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D B Lindsay

Publications and source records attributed to D B Lindsay.

At least 37 records · Page 2Linked to original sources
PubMed1981

Acetate supply and utilization by the tissues of sheep in vivo.

1. The supply and utilisation of acetate has been estimated simultaneously in the whole animal and tissues of sheep using a combination is isotope-dilution and arteriovenous-difference techniques. Animals were made alloxani-diabetic and acetate metabolism was compared when stabilized to normal metabolite levels with insulin (ITA sheep) and when food and insulin had been withdrawn for 36 h (fasted, diabetic sheep). 2. Acetate was simultaneously produced and utilized by all tissues. The exogenous (or gut) supply of acetate was the most important determinant of circulating acetate level. Endogenous acetate was produced mainly in the liver; 77 and 94% in fasted, diabetic and ITA sheep respectively. The production of endogenous acetate remained fairly constant and was not related to ketogenesis, which supports the idea that circulating acetate is largely a produce of fermentation. The liver, gut and muscle utilized 17, 25 and 54% respectively (96% total) of the acetate entry rate in ITA sheep; a similar percentage utilization was found in fasted, diabetic sheep. 3. Acetate is largely oxidized to carbon dioxide in the gut and muscles of sheep and may account for 30-40% of their oxidative metabolism. This figure is similar to that for the whole animal. The total acetate taken up by the liver could account for 30% of the oxygen consumption; however, the liver may not directly oxidize all the utilized acetate. 4. The over-all conclusion from this study is that acetate is largely of dietary origin and the major factor determining its rate of utilization is the arterial concentration.

Acetates↗
PubMed1981

The utilization of lactic acid by sheep in late pregnancy.

The irreversible loss of lactate and the respiratory exchange in four conscious ewes that were about 138 days pregnant were measured at least seven days after surgery. In addition, the uptake and net output of lactate and the net uptake of glucose and alanine by the gravid uterus and an upper hind limb (primarily skeletal muscle) were measured. Calculated heat production of the ewes was 496 kJ/d.kg 3/4; irreversible loss of lactate was 9.5 mumol/min.kg of which 73% was oxidized to CO2, contributing 9% to the ewes' CO2 production. About 2% of the glucose and 65% of the alanine was derived from lactate. Lactate was taken up by both the gravid uterus and the upper hind limb; output of lactate could have accounted for from 8-12% of glucose uptake by the gravid uterus but from 35-50% of that by the upper hind limb. The carbohydrate/O2 quotient was 1.07 for the gravid uterus and 0.35 for the upper hind limb.

Alanine↗
PubMed1979

The low availability of dietary choline for the nutrition of the sheep.

1. Choline, which is present in the diet of the sheep either in the non-esterified form or combined in phospholipids, is rapidly degraded in the rumen. The ultimate product formed from the N-methyl groups is methane. 2. Analysis of the non-esterified choline and the phosphatidylcholine in ruminal and abomasal digesta indicate that the phospholipid is the main vehicle for the passage of choline to the lower digestive tract. 3. The concentration of phosphatidylcholine in abomasal digesta is lower than that of ruminal digesta, which is in line with a selective retention of protozoa in the rumen as observed by others. 4. On defaunation of the rumen to remove ciliated protozoa the concentration of phosphatidylcholine in ruminal digesta falls markedly and becomes lower than that in abomasal digesta. 5. Calculation shows that the adult sheep obtains at most only about 20--25 mg of effective choline per day from its diet (0.002--0.0025% of dietary total dry-weight intake). This is some fifty times less than the minimum required to avoid pathological lesions and death in other species investigated (0.1%+ of dietary dry-weight intake). 6. Sheep liver can synthesize choline from [14C]ethanolamine both in vitro and in vivo, but the synthesis of choline per kg body weight is many times less than it is in the rat. 7. The intact sheep oxidizes an injected dose of [1,2-14C]choline to CO2 at a rate that is several times less than that observed for the rat. This could help to explain the apparent minimal requirement of sheep for dietary choline.

Animal Nutritional Physiological Phenomena↗
PubMed1976

The oxidation of glucose, ketone bodies and acetate by the brain of normal and ketonaemic sheep.

1. The utilization and oxidation of glucose, acetate and ketone bodies by the brain of sheep has been determined from measurements of arteriovenous (A-V) differences and cerebral blood flow, as well as by infusing 14C-labelled metabolites. 2. The A-V difference for glucose was generally more than one sixth, on a molar basis, that of oxygen. 3. The mean rate of glucose utilization by the brain of conscious sheep (0-508 +/- 0-063 mumole/g per minute) was maintained even when the capillary glucose concentration was below 1-4 mM. 4. The amount of 14CO2 produced from [U-14C]glucose by the brain was consistent with glucose being the only energy source for the brain, even during hypoglycaemia and hyperketonaemia. 5. There was no appreciable production of lactate or pyruvate by the brain. 6. There was no significant A-V difference for acetate across the brain in normal or undernourished pregnant sheep. The small A-V differences that were measured show that less than 5% of the CO2 produced could be derived from acetate, a conclusion that is supported by experiments using [U-14C]acetate. 7. No significant A-V difference was detectable across the brain for 3-hydroxybutyrate or acetoacetate in normal fed, pregnant ketonaemic or even anaesthetized sheep infused with acetoacetate. Experiments in which [U-14C]-D(-)-3-hydroxybutyrate was infused also showed that less than 5% of CO2 was derived from ketone bodies. 8. In anaesthetized sheep infused with acetoacetate, measurements were made simultaneously across brain, heart and skeletal muscle. In contrast to the non-significant uptake of ketone bodies by the brain, uptake by heart and skeletal muscle was sufficient to account for nearly 60% of their oxygen consumption. 9. Experiments using [14C]hydroxybutyrate confirmed that during infusion of acetoacetate most of the CO2 produced by the heart, but not by the brain, was derived from ketone bodies. 10. In anaesthetized sheep ketone bodies penetrate only slowly into cerebrospinal fluid. 11. It is proposed that mechanisms for the utilization of ketones by the sheep brain have not evolved because glucose utilization by the brain is a smaller fraction of whole body glucose utilization than in man and rats.

Acetates↗
PubMed1975

Utilization of amino acids by the isolated perfused sheep liver.

To test Elwyn's suggestion [1970], that high concentrations of amino acids supplied to the liver from the hepatic artery do not stimulate protein synthesis, substrates containing amino acids have been infused into either the hepatic artery or portal vein of isolated sheep livers. The livers received highly oxygenated blood from the hepatic artery and partly deoxygenated blood from the portal vein. There were no significant differences in amino acid uptake (81 +/- 4% of input), urea output (69 +/- 6% of uptake) or 'protein synthesis' as assessed by N accumulation in the liver. Amino acids were actively extracted from the plasma by both routes of infusion and , when the concentrations simul-ted those occurring in the portal vein of fed sheep, the uptake was very similar to that in vivo. When an amino acid mixture based on that absorbed in dogs was infused, the extraction of individual amino acids was similar except for a negligible uptake of valine, leucine and isoleucine. In these experiments protein synthesis was also very low.

Alanine↗