Robert J. Hansen

The effects of insulin on the turnover of glucose-6-phosphate dehydrogenase in epididymal adipose tissue of the rat

The effects of insulin on the turnover of glucose-6-phosphate dehydrogenase in rat epididymal adipose tissue were studied by immunochemical technique in in vitro incubations. Insulin increased the relative rate of synthesis of glucose-6-phosphate dehydrogenase by two-fold in tissue obtained from normal rats. Insulin also had an effect on the rate of degradation of this enzyme. In the absence of insulin in the incubation medium the rate constant of degradation was 0.11 h-1 (half-life, 6.3 h). When insulin was added to the medium degradation of this enzyme was slowed. The new rate constant of degradation was 0.04 h-1 (half-life, 17 h). In the presence of insulin, the rate constant of degradation of total protein in adipose tissue was unchanged; therefore the effects of insulin on the degradation of glucose-6-phosphate dehydrogenase are specific to that protein and perhaps to a few other specific proteins.

Influence of diet on the in vivo turnover of glucose-6-phosphate dehydrogenase in rat liver

Abstract In vivo turnover of rat liver glucose-6-phosphate dehydrogenase was studied. A specific antibody was used in comparing the rates of synthesis and degradation of the enzyme between rats fed a commercial chow diet and those fed a semi-purified high-carbohydrate diet. In livers of rats fed the semi-purified diet, the rate of synthesis of the enzyme was two-fold greater than in livers of rats fed the commercial diet. The rate of degradation of glucose-6-phosphate dehydrogenase was determined by following the loss with time of [guanido-14C]-arginine from previously labelled enzyme. The rate of degradation of the enzyme was decreased in livers of rats fed the semi-purified diet, being 0.044 h−1 (half-life, 16 h) as compared to 0.120 h−1 (half-life, 6 h) in rats fed the chow diet. It was concluded that the increases in enzyme activity observed with this dietary manipulation are solely the result of changes in the rates of synthesis and degradation of enzyme. No evidence was found to support the hypothesis that an activation-inactivation process is involved as a major regulatory mechanism of glucose-6-phosphate dehydrogenase activity in rat liver.

Plasma lipoprotein changes in hens (Gallus domesticus) during an induced molt

Blood plasma lipoproteins were studied during food and light deprivation or prolactin injection-induced involution of ovarian follicles (molt) of laying hens. Egg laying stopped 3 days after initiation of either treatment. Food and light-deprived hens lost 29% of initial body weight during the 10-day experiment (P < 0.05), whereas prolactin-treated hens lost 9% of body weight. Yolk-directed very low density lipoprotein (VLDLy) concentration in plasma decreased in both groups, but declined more rapidly in food and light-deprived hens. Very low density lipoprotein triacylglycerol decreased 40% in food and light-deprived hens by day 2 compared with a 13% decrease in the prolactin-treated hens. By day 5, a lipoprotein particle 21-22 nm in diameter appeared in the d = 1.019-1.046 g/ml density fraction of plasma in both groups. A similar lipoprotein particle, termed HDLR, developed in overfed hens with involuting ovarian follicles. In conclusion, hens undergoing ovarian regression due to food and light deprivation, prolactin treatment or overfeeding display marked decreases in plasma yolk-directed very low density lipoproteins and the appearance of HDLR. Other lipoprotein populations varied depending on whether the hens continued to feed or not.

Immunological titration of rat liver glucose-6-phosphate dehydrogenase from animals fed high and low carbohydrate diets☆

Abstract Recent work (Hizi and Yagil [1974] Eur. J. Biochem. 45 : 211–221, and Kelly et. al. [1975] Fed. Proc. 34 : 881) suggests that the marked increase in rat liver glucose-6-phosphate dehydrogenase activity which is observed upon feeding an animal a high carbohydrate diet does not involve an increase in the total amount of enzyme present. In contrast, the data presented herein involving immunological titrations of rat liver glucose-6-phosphate dehydrogenase indicates that the increase in enzyme activity resulting from feeding a high carbohydrate diet does involve an increase in the total amount of enzyme present.

Metabolism of Methyl and Benzyl Esters of Penicillin by Different Species

Conclusions Plasma levels following administration of benzyl and methyl esters of penicillin G have been determined in a variety of species of animals. Mice hydrolyze both of these esters rapidly and probably completely. Rats are able to hydrolyze the esters less completely. Monkeys, dogs, and rabbits show no appreciable plasma level of free penicillin following subcutaneous injection of ordinary doses of these esters.

Hexose-ATP phosphotransferases: Comparative aspects—III. Interrelationships of animal hexokinases

Abstract 1. 1. Antisera to partially purified hexokinase II from rat muscle was prepared. 2. 2. The antisera inhibited the enzymatic activity of the muscle antigen and hexokinase II which was isolated from rat adipose tissue. Hexokinase IVs isolated from rat kidney was also inhibited whereas neither hexokinase I from rat adipose and brain nor hexokinase IVf from rat liver were inhibited. 3. 3. Crystalline yeast hexokinase isoenzymes were not inhibited by the antisera. 4. 4. In general, hexokinase activity in muscle and liver but not brain from birds, rodents, primates, ungulates and carnivores was inhibited by the antisera. The antisera did not inhibit hexokinase activity from the amphibian tested.

Muscle Protein Metabolism of Rats in Surgical Trauma

The effects of decreased food intake and degree of surgical trauma on total, myofibrillar and sarcoplasmic muscle protein synthesis and degradation were assessed in two experiments (A and B). Trauma consisted of an abdominal incision with or without hysterectomy. The degree of trauma in experiment B was increased relative to that in experiment A by extending the length of the incision, operative manipulation and time required to perform the surgery. To account for postoperative diminutions in food intake on protein turnover, a group of nonoperated rats were pair-fed to the level of food consumed by hysterectomized rats. Traumatized rats in experiment B lost more weight, ate less, and had a lower muscle total protein concentration than corresponding rats in experiment A, confirming a more severe trauma in experiment B. In both experiments, trauma depressed total protein content of muscle. Synthesis was measured by the incorporation of L-[U-14C] tyrosine from a single meal into total, sarcoplasmic and myofibrillar proteins of gastrocnemius muscle. Degradation was calculated as the difference between the growth rate and the synthetic rate. Synthetic rate (ks) of total protein was depressed by surgical trauma; the more severe the trauma, the greater the depression. In mild trauma, the depression in ks was due only to a decrease in sarcoplasmic protein synthesis (ke), whereas with more severe trauma, synthetic rates of both sarcoplasmic (kes) and myofibrillar (kem) proteins were decreased. Protein degradation (kd,) was increased on day 2 in experiments A and B, had returned to control values on day 4 in experiment A and had decreased below control values in experiment B.(ABSTRACT TRUNCATED AT 250 WORDS)

Postsurgical Muscle Protein Turnover in Perfused Hindquarters of the Rat

Skeletal muscle protein synthesis and degradation were measured simultaneously in perfused hindquarters of adult female rats 0, 2, and 4 days after surgical trauma. In order to explore the role of decreased postoperative nutrient intake on muscle protein turnover, a group of rats were pair-fed to the level of food consumed by surgical traumatized animals. Protein synthesis was measured by the incorporation of 3H-L-phenylalanine into the myofibrillar (contractile) and sarcoplasmic (soluble) proteins of gastrocnemius muscle. Protein degradation rates were calculated from the release of myofibrillar 3-methyl histidine (3MH) during the perfusion. Surgical trauma significantly depressed myofibrillar and sarcoplasmic protein synthetic rates by 33 and 29%, respectively. Protein degradation, as assessed by 3MH release into perfusate, increased 25% on the second postoperative day but returned to control levels by the 4th day after surgery. Food restriction of the pair-fed control rats did not alter protein synthesis, however, protein degradation decreased significantly. In conclusion, the effect of trauma on protein turnover appears not to be due to decreased nutrient consumption.

Effects of insulin on the adaptation of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in rat adipose tissue☆

Abstract 1. 1. The effects of insulin on adipose tissue glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were studied. 2. 2. At physiological concentrations of glucose, insulin, added to the incubation medium, stimulated the activity of glucose-6-phosphate dehydrogenase, but not 6-phosphogluconate dehydrogenase, in epididymal adipose tissue, from starved or diabetic rats, incubated in vitro for 16 h. 3. 3. The inhibitors actinomycin D (5 μg/ml) and cycloheximide (1 mg/ml) blocked the insulin stimulation.

COMPARATIVE EFFECTS OF THERMAL AND SURGICAL TRAUMA ON RAT MUSCLE PROTEIN METABOLISM

A modified intraperitoneal pool flooding technique, employing L-3H-tyrosine, was developed for measuring muscle protein synthetic rates following traumatic injury. Sufficient radiolabeled tyrosine was injected intraperitoneally to effect a six-fold increase in plasma tyrosine concentration (124-800 microM) resulting in constant, sustained specific radioactivities in plasma- and intracellular-free tyrosine pools. Localized vs systemic effects of thermal and surgical trauma on gastrocnemius muscle protein turnover were assessed 2 and 4 days postinjury. Thermal trauma increased total, myofibrillar, and sarcoplasmic muscle protein synthesis (44%) and protein degradation (300%). Conversely, surgical trauma decreased synthesis of total (24%), myofibrillar (14%), and sarcoplasmic (43%) muscle proteins without altering protein degradation. Short-term restriction of pair-fed controls did not affect either aspect of protein turnover.