availability activates the G6PDH enzyme (Martin et al, 1973;Pothoven and Beitz, 1973;Yang and Baldwin, 1973;Whitehurst et al, 1978). This fact could contribute to explain the increase in G6PDH activity observed in this study from 24 kg LW.…”