Arteriovenous differences across human adipose and forearm tissues after overnight fast.

Measurements of arteriovenous differences across subcutaneous abdominal tissue (mainly adipose) and deep forearm tissue (mainly muscle) were made on 25 occasions in normal subjects after an overnight fast. Adipose tissue was shown to be strongly lipolytic (releasing nonesterified fatty acids and glycerol), to clear circulating triacylglycerol, glucose, ketone bodies and acetate, and to produce lactate. Uptake of circulating carbohydrate and ketones was sufficient to account for only 51% of the adipose tissue oxygen consumption, implying that adipose tissue utilizes fuel(s) stored within it. The mean fractional re-esterification rate of fatty acids in adipose tissue was 13% to 19%. Arteriovenous differences were converted to fluxes of carbon atoms to compare the movements of different fuels. (Amino acids were not included in these calculations.) Adipose tissue after an overnight fast was a net exporter of carbon, whereas in resting muscle the uptake of carbon atoms from circulating carbohydrate and lipid fuels approximately balanced the CO2 production. Fatty acids were the main form in which carbon left adipose tissue, and the main source of carbon atoms entering the resting forearm.

Metabolic characteristics of human adipose tissue in vivo.

1. A method was developed for sampling the venous drainage from the subcutaneous adipose tissue of the anterior abdominal wall. This is a large depot in many subjects, and seems well suited to such studies as it is completely separated from the venous drainage of the underlying muscle by the aponeurosis of the external oblique muscle. 2. Eight normal subjects were studied after an overnight fast, and for 120 min after ingestion of 75 g of glucose. Concentrations of substrates in the abdominal wall drainage were compared with those in arterialized blood and in forearm muscle drainage. 3. Non-esterified fatty acid and glycerol concentrations in the abdominal wall drainage were high (three to four times the arterial level) after overnight fast. After glucose ingestion, arterial and abdominal venous levels fell and the arteriovenous differences narrowed. The forearm showed uptake of non-esterified fatty acids when fasting but not after glucose ingestion, with no significant arteriovenous difference for glycerol at any time. 4. The abdominal wall tissues showed a small arteriovenous difference for glucose uptake during fasting, which increased after glucose ingestion. Although lactate was produced throughout, its molar ratio to glucose uptake was less than that reported for other superficial sites, suggesting only a minor contribution of skin metabolism. Forearm muscle showed a larger and more prolonged increase in arteriovenous difference for glucose uptake after the glucose load, but no consistent release or uptake of lactate. 5. We conclude that the tissue studied by this technique is predominantly adipose. This technique may have wide application in studies of the metabolic basis for body weight regulation in man.

Changes in forearm blood flow at elevated ambient temperature and their role in the apparent impairment of glucose tolerance.

1. Antecubital venous plasma glucose and insulin concentrations after ingestion of 75 g of glucose were higher in six normal subjects when studied at an ambient temperature of 33 degrees C at an ambient temperature of 23 degrees C; the mean area under the glucose-time curve increased from 833 at 23 degrees C to 990 mmol min-1 at 33 degrees C, that for insulin from 5300 to 7900 m-units min 1-1. 2. Core temperature was elevated by 0.5 degree C at 33 degrees C ambient, although there was no marked stress response as judged by plasma levels of catecholamines, cortisol and growth hormone; at 2 h after glucose ingestion, mean noradrenaline levels were lower at 33 degrees C than at 23 degrees C (1.1 at 33 degrees C vs 1.8 nmol/l at 23 degrees C), adrenaline slightly higher (0.18 at 33 degrees C vs 0.09 nmol/l at 23 degrees C), cortisol and growth hormone unchanged. 3. Forearm blood flow was markedly elevated at 33 degrees C ambient (mean total flow 9.1 at 33 degrees C vs 1.8 ml min-1 100 ml-1 at 23 degrees C), as were antecubital venous partial pressure of oxygen (mean 10.1 at 33 degrees C vs 5.6 kPa at 23 degrees C) and oxygen saturation (mean 92% at 33 degrees C vs 70% at 23 degrees C). There was a positive correlation between oxygen saturation and area under the glucose tolerance curve. 4. In separate experiments, arterialized glucose concentrations were measured after glucose ingestion at 23 degrees C ambient.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen and carbon dioxide tensions, breathing and heart rate in normal infants during the first six months of life.

Daytime measurements were made of the relationship between sleep state, cardio-respiratory changes and oxygen (transcutaneous PO2) and carbon dioxide (mass spectrometer alveolar PCO2) tensions in eleven normal infants from birth to 6 months of age. Sequential records were made at 1 week, 1, 3 and 6 months. The babies were not restrained, slept in a cot, and were constantly observed. Heart rate was higher in active sleep than in quiet sleep at all ages and rose between 1 week and 1 month (P less than 0.01) in both quiet sleep and active sleep and then decreased at 3 and 6 months. Respiratory rate only changes with age in active sleep at 6 months, showing a decrease (P less than 0.05) but was higher in active sleep that in quiet sleep at 1 month (P less than 0.002) and 3 months (P less than 0.02). A fall in heart rate (less than 100 beats/min) occurred chiefly in association with apnoea. The incidence of apnoea (of greater than 3 s duration) varied widely between babies at the same age and in the same baby at different ages but was most common in the first 3 months of life. No evidence of obstructive apnoea was found and no apnoea of greater than 12 s duration was observed. Period breathing occurred in all babies at 1 month normally following sighs but was uncommon at 1 week and 3 months and absent at 6 months. A fall in transcutaneous PO2 did not precede but often resulted from an episode of periodic breathing.

Studies on the control of respiration and behaviour during development in ewe-reared lambs.

Radiotelemetric recordings have been made in a series of newborn lambs with implanted electrodes and transducers and an external back-pack transmitter. Cardiac, respiratory and behavioural data have been gathered. These data have been analysed firstly with respect to age. The cardiac and respiratory data have then been related to both sleep state and age. An unexpected rise in both heart and respiratory rates was found after birth and marked differences were obvious in respiratory control in REM and non-REM sleep states.

Continuous transcutaneous and intraarterial oxygen measurement during experimental hypoxemia in infant monkeys.

The relationship between PaO2 and tcPO2 is an important one and provides a physiologic measure of impaired circulatory control or vascular damage. The central and peripheral mechanisms involved have to be studied further. Although tcPO2 equates well with PaO2 in many circumstances, appropriate oxygen conserving, centrally mediated vasoconstriction can overcome the thermally induced local vasodilation. Investigation of the control of peripheral circulation in both clinical medicine and the experimental animal is advanced by the technique of transcutaneous oxygen recording.