Metabolic response to starvation in late pregnant rats. II. Fetal response

Effect of prolonged maternal fasting on the fetal liver and heart glycogen and triglyceride content and on concentration of glucose, urea, uric acid and alpha amino-nitrogen in the amniotic fluid has been studied in rats. The animals were divided into four groups: fed (control), fasted for one day (from 20 to 21 day of pregnancy), fasted for two days (from 19 to 21 day) and fasted for three days (from 18 to 21 day). Maternal fasting for two and three days resulted in reduction in fetal growth. The fetal liver glycogen content was reduced already after one day of fasting, stabilized after two days and then further decreased after three days. The fetal heart glycogen content was reduced only after three days of fasting. The fetal liver triglyceride content increased gradually during the first two days of fasting and then stabilized. The content of triglycerides in the heart was elevated after two and three days of food deprivation. The amniotic fluid glucose concentration decreased after one day of fasting and then stabilized. Fasting did not effect the concentration of the nitrogenous compounds in the amniotic fluid. It is concluded that maternal fasting affects markedly metabolism of energy substrates stored in the fetal liver and the heart and the composition of the amniotic fluid.     

Effect of exercise on energy substrates metabolism in tissues of adrenalectomized rats

Effect of adrenalectomy and exercise on skeletal muscle, heart and liver glycogen and triglycerides, blood glucose and plasma free fatty acid level has been studied in the rat. It has been found that exercise-induced mobilization of glycogen in vastus deepest and soleus was diminished whereas utilization of liver glycogen was accelerated in adrenalectomized rats as compared to sham-operated controls. Triglyceride content in vastus deepest was reduced and in the liver increased in control rats but remained stable during exercise in adrenalectomized rats. In the latter group hypoglycemia occurred earlier and was more pronounced, whereas plasma free fatty acid level was markedly lower than in the control group.     

Glycogen utilization in rat respiratory muscles during intense running

Glycogen concentration in the adult rat diaphragm and intercostal muscles has been examined following heavy treadmill exercise to determine the recruitment strategy and the significance of glycogen as a substrate to satisfy the elevated energy requirements accompanying hyperpnea. Short-term continuous running at 60 m/min and a 12 degree grade resulted in a reduction (p less than 0.05) in the concentration of glycogen (39%) in the costal region of the rat diaphragm. Similarly, glycogen concentration was significantly reduced (p less than 0.05) with this exercise protocol in all respiratory muscles studied, with the exception of the sternal region of the diaphragm. With the less intense running protocols, glycogen degradation continued to be pronounced (p less than 0.05) in the majority of the respiratory muscles sampled. The significance of muscle glycogen as a substrate for energy metabolism in the respiratory muscles was not affected by the procedure used to prepare the animal for tissue sampling (Somnitol, diethyl ether, decapitation). Examination of selected locomotor muscles revealed extensive glycogen loss in muscles composed of essentially slow oxidative fibres (soleus), fast oxidative glycolytic fibres (vastus lateralis red), and fast glycolytic fibres (vastus lateralis white). It is concluded that during heavy exercise in the rat, recruitment of motor units occurs in all regions of the diaphragm and in the intercostal muscles. At least for the costal region of the diaphragm and as evidenced by the modest (two- to four-fold) but significant (p less than 0.05) increases in lactate concentration, the increased ATP requirements in these muscles are met to a large degree by increases in aerobic metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fiber type specific glycogen utilization in rat diaphragm during treadmill exercise

To examine the significance of endogenous stores of glycogen in specific fiber types (I, IIa, IIb) of the costal region of the diaphragm, adult male Wistar rats performed continuous running (25 m/min, 8 degrees grade) exercise for either 30 min or until fatigue. At 30 min of exercise, glycogen loss, as measured microphotometrically using the periodic acid-Schiff technique averaged between 73 and 80% (P less than 0.05) in the different fiber types. When exercise was performed to exhaustion, representing an additional 94 min, no further reduction in glycogen was observed in any fiber type. Biochemical determinations of glycogen from the diaphragm confirmed the extensive reduction in glycogen concentration with exercise. Large reductions (P less than 0.05) in glycogen were also noted in the soleus, plantaris, and vastus lateralis red. Although significant depletion (P less than 0.05) occurred in the vastus lateralis white, it was not as pronounced as in these other muscles. Repletion to preexercise glycogen concentration was complete by 4 h of recovery in all muscles except the vastus lateralis white. It is concluded that endogenous glycogen is a significant substrate in all muscles sampled regardless of fiber composition. In the case of the costal region of the diaphragm, the increased work of breathing resulting from heavy exercise leads to the recruitment of all fiber types, and each fiber type depends on glycogen as a substrate at least early in the exercise.     

Opposite metabolic response to fenofibrate treatment in pregnant and virgin rats.

The level of maternal circulating triglycerides during late pregnancy has been correlated to newborns' weight in humans. To investigate the response to fenofibrate, a hypotriglyceridemic agent, in pregnant rats, 0, 100, or 200 mg of fenofibrate/kg body weight as oral doses were given twice a day from day 16 of gestation and studied at day 20. Virgin rats were studied in parallel. Liver weight was higher in pregnant than in virgin rats, and either dose of fenofibrate increased this variable in both groups. The highest dose of fenofibrate decreased fetal weight. Although plasma triglycerides decreased during the first 2 days of fenofibrate treatment in pregnant rats, the effect disappeared on day 3, and plasma triglycerides were even enhanced at day 4. In virgin rats, fenofibrate decreased plasma triglycerides throughout the experiment. Plasma cholesterol levels in pregnant rats decreased during the first 3 days of treatment, and the effect disappeared on day 4, whereas in virgin rats, values remained decreased. Changes in plasma triglycerides paralleled those of VLDL triglycerides. In pregnant rats, VLDL cholesterol levels increased while LDL cholesterol decreased with the treatment, whereas in virgin rats, cholesterol levels decreased in all lipoprotein fractions. Only in virgin rats did liver triglyceride concentration increase with fenofibrate treatment. Lumbar adipose tissue LPL was lower in pregnant than in virgin rats, and fenofibrate treatment decreased this variable in both groups. Maternal fenofibrate treatment increased fetal plasma and liver triglyceride and cholesterol concentrations.It is proposed that the opposite effects of fenofibrate treatment in virgin and pregnant rats are a consequence of both the enhanced liver capability for VLDL triglyceride production and a rebound response to the drug in the latter.     

Hepatopancreas gluconeogenesis and glycogen content during fasting in crabs previously maintained on a high-protein or carbohydrate-rich diet

The present study assessed the effect of different fasting times on the in vitro gluconeogenic capacity of Chasmagnathus granulata crabs previously adapted to a high-protein (HP) or carbohydrate-rich (HC) diet using the incorporation of [U-(14)C]l-lactate or [U-(14)C]l-alanine into glucose. We also recorded haemolymphatic glucose and hepatopancreatic glycogen levels. In the HP group, on the third day of fasting there were decreases in the synthesis of glucose from (14)C-alanine and in haemolymph glucose. After 15 days of fasting, haemolymph glucose and hepatopancreatic glycogen levels were maintained by an increase in the conversion of (14)C-alanine into glucose. However, after 21 days of fasting the gluconeogenic capacity was decreased and hepatopancreas glycogen concentration was reduced. In the HC group, hepatopancreatic glycogen was the energy source during the first 6 days of fasting. Gluconeogenesis from (14)C-lactate decreased after 6 days of fasting, remaining low until 21 days of fasting. The conversion of (14)C-alanine into glucose was increased after 15 days fasting and hepatopancreatic glycogen was raised in relation to that present after a 6-day fasting. In both dietary groups the stabilization in the levels of haemolymph glucose after 21 days fasting may result from a reduction in metabolic rate during restricted feeding.     

Effects of exercise on maternal glycogen storage patterns and fetal outcome in mature rats.

The purpose of the present study was to examine the effects of exercise on maternal glycogen storage patterns and fetal outcome in mature (approximately 12 months of age) Sprague-Dawley rats. The exercise consisted of treadmill running at 30 m.min-1, on a 10 degree incline, for 60 min, 5 days per week, for 4 weeks prior to pregnancy, which continued until day 19 of gestation. In mature animals, chronic exercise increased (p < 0.05) liver glycogen concentration in both pregnant and nonpregnant rats. In pregnant exercised animals, the glycogen concentration of the maternal liver increased almost twofold (p < 0.05) compared with the sedentary pregnant group. There was no difference in the amount of glycogen stored in the gastrocnemius or soleus muscles in response to training, pregnancy, or chronic maternal exercise in the mature rat. In the pregnant groups, there were fewer (p < 0.05) viable fetuses and more (p < 0.05) resorption sites than in young rats. In addition, exercise during pregnancy in the mature animal decreased (p < 0.05) fetal body weight. These results demonstrate that a conflict may exist between maternal exercise and fetal demands for energy in the mature rat. This conflict seems to favour the maternal system, as evidenced by the enhanced maternal liver glycogen storage and the negative effect on fetal growth.     

Differential response of rat skeletal muscle glycogen metabolism to testosterone and estradiol.

Although reports on sex steroids have implicated them as promoting protein synthesis and also providing extra strength to the skeletal muscle, it remains unclear whether sex steroids affect glycogen metabolism to provide energy for skeletal muscle functions, since glycogen metabolism is one of the pathways that provides energy for the skeletal muscle contraction and relaxation cycle. The purpose of the current study was to show that testosterone and estradiol act differentially on skeletal muscles from different regions, differentially with reference to glycogen metabolism. To study this hypothesis, healthy mature male Wistar rats (90-120 days of age, weighing about 180-200 g) were castrated (a bilateral orchidectomy was performed to test the significance of skeletal muscle glycogen metabolism in the absence of testosterone). One group of castrated rats was supplemented with testosterone (100 microg/100 g body weight, i.m., for 30 days from day 31 postcastration onwards). To test whether estradiol has any effect on male skeletal muscle glycogen metabolism 17beta-estradiol (5 microg/100 g body weight, i.m., for 30 days from day 31 postcastration onwards) was administered to orchidectomized rats. To test whether these sex steroids have any differential effect on skeletal muscles from different regions, skeletal muscles from the temporal region (temporalis), muscle of mastication (masseter), forearm muscle (triceps and biceps), thigh muscle (vastus lateralis and gracilis), and calf muscle (gastrocnemius and soleus) were considered. Castration enhanced blood glucose levels and decreased glycogen stores in skeletal muscle from head, jaw, forearm, thigh, and leg regions. This was accompanied by diminished activity of glycogen synthetase and enhanced activity of muscle phosphorylase. Following testosterone supplementation to castrated rats, a normal pattern of all these parameters was maintained. Estradiol administration to castrated rats did not bring about any significant alteration in any of the parameters. The data obtained suggest a stimulatory effect of testosterone on skeletal muscle glycogenesis and an inhibitory effect on glycogenolysis. Estradiol did not play any significant role in the skeletal muscle glycogen metabolism of male rats.     

Modulation of lipoprotein lipase activity in the rat by the beta 2-adrenergic agonist clenbuterol.

This study evaluated the effects of beta 2-adrenoceptor stimulation on some determinants of triglyceride metabolism. Male Sprague-Dawley rats were injected twice daily with clenbuterol (30 micrograms.kg-1) for 7 days, or with an equivalent volume of vehicle. Serum triglycerides, hepatic triglyceride secretion rate, and lipoprotein lipase activity in white and brown adipose tissues as well as in red vastus lateralis muscle and heart were evaluated in the fasting state and following a fat-free, high-sucrose meal, 3 h after the last agonist injection. In rats killed in the fasting and postprandial states, clenbuterol reduced the mass of white adipose tissue (-25 and -12%, respectively; p < 0.02), whereas it increased the mass of vastus lateralis muscle (+11 and +7%; p < 0.002) and heart (+13 and %; p < 0.0001). In vehicle-injected animals, the fasting state was associated with lower lipoprotein lipase activity in white and brown adipose tissues, and higher enzyme activity in vastus lateralis and heart, compared with the postprandial state. Postprandially, treatment with clenbuterol reduced lipoprotein lipase activity in white adipose (-24%), whereas it increased enzyme activity in brown adipose (+107%) as well as in vastus lateralis (+35%). In fasted animals, no significant variation of enzyme activity in these tissues was observed following clenbuterol treatment, whereas in the heart, a decrease of lipoprotein lipase activity was observed (-22%). Clenbuterol lowered serum triglycerides significantly (-23%), but not their rate of secretion, whereas the agonist decreased the insulin to glucagon ratio only in the postprandial state.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of hyperthyroidism on the sensitivity of glycolysis and glycogen synthesis to insulin in the soleus muscle of the rat.

1. The effects of hyperthyroidism on the sensitivity and responsiveness of glycolysis and glycogen synthesis to insulin were investigated in the isolated incubated soleus muscle of the rat. 2. Hyperthyroidism, which was induced by administration of tri-iodothyronine (T3) to rats for 2, 5 or 10 days, increased fasting plasma concentrations of glucose, insulin and free fatty acids. 3. Administration of T3 for 2 or 5 days increased the rates of glycolysis at all insulin concentrations studied: this was due to increased rates of both glucose phosphorylation and glycogen breakdown, but there was no effect of T3 on the sensitivity of glycolysis to insulin. However, administration of T3 for 10 days increased the sensitivity of the rate of glycolysis to insulin. 4. The concentration of adenosine in the gastrocnemius muscles of the rats was not different from controls after 5 days, but it was markedly decreased after 10 days of T3 administration. If these changes are indicative of changes in the soleus muscle, the increased sensitivity of glycolysis to insulin found after 10 days' T3 administration could be due to the decrease in the concentration of adenosine. 5. Administration of T3 decreased the sensitivity of glycogen synthesis to insulin and the glycogen content of the soleus muscles. This may explain the decreased rates of non-oxidative glucose disposal found in spontaneous and experimental hyperthyroidism in man. 6. The rates of glucose oxidation did not change after 2 days, but they were increased after 5 and 10 days of T3 administration.     

Metabolic control of phosphorylase conversion in muscle. Effect of fasting and refeeding on the response of rat diaphragm glycogen phosphorylase, cyclic AMP Dependent protein kinase, and phosphorylase b kinase to adrenergic stimulation.

The influence of fasting and refeeding on the response to adrenergic stimulation of several enzymes involved in glycogen metabolism has been investigated in the isolated, intact rat diaphragm. The in vitro response of the phosphorylase system to terbutaline was found to decrease markedly following fasting. A pronounced increase in this response was seen upon refeeding. This increased responsiveness was normalized by incubation of isolated tissues with palmitate (1.5 mM). Plasma free fatty acid concentration was increased in fasted rats compared to the value found in refed animals. The effect of terbutaline on cyclic AMP concentration and protein kinase activity was not significantly influenced by fasting and refeeding while fasting decreased the effect of terbutaline upon phosphorylase b kinase. Diaphragm glycogen levels were reduced by more than 50% in rats fasted for 24 hours and were significantly increased upon refeeding compared to fed rats. The results indicate that the nutritional state can modulate the sensitivity of the interconverting system for phosphorylase. It is suggested that this modulation might depend upon fatty acid metabolism.     

Diminished AMPK signaling response to fasting in thioredoxin-interacting protein knockout mice

Thioredoxin-interacting protein (Txnip) knockout (TKO) mice exhibit impaired response to fasting. Herein, we showed that activation of adenine monophosphate-activated protein kinase and cellular AMP levels were diminished in the heart and soleus muscle but not in gastrocnemius muscle of fasting TKO mice. Similarly, glycogen content in fasted TKO mice was increased in oxidative muscles but was not different in glycolytic muscles. These data suggest Txnip deficiency has a higher impact on oxidative muscle than glycolytic muscles and provide new insights into the metabolic role of Txnip.     

Effect of Bauhinia forficata extract in diabetic pregnant rats: maternal repercussions.

Bauhinia forficata, commonly known as "paw-of-cow", is widely used in Brazil folk medicine for the treatment of Diabetes mellitus. The purposes of present study were to determine the repercussions of diabetes on the defense system against oxidative stress in pregnant female rats and to characterize the influence of the treatment with Bauhinia forficata extract on the antioxidant system, glycemic control, hepatic glycogen, cholesterol, triglycerides, total proteins and lipids. Virgin female Wistar rats were injected with 40 mg/kg streptozotocin (STZ) before mating. Oral administration of an aqueous extract of Bauhinia forficata leaves was given to non-diabetic and diabetic pregnant rats in 3 doses: 500 mg/kg from 0 to 4th day of pregnancy, 600 mg/kg from 5th to 14th day and 1000 mg/kg from 15th to 20th day. All the females were killed on the day 21 of pregnancy. A maternal blood sample was collected by venous puncture and the maternal liver was removed for biochemical measurement. The diabetic pregnant rats presented hyperglycemia, hyperlipemia, hypertriglyceridemia, hypercholesterolemia, hyperuricemia, decreased determinations of reduced glutathione (GSH) and superoxide dismutase (SOD). Treatment with B. forficata extract did not interfere in the albumin, total protein and lipid, triglyceride, cholesterol and SOD determinations. Increased hepatic glycogen, decreased uric acid concentration and increased GSH activity was observed. This last fact suggests that the plant may have some action on antioxidant defense system. However, the demonstration of the active component present in B. forficata responsible for its antioxidant effect and the increase in hepatic glycogen deserve further investigation.     

Alanine and aspartate aminotransferase activities in muscles of diabetic rats

Activities of alanine and aspartate aminotransferase in different muscle types and in the liver of streptozotocin diabetic rats were studied 1,2 and 3 days after administering of streptozotocin. It was shown that the activity of both enzymes was elevated in the "white" layer of the vastus lateralis, in the liver and in the heart, whereas it remained unchanged in the "red" layer of the same muscle, in the soleus and the diaphragm. It is concluded that the effect of acute insulin deficiency on the aminotransferase activity in skeletal muscles depends on the muscle fiber composition and does not appear in muscles with a high oxidative potential. These results indicate that muscle fiber composition should be taken into account when evaluating the role of insulin in amino acid metabolism in the muscle.     

The whey proteins of the milk of red deer (Cervus elaphus L.). A homologue of bovine beta-lactoglobulin.

Increasing plasma free fatty acids decreased the degree of glycogen depletion, and increased the citrate concentration, in slow-red (soleus) and fast-red (deep portion of vastus lateralis) muscle during exercise (approx. 50% depletion of glycogen, as against 75% in control animals). There was no effect in fast-white muscle (superficial portion of vastus lateralis). Glycogen concentration in the liver decreased by 83% in controls, but only by 23% in animals with increased free fatty acids during exercise. The decreased glycogen depletion may be partly explained by the findings that (a) plasma-insulin concentration was two- to three-fold higher in animals with increased plasma free fatty acids and (b) the exercise-induced increase in plasma glucagon was lessened by increased free fatty acids. Blood glucose was higher in the animals with increased free fatty acids after the exercise. The rats with increased plasma free fatty acids utilized approx. 50% as much carbohydrate as did the controls during the exercise.     

Glycogen depletion and resynthesis in the rat after downhill running

To study the effect of downhill running on glycogen metabolism, 94 rats were exercised by running for 3 h on the level or down an 18 degrees incline. Muscle and liver glycogen concentrations were measured before exercise and 0, 48 and 52 h postexercise. Rats were not fed during the first 48 h of recovery but ingested a glucose solution 48 h postexercise. Downhill running depleted glycogen in the soleus muscle and liver significantly more than level running (P less than 0.01). The amount of glycogen resynthesized in the soleus muscle and liver in fasting or nonfasting rats was not altered significantly by downhill running (P greater than 0.05). On every day of recovery the rats were injected with dexamethasone, which induced similar increases in glycogen concentration in the soleus muscle and liver after the 52nd h of the postexercise period in the case of downhill and level running. The glycogen depletion and repletion results indicated that, under our experimental conditions, downhill running in the rat, a known model of eccentric exercise, affected muscle glycogen metabolism differently from eccentric cycling in humans.     

Effects of re-feeding after prolonged starvation on pyruvate dehydrogenase activities in heart, diaphragm and selected skeletal muscles of the rat.

We investigated the capacity for pyruvate oxidation in skeletal muscle, diaphragm and heart after starvation and re-feeding. Starvation for 48 h decreased pyruvate dehydrogenase (PDH) activity in soleus (by 47%), extensor digitorum longus (64%), gastrocnemius (86%), diaphragm (87%), adductor longus (90%), tibialis anterior (92%) and heart (99%). Chow re-feeding increased PDH activity in all muscles to 43-78% of the fed value within 2 h. However, complete re-activation was not observed for at least 4-6 h, during which time hepatic glycogen was replenished. We discuss the importance of muscle PDH activity in relation to sparing carbohydrate for hepatic glycogen synthesis.     

Increased response to insulin of glucose metabolism in the 6-day unloaded rat soleus muscle

Hind leg muscles of female rats (85-99 g) were unloaded by tail cast suspension for 6 days. In the fresh-frozen unloaded soleus, the significantly greater concentration of glycogen correlated with a lower activity ratio of glycogen phosphorylase (p less than 0.02). The activity ratio of glycogen synthase also was lower (p less than 0.001), possibly due to the higher concentration of glycogen. In isolated unloaded soleus, insulin (0.1 milliunit/ml) increased the oxidation of D-[U-14C]glucose, release of lactate and pyruvate, incorporation of D-[U-14C]glucose into glycogen, and the concentration of glucose 6-phosphate more (p less than 0.05) than in the weight-bearing soleus. At physiological doses of insulin, the percent of maximal uptake of 2-deoxy-D-[1,2-3H]glucose/muscle also was greater in the unloaded soleus. Unloading of the soleus increased by 50% the concentration of insulin receptors, due to no decrease in total receptor number during muscle atrophy. This increase may account for the greater response of glucose metabolism to insulin in this muscle. The extensor digitorum longus, which generally shows little response to unloading, displayed no differential response of glucose metabolism to insulin.     

Effects of starvation and exercise on concentrations of citrate, hexose phosphates and glycogen in skeletal muscle and heart. Evidence for selective operation of the glucose-fatty acid cycle.

Concentrations of citrate, hexose phosphates and glycogen were measured in skeletal muscle and heart under conditions in which plasma non-esterified fatty acids and ketone bodies were physiologically increased. The aim was to determine under what conditions the glucose-fatty acid cycle might operative in skeletal muscle in vivo. In keeping with the findings of others, starvation increased the concentrations of glycogen, citrate and the fructose 6-phosphate/fructose 1,6-bisphosphate ratio in heart, indicating that the cycle was operative. In contrast, it decreased glycogen and had no effect on the concentration of citrate or the fructose 6-phosphate/fructose 1,6-bisphosphate ratio in the soleus, a slow-twitch red muscle in which the glucose-fatty acid cycle has been demonstrated in vitro. In fed rats, exercise of moderate intensity caused glycogen depletion in the soleus and red portion of gastrocnemius muscle, but not in heart. In starved rats the same exercise had no effect on the already diminished glycogen contents in skeletal muscle, but it decreased cardiac glycogen by 25-30%. After exercise, citrate and the fructose 6-phosphate/fructose 1,6-bisphosphate ratio were increased in the soleus of the starved rat. Significant changes were not observed in fed rats. The data suggest that in the resting state the glucose-fatty acid cycle operates in the heart, but not in the soleus muscle, of a starved rat. In contrast, the metabolite profile in the soleus was consistent with activation of the glucose-fatty acid cycle in the starved rat during the recovery period after exercise. Whether the cycle operates during exercise itself is unclear.     

Effects of the beta(2)-agonist clenbuterol on respiratory and limb muscles of weaning rats

The aim of this study was to analyze the effects of chronic administration of the beta(2)-agonist clenbuterol (1.5 mg x kg(-1) x day(-1) for 4 wk in the drinking water) on respiratory (diaphragm and parasternal intercostal) and hindlimb (tibialis and soleus) muscles in young rats during postnatal development (21 to 49 postnatal days). The treatment resulted in very little stimulation of muscle growth. Significant slow-to-fast transitions in the expression of myosin heavy chain isoforms and significant increases in the myofibrillar ATPase activity were found in the diaphragm and soleus, whereas tibialis anterior and intercostal muscles did not show any significant fiber-type alteration. Decrease of oxidative enzyme activities and increase of glycolytic enzyme activities were also observed. It is concluded that whereas the growth stimulation is age dependent and only detectable in adult rats, the fiber-type transformation is also present in weaning rats and particularly evident in the soleus and diaphragm. The fiber-type transformation caused by clenbuterol might lead to an enhancement of contractile performance and also to a reduced resistance to fatigue.