Method for the study of metabolite transfer from rat mother to fetus

Infusion medium containing a tracer was introduced through the left uterine artery to 20.5-day pregnant rats. In this way, the left uterine horn received the tracer directly while it reached the right horn after dilution in the mother's circulation. When U-14C-D-glucose or U-14C-L-alanine was infused, radioactivity in fetal blood from the left uterine horn was 3 or 8 times higher respectively than in the right horn and 2 or 6 times higher than in maternal blood. When the infusion was carried out with 125I-labelled growth hormone, which is known not to cross the placental barrier, very little radioactivity was found in fetuses compared with that in the mother's plasma and no differences were observed in blood radioactivity levels of fetuses from either horn. After infusion of U-14C-D-glucose through the maternal jugular vein instead of left uterine artery, radioactivity was the same in fetuses from the left and right horns, indicating that manipulations of the left uterine side did not greatly affect its circulation. These findings. together with the determination of specific radioactivity of the tracer used in both maternal and fetal plasma, validate the technique as a semiquantitative means to determine the direct transfer of any product through the placental barrier in the rat.

Effects of streptozotocin-diabetes and l-thyroxine treatment on plasma amino acid levels in thyroidectomized rats

1) Thirty days after surgical thyroidectomy, one group of rats were made diabetic by treatment with streptozotocin and were studied for the next 14 days. These diabetic thyroidectomized animals were similar in body weight to their thyroidectomized controls but had higher plasma concentrations of most amino acids. 2) Treatment with 0.5, 1.0 or 2.0 micrograms of L-thyroxine/100 g body wt for 7 days prior to sacrifice produced no changes in either parameter in the diabetic thyroidectomized animals. On the contrary, in thyroidectomized controls, the L-thyroxine treatment was followed by a dose-dependent increment in body weight. In these animals, the administration of 0.5 microgram of L-thyroxine per day was associated with a marked rise in the plasma level of most amino acids, while only basic amino acid levels increased with 1.0 microgram, and levels decreased with 2.0 micrograms. 3) In the diabetic thyroidectomized rats treated with insulin for the last 7 days before sacrifice, body weight gain and the biphasic change of plasma amino acid levels were restored. 4) It is proposed that treatment of thyroidectomized controls with small doses of L-thyroxine accelerate protein breakdown accompanied by minor changes in amino acid utilization, while this latter effect increases with higher doses of the hormone. 5) Present results demonstrate that a certain amount of circulating insulin is required to obtain the response to exogenous thyroxine in diabetic thyroidectomized animals. Results are discussed in terms of the role of interhormone synergism as it affects normal sensitivity of the different hormones.

Effects of maternal ethanol ingestion on cerebral neurotransmitters and cyclic-AMP in the rat offspring

1. To study the effects of maternal alcohol ingestion on brain parameters in offspring, rats were given ethanol for drinking (25% w/v) from the time of mating until sacrifice. Controls drank tap water. 2. Alcohol ingestion reduced daily food and liquid consumption but total caloric intake was only slightly diminished. 3. Maternal body weight increased and offspring body weight, size and brain weight were reduced in the animals receiving alcohol. 4. Brain concentrations of tryptophan, tyrosine and GABA were augmented in ethanol treated mothers at 1 day post-partum. 5. Comparison of brain parameters in offspring of alcoholic mothers with those of controls showed that tryptophan and 5HT concentrations were augmented in 4 day old neonates, NA was increased in 21 day fetuses and 1 day old neonates, and adenylate cyclase activity was also greater in the brains of 21 day fetuses and the cerebellums of 4 day old neonates. 6. Neither phosphodiesterase nor cyclic-AMP concentrations differed in offspring of alcoholic and control mothers. 7. Data showed alterations in brain NA and 5HT systems in the offspring of alcoholic mothers.

Comparative changes with age of the fasting response in circulating ketone bodies, glucose and insulin and oral glucose tolerance test in the rat

1. Body weight loss in 48 hr fasted rats decreased with age. 2. Blood glucose and plasma RIA-insulin levels correlated negatively and positively respectively with body weight in fed rats. Fasting produced a greater fall in blood glucose and a smaller decrease in RIA-insulin in young than in old rats. 3. Blood ketone bodies correlated negatively with body weight after 48 hr fasting. 4. In oral glucose tolerance tests, blood glucose rose more in adult and old rats than in prepuberals when both fed and fasted. RIA-insulin levels rose more in prepuberals than in older rats when fed but not when fasted. 5. Changes in body composition and reduced insulin sensitivity with age are discussed.

Fetal and Early postnatal development of adenylate cyclase and cyclic AMP phosphodiesterase activities in rat brain

Brain cyclic AMP metabolism was studied in rat offspring at 17, 19 and 21 days of intrauterine life and 0, 1 and 4 postnatal days. Wet weight and protein and DNA and RNA concentrations in brain increased in parallel with body weight until the 4th postnatal day although during the perinatal phase some of these parameters suffered a manifest temporal retardation. In the brain, similar qualitative changes were observed in both adenylate cyclase and high Km cyclic AMP phosphodiesterase activity while the low Km enzyme showed a rise from 17-day fetuses to those of 19 days with no further changes. The increase in cyclic AMP concentration was very mild and the values found in the 21-day fetuses were already similar to those in adults. In the mother's brain a significant reduction in adenylate cyclase activity appeared at 19 and 21 days of gestation. The retardation in the ontogenic development of cyclic AMP metabolism during the perinatal phase in offspring is probably a consequence of their specific metabolic situation while in the mother it may be the result of its endocrine preparation for parturition.

Changes in lipid composition of plasma lipoproteins after total hepatectomy in the rat

Lipidic composition of plasma lipoproteins were determined at different times after total hepatectomy in the rat and compared with those in sham-operated animals. After hepatectomy there was a progressive decrease in the plasma triglycerides amounts corresponding to changes in the content of very low density lipoproteins (VLDL) triglycerides. Phospholipid concentrations in both low density lipoproteins (LDL) and VLDL decreased after hepatectomy but theses lipids were unchanged in high density lipoproteins (HDL) which are the main contributors to plasma phospholipid content. Contrary to the other lipid components, plasma cholesterol levels increased after hepatectomy, due mainly to the increment in HDL-esterified cholesterol. Modifications in plasma triglyceride levels after hepatectomy are interpreted as the result of total reduced synthesis and the effect of extrahepatic lipoprotein lipase activity on VLDL-triglycerides. Changes in cholesterol are considered due to its enhanced production by extrahepatic tissues.

Effect of ether, sodium pentobarbital and chloral hydrate anesthesia on rat plasma metabolite concentrations

The effect of ethyl ether, pentobarbital sodium (Nembutal) and chloral hydrate anesthesia on the concentrations of glucose, lactate, glycerol, insulin, individual amino acids and urea have been studied in rat plasma, as well as the glycogen content in the animal liver and striated muscle. Control animals were injected with saline solution. Two samples were taken from each animal at 15 and 30 minutes from the beginning of anesthesia. These samples were obtained from the cut tail's tip and from the neck wound produced by beheading the animal. Results show considerable differences between the three sets of animals and their controls as well as in their tail verus neck values. The overall effect of the three anesthetics used were roughly the same in spite of their different actions upon the different parameters studied. This was most marked in the aminograms. Significant changes induced were rather similar in number for all. The metabolite concentration profile in each situation may be used as a reference for possible artifacts induced by any experimental approach using these anesthetics.

Tryptophan overload in the pregnant rat: effect on brain amino acid levels in in vitro protein synthesis

The concentration of most amino acids was higher in the brains of 19- and 21-day rat fetuses than in their respective mothers. After an intraperitoneal load of tryptophan to the mother, the intracerebral concentration of several amino acids (including leucine) decreased not only in the mothers, but also in their fetuses. The in vitro incorporation of [3H]leucine into proteins in brain postmitochondrial supernatant fractions was enhanced in both the mothers and fetuses after tryptophan administration, but this effect disappeared when protein synthesis was calculated by using specific activities corrected for the amount of unlabeled leucine in the preparation. By this criterion, protein synthesis activity appeared similar in the brains of 19- and 21-day pregnant rats but was higher in their fetuses, especially in the 21-day subjects. Thus, protein synthesis in the brain was not altered by marked changes in the amino acid pool and more profound and prolonged metabolic disturbances must occur to cause permanent damage in the developing brain.

Changes in circulating glycerol, free fatty acids and glucose levels following liver transplant in the pig

Female pigs, fasted overnight, received an orthotopic liver transplant. During the nonhepatic phase, both blood glycerol and plasma free fatty acid concentrations increased, returning to basal values after the transplant, indicating that the liver is the main receptor of these products released in the blood from the glyceride breakdown in peripheral fat deposits. Blood glucose level rose during the nonhepatic phase, probably due in part to the perfusion of glucosated saline received by the animals during this phase. After liver transplant, blood glucose levels progressively decreased and this effect was greatly reduced by administering L-alanine. Our data indicate that metabolic changes in the donor's liver diminish the availability of gluconeogenetic substrates immediately following transplant, while administration of exogenous alanine permits faster restoration of gluconeogenetic function in the transplanted liver.

"In Vitro" utilization of labelled esterified fatty acids and glyceride glycerol from triglyceride-rich lipoproteins in rat adipose tissue

Triglyceride-rich lipoproteins (chylomicrons and very low density lipoproteins) were labelled "in vivo" by injecting (U-14C)-glycerol and (9-10(n)-3H)-palmitate in female rats. After purification, these lipoproteins contained most of the 3H in esterified fatty acids and the 14C in glyceride glycerol of neutral lipids. This preparation was incubated "in vitro" in the presence of either isolated adipocytes or epididymal fat pad pieces from male rats. With the incubation, a certain proportion of both 3H-esterified fatty acids and 14C-glyceride glycerol disappeared from the medium, the effect being greater when the incubations were performed with adipocytes than with fat pad pieces. Much greater radioactivity appeared in the lipids of adipocytes than in those of fat pad pieces at the end of 60 or 120 min incubation, and the incorporation of 3H being relatively greater than that of 14C. With the latter isotope, the label appeared not only in the glyceride glycerol fraction but also in the free and esterified fatty acids. Although it is known that lipoproteins lipase activity is lower in adipocytes than in fat pad pieces, our results indicate that, in the former preparation, the enzyme may be more accessible for the substrate. These data also demonstrate that glycerol released by the hydrolysis of lipoprotein glycerides may be partially incorporated into lipids by adipose tissue.

Metabolic effects of short term food deprivation in the rat

The effects of food deprivation for up to 24 hours on plasma metabolic parameters in the rat have been studied. Liver dry weight and glycogen content dropped significantly from 3 hours of food deprivation onwards. Total muscle glycogen supplied about as much glycosyl residues or precursors as did the liver. Plasma glucose, urea, lactate and total and essential amino acids decreased significantly from 3 hours of fasting onwards. Glycerol, free significantly from 3 hours of fasting onwards. Glycerol, free fatty acids, beta-hydroxybutyrate and acetoacetate showed significant increases with fasting. Alanine, serine, arginine, threonine, aspartate plus asparagine and proline showed significant decreases with fasting. Several other amino acids showed almost no change with fasting. Lysine, leucine plus isoleucine and taurine showed biphasic changes in their concentrations with a minimum at 6 hours and a transient recovery at 12 hours of fasting Essential amino acids decreased more than the non essential ones. With fasting there is a shift in ammonia disposal with lower urea concentrations as nitrogen is better conserved. The results seem to suggest that there is a constant release of substrates, through liver and peripheral tissue proteolysis, that is counteracted by differential utilization of amino acids during fasting.

Morphological and compositional changes of rat plasma triglyceride-rich lipoproteins incubated with adipose tissue

Triglyceride-rich rat lipoproteins (mainly VLDL), purified by ultracentrifugation and dialysis, were incubated for 120 min in the presence of epididymal fat-pad pieces from fed rats in media containing heparin. During this process, the lipoproteins were depleted of triglycerides and proportionally enriched with proteins, causing their increased density. After incubation, electron microscopic study of the triglyceride-rich lipoproteins revealed partially degraded structures, and some particles had atypical discoid flattened form and marked lamellar structure. These findings are in agreement with those of Blanchette-Mackie & Scow (1976) in triglyceride hydrolysed chylomicrons and confirm their observation of monolayers formed by accumulated lipolytic products that move by lateral diffusion, giving rise to a spiral fold between the core triglycerides and the aqueous space.

Lipids and lipoproteins in maternal and fetus plasma in the rat

Plasma lipidic components appear augmented in 19- and 21-day pregnant rats compared with virgin controls, the greatest effect being in triglycerides, corresponding to the augmented proportion of plasma very low density lipoproteins (VLDL). The plasma lipidic components in fetuses of 19 and 21 days are lower than in their mothers, the greatest decrease occurring in triglycerides. In the plasma of 19-day fetuses, there is only one lipoprotein electrophoretic band which corresponds to the beta-lipoproteins of adults (low density lipoproteins, LDL) according to its mobility and floating characteristics, while in the fetus of 21 days there are also pre-beta-lipoproteins (VLDL). In the 1- and 5-day-old newborns, the four main lipoprotein fractions are already present as in the adults. The late appearance of VLDL and the lack of high density lipoproteins in the rat fetus determine various specific metabolic characteristics.

Extra-hepatic utilization of 14C-glucose and 14C-glycerol in the eviscerated rat

Hepatectomy and nephrectomy in the rat produced an increase in blood glycerol levels which was observed before the fall in blood glucose. The disappearance of total radioactivity from plasma after the i.v. injection of either (U-14C)-glycerol or (U-14C)-glucose in these animals was slower than in their sham operated controls. Total radioactivity in plasma was always lower after (U-14C)-glycerol administration than after (U-14C)-glucose. The loss of either tracer from plasma in the eviscerated animals was followed by the appearance of 14C-lactate, demonstrating their rapid metabolism. The radioactivity appearing in the water soluble fraction of lumbar fat pads was increased in eviscerated animals while in the lipid fraction it was reduced from both tracers. These results show that adipose tissue is able to metabolize small quantities of glycerol directly in vivo. The use of both (14C)-glycerol and (14C)-glucose by skeletal and heart muscles was enhanced in hepatectomized rats but the effect on synthesis of labelled glyceride glycerol was greater for (14C)-glycerol, suggesting its important role in the esterification of fatty acids in these tissues.

Effect of rat serum on glycerol metabolism in adipose tissue in vitro

It has been proposed that the lipolytic effect of serum is based on the presence of either lipoproteins or catecholamines. To test these hypotheses, pieces of epididymal fat pads from fed rats were incubated in the presence of albumin and glucose for 120 min. The addition of rat serum (5 mul/vial) enhanced the rates of both glycerol release to the media and [U-14C] glycerol utilization by the tissue. Heparin did not alter these parameters or the response produced by serum. VLDL from rat plasma also enhanced glycerol release and utilization for the formation of CO2 and lipids, and heparin significantly augmented these effects. Neither of the conditions studied affected the percentual distribution of 14C-lipid fractions in the tissues. It is known that in similar conditions to those used in the present study, adrenaline produces a decrease in the utilization of glycerol. Thus our findings do not support the proposed hypothesis explaining the fat-mobilizing action of serum, the mechanism of which remains to be determined.

Effect of heparin on the utilization in vitro of labelled glycerides from triglyceride-rich lipoproteins in rat adipose tissue

Triglyceride-rich lipoproteins from adult rat plasma were labelled in vivo with 3H in the esterified fatty acids and 14C in the labelled glyceride glycerol of neutral lipids by injecting i.v. sodium 9-10 (n)-[3H] palmitate and [U-14C] glycerol, after which the prelabelled lipoproteins were purified by ultracentrifugation and dialysis. The lipoproteins were incubated in vitro, in the presence or not of heparin, with pieces of epididymal fat pads or isolated adipocytes from fed rats. The disappearance of both [3H]- and [14C] lipids from the media was greater when incubations were performed with adipocytes than with fat-pad pieces and it increased with heparin in both preparations. More 3H-label than 14C was found in the tissue lipids, a higher percentage being present in adipocytes than in fat-pad pieces, and the amount of label in tissue lipids was always enhanced by heparin. Some 14C-label appeared as esterified fatty acids in both tissue preparations and it also was enhanced by the presence of heparin. These findings are in agreement with the recognized influence of heparin on the release of lipoprotein lipase and show the direct relationship between heparin action and tissue ability to take up products of lipoprotein triglyceride breakdown. They also demonstrate the ability of adipose tissue to metabolize glycerol coming from the hydrolysis of lipoprotein glycerides.

Monoamine metabolism in rat brain regions following long term alcohol treatment

Female Wistar rats (150--200 g) were treated with ethanol (15% w/v) for 21 days and compared with control rats given water. Ethanol administration produced a reduction of fluid and food consumption and changes in the metabolism of cerebral monoamines. There was an increase in serotonin (5-HT) turnover statistically significant in the striatum, and a decrease in noradrenaline (NA) turnover in ethanol rats as compared to controls. Endogenous NA levels were significantly increased in the diencephalon and dopamine (DA) levels were increased in the striatum. After inhibition of catecholamine synthesis with alpha-methyltyrosine (alpha-MT), NA depletion was significantly retarded but no changes in DA depletion were noted. DOPA accumulation after decarboxylation inhibition showed no significant change in any brain region studied.