The incorporation of acetate, stearate and d(-)-β-hydroxybutyrate into milk fat by the isolated perfused mammary gland of the goat

Abstract

1. Mammary glands of lactating goats were perfused for 12.5-15hr. with heparinized whole blood and infused with a substrate mixture of glucose, acetate and amino acids (and sometimes chylomicra) containing either [1-(14)C]acetate, d(-)-beta-hydroxy[1-(14)C]butyrate or [U-(14)C]stearate. 2. There was a substantial net uptake of acetate by the glands and transfer of radioactivity into milk fat. Acetate was extensively utilized for the synthesis of milk fatty acids of chain length up to C(14) and to a smaller extent for the synthesis of palmitate. 3. There was a small and variable net uptake of stearate and beta-hydroxybutyrate and negligible oxidation of these substrates. However, tissue uptake was demonstrated by a substantial fall in specific radioactivity across the glands and an extensive transfer of radioactivity into milk fatty acids. 4. With beta-hydroxybutyrate the labelling of milk fat was very similar to that with acetate, but the distribution of radioactivity suggested a cleavage into C(2) fragments of about 40%. 5. Labelled stearate gave rise to highly labelled stearate and oleate in the milk fat. Small amounts of radioactivity were detected in stearate of plasma triglycerides and oleate of plasma free fatty acids. 6. In experiments where there was a decline in milk-fat secretion late in perfusion, the milk fatty acids showed a marked decline in the proportion of stearate and oleate and a rise in the proportion of myristate and palmitate. This did not occur in experiments where milk-fat secretion was maintained at a higher level. 7. The present results confirm that there is a large pool of long-chain fatty acids in mammary tissue that can act as an endogenous source of these substrates.

Effect of Feefing Protected Lipid on the Uptake of Precursors of Milk Fat by the Bovine Mammary Gland

“…However, in accord with earlier reports for cows (Hartmann and Lascelles 1964) and goats (Linzell et al 1967) fed forage diets, triglyceride was the only lipid fraction taken up in significant quantities by the mammary gland.…”

Relationship between Occurrence of White Diarrhea and Changes of Properties and Components of Blood and Milk in Their Dams after Parturition in Japanese Black Calves.

“…This may be due to an increase in the fat uptake from the intestinal tract [13] accelerated excretion of lipoproteins from the liver, or depression of lipoprotein metabolism due to a reduction in lipoprotein lipase activity. Depression of lipoprotein metabolism decreases the supply of TG to the mammary glands, which results in a decrease in the fat content of milk [7]. But in this study the fat content in the milk increased.…”

Mammary metabolism in lactating sows: arteriovenous differences of milk precursors and the mammary metabolism of [14C]glucose and [14C]acetate

“…However, in both acetate and glucose experiments radioactivity was transferred to milk fat and to a much greater extent to mammary tissue lipids. This confirms that, as in goat udder perfusions (Linzell, Annison, Fazakerley & Leng, 1967), in view of the slow turnover time of mammary tissue lipid pool, perfusions must be continued for a considerable time before constant SRAs are obtained; this is not always technically feasible. Thus in the present experiments the contributions of glucose and acetate to milk fat were not maximal.…”