Effect of medroxyprogesterone acetate on the intestinal absorptive functions in protein-deficient rat

Effect of Medroxyprogesterone acetate (MPA) at a dose level of 35mg/Kg body weight per week for four weeks on the intestinal uptake of nutrients viz glucose, amino acids, (alanine and leucine), calcium and zinc has been investigated in protein-deficient female rats. The administration of MPA was found to enhance significantly the uptake of glucose and amino acids in both the pair-fed and the protein-deficient rats. In contrast, calcium uptake was depressed as a result of treatment with the drug as well as protein-deficiency. The uptake of zinc was not affected on drug administration. This steroidal contraceptive caused elevation in sodium-dependent glucose uptake, while the sodium-independent uptake remained unaltered. The kinetic parameters of glucose and leucine uptake indicate that MPA might be inducing the transport carrier protein of these nutrients as elevation in Vmax of these nutrients transport system was observed following its administration.     

Effect of a selectiveβ 2-adrenergic agonist (Cenbuterol) on energy balance and body composition in normal and protein deficient rats

In rats fed a normal (22% protein) diet, injection of clenbuterol (1 mg/kg/d for 21 d) did not affect energy intake, energy expenditure or weight gain, but reduced energetic efficiency, and fat and energy gains and increased body protein content. Presenting a low-protein (8%) diet reduced energy intake, gain and efficiency, body protein content and the mass of the gastrocnemius muscle when compared to rats fed the control diet. Injection of the protein-deficient rats with clenbuterol (1 mg/kg/d for 21 d) caused hypophagia and reduced body weight and energy gains, energy expenditure and total body fat. However, the total body content of protein was not significantly reduced and the percentage of body protein in this protein deficient, clenbuterol-treated group was greater than that of untreated rats on both the high- and low-protein diets. The ratio of body protein to fat following clenbuterol treatment was increased by over 50% in both normal and protein-deficient rats. The results show that in protein deficient animals, clenbuterol treatment may help conserve body protein at the expense of fat, resulting in a smaller, but leaner body mass.     

Changes in protein turnover during gestation in the foetuses,placentas, liver,muscle and whole body of rats given a low-protein diet

(1)Protein synthesis and content have been studied in skeletal muscle, liver, foetuses and placentas of pregnant rats given a protein-deficient diet. Changes which occurred during the anabolic and subsequent catabolic phases of pregnancy are compared with those in well-fed pregnant and in protein-deficient non-pregnant rats. (2) The normal increase in liver protein did not occur during pregnancy in the protein-deficient group. (3) Protein deficiency affected protein content of the placenta earlier and more severely than that of the foetus. (4) Rates of protein synthesis in liver, placentas and foetuses were enhanced above control values by protein deficiency. (5)_Muscle protein increased normally during the anabolic phase of pregnancy but fell during the catabolic phase, unlike values for weel-fed animals. (6) Muscle protein synthesis rates rose by similar amounts in well-fed and protein-deficient animals during the anabolic phase of pregnancy. The fall to starting values during the catabolic phase was sharper and earlier in protein-deficient animals, which could reduce demands on the body amino acid pool by an amount equivalent to over 50% of the needs for protein deposition in foetuses and placentas. Thus, changes in muscle protein synthesis in both anabolic and catabolic phases of pregnancy may afford some protection to foetal protein synthesis.     

The phospholipid-dependence of uridine diphosphate glucuronyltransferase. Effect of protein deficiency on the phospholipid composition and enzyme activity of rat liver microsomal fraction

After force-feeding a protein-free diet to male rats for 5-7 days a substantial (2.4-fold) increase in the specific activity of the liver microsomal enzyme UDP-glucuronyltransferase (EC 2.4.1.17) was observed. A similar activation of the enzyme occurred when rats were fed on a low-protein (5%, w/w, casein) diet for 60 days. Although both the short- and long-term protein-deficient diets decreased the contents of microsomal protein and phospholipid in liver tissue they did not significantly alter the ratio of these major membrane components. Protein deficiency profoundly altered the phospholipid composition of microsomal membranes. The most striking difference in microsomal phospholipid composition between control and protein-deficient rats was their content of lysophosphatides. Whereas microsomal membranes from protein-deficient rats contained significant proportions of lysophosphatidylcholine and lysophosphatidylethanolamine very little or no lysophosphatides were detected in control preparations. Pretreatment of microsomal fractions from normal rats with phospholipase A markedly increased their UDP-glucuronyltransferase activity as did their pretreatment with lysophosphatidylcholine. It is concluded that the quantities of lysophosphatides present in microsomal membranes from protein-deficient rats were sufficient to have caused the increased UDP-glucuronyltransferase activities of these preparations. Evidence is presented suggesting that these changes in microsomal phospholipid composition and UDP-glucuronyltransferase activity caused by protein deficiency reflect changes that occur in vivo. The possible physiological significance of these findings is discussed.     

Modulation of the mutagenicity of three dinitropyrene isomers in vitro by rat-liver S9, cytosolic, and microsomal fractions following chronic ethanol ingestion.

The effects of chronic ethanol feeding of rats on the ability of liver fractions to modulate the bacterial mutagenicity of three dinitropyrene isomers (1,3-, 1,6- and 1,8-DNP), which require bacterial enzymes but not an exogenous enzyme source for activation, were studied. The mutagenicity of the DNP isomers toward S. typhimurium TA98 and TA100 was attenuated in the presence of post-mitochondrial supernatants (S9) from both ethanol-fed and pair-fed rats albeit, that from the ethanol-fed group was more efficient in lowering the mutagenicity. The cytosolic fraction from ethanol-fed rats enhanced the mutagenicity of all of the DNP isomers in TA100. The most notable enhancement was with 1,3-DNP in which a more than 4-fold enhancement was obtained. Cytosol from pair-fed rats enhanced only the mutagenicity of 1,3-DNP, this by 2.9-fold. Cytosolic NADPH-nitroreductase activity from ethanol-treated rats toward 1,6-, 1,8- and 1,3-DNP was increased 2.8-, 1.7- and 1.3-fold, respectively over pair-fed controls. Cytosolic NADH-nitroreductase from ethanol-fed rats was increased with 1,3-DNP (1.7-fold) and 1,8-DNP (1.4-fold) as substrates, but not with 1,6-DNP. Microsomes decreased the mutagenicity of DNP similarly to S9, i.e., fractions from ethanol-fed rats were more efficient than those of pair-fed rats in deactivating all the DNP isomers. Per mg of protein, detoxification of DNP by S9 was more efficient than with microsomes, thus both cytosolic and microsomal enzymes are required for maximal detoxification. In summary, ethanol feeding modulates both the augmented cytosolic activation of DNP to mutagens and the deactivation of the direct-acting mutagenicity of DNP by microsomes. In combination, as is the case with S9, the microsomal detoxifying activity outcompetes the cytosolic activation.     

Elevation of brain histamine content in protein-deficient rats.

—Male rats of the Sprague-Dawley strain (80–250 g body wt) were fed either an adequate protein diet (18% lactalbumin) or a protein-deficient diet (0.5% lactalbumin). After 5–8 weeks of receiving the low protein diet, some of the malnourished rats were rehabilitated with an adequate protein diet. The malnourished rats exhibited significant elevations in brain levels of histidine (+415%) and homocarnosine (+100%) in comparison to findings in the control animals of similar age. Associated with the elevated brain levels of histidine in malnutrition was a prominent increase in brain content of histamine (+ 150-+ 238%). The mean brain histamine levels (ng/g) in the control rats varied from 45.96 to 56.15 in several experiments. In the protein-deficient rats, values ranged from 115 to 190. Refeeding the malnourished rats with adequate protein diet elicited reversal of histidine and histamine levels to near normal values within 1 week. The increased brain content of histamine in malnutrition was attributed to enhanced rate of production resulting from increased availability of the precursor amino acid, a conclusion consistent with elevation also of the brain content of homocarnosine (γ-aminobutyryl-l -histidine) which is another major route of disposal of histidine in the brain. The relevance of these neurochemical alterations to the behavioural changes often associated with protein malnutrition, deserves some intensive examination.     

Effect of alimentary thiamine deficiency on the activity of gluconeogenic key enzymes in rat liver and kidney

Activity of the key enzymes of gluconeogenesis under alimentary thiamine deficiency (15 days of dietary treatment) was studied in the liver and kidney of fed and 48 h starved rats. As compared to pair-fed controls vitamin B1-deficiency was followed by a decrease of glucose 6-phosphatase and fructose 1,6-bisphosphatase activities in both organs; the activity of phosphoenolpyruvate carboxykinase was diminished only in the liver. Starvation of thiamine-deficient rats (as compared to pair-fed starved group) resulted in lower activation of these enzymes. The decrease of the enzyme activities in thiamine-deficient animals indicates that de novo glucose synthesis in the tissues is depressed, though thiamine-requiring enzymes are not directly involved in this process. Possible mechanisms of alterations described are discussed.     

A Novel Gene Required for the Alkaliphily of the Facultative Alkaliphile Bacillus sp. Strain C-125

This study clarifies the effect of exposure to cigarette smoke on L-ascorbic acid (AsA) metabolism and on the activities of drug-metabolizing enzymes. Male Wistar rats were used. The test rats (group T) were exposed to sidestream smoke from cigarette for 2 h every day for 25 days. During the experimental period, the excreted amount of AsA in the urine from group T was higher than that from the control group (group C). At the end of the experimental period, the AsA content of the plasma and tissues, the liver cytochrome P-450 content and the activities of drug-metabolizing enzymes in group T were each higher than those in group C.     

Medroxyprogesterone acetate has opposite effects on the androgen binding protein concentrations in serum and epididymis

In the rat, the effects of progestin and androgen administration on serum, testicular and epididymal androgen binding protein (rABP) concentrations were determined and related to the organ weight and morphology. Adult rats were treated with medroxyprogesterone acetate (MPA; 17 alpha-acetoxy-6 alpha-methylprogesterone), testosterone propionate (TP) and mibolerone (MB; 7 alpha, 17 alpha-dimethyl-19-nortestosterone). MPA reduced testicular and epididymal weights and the concentrations of serum follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone. During MPA treatment testicular and epididymal ABP content declined in parallel with organ weights and hormone concentrations, whereas serum ABP concentrations increased. Combinations of MPA and TP reduced testicular and epididymal ABP, but the reductions were less than with MPA alone; this combined treatment also elevated serum AMP. Both MB and TP reduced ABP in the male reproductive tract, but unlike MPA did not increase the concentration of this protein in serum. The results suggest that MPA acts directly on Sertoli cells resulting in increased ABP release into the blood. The comparison was made of steady state polyacrylamide gel electrophoresis (SS-PAGE) and radioimmunoassay (RIA) methods of estimating rABP. The potency ratio of testicular ABP estimated by the two methods (RIA:SS-PAGE) was three times higher than this ratio in the epididymis in normal and hormonally treated animals. Due to differences in end points, these observations imply that these assays do not quantify the molecules in the same way in one or both of these tissues. The results indicate, however, that both assays are suitable for following rABP concentration in animals with altered hormonal states.     

Effect of long-term restriction of protein intake,from gestation onward,on free-choice consumption of ethanol by rats

Long-term (including gestational and lactational) restriction of protein (8% of diet) significantly lowered the absolute and relative consumption of 6% ethanol (EtOH) in a two-bottle, free-choice (H₂O vs EtOH) situation during a 76-day test period. This difference in response between rats fed the low protein diet and those fed an isocaloric normal protein (24%) diet became non-significant in two subsequent 100-day test periods. Statistical analysis of observations on individual performance indicated that regularity, cyclicity, and duration of drinking in each animal was random over all three time intervals for both groups. The early, significantly lower EtOH consumption by the protein-restricted group may be due to a paucity of EtOH-metabolizing enzymes in brain and liver, thereby prolonging the CNS effects of lower doses of EtOH consumed. The disappearance of this difference in subsequent test periods may reflect either a behavioral or metabolic adaptation in the developing protein-deficient rat.     

Effect of chronic uremia on fructose 2,6-bisphosphate glycolytic and gluconeogenic enzymes in rat liver

The level of fructose 2,6-bisphosphate and the maximal activities of key gluconeogenic and glycolytic enzymes were determined in the liver of a rat model of chronic uremia and in ad libitum-fed control and pair-fed control animals. Fructose 2,6-bisphosphate was decreased in uremia and its level negatively correlated with the concentration of blood urea nitrogen. The changes in gluconeogenic enzymes in uremic rats were not different from those in the pair-fed controls. However, pyruvate kinase was decreased in uremia when compared to both controls. These studies offer a possible mechanism for the role of the liver in the carbohydrate intolerance of uremia.     

Effect of a steroidal oral contraceptive on intestinal absorptive functions in proteins deficient rat

The effects of steroidal oral contraceptive norethynodrel plus ethinylestradiol-3-methyl ether (SOC) at a daily dose of 5 mg: 0.06 mg per kg body weight for 28 days on intestinal absorptive functions have been investigated in protein-deficient female albino rats. The administration of this contraceptive caused significant increase in glucose and amino acids uptake but had no effect on calcium and zinc uptake in pair-fed as well as in protein-deficient rat. Further studies carried out on glucose transport system showed that the transport of sodium-dependent glucose was significantly enhanced while that of sodium-independent glucose remained unaltered in drug-treated animals. Kinetic studies of glucose transport in the presence of sodium ions revealed that SOC treatment affected the rate of uptake of glucose by elevating Vmax, but the apparent Kt value remained the same in treated and untreated animals.     

Impairment of pancreatic acinar function by reserpine in vivo and in vitro

Summary Chronic reserpine treatment of animals, an experimental model for cystic fibrosis (CF), results in generalized exocrinopathy, impaired pancreatic secretion, and decreased pancreatic content of amylase. The mechanisms of altered acinar function and decreased amylase content in both CF and the reserpine-treated rat are unknown. To examine this alteration, the rate of [³H]phenylalanine (phe) incorporation into cellular protein was determined in pancreatic acinar cells after reserpine treatment of rats in vivo (7 d) and of cells in vitro (1 to 24 h). Acinar cells isolated from control, chronic reserpine-treated, and pair-fed rats were incubated in vitro with 0, 30, 50, or 100 μM reserpine. Reserpine treatment in vitro for 24 h of acinar cells from control rats significantly decreased amylase activity (20 to 70%), an effect similar to that of reserpine treatment in vivo. In vivo, reserpine treatment decreased [³H]phe incorporation (disintegrations per minute per milligram protein) 56% in freshly isolated cells, but did not alter intracellular specific activity (disintegrations per minute per nanomole phe, SA) of [³H]phe. Reserpine treatment (30 and 50 μM) in vitro for 1 h also decreased [³H]phe incorporation by freshly isolated cells from control (53 to 85%) and pair-fed (40 to 68%) rats. Reserpine treatment for 24 h in vitro significantly decreased [³H]phe incorporation by cells from control (82 and 98%), pair-fed (80 and 95%), and chronic reserpine-treated (90 and 97%) rats as compared with cells from respective in vivo treatments cultured with no reserpine. In vitro reserpine treatment also decreased the intracellular SA of [³H]phe in freshly isolated cells from control (14 and 36%) and pair-fed (35 and 39%) rats and in cultured cells from control (11 and 86%), pair-fed (60 and 88%), and chronic reserpine-treated (49 and 76%) rats. However, these alterations of SA by reserpine did not account for the decreased incorporation of [³H]phe into acinar protein, which remained significantly lower (70 to 88%) when expressed as total phe incorporation. These results suggest (a) that reserpine acts directly on acinar cells to alter function and (b) that the ability of the pancreas to synthesize digestive enzymes may be impaired in this model of cystic fibrosis. This study was supported in part by the Cystic Fibrosis Foundation, Bethesda, MD.     

Regulation of hepatic drug metabolism by elaidic and linoleic acids in rats.

Elaidic and linoleic acids were administered at doses of 40 and 200 mg/kg i.p. every second day for 4 weeks to rats fed a fat-free diet. The fatty acids had only a slight effect on the weight gain of the animals. The amount of microsomal protein was slightly decreased with the higher dose of linoleic acid. The higher dose level of both fatty acids decreased the microsomal phospholipid content. The relative amounts of microsomal phospholipid fatty acids were also altered due to fatty acid administration. The activity of microsomal NADPH cytochrome c reductase and microsomal cytochrome P-450 contents were decreased by the higher dose of linoleic acid. The hepatic aryl hydrocarbon hydroxylase and p-nitroanisole O-demethylase activities decreased in fatty acid-treated rats. The UDP-glucuronosyltransferase activity was also lowered after the fatty acid administration. The results suggest that fatty acid-induced changes in the activities of drug-metabolizing enzymes may be due to the microenvironmental changes of membrane-bound enzymes.     

Adipose tissue development, growth, and food consumption in protein-malnourished rats.

Effects of protein malnutrition on adipose tissue development were studied in weanling male Sprague-Dawley rats fed isocaloric diets ad libitum containing either 22% (controls) or 8% (protein-malnourished rats) casein, and in rats pair-fed to the protein-malnourished rats with the 22% casein diet. After 32 days on the diet, protein-malnourished rats were 37% and pair-fed 67% the weight of the controls, while torso length was 37% and 73% of controls, respectively. Food consumption relative to body weight was greatest in protein-malnourished rats. Compared to control rats, the distal epididymal adipocyte number in the protein-malnourished rats was decreased in proportion to the decrease in body size and was more closely related to the protein intake than to the total calories consumed. After 32 days on diet, mean adipocyte number per 2 distal pads was 11.7 x 10(6) in controls and 4.3 x 10(6) in protein-malnourished rats. In pair-fed rats, cell number lagged behind controls at 4 and 11 days, but was normal at 32 days (11.4 x 10(6) cells). The distal epididymal pad adipocyte size and percent lipid were similar in all groups during the first 25 days of dietary treatment. Adipocyte size was increased significantly in controls at day 32 compared to the other two groups. At each time studied through day 25 on diet, epididymal pad weight was related to the adipose cell number rather than the cell size. It is concluded that severe restriction of dietary protein during the postweaning period of growth in rats results in decreased epididymal adipocyte proliferation and/or differentiation concomitant with generalized growth retardation, whereas isocaloric feeding of a diet of normal protein content is associated with only a transient delay in adipose tissue development.     

Protein synthesis in liver,skeletal muscle,and brown adipose tissue of rats fed a protein-deficient diet

Feeding protein-deficient diets to rats is known to stimulate diet-induced thermogenesis and activate brown adipose tissue (BAT). The fact that BAT protein content, unlike that of other tissues, is unnaffected by protein deficiency prompted us to measure tissue protein synthesis in vivo in animals maintained on normal- (18.8%) and low- (7.6%) protein (LP) diets. Protein synthesis was depressed in the liver of the LP rats due to a fall in RNA activity, with no change in RNA content, and synthesis was also reduced in skeletal muscle from the LP group, but this was due to decreased RNA content with no change in RNA activity. Conversely, protein synthesis, RNA, DNA, and protein content of interscapular BAT were all unaltered in protein-restricted animals. These data indicate that, unlike liver, skeletal muscle, and whole carcass, BAT protein synthesis is not reduced in protein-restricted rats, and this may be related to activation of thermogenesis in the tissue.     

Effect of Undernutrition on Tryptophan and Tyrosine Hydroxylases in the Developing Rat Brain

Rats born to well-fed mothers (20% protein diet ad libitum), protein-restricted mothers (7.5% protein diet ad libitum) or pair-fed with protein-restricted mothers were killed on days 0, 7, 14, 21, 28 and 35 and activities of the two enzymes of neurotransmitter synthesis, tryptophan-5-hydroxylase (EC 1.14.16.4) and tyrosine hydroxylase (EC 1.14.16.2) were assayed. Enzyme activities in normal animals were low at birth and progressively increased to reach adult levels by day 15. Protein-restricted and pair-fed animals also showed a similar pattern. However, significantly higher activities were observed from day 15 onwards in both experimental groups.     

Influence of zinc depletion and zinc status on serum growth hormone levels in rats

In a preceding trial, the growth hormone concentrations in the serum of zinc-deficient rats were greatly reduced compared to thead libitum- fed control animals. The same reduction, however, was also noted in the case of the pair-fed control animals with strongly diminished feed intake. Therefore, it was not possible to distinguish between the effects of zinc deficiencyper se and the effects resulting from restricted feed intake. A new study with 136 young male Sprague-Dawley rats showed again that zinc deficiency as well as strongly restricted feed intake reduced the growth hormone content in the serum. But in a marginal zinc deficiency status, when feed intake was only slightly or not reduced, there were lowered serum growth hormone levels in comparison to pair-fed control rats. A 1-wk zinc repletion did not increase the serum growth hormone content of the rats to a normal level, although the serum zinc concentration was normalized.     

Skeletal and heart muscle protein turnover during long-term exposure to high environmental temperatures in young rats

A study was undertaken to determine the long-term effects of a hot environment on protein turnover in skeletal and cardiac muscles of young homeothermic animals. Three groups of 36 male 28 day old rats were housed at 35 degrees C (hot group), 25 degrees C (control group), or 25 degrees C but pair-fed to the intake of the hot group (pair-fed group). Rates of protein synthesis and degradation were measured in vivo on days 5, 10, 15, and 20. By day 20, soleus and gastrocnemius (skeletal muscle) protein masses were 7 and 14% lower in the hot group and 31 and 21% lower in the pair-fed group compared with the control group (P < 0.05). The fractional rate of protein synthesis (k(syn)) was on average 11% lower (P < 0.05) in the hot group compared with control rats and was not different from pair-fed rats. The fractional rate of skeletal muscle protein degradation (k(deg)) in hot rats was slightly lower than in control rats; k(deg) was on average 18% higher (P < 0.05) in the pair-fed group compared with the hot group and this difference appeared to be most prominent on day 5. In heart, by day 20, protein mass was 30% lower in the hot group and 40% lower in the pair-fed group compared with control rats (P < 0.05). k(syn) was on average 19% lower (P < 0.05) in the hot group compared with the control group, but not different from pair-fed rats. In the heart there were no differences in k(deg) among treatments. Plasma triiodothyronine (T3) concentration was lower in the hot group, but not in the pair-fed group, compared with controls. In conclusion, chronic exposure to hot environments was associated with lower skeletal and cardiac muscle mass and protein turnover; lower protein mass in this tissue was due to decreased k(syn); this is consistent with lower plasma T3 concentrations. In pair-fed rats, k(syn) was also reduced, but interestingly k(deg) was not, resulting in a greater loss of skeletal muscle mass. These results suggest that heat exposure invokes physiological adaptations to preserve skeletal muscle mass despite decreased food intake. In the heart, loss of protein was a result of decreased k(syn), which can be primarily ascribed to lower food intake.     

Gonadotropin secretion in azotemic male rats--effect of opioid blockade

The role of endogenous opioids in the control of gonadotropin secretion in uremic male rats was investigated using the narcotic antagonist, naloxone. In order to eliminate the effect of weight loss due to uremia-induced anorexia as a cause of previously described altered gonadotropin secretion in uremia, we also studied a group of normal pair-fed control animals who exhibited a weight loss comparable to that of the uremic animals. Naloxone administration had no effect on the basal or LRH-stimulated peak concentrations of LH and FSH in the normal or the uremic rats. Basal and LRH-stimulated gonadotropin responses in the pair-fed rats were comparable to those seen in the normal rats. Similarly, opioid blockade produced no change in the basal or LRH-stimulated gonadotropin responses in the pair-fed animals. Testosterone concentrations were significantly lower in the uremic and pair-fed animals compared to the normal rats. The data suggest that experimental renal failure is not associated with altered opioidergic tone, as it relates to gonadotropin secretion, or to diminished sensitivity of the gonadotroph to LRH stimulation. The decreased testosterone concentration seen in the uremic and pair-fed rats may reflect abnormalities in gonadal hormone secretion due to primary pathology occurring at the level of the gonad. These abnormalities may be reflected as diminished Leydig cell sensitivity to LH. The inappropriately low concentrations of LH in the presence of low testosterone together with normal gonadotropin response to exogenous LRH also suggest an abnormal secretion of endogenous LRH. It is not clear whether this presumed abnormality in LRH secretion is a primary event or is related to decreased testosterone production by the testes in the uremic and pair-fed rats.