Comparative utilization in vivo of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose and [1-C14] palmitate in the rat

Female rats were injected i.v. with comparable trace amounts of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose, or [1-14C] palmitate, and killed 30 min afterwards. The radioactivity remaining in plasma at that time was maximal in animals receiving [U-14C] glucose while the appearance of radioactive lipids was higher in the [U-14C] glycerol animals than in other groups receiving hydrosoluble substrates. The carcass, more than the liver, was the tissue where the greatest proportion of radioactivity was recovered, while the greatest percentage of radioactivity appeared in the liver in the form of lipids. The values of total radioactivity found in different tissues were very similar when using either labelled glucose or glycerol but the amount recovered as lipids was much greater in the latter. The maximal proportion of radioactive lipids appeared in the fatty-acid form in the liver, carcass, and lumbar fat pads when using [U-14C] glycerol as a hydrosoluble substrate, and the highest lipidic fraction appeared in adipose tissue as labelled, esterified fatty acids. In the spleen, heart, and kidney, most of the lipidic radioactivity from any of the hydrosoluble substrates appeared as glyceride glycerol. The highest proportion of radioactivity from [1-14C] palmitate appeared in the esterified fatty acid in adipose tissue, being followed in decreasing proportion by the heart, carcass, liver, kidney, and spleen. Thus at least in part, both labelled glucose and glycerol are used throughout different routes for their conversion in vivo to lipids. A certain proportion of glycerol is directly utilized by adipose tissue. The fatty acids esterification ability differs among the tissues and does not correspond directly with the reported activities of glycerokinase, suggesting that the alpha-glycerophosphate for esterification comes mainly from glucose and not from glycerol.

Changes in plasma glucose, insulin and glucagon levels, glucose tolerance tests and insulin sensitivity with age in the rat

Glucose and insulin relationships with aging were studied in fed rats. Levels of basal circulating glucose did not change while those of RIA-insulin increased and RIA-glucagon decreased lineary with animal weight. The oral glucose tolerance test revealed a greater increase in blood glucoe in adult and old rats than in prepuberals, while the rise in plasma insulin was faster and greater in the oldest group. After intravenous glucose load, plasma insulin increase was greater in adult than in prepuberal and old rats, and in the latter grup values remained elevated for a longer period. The hypoglycemic response to i.v. insulin was greatest in the prepuberals with no difference between adult and old rats. In prepuberals, the augmented insulin sensitivity was counteracted by retarded insulinotropic glucose action and an enhanced basal glucagon level, while in the old animals normoglycemia was maintained due to an augmented secretory response of B cells, counteracted by reduced sensitivity to endogenous insulin.

Effect of stress and sampling site on metabolite concentration in rat plasma

The effect of mild stress on various plasma metabolites in the rat has been studied. Mild stress resulted in significant decreases in liver size and glycogen content, as well as in an increase of blood glucose. In addition, plasma lactate, insulin, glycerol and urea, as well as a number of amino acids were altered by stress. These data indicate that minimal stress can have major effects upon the composition of blood, and suggest the need for strict precautions on the handling of animals during blood sampling. The site of blood extraction--tail tip vs. neck--was also found to have a significant effect on plasma lactate, glucose and urea concentrations. In stressed animals the differences between tail- and neck blood composition were increased.

Effects of starvation on in vivo gluconeogenesis in hypo- and hyperthyroid rats

Studies were performed on rats in vivo to determine whether starvation disrupts glucose metabolic balance after removal of the thyroid gland. Intact controls and thyroidectomized rats were injected daily with 0, 0.1, 1.8, or 25 microgram L-T4/100 g BW. Glucose spaces were similar in all groups. The disappearance of labeled glucose from blood was faster in the thyroidectomized rats injected with 25 microgram L-T4 than in the other groups. Starvation enhanced the production of [14C]glucose from [3-14C]pyruvate in all groups, but this effect occurred earlier in control rats and thyroidectomized rats given 1.8 or 25 microgram L-T4 than in thyroidectomized rats given either 0 or 0.1 microgram L-T4. Starvation also enhanced the appearance of radioactivity in liver glycogen 30 min after the injection of [3-14C]pyruvate in all groups, but this effect was lesser in thyroidectomized rats given 0, 0.1, or 25 microgram L-T4 than in other groups. The normal net production of glucose in fed thyroidectomized rats may be the result of a balanced equilibrium between reduced gluconeogenesis and glycolysis. Results obtained in thyroidectomized rats given 25 microgram L-T4 are discussed in terms of the augmented utilization of the newly formed glucose which compensates for their enhanced gluconeogenesis.

In vitro response of glycerol metabolism to insulin and adrenaline in adipose tissue from fed and fasted rats during pregnancy

Pieces of lumbar adipose tissue from 19-day pregnant rats and their virgin controls were incubated in the presence of albumin, glucose, U-14C-glycerol, and either bovine insulin (200 microU/ml) or adrenaline (2.6 microM). The rate of glycerol release in the medium was augmented in both fed and 48-hour fasted pregnant rats. Insulin reduced this parameter in tissues from pregnant rats but not from controls. Adrenaline enhanced it in all groups, expecially in tissues from fed pregnant rats. The rates of CO2, fatty acids and glyceride glycerol formation from glycerol were higher and the effect of insulin was greater in pregnant than in control rats when fed. Fasting produced a decrease in all these parameters, the effect being greater in pregnant than in control rats. The augmented sensitivity of adipose tissue from the mother allows for a rapid switch from the anabolic to the catabolic state according to the necessities of the fetus.

Effect of evisceration on the disposal of [14C] palmitate in the rat

The utilization in vivo of [1-(14)C] palmitate was studied in hepatectomized-nephrectomized rats and their sham-operated controls. After i.v. injection of the tracer, the [14C] lipids in plasma disappeared more slowly in eviscerated animals than in their controls. More label reappeared in plasma as esterified fatty acids in the latter group. At 30 min after the tracer, the amount of label found in the lipidic fraction of carcass and heart was much greater in eviscerated animals than in their controls although the percentile distribution of labelled lipidic fractions remained stable, a considerable proportion being present in the esterified fatty acid form. On the basis of these findings, the rapid increase in the plasma levels of FFA in eviscerated animals must be the result of augmented lipolytic activity more than reduced utilization of these metabolites.

Conversion of (U-14C)-glycerol, (2-3H)-glycerol and (1-14C)-palmitate into circulating lipoproteins in the rat

The in vivo formation of labelled very low density lipoproteins (VLDL) from (U-14C)-glycerol, (2-3H)-glycerol and (1-14C)-palmitate was studied in fed female rats. The rate of disappearance of radioactivity from plasma after the i.v. injection with these tracers was similar for (U-14C)-glycerol and (1-14C)-palmitate. With (2-3H)-glycerol, plasma radioactivity at 10 min was lower than with the other substrates although it did not change thereafter. A certain proportion of radioactivity administered as glycerol appeared in plasma lipids, mainly in the VLDL glyceride glycerol fraction, although when (U-14C)-glycerol was the substrate, a considerable portion also appeared in the esterified fatty acids of these lipoproteins. When using (1-14C)-palmitate, practically all the circulating labelled esterified fatty acids appeared in the VLDL fraction, while the labelled free fatty acids appeared in lipoprotein of higher density, presumable free fatty acid-albumin complexes. This data is discussed in terms of the role of the liver in the rapid, continuous cycling of these substrates to yield VLDL-glycerides for their extrahepatic utilization.

Effect of fasting on urinary excretion of water and nitrogen in the rat

Rats housed in metabolic cages undergoing 48 h fasting showed reduced daily intake of drinking water and increased urinary volume. Both the daily amount of urinary creatinine and urea excreted were diminished with fasting, while that of ammonia was augmented. Besides demonstrating metabolic water loss under fasting, results suggest that ammonia derived from glutamine in the kidney, rather than urea formed in the liver, is the main nitrogenous catabolic product of amino acids in fasting.

Effects of hypo- and hyper-thyroidism on in vivo lipogenesis in fed and fasted rats

Thyroidectomized rats (T) daily injected with either 0, 0.1, 1.8 or 25 microgram of L-thyroxine/100 g body wt. were compared with intact controls (C). The appearance of radioactivity in fatty acids 30 min after the i.p. injection of (3-14C)pyruvate was reduced in adipose tissue and enhanced in liver of T+25, being no differences between the other groups and C. (14C)-Fatty acids are reduced with 3 h of fasting only in the adipose tissue of T+1.8 and C, while 24 h produces a reduction in liver in the T+1.8, T+25 and C, and in adipose tissue in the T+1.8 and C animals. The highest percentage of radioactivity was observed in the liver glyceride glycerol fraction, being greater in T+25 than in the other groups. Fasting produces an increment in the (14C)-glyceride glycerol fraction. Being significant only in thehypothyroid animals in both liver and adipose tissue. The most sensitive parameter to fasting was the formation of (14C)-non-saponifiable lipid in both the C and T+1.8 animals, while it does not change in T+0 or T+0.1, but is enhanced within 24 h in the adipose tissue of T+25. It is proposed that most of the observed changes are due to the other endocrine disfunction s which appear in hypo- and hyperthyroidism, as the in vivo results do not comply with in vitro effects of thyroxine onlipogenesis of others.

Effect of fasting on circulating glucose, ketone bodies and insulin levels in the suckling rat

Suckling rats from 5 to 30 days of age were subjected to fasting in a 37 degrees C chamber to avoid possible metabolic effects from low environmental temperature. The percentage of body weight loss in 24 h fasting increased along with the age of the rats. Blood glucose levels were the same in 5, 10, 20 and 30 day old animals when fed, whereas fasting produced a fall in all the groups which was minimal in the 20 day old animals. Plasma insulin levels were rather low in 10-day-old fed animals; the maximal decrease in this parameter was reached by 5-day-old rats under fasting. Both beta-hydroxybutyrate and acetoacetate levels were higher in animals of 5 and 10 days of age than in those of 30 days, but fasting did not produce any changes in the former while those parameters augmented in the 20 and 30-day-old animals. The results are discussed in relation to the high fat content in the mother's milk, which affects the metabolic situation of the suckling rats when fed and their response to the fasting situation.

A method for the estimation of striated muscle mass in small laboratory animals

A method for the determination of the total muscle mass in small experimental animals is presented. Muscle proteins were quantified in the 1 M LiCl-soluble and distilled water-insoluble fraction of the eyeless, brainless, eviscerated and skinned carcass, as compared with a striated muscle sample from the same animal used as standard and processed in the same way as the whole carcass. The non-muscular tissues left in the carcass do not interfere with the final results. The total muscle mass in adult rats was estimated as 42.0 +/- 2.8% of the in vivo weight.

Human sperm penetration into zona-free hamster oocytes as a test to evaluate the sperm fertilizing ability

Human sperm entry into zona-free hamster oocytes was used to test the fertile ability of spermatozoa from semen samples of men attending an Infertility Clinic. Sperm chromatin dispersion as seen under the phase-contrast microscope, was used as criterion for sperm entry. The ultrastructural study showed that the behaviour of the gamete membranes during fusion did not basically differ from that of normal fertilization. Eighty four samples were classed as normal (according to the spermiogram) but only 62 (74%) gave a positive test, as compared to only 30 (32%) positive test of 95 samples with abnormal spermiograms. Eight hundred and ten oocytes inseminated with spermatozoa from normal samples gave a 25% penetration, while 1046 oocytes inseminated with spermatozoa from abnormal samples gave a 7% penetration. The normality of hamster oocytes was demonstrated by contemporary insemination with human and hamster spermatozoa. While the percentages of human sperm penetration remained low, hamster sperm penetration was over 70%. The present bioassay is recommended as an additional parameter to the spermiograms for the study of male fertility.

Adipose tissue cellularity in hypo-and hyperthyroid rats

To determine adipose tissue cellularity in hypo- and hyperthyroidism, male rats were thyroidectomized after weaning (T) and injected daily with either 0, 0.1, 1.8 or 25 microgram of L-thyroxine/100 g body weight for 40 days. They were compared with intact controls (C). Both epididymal fat-pad weight and adipocyte diameter were reduced in T+0, T+0.1 and T+25 animals. When corrected per unit of body weight, the diameters of adipocytes from T+0 and T+0.1 animals were larger than in the other groups. Those same animals have reduced absolute adipocyte number but not when corrected per unit of body weight. The fat-pad protein concentration varied conversely with the fat cell diameter. These findings indicate that thyroid hormone deficiency reduces the proliferation of fat cells in parallel with body growth while hyperthyroidism causes reduction in the size, but not the number, of fat cells which corresponds to its depletion of fat storage.

Effects of glucose on the metabolization of fructose and glycerol by isolated adipocytes from rat

Isolated white fat cells were incubated in medium containing (14C)-fructose (UL), supplemented with either 1 or 5 mM fructose, in the presence or absence of 5 mM glucose. The utilization of fructose for the formation of CO2, fatty acids or glyceride glycerol was very much dependent on its concentration in the medium. It was significantly inhibited by glucose only at fructose concentration of 5 mM. When the cells were incubated in the presence of (1(-14)C) glycerol, fructose produced a significant increase in the conversion of the tracer to CO2, fatty acids and glyceride glycerol, while glucose produced an increase in the formation of both CO2 and fatty acids, but a significant decrease of glyceride glycerol from the same labelled precursor. Glucose causes the effects of fructose, enhancing the uptake of labelled glycerol by the cells, to disappear.

Utilization of pyruvate, alanine and glutamate by isolated fat cells and their effects on glycerol metabolism

To study the metabolic interactions of different substrates in adipose tissue in vitro, isolated fat cells from fed rats were incubated in medium containing either (U-14C)-pyruvate, L-(U-14C)-alanine, L-(U-14C)-glutamate or (1(-14)C)-glycerol, and supplemented or not with 5 mM glucose or with non-radioactive pyruvate, alanine or glutamate (2 or 10 mM). The utilization of pyruvate for CO2 or fatty acid formation was greater than that of alanine and glutamate, both in the absence and presence of glucose. Glucose enhanced the formation of fatty acids from all the labelled substrates, decreased the synthesis of glyceride glycerol from pyruvate and glycerol, and enhanced it from alanine and glutamate. Pyruvate and glutamate enhanced the utilization of glycerol by the adipocytes and these effects were significantly reduced in the presence of glucose. Thus, the metabolic fate of the glycerol taken up by the cells varied according to the nature of the available substrates.

[Modifications of insulin and growth hormone after medium chain triglycerides ingestion (author's transl)]

Authors determined the variation of glucose, ketone bodies (KB), free fatty acids (FFA), insulin and growth hormone (HGH) in blood produced by the ingestion of 1.5 g./kg. of medium chain triglycerides (MCT) in 10 healthy children between 5 and 11 years. Blood values were determined starting 30 minutes before the MCT ingestion and at 30 minutes intervals until 120 minutes post ingestion and a final determination at 180 minutes. The glucose did not change. The KB were increased (p less than 0.01) from 30 to 120 minutes and the FFA from 90 (p less than 0.01) to 120 minutes (p less than 0.001) after ingestion. Insulin secretion was elevated between 30--90 minutes with a peak value at 60 minutes (p less than 0.001). HGH began to increase at 60 minutes, remaining elevated at the last determination at 180 minutes. The HGH basal value was 0.5 +/- 0.2 ng./ml.; began to increase at 60 minutes and reached the value of 3.9 +/- 1.06 ng./ml. and 4.8 +/- 2.04 ng./ml. at 90 and 120 minutes respectively (p less than 0.001). We do not know the origin of the HGH increase. The changes may explain FFA elevation and other metabolic actions of MCT. The glucose-insulin ratio showed that the hyperinsulinemia was not caused by an increased glucose level.

Different expressions for enzyme activities in organs of rat. Application to aspartate transaminase, glutamate dehydrogenase and AMP-deaminase

The widely used activity expressions for enzyme levels in tissues are discussed: microkatals per unit of tissue weight, protein weight, and DNA weight. The expression of microkatals present in a definite organ in reference to a standard animal weight, 100 g in the case of rat, is also used. The different expressions are applied to aspartate transaminase, glutamate dehydrogenase and AMP deaminase activities in liver, hind leg striated muscle and kidneys in rat. The conclusion is reached that measurements of enzyme activity in tissues should be expressed in more than one form, as the information drawn from one could differ substantially from that obtained from other, giving artifactual views of the metabolic role played by the enzyme in a given tissue.