Carbohydrate metabolism in pregnancy. 8. Metabolism of adipose tissue isolated from fed and fasted pregnant rats during late gestation

Adipocyte insulin receptor binding and lipogenesis at term in normal pregnancy

Lipogenesis in subcutaneous abdominal adipocytes during late human pregnancy was investigated by studying insulin receptor binding, 3-O-methyl-(14C-(U]-glucose flux and incorporation of (14C(U]-glucose into CO2 (oxidation) and total lipids (lipogenesis) in adipocytes from 18 health pregnant women undergoing Caesarean section at term, and 19 non-pregnant women undergoing gynaecological surgery. The cell diameter and fasting insulin were increased in the pregnant women, compared with controls (P less than 0.01 and P less than 0.05, respectively). The insulin receptor binding, 3-O-methyl-glucose flux, and basal oxidation were similar in both groups. Basal lipogenesis was higher in adipocytes from pregnant women than from controls (P less than 0.05), but the maximally stimulated increment was similar in both groups. Basal and maximally stimulated lipogenesis correlated positively with the cell diameter (P less than 0.001 and P less than 0.05, respectively). The findings indicate that lipogenesis in subcutaneous abdominal adipocytes from pregnant women is increased due to post-receptor events and that adipocytes do not contribute to the insulin resistance in late pregnancy.

Pregnancy and pentobarbital anaesthesia modify hepatic synthesis of acylglycerol glycerol and glycogen from gluconeogenic precursors during fasting in rats

1. Incorporation of gluconeogenic precursors into blood glucose and hepatic glycogen and acylglycerol glycerol was examined in 24 h-fasted virgin rats by using a flooding procedure for substrate administration. At 10 min after their intravenous injection, the conversion of alanine or glycerol into liver glycogen or acylglycerol glycerol was proportional to glucose synthesis. 2. In 24 h-fasted 21-day-pregnant rats, the incorporation of alanine and glycerol into hepatic acylglycerol glycerol was markedly enhanced compared with the control group. In addition, during fasting at late pregnancy, the proportion of substrates directed to acylglycerol glycerol as compared with the fraction incorporated into glucose was augmented. 3. In pentobarbital-treated fasted rats, the incorporation of both alanine and pyruvate into circulating glucose and into hepatic glycogen and acylglycerol glycerol was increased. Pentobarbital treatment increased the proportion of substrates incorporated into liver glycogen, compared with the fraction appearing in circulating glucose. These changes were concomitant with a marked accumulation of glycogen. 4. The data indicate that, during fasting, gluconeogenesis provides glucose as well as hepatic glycogen and acylglycerol glycerol, independently of whether the substrates enter gluconeogenesis at the level of pyruvate or dihydroxyacetone phosphate.

Effect of protein quality on weight and composition of the carcass in pregnant and non pregnant rats

The effect of diets with different protein qualities on net weight and on the composition of the carcass (the animal being skinned and gutted) were studied in pregnant and non-pregnant rats of the Wistar breed. The animals were fed with diets containing the following protein sources: casein + 5% DL-methionine, beans and a mix of beans and wheat, all with a protein level of 14%. Percentage weight gains in the carcass were in all cases greater in non-gestating animals than in gestating animals. The water content of the body was similar in all the groups tested. The quality of protein did not affect nitrogen content; however, a smaller proportion of nitrogen was observed in gestating animals than in non-gestating animals. With respect to fat content of the carcass, a greater quantity of fat was observed in the bodies of gestating rats than in non-gestating rats, which was only significant in the case of the bean-wheat mix diet. Within each group of gestating and non-gestating rats, there was a greater quantity of fat in those animals fed with casein.

Hepatic uptake of gluconeogenic substrates in late-pregnant and mid-lactating rats

Lactate uptake by liver is markedly increased in late-pregnant and mid-lactating rats without concomitant changes in its availability. Glycerol contribution to the liver 3-C unit uptake is only significant at term gestation (50% of lactate uptake) but almost negligible at mid-lactation (10% of lactate uptake). Pyruvate is only taken up by the liver of 15-day lactating rats. As a general trend, the livers of either pregnant or lactating rats are provided with an enhanced capacity to take up gluconeogenic substrates.

Effect of fetal growth on maternal protein metabolism in postabsorptive rat

Rates of protein synthesis were measured in whole fetuses and maternal tissues at 17 and 20 days of gestation in postabsorptive rats using continuous infusion of L-[1-14C]leucine. Fetal protein degradation rates were derived from the fractional rates of synthesis and growth. Whole-body (plasma) leucine kinetics in the mother showed a significant reduction of the fraction of plasma leucine oxidized in the mothers bearing older fetuses, a slight increase in the plasma flux, with total leucine oxidation and incorporation into protein remaining similar at the two gestational ages. Estimates of fractional protein synthesis in maternal tissues revealed an increase in placental and hepatic rates at 20 days of gestation, whereas the fractional synthetic rate in muscle remained unchanged. A model for estimation of the redistribution of leucine between plasma and tissues is described in detail. This model revealed a more efficient utilization of leucine in fetal protein synthesis in comparison with other maternal tissues, a greater dependency of the fetus on plasma supply of leucine, and a significant increase (2-fold) in the release of leucine from maternal muscle as the fetal requirements increased proportionately with its size. The latter conclusion, supported by nitrogen analysis and the ratio of bound-to-free leucine in maternal tissues, confirms the importance of maternal stores in maintaining the homeostasis of essential amino acids during late pregnancy.

The metabolism of acetone in the pregnant rat

The administration of a single dose of acetone (100 mg/kg bw) to virgin and 21-day pregnant rats resulted in the appearance of relatively high concentrations of 1,2-propanediol, acetol and methylglyoxal in plasma and liver. In the fetuses no methylglyoxal was detectable. The acetone metabolism curves tend to indicate that the capacity for acetone disposal may be enhanced in the 48 hr-fasted pregnant rat, thus enabling the animal to re-use acetone metabolically, possibly for accelerated gluconeogenesis.

Body fat in pregnant rats at mid- and late-gestation

Carcass fat content was estimated in fed 12- and 19-day pregnant rats and fed and 48 hour starved virgin females following both specific gravity determination and direct gravimetry of extracted lipids. No change in body fat accumulation was found in 12-day pregnant rats whereas in 19-day pregnant animals it increased significantly. A significant correlation was also found when the percentage of carcass fat was plotted against specific gravity considering values from all subjects. Results indicate that in spite of reported maternal anabolic changes in the rat at midgestation fat accumulation occurs later in pregnancy when the mother has the highest food intake, which makes available sufficient substrates to support both fetal growth and body lipidic deposition.

Role of the availability of substrates on hepatic and renal gluconeogenesis in the fasted late pregnant rat

Studies were conducted to examine the role of gluconeogenetic substrate availability on glucose production in the fasted late pregnant rat. Virgin and 21-day pregnant rats were studied after 24 hours' food deprivation. Pregnant animals showed decreased circulating glucose and gluconeogenic amino acid and increased plasma glycerol concentration. Glucose formation was studied in vivo two, five, and ten minutes after the intravenous administration of two concentrations of 14C-alanine, 14C-pyruvate, or 14C-glycerol. Concentrations of 0.2 mmols of 14C-glycerol or 14C-pyruvate, but not of 14C-alanine, enhanced 14C-glucose production in pregnant rats, whereas 1 mmol of any of the three 14C-substrates always enhanced 14C-glucose production in these rats. Both 1 mmol/L and 5 mmol/L 14C-alanine increased 14C-glucose formation in 90-minute-incubated liver slices of fasted pregnant rats, in spite of decreased cytosolic activity of alanine aminotransferase. The three substrates enhanced "in vitro" renal gluconeogenesis in pregnant rats. Under all experimental conditions studied, labeled glycerol was converted more efficiently into glucose than equivalent amounts of any other substrate used, and this difference was greater in pregnant, than in virgin animals. Results indicate that, in spite of enhanced gluconeogenetic activity, maternal glucose production in the fasted state at late gestation is limited by the deficiency of certain substrates, such as amino acids. It is proposed that glycerol derived from enhanced maternal adipose tissue lipolysis constitutes a preferential gluconeogenetic substrate in comparison with others, such as alanine, that are more efficiently transferred through the placenta to the fetus.

Comparative utilization of glycerol and alanine as liver gluconeogenic substrates in the fed late pregnant rat

The appearance of plasma [14C]glucose in the inferior cava vein after a pulse of 0.2 mmol of [U-14C]L-alanine or [U-14C]glycerol/200 g body wt given through the portal vein was studied in fed 21 day pregnant rats and virgin controls under pentobarbital anesthesia. In both groups values were much higher when [U-14C]glycerol was the administered tracer than when [U-14C]L-alanine, and they were augmented in pregnant versus virgin animals at 1 min when receiving [U-14C]glycerol and at 2 min when receiving [U-14C]L-alanine. 20 min after the tracers rats receiving [U-14C]glycerol showed much higher liver [14C]glycogen and [14C]glyceride glycerol than those receiving [U-14C]L-alanine. Radioactivity present in liver as [14C]glyceride glycerol was greater in pregnant than in virgin rats receiving [U-14C]glycerol whereas radioactivity corresponding to [14C]fatty acids was lower in the former group receiving either tracer. At 20 min after maternal treatments fetuses showed lower plasma [14C]glycerol than [14C]alanine values but plasma [14C]glucose and liver [14C]glycogen values were much greater in fetuses from mothers receiving [U-14C]glycerol than [U-14C]L-amine. Besides showing the higher gluconeogenic efficiency in pregnant than in virgin rats, results indicate that at late gestation glycerol is used as a preferential substrate for both glucose and glyceride glycerol synthesis in liver.

Hepatectomy-nephrectomy effects in the pregnant rat and fetus

Levels of circulating glucose, glycerol, and FFA concentrations were determined before and after hepatectomy-nephrectomy in 20 day pregnant rats and virgin controls. After evisceration, blood glucose levels decreased in a parallel way in both groups whereas in pregnant rats, the blood glycerol level increased less and plasma-FFA rose more than in controls. Maternal evisceration caused reduced blood glucose and enhanced glycerol levels in fetuses, whereas fetal plasma-FFA levels were unmodified. Results indicate that extrahepatic glucose utilization remained stable in the late pregnant rat. Fetal levels of circulating glycerol, but not of FFA, appeared directly dependent on maternal levels. It is proposed that under normal conditions, glycerol availability to the fetus is low, due to its preferential utilization by maternal gluconeogenic organs which reduced the amount available for possible placental transfer.

Similar metabolic response to acute ethanol intake in pregnant and non-pregnant rats either fed or fasted

Plasma ethanol concentration 3 hr after its oral administration (3 g/kg body wt) did not differ in 20 day pregnant rats with virgin controls, and in both groups values were higher when studied after 24 hr fasted than when fed. In fed animals, blood glucose and liver glycogen concentrations were lower in pregnant than in virgin rats, whereas ethanol intake in both groups enhanced blood glucose levels, it reduced liver glycogen content only in virgins. In fetuses, maternal ethanol intake enhanced blood glucose levels. In fasted animals, ethanol intake decreased blood glucose levels in pregnant and virgin animals but did not affect these levels in fetuses. Ethanol intake enhanced beta-hydroxybutyrate/acetoacetate ratio similarly in blood of pregnant and virgin rats when either fed or fasted, and it produced the same change in fetuses from fasted mothers. Results indicate that the metabolic response to acute ethanol does not differ between pregnant and non-pregnant animals, and it is proposed that fetuses passively follow the metabolic changes occurring in their mothers after receiving ethanol.

Effect of insulin on glucose metabolism in adipocytes from virgin and late-pregnant rats

Under basal conditions (zero insulin), paraovarian adipocytes from 19-day-pregnant rats exhibited the same rates of [U-14C]glucose conversion into CO2 and total lipids as did those from age-matched virgin rats. The dose-response curves for insulin stimulation of glucose metabolism were similar in both groups: maximal response (+100% over basal values) and high sensitivity (half-maximal effect at 0.05 nM-insulin). The present results suggest that the insulin resistance in vivo that occurs during late pregnancy may involve circulating factors lost in vitro.

Effects of 24-hour starvation period on metabolic parameters of 20-day-old rats

The effects of a 24-hour starvation period upon 20-day-old rat pups were studied both in animals kept in the presence of their starved dams and in their absence. The relative loss of body weight was more intense in the rats that received no milk, being however, severe in both groups. There was a significant maintenance of both plasma glucose levels and total amino acids, with differences in blood glucose compartmentation and a remarkable uniformity in the effects of starvation upon individual amino-acid concentrations. A significant increase in plasma urea was observed, higher in the rats kept in the presence of the dam. Ketone bodies increased with starvation but their final levels were lower than in adults. The general pattern of metabolic change observed suggests a situation, after 24-h food deprivation, similar to that of long term starvation in adults; with an active protein amino-acid catabolism but with a remarkable maintenance of circulating foodstuff levels.

Pregnancy-induced insulin resistance in the rat: assessment by glucose clamp technique

To quantify and characterize the insulin resistance during pregnancy in the rat, a euglycemic hyperinsulinemic clamp was set up. Dose-response curves for the effects of five concentrations of insulin on glucose production, glucose utilization, and glucose clearance were performed in age-matched virgin and 19-day-pregnant rats. Glucose production and glucose utilization were measured by using [3-3H]-glucose. Glucose production was totally suppressed at plasma insulin concentrations higher than 1,000 microU/ml in the two groups. Insulin concentration causing half-maximal suppression of glucose production was about 70 microU/ml in virgin rats and 250 microU/ml in pregnant rats. Maximal glucose utilization was obtained at plasma insulin concentrations of 2,000 microU/ml. In pregnant rats maximal increment in glucose utilization was significantly lower (P less than 0.01) than in virgin rats. Insulin concentrations causing half-maximal stimulation of glucose utilization were 200 microU/ml in virgin rats and 500 in pregnant rats. As blood glucose concentration in virgin and pregnant rats was clamped at, respectively, 0.97 +/- 0.03 and 0.73 +/- 0.03 mg/ml, glucose clearance rates were calculated because this parameter is minimally affected by the changes in blood glucose concentrations. A normal maximal increment in glucose clearance in response to insulin was restored in pregnant rats but the rightward shift of the dose-response curve was maintained. Plasma insulin concentrations necessary for half-maximal increment of glucose clearance in the two groups were similar to that observed when the results were expressed as glucose utilization. Thus, insulin resistance during late pregnancy in the rat is characterized by a decreased sensitivity of liver and peripheral tissues to insulin.

Maternal adipose tissue response to nicotine administration in the pregnant rat: effects on fetal body fat and cellularity

Nicotine has been implicated as a causative factor in the intrauterine growth retardation associated with smoking in pregnancy. A study was set up to ascertain the effect of nicotine on fetal growth and whether this could be related to the actions of this drug on maternal adipose tissue metabolism. Sprague-Dawley rats were mated and assigned to control and nicotine groups, the latter receiving nicotine in the drinking-water throughout pregnancy. Animals were weighed at regular intervals and killed on day 20 of pregnancy. Rates of maternal adipose tissue lipolysis and lipogenesis were measured. Fetal and placental weights were recorded and analysis of fetal body water, fat, protein and DNA carried out. Weight gains of mothers in the nicotine group were less in the 1st and 2nd weeks of pregnancy, but similar to controls in the 3rd week. Fetal body-weights, DNA, protein and percentage water contents were similar in both groups. Mean fetal body fat (g/kg) was significantly higher in the nicotine group (96.2 (SE 5.1] compared with controls (72.0 (SE 2.9]. Rates of maternal lipolysis were also higher in the nicotine group. The cause of these differences and their effects on maternal and fetal well-being is discussed.

Metabolic changes in the rat liver during pregnancy. II. Tricarboxylic acid cycle

During pregnancy the rat liver shows alterations in metabolism which apparently do not to occur in the non-pregnant animal. In our study, the following metabolite concentrations and enzyme activities in the liver of pregnant and non-pregnant rats were measured after fasting periods of 6 and 12 h: malate, fumarate, isocitrate, alpha-keto-glutarate, glutamate, malate-dehydrogenase, fumarate-hydratase, glutamate-dehydrogenase, isocitrate-dehydrogenase, aspartate-aminotransferase and after 12 h fast, the concentrations of acetyl coenzyme A and citrate. These results are discussed with regard to their possible importance for the maternal and fetal energy supply.

Adipose tissue metabolism during early pregnancy in the rat: temporal relationships of changes in the metabolic activity, number of insulin receptors, and serum hormone concentrations

The temporal relationships between changes in rates of fatty acid and acylglycerol glycerol synthesis; the activity of lipoprotein lipase of parametrial adipocytes and their capacity to bind insulin; and the serum concentrations of insulin, progesterone, prolactin, and total lactogenic activity have been examined in rats during the first 15 days of pregnancy. The rate of fatty acid and acylglycerol synthesis showed a transient increase at Days 9 and 12 of pregnancy, whereas there was no change in the activity of lipoprotein lipase activity except for a fall between Days 12 and 15 of pregnancy. The capacity of adipocytes to bind insulin was increased by Day 6 of pregnancy and remained elevated until at least Day 15; no changes in the affinity for insulin were observed. Serum progesterone, insulin, and total lactogenic activity were elevated by Days 3, 9, and 12 of pregnancy, respectively. The results show that progesterone but not placental lactogen could be responsible for the rise in the insulin-binding capacity of rat adipocytes during pregnancy, whereas the fall in lipogenic capacity at about Day 12 of pregnancy coincides with the rise in serum placental lactogen.

Circulating triacylglycerols, lipoproteins, and tissue lipoprotein lipase activities in rat mothers and offspring during the perinatal period: effect of postmaturity

Mammary gland and adipose tissue lipoprotein lipase activities have been implicated in the changes of circulating triacylglycerol levels which occur in the mother at late gestation. In the newborn the temporal accumulation of triacylglycerols in the liver coincides with the appearance of a lipoprotein lipase peak. The relationships of these changes with the rise in circulating prolactin in the mother before parturition and the extrauterine nutritional status in the offspring were studied in a postmaturity model produced in the rat by subcutaneous injection of 7 mg progesterone/day to pregnant animals from the 20th day of gestation. Pregnant controls received the medium. Parturition occurred at day 21.5 of gestation in pregnant controls while it did not occur before the 23rd day in those receiving progesterone. At the 20th day of gestation, plasma triacylglycerol concentrations and all lipoprotein fractions (especially VLDL) were much higher in mothers not receiving progesterone than in age-matched virgins, and these differences disappeared at the 21st day of gestation. Lipoprotein lipase activity was maintained low in control mothers' adipose tissue until the 23rd postfecundation day while it greatly increased in mammary gland from parturition time. In progesterone treated mothers, both triacylglycerol and lipoprotein fractions (especially VLDL) in plasma were maintained elevated until the 23rd postfecundation day and adipose tissue and mammary gland lipoprotein lipase activities were maintained low until this time.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of alcohol ingestion in the pregnant rat on daily food intake, offspring growth and metabolic parameters

1. Daily food intake, fluid consumption, offspring growth and metabolic parameters were studied in rats receiving ethanol in the drinking water before, during and after gestation. 2. Ethanol treatment always reduced daily food, liquid and caloric intake in the rat, except during gestation when total daily caloric intake was greater in rats receiving ethanol than in control animals. The increase in both food and liquid intake during lactation in controls was also observed in alcohol-deprived mothers but was significantly reduced in mothers maintained under alcohol treatment. 3. Offspring from alcohol-treated mothers were retarded in body weight and size compared with controls, the differences becoming greater as the suckling period advanced. 4. The 15 day-old pups from alcohol-treated mothers had reduced glucose and augmented beta-hydroxybutyrate levels in blood, and markedly reduced liver glycogen concentrations, indicating their acutely malnourished state. 5. In pups from mothers that received alcohol until the 21st day of gestation, body weight and size were normalized at the 15th day but skeletal maturation and liver glycogen concentration were reduced and blood acetoacetate and beta-hydroxybutyrate were augmented as compared with values in pups from control mothers. If these parameters are interrelated, metabolic changes may be used for early diagnosis of fetal alcohol syndrome.

Effects of fasting during mid pregnancy or early lactation on mammary development and milk yield in mice

Mice were fasted during pregnancy or early lactation and the effects on mammary development and milk yield studied on d 13 and d 18 of pregnancy and on d 7 of lactation. Fasting during pregnancy reduced body weight and mammary weight on d 13 of pregnancy but not on d 18. Mammary concentrations and total contents of DNA and RNA ([DNA], [RNA], DNAt, RNAt) were increased or unchanged on d 13 but significantly decreased on d 18. Fasting had no effect on fetal number or weight at either stage of pregnancy. Fasting on d 1 of lactation reduced mammary weight, DNAt and RNAt (but not [DNA] or [RNA]) and the incorporation of tritiated thymidine into DNA or d 2 of lactation. Mammary gland weight and composition on d 7 of lactation were not significantly affected by fasting for 24 h on d 1 of lactation or for 40 h on d 11-13 of pregnancy, except that DNAt was decreased slightly by the latter treatment. Milk yield (litter weight gain) was depressed markedly during fasting on d 1 of lactation, but thereafter recovered so that it was the same as controls between d 3 and 13 of lactation; after d 13 it fell once more. A 40 h fast on d 11-13 of pregnancy had no effect on milk yield. Thus, although normal mammary development was inhibited by starvation, the gland was subsequently able to compensate so that milk yield was not reduced.

Changes induced in rat plasma composition by lactation

Changes in rat plasma composition in post-partum period were studied from day 1 to post weaning recovery situation (day 40). Urea levels showed a significant increase at the peak of lactation, and glycerol levels showed a decrease towards late lactation. Changes in the plasma aminogram were more marked during the maximal intensity of lactation (days 10-20) and in postlactation. Low trypthophan levels were sustained throughout the lactation period. The combined amino acids showed significant increases on day 10 of lactation, and increases in non-essential and total amino acids in post-lactation (40 days). These results point towards increased amino-acid utilization during lactation.

"Accelerated starvation" and the skipped breakfast in late normal pregnancy

After dinner at 6 P.M. food was withheld from non-pregnant women and women in the third trimester of pregnancy: there were lean and obese women in each group, and all had normal carbohydrate metabolism. Levels of circulating fuels and glucoregulatory hormones were monitored between 6 A.M. (12 h fast) and noon (18 h fast) the following day. In non-pregnant women plasma levels of glucose, alanine, free fatty acids (FFA) beta-hydroxybutyrate, insulin, and glucagon remained constant between 6 A.M. and noon except for slight fall in plasma alanine in the obese women and slight increases in beta-hydroxybutyrate in the lean. By contrast, in pregnant women the concentrations of all substances measured changed profoundly after extension of the overnight fast. Levels of plasma glucose, which were significantly lower than those in non-pregnant women at 6 A.M., fell further during the subsequent 6 h; plasma alanine levels declined significantly during the same interval, and there were coincident rises in plasma FFA and beta-hydroxybutyrate and reductions in plasma insulin. The changes in lean and obese women were of similar magnitude; habitus did not therefore seem to have effects additional to those of pregnancy on the response to skipping breakfast. In all the pregnant women final levels of FFA and beta-hydroxybutyrate were strongly correlated and inversely related to final levels of plasma glucose. The studies indicate that "accelerated starvation" can be unmasked during pregnancy even with the minor dietary deprivation common in conventional clinical circumstances. Thus, insofar as it may be desirable to avoid ketonaemia during pregnancy, the common practice of skipping breakfast whether by personal preference or for doctor-initiated laboratory testing should be avoided in pregnant women.

Lipolysis in rat adipocytes during pregnancy and lactation. The response to noradrenaline

1. Lipolysis has been measured in parametrial adipocytes from virgin, pregnant and lactating rats. 2. The basal rate and the maximal rate of lipolysis, the latter measured in the presence of noradrenaline and theophylline, remained constant between the three experimental categories, with the exception of a significant transient increase in the basal rate at parturition. 3. The noradrenaline-stimulated lipolysis rate rose above the virgin rate during pregnancy and fell below it during lactation; inclusion of adenosine deaminase in incubations abolished these differences in response to noradrenaline. 4. Cyclic AMP phosphodiesterase activity was lower in adipocytes during pregnancy and lactation than in virgin animals.

Carbohydrate metabolism in pregnancy XVI: longitudinal estimates of the effects of pregnancy on D-(63H) glucose and D-(6-14C) glucose turnovers during fasting in the rat

We measured blood glucose concentrations and glucose turnover rates in 24 hr fasted, conscious, unrestrained pregnant rats and nongravid controls on days 18, 19, and 20 of gestation. Turnover measurements were secured with simultaneous equilibrium infusions of D-(6-3H) and D-(6-14C) glucose so that gluconeogenic recycling could also be determined. "Steady state" values for blood glucose in the mother after 24 hr of fasting did not significantly differ on each of the days, and these concentrations were significantly lower than the values in 24 hr fasted nongravid rats. At 18 days gestation, glucose turnover did not differ from nongravid values. By contrast, values for glucose turnover after 24 hr fasting increased significantly and progressively in the 19 and 20 day pregnant rats. The increase in turnover correlated with the increasing growth of the conceptus. The ratio between D-(6-14C) glucose and D-(6-3H) turnover remained constant (and the same as in the nongravid rats) during all 3 days of gestation suggesting that rates of glucose recycling remained unaltered. These longitudinal studies indicate that the factors contributing to the pattern of "accelerated starvation" during dietary deprivation in pregnancy may vary as pregnancy progresses. The exaggerated lowering of blood glucose which accompanies fasting occurs before total glucose turnover increases. This could provide a potential mechanism for conserving maternal glucose. Since transplacental transfer of glucose is concentration-dependent, the early establishment of a lower "steady state" for circulating glucose could diminish the magnitude of loss of this key nutrient to the fetus.

Metabolic response to starvation. I. Relative effects of pregnancy and sex steroid administration in the rat

Increased sensitivity to a fast with rapid onset of ketosis, hypoalaninemia, and hypoglycemia is characteristic of rat and human gestation. The present study examines the role of sex steroids in the development of these metabolic changes. Subgroups of female rate received 10 microgram of estradiol (E), 10 mg of progesterone (P), or the two in combination (E + P) s.c. daily for 5 days. Control rats (C) received sesame oil alone. Different groups were starved 12, 24 and 48 hr during days 4 and 5 or treatment. Plasma substrate and insulin responses were measured and compared to results of similar studies performed on rats in late gestation. Administration of E or P along had no significant effects on measured parameters as compared to control values. However, the combined E + P regimen resulted in significantly higher ketonemia, greater hypoalaninemia, and relatively higher triglyceride concentrations than in control groups during fasting. Plasma triglyceride, free fatty acid, and ketone concentrations in the pregnant group exceeded values of both the E + P and control animals. However, plasma free fatty acids in the E + P group were significantly lower as compared to control values during starvation. These data suggest that the combined effects of estradiol and progesterone enhance ketogenesis and hypoalaninemia independent of the fetal-placental unit during starvation in pregnancy. Since the ketogenic effect was associated with a relative suppression of plasma free fatty acids, this may be indicative of a direct action of these hormones on hepatic disposition of free fatty acids and/or the biosynthetic pathways for ketone body production.

Metabolic response to starvation. II. Effects of sex steroid administration to pre- and postmenopausal women

Premenopausal women become more ketotic than do men during short term starvation. The possible influence of female sex steroids on ketosis during an 84-hr fast was studied in premenopausal women receiving combined oral contraceptive steroids. The results were compared to age and weight-matched women on no steroid birth control regimen. Although concentrations of several plasma substrates, insulin, and glucagon were measured throughout the fast, no differences between groups were observed with the exception of the 36-hr interval. At this time total plasma ketones and betahydroxybutyrate were significantly higher in women receiving oral contraceptives. In a second study six postmenopausal women were investigated in a similar fashion during a 36-hr fast. The procedure was repeated following a 5 day treatment regimen of oral estradiol and medroxyprogesterone acetate. After sex steroid treatment, total plasma ketones and betahydroxybutyrate concentrations exceeded control values significantly at 36 hr while plasma alanine and free fatty acid levels were significantly lower. The results suggest that oral estrogen-progestin combinations increase the ketogenic response of pre- and postmenopausal women during the early phases of total starvation. This hormonal effect may explain, in part, why women are more sensitive to fasting than are men.

In vivo insulin resistance during pregnancy in the rat

The glucose disappearance rate measured after IV glucose injection (1g/kg body wt) remained unchanged between 12 and 21 day of gestation in the rat. In contrast, insulin secretion in response to IV glucose was markedly increased on day 19 and 21 of pregnancy, suggesting resistance to endogenous insulin. Glucose kinetics (glucose production, utilization and clearance) in response to various doses of IV insulin have been studied in anaesthetised post-absorbtive 19 day pregnant and virgin rats using 6-(3)H glucose. With the supramaximal dose of insulin (4 U/kg body wt) no differences in glucose kinetics were found between pregnant and virgin rats. In contrast, with the two lower doses of insulin (0.15 and 0.05 U/kg body wt) glucose production was inhibited by 36 plus or minus 3% and 13 plus or minus 2% (Mean plus or minus SEM) respectively in virgin rats, but was not decreased in pregnant rats. When the effect of insulin on glucose clearance was expressed as % of the maximal effect obtained with 4 U/kg body weight, the rise in glucose clearance in response to the two lower doses of insulin (0.15 and 0.05 U/kg body wt) was lower in pregnant (57.5 plus or minus 6 and 27. 4 plus or minus 4%) than in virgin rats (73.3 plus or minus 6 and 42.2 plus or minus 7%). These results suggest that a decreased sensitivity to insulin appears in late pregnancy in the rat and could involve both liver and skeletal muscle.

Role of insulin receptors in the changing metabolism of adipose tissue during pregnancy and lactation in the rat

Changes in the volume, the rates of fatty acid synthesis and synthesis of the glycerol moiety of acylglycerols, the activity of lipoprotein lipase, and the number and affinity of insulin receptors of adipocytes, and concentrations of serum insulin, prolactin and progesterone were determined in virgin rats and in rats at various stages of pregnancy and lactation. Changes in the metabolic activities of adipose tissue appeared to be synchronized and primarily comprised a marked decrease in anabolic activity around parturition. In contrast, the number of insulin receptors (Kd 1.5 nM) per adipocyte doubled during pregnancy before returning to normal values around parturition. It is postulated that the increase in the number of insulin receptors is an adaptation to counteract the effects of insulin-antagonistic hormones during pregnancy and that the decrease in the number of receptors is primarily responsible for the loss of anabolic activity around parturition.

Adipose tissue metabolism in pregnancy: the lipolytic effect of human placental lactogen

In vitro adipose tissue lipolysis was investigated in pregnant and non-pregnant women. Basal and hormone-stimulated rates of lipolysis were significantly higher in the pregnant group. Human placental lactogen (HPL) was shown to be lipolytic on adipose tissue from both pregnant and non-pregnant women; the response being more marked in the pregnant group. We postulate that HPL is responsible for this increased lipolytic sensitivity in pregnancy, the result of which is the elevation in levels of plasma free fatty acids in the third trimester.

Plasma amino acid concentrations in pregnant rats and in 21-day foetuses

Plasma amino acid concentrations were determined in virgin female rats, in pregnant rats (12 and 21 days after impregnation) and in 21-day foetuses. The total amino acid concentration in plasma decreases significantly with pregnancy, being lower at 12 than at 21 days. Alanine, glutamine+glutamate and other 'gluconeogenic' amino acids decrease dramatically by mid-term, but regain their original concentrations at the end of the pregnancy. With most other amino acids, mainly the essential ones, the trend is towards lower concentrations which are maintained throughout pregnancy. These data agree with known nitrogen-conservation schemes in pregnancy and with the important demands on amino acids provoked by foetal growth. In the 21-day foetuses, concentrations of individual amino acids are considerably higher than in their mothers, with high plasma foetal/maternal concentration ratios, especially for lysine, phenylalanine and hydroxy-proline, suggesting active protein biosynthesis and turnover. All other amino acids also have high concentration ratios, presumably owing to their requirement by the foetuses for growth. Alanine, glutamine+glutamate, asparagine+aspartate, glycine, serine and threonine form a lower proportion of the total amino acids in foetuses than in the virgin controls or pregnant rats, probably owing to their role primarily in energy metabolism in the adults. The results indicate that at this phase of foetal growth, the placental amino acid uptake is considerable and seems to be higher than immediately before birth.

Fetal fuels. I. Utilization of ketones by isolated tissues at various stages of maturation and maternal nutrition during late gestation

The availability and utilization of B-hydroxybutyrate as an alternate oxidative fuel during fasting hypoglycemia has been examined in the rat conceptus at 18 and 20 days gestation. A 48-hr maternal fast between days 16 and 18 or 18 and 20 resulted in a 50% fall in fetal glucose levels and a marked rise in B-hydroxybutyrate, i.e., 30-fold at 18 and 60-fold at 20 days. Tissue concentrations of B-hydroxybutyrate or acetoacetate did not exceed extracellular levels. Placenta, fetal brain, carcass, and liver all oxidized 14C-labeled B-hydroxybutyrate to 14CO2 when incubated in vitro in the presence of B-hydroxybutyrate. Highest rates of oxidation were apparent in the placenta, followed by brain, liver, and carcass. The D isomer of B-hydroxybutyrate appeared to be oxidized preferentially by all tissues studied. Despite levels of 3-ketoacid CoA transferase and acetoacetyl CoA thiolase lower at 18 than at 20 days, rates of oxidation in individual tissues incubated under identical concentrations of substrate were similar at both times. In liver and brain, increasing rates of 14CO2 generation proportionate to graded concentrations of B-hydroxybutyrate in vitro indicated that such rates were probably determined by substrate availability. B-hydroxybutyrate oxidation in extrahepatic fetal tissues was unaffected by maternal fasting. By contrast, fetal liver derived from fasted mothers generated significantly less 14CO2 from B-hydroxybutyrate than livers from fed mothers. It has been suggested that capabilities for ketone utilization are widespread in tissues of the conceptus, and that such utilization may fulfill in part the oxidative demands for continued anabolic growth during fasting hypoglycemia in the mother.

Lipid metabolism and mobilization in the guinea pig during pregnancy

The liver of the foetal guinea pig accumulates a large quantity of triacyglycerol late in gestation at the same time that adipose-tissue mass grows at its maximum rate and foetal adipose-tissue lipoprotein lipase activity and sensitivity to lipolytic hormones has substantially declined. The fatty acid for triacyglycerol synthesis is not synthesized in the foetal liver and it is unlikely that it originates from any of the foetal tissues. Before the accumulation of hepatic triacyglycerol the concentration of free fatty acids increases in both the umbilical vein and the maternal inferior vena cava. This occurs at a time when the triacyglycerol lipase activity in maternal adipose tissue is elevated and the rate of lipolysis, but not of fatty acid esterification, is higher than earlier in gestation or than in the non-pregnant state. It is proposed that the increase in lipolysis in maternal adipose tissue, brought about by an increase in circulating lipolytic hormones, mobilizes fatty acid, which passes to the foetus and is partly stored as hepatic triacylglycerol. The foetal liver effectively removes both long-and short-chain fatty acids from umbilical-vein blood. The rate of placental fatty acid transfer is more than adequate to account for the triacylglycerol accumulation.

Effect of lactation on lipolysis in rat adipose tissue

The concentrations of nonesterified fatty acids and glycerol in rat parametrial adipose tissue increased at peak lactation. Adipose tissue from lactating rats showed higher rates of release of nonesterified fatty acids and glycerol when incubated in vitro than did tissue from nonlactating rats, but there was a substantial increase in the esterification of fatty acids during involution. These results support earlier evidence that fat reserves were mobilized during lactation.

Effect of insulin on adipose tissue lipolysis in human pregnancy

Adipose tissue has been shown to retain its sensitivity to the antilipolytic effects of insulin during late pregnancy. This suggests that during late pregnancy, increased adipose tissue lipolysis is due to a lipolytic factor rather than insulin resistance.

The effect of pregnancy on the control of lipolysis in fat cells isolated from human adipose tissue

1. Lipolysis has been estimated by measuring the release of glycerol in isolated adipose tissue cells obtained from women in early prognancy, late pregnancy and 1 - 3 days post partum and from non-pregnant women. 2. Adipocytes of women at the end of pregnancy exhibited higher rates of lipolysis in response to adrenaline (1.5 - 15 muM) plus phentolamine (13 muM) than those of non-pregnant women or those in early pregnancy. 3. Lipolysis in response to adrenaline plus phentolamine in fat cells from women 1 - 3 days post partum was reduced compared to that at the end of gestation but was enhanced relative to that in the non-pregnant or early pregnant state. 4. Basal lipolysis also tended to be greatest at term. 5. Under conditions where the production of cyclic AMP was not rate limiting for the stimulation of lipolysis, that is in the presence of dibutyryl cyclic AMP (1 mM) or adrenaline (15 muM) plus phentolamine (13 muM) plus caffeine (1 mM), the release of glycerol in cells from women at term and in the puerperium was greater than that in women in the non-pregnant or early pregnant state. 6. Cell levels of cyclic AMP rose after incubation with adrenaline (6 muM) plus phentolamine or adrenaline (15 muM) plus phentolamine plus caffeine (1 mM) but were similar in all four groups of women. 7. It is concluded that the observed enhancement of lipolysis demonstrated in fat cells from women at the end of pregnancy reflects an increase in hormone-sensitive lipase activity rather than a modification of hormone receptor site sensitivity or of the rates of synthesis or breakdown of cyclic AMP. 8. This increase in adipose tissue lipolysis at the end of gestation could contribute to the reported rise in plasma nonesterified fatty acids in the final weeks of pregnancy.

Lipid metabolism in pregnancy. II. Postheparin lipolytic acitivity and hypertriglyceridemia in the pregnant rat

Plasma postheparin lipolytic activity (PHLA) has been measured in rat pregnancy to qualitatively assess mechanisms of triglyceride removal from the circulation. This assessment can be made if the larger plasma volume of pregnancy is considered. A supramaximal dose of heparin avoids dilution of the heparin stimulus to PHLA release. Dilution of the released PHLA is corrected using measurements of plasma volume. In addition, no evidence of circulating inhibitors is present, and timing of PHLA appearance is unaffected by pregnancy. Prior studies of postheparin lipolytic activity in human pregnancy have not taken the effect of plasma volume into account and must therefore be reconsidered in light of the present results. We observed a biphasic pattern in PHLA over the course of gestation. Levels were increased in midgestation (day 12), declined to normal by day 19, and fell rapidly to one-half of control by day 21. Assuming a functional role for the triglyceride lipases represented in PHLA, the data suggest the following hypothesis: triglyceride removal is increased or normal for the greater part of gestation and is decreased only at term. If this hypothesis proves true, the hypertriglyceridemia of pregnancy should be due largely to overproduction, with decreased removal contributing only near term.

Plasma glucagon and insulin in rat pregnancy. Roles in glucose homeostasis

To determine if pancreatic glucoregulatory hormones can be implicated in the glucose fall of pregnancy, we have measured plasma immunoreactive insulin and glucagon (IRI and IRG) in rats. Fed rats in midgestation show a rise in IRI without a corresponding increase in IRG. In late gestation, IRG rises significantly, but only enough to keep pace with a further rise in IRI. On a molar basis, IRI remains the predominant hormone despite a marked fall in blood glucose. After a 48-h fast IRI falls to comparably low levels in pregnant and virgin rats. A small rise in IRG is seen in virgin but not in pregnant rats despite frank hypoglycemia in the latter. Thus, IRG secretion in pregnancy is diminished relative to IRI in the fed state and fails to increase in the fasted state despite the stimulus of a lower glucose in both instances. To evaluate IRG secretory reserve, the IRG response to i.v. alanine was assessed in late gestation. In fed rats a greater IRG increase is seen in pregnancy; after fasting no difference is seen between pregnant and virgin rats. These results preclude an absolute deficiency in glucagon secretion. Pancreas hormone stores were alos measured in an effort to explain the altered secretory state. We find reciprocal changes in IRI and IRG content favoring IRG in midgestation and IRI in late gestation. Thus, pancreas hormone storage is altered in pregnancy but does not account for the changes in hormone secretion. Rather, pregnancy exerts an effect on the islet secretory process itself. Release of IRI is enhanced relative to IRG regardless of the blood sugar level. These observations suggest that in the pregnant rat circulating levels of insulin and glucagon may act to limit hepatic glucose output. Available evidence from the literature supports the concept of restrained glucose production. It is proposed that a lower blood glucose production. It is proposed that a lower blood glucose in rat pregnancy may be a lesser liability teleologically than would be the obligate nitrogen wasting which accompanies gluconeogenesis.

Glucose metabolism and lipid mobilization by adipocytes from mice selected for growth

1. Experiments were conducted to compare the abilities of epididymal adipocytes from mice selected for growth (line G) and from unselected mice (line C) to: (a) incorporate glucose, (b) respond to insulin, and (c) mobilize lipids, and to relate these abilities to the food intake of the donors.2. During the 3-week pre-experimental period, line G mice gained body weight 78% faster and ate 35% more food than line C mice; both lines had similar intakes per unit of metabolic body size.3. Line G epididymal fat pads weighed 227% more than those of line C and contained adipocytes which were 38% larger; it was estimated that they contained approximately 65% more cells.4. The basal rate of glucose incorporated into lipids (per unit protein) was highest in line C adipocytes, whereas the basal rates of glucose oxidation to CO(2) and the total glucose incorporation (uptake) were similar for adipocytes from both lines.5. Insulin (1000 muu./ml.) caused adipocytes from both lines of mice to increase significantly the incorporation of glucose into CO(2) and lipids; the largest elevation occurred when the incubation medium contained 0.1 mg glucose/ml. At this concentration of glucose, the minimum effective dose (MED) of insulin to produce a significant increase in glucose oxidation was similar for both lines. However, the MED of insulin necessary to significantly increase glucose incorporation into lipids and into the sum of CO(2) and lipids was highest in the larger, line G adipocytes. Furthermore, the magnitude of the insulin-induced increase in glucose incorporation was much less for line G than for the line C adipocytes.6. Epinephrine significantly elevated the rates of NEFA and glycerol release and NEFA re-esterification. The highest rates of NEFA and glycerol release occurred in line C adipocytes, whereas the highest rate of NEFA re-esterification occurred in the line G adipocytes.7. Glucose had no effect on NEFA release but significantly elevated the rates of glycerol release (in most instances) and NEFA re-esterification.8. The larger number of adipocytes in line-G adipose tissue allows for more total incorporation of glucose and a greater overall release of glycerol by this tissue. Consequently, a greater reduction of glucose concentration and a larger elevation of glycerol concentration in the blood can occur; either of these could be the feed-back signal which resulted in the larger long-term food intake by the line G mice.