No 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.

SUMMARY1. Measurements were made of milk yield, mammary blood flow and mammary arteriovenous differences during the measurement of substrate entry rate by the isotope dilution method using [U-14C] acids at 094-6-8 mg/min/kg and 6-9 % of total CO2 was derived from each. The udder took up 3-0-5*7 mg/min/kg of tissue and 4-8 % of mammary CO2 was derived from each acid. In the udder 8 and 5-5 % of stearate and oleate were oxidized and 25 % of palmitate. Mammary uptake of stearate was 31-5 % of the total entry rate, palmitate 1 %, and oleate 7-5 %. Only long chain milk fatty acids were labelled. 6. During fasting the mammary R.Q. was 0-85 + 0 045 compared with a value in fed animals of 1-24 + 0-02, when the udder is synthesizing fatty acids from acetate. The total mammary uptake of lipid precursors was only 74 % of the rate of milk fat secretion and there was an 18 % shrinkage in empty udder volume, suggesting the use of endogenous mammary tissue substrates.

An improvement in iodine status, rather than iodine status itself, determined mental performance in this population, which was initially iodine deficient. These findings suggest a "catch-up" effect in terms of mental performance.