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

Abstract

1. The following techniques, which have been applied successfully to goats, were used to study mammary metabolism in lactating sows:(I) measurements of mammary arteriovenous (A-V) differences in milk precursors in the conscious undisturbed animal (five sows); (2) continuous intravenous infusion of [U-14C]glucose with concomitant arterial and mammary venous blood sampling for measurement of mammary blood flow and specific radioactivity of glucose and CO, (one sow); (3) perfusion of the isolated gland in vitro (eight glands from four sows), with the inclusion of [U-14C]glucose (two glands) and [U-14C]acetate(two glands) in the substrate mixture.2. Sow mammary tissue was similar to that goats in its milk yield, blood flow, and glucose uptake per unit weight of tissue. As in goats, mammary uptake of glucose was many times that of the rest of the body and the total mammary tissue was utilizing about half of the total glucose entering the circulation. Glucose was a major source of milk lactose and glycerol and of mammary CO2.3. Of the plasma lipid components, only the triglyceride fraction was consistently and significantly removed by the gland. In contrast to the results obtained for the goat, both [U-14C[acetate and [U-14C]glucose carbon were used for milk fatty acid synthesis, and although the pattern of labelling of fatty acid from each precursor was similar, the formation of fatty acids from glucose was at least five times greater than that from acetate. Quantitative evaluation of the contribution of these precursors was not possible, but the RQ (1.09–1.63) suggest that in some instances it may have been considerable.4. The substantial A-V differences of most plasma essential amino acids suggest that these are the sole precursors of the corresponding residues in the mammary synthesized protein. The low A-V differences for several non-essential amino acids suggest that these are synthe- sized in the gland; this suggestion is supported by the incorporation of glucose carbon into non-essential amino acid residues of casein observed in one experiment. However, in contrast to results with the goat, mammary absorption of serine was consistently large.

Influence of feed restriction in primiparous lactating sows on body condition and metabolic parameters

“…Our data indicated that concentrations of NEFA were relatively high on the day of weaning, whatever the level of feeding. This increase in plasma NEFA concentrations might result from the cessation of NEFA uptake by the mammary gland, although previous studies have shown a very low uptake of plasma NEFA by the mammary gland of the sow [28,46]. Indeed, Boyd et al [9] suggested that plasma NEFA probably contribute to milk synthesis in sows with a negative energy balance, in agreement with data from Dourmad (pers.…”

Arginine metabolism: nitric oxide and beyond

“…As the high content of these amino acids in milk greatly exceeds their accumulation via uptake by the lactating mammary gland [258,265], they must be synthesized within this organ. As in the case of proline synthesis during lactation, arginase also plays an important role in providing substrate for glutamate synthesis in the mammary gland via type II arginase, OAT and P5C dehydrogenase [249,257].…”

Amino Acid and Glucose Uptake by the Isolated Perfused Guinea‐pig Mammary Gland

“…Glucose has been shown to be a significant amino acid carbon precursor in the lactating goat mammary gland [see Mepham, 1971]. During perfusion of the isolated sow mammary gland the incorporation of [U-14C]glucose carbon into casein was very low, alanine residues being labelled to the greatest extent [Linzell, Mepham, Annison and West, 1969]. In our experiments with [U-14C]glucose its contribution to casein amino acid synthesis resembled that in the sow in that the maximum specific activity obtained was that for alanine.…”