The effects of surgical stress and short-term fasting on protein synthesis in vivo in diverse tissues of the mature rat.

1. We measured fractional rates of protein synthesis, capacities for protein synthesis (i.e. RNA/protein ratio) and efficiencies of protein synthesis (i.e. protein-synthesis rate relative to RNA content) in fasted (24 or 48 h) or fasted/surgically stressed female adult rats. 2. Of the 15 tissues studied, fasting caused decreases in protein content in the liver, gastrointestinal tract, heart, spleen and tibia. There was no detectable decrease in the protein content of the skeletal muscles studied. 3. Fractional rates of synthesis were not uniformly decreased by fasting. Rates in striated muscles, uterus, liver, spleen and tibia were consistently decreased, but decreases in other tissues (lung, gastrointestinal tract, kidney or brain) were inconsistent or not detectable, suggesting that, in many tissues in the mature rat, protein synthesis was not especially sensitive to fasting. 4. In fasting, the decreases in fractional synthesis rate resulted from changes in efficiency (liver and tibia) or from changes in efficiency and capacity (heart, diaphragm, plantaris and gastrocnemius). In the soleus, the main change was a decrease in capacity. 5. Surgical stress increased fractional rates of protein synthesis in diaphragm (where there were increases in both efficiency and capacity) by about 50%, in liver by about 20%, in spleen by about 40%, and possibly also in the heart. In liver and spleen, capacities were increased. In other tissues (including the skeletal muscles), the fractional rates of protein synthesis were unaffected by surgical stress.     

The inhibition of protein synthesis in a rat brain system by ethionine in vitro and in vivo

Abstract— An amino acid incorporating system from rat brain has been used to study in vitro four aspects of protein synthesis: amino acid-AMP-enzyme complex formation; amino acid-tRNA synthesis; amino acid incorporation into protein and protein synthesis from presynthesized amino acid-tRNA. Ethionine (0.5 mm ) inhibited the system and the inhibition appeared to be in the formation of amino acid-tRNA. The inhibition in vitro was independent of the sex of the animal from which the system was derived. Pretreatment of animals in vivo with ethionine yielded in females only preparations deficient in incorporating capacity when tested in vitro. Exchange experiments demonstrated that the defect was in the pH 5 enzymes and not in the ribosomes. The inhibition in vitro was not reversed by addition of ATP and appeared to be competitive with the amino acid substrate.     

The response of the rat liver to normobaric hypoxia stimulated in vivo and in vitro

The metabolic features of the rat liver were studied in artificial homeostasis conditions, using an isolated perfused organ as a model. The metabolism of the liver isolated from an intact rat and perfused with a normobaric hypoxic medium was compared with that of a liver that was isolated from a rat preliminarily kept in a chamber to simulate hypoxia of the total body and perfused using a medium with a normal oxygen content. The functional activity of the liver was assessed by portal pressure; oxygen consumption; and carbon dioxide gas, urea, glucose, and lactate contents in the perfusion medium. Metabolic changes in the perfused liver during oxygen deficiency became detectable at the same time point after exposure regardless of the method used to experimentally simulate hypoxia. This finding directly points to the metabolic autonomy of the liver.     

Effects of nicotine and vitamin E on 6-phosphogluconate dehydrogenase activity in some rat tissues in vivo and in vitro

The aim of this study was to investigate whether nicotine affects 6-phosphogluconate dehydrogenase (6PGD) enzyme activity in some rat tissues, and to see the modulatory effects of vitamin E on this effect in vivo. In addition, the effects of nicotine and vitamin E on 6PGD activity were also tested in vitro. The groups were: nicotine [0.5 mg/kg/day, intraperitoneal (i.p.)]; nicotine + vitamin E [75 mg/kg/day, intragastric (i.g.)]; and control group (receiving only vehicles). There were eight rats per group and supplementation period was 3 weeks. The results of in vivo study showed that nicotine activated the muscle, lungs, and testicular 6PGD enzyme activity but had no effect on heart and liver 6PGD activity. Also, nicotine + vitamin E activated the muscle, testicle, and liver 6PGD enzyme activity, while this combination had no effect on heart, and lungs in vivo. When nicotine is administered with vitamin E the increase in 6PGD enzyme activity in muscle and testicles were lower. On the other hand the increase in 6PGD enzyme activity was eliminated by vitamin E in lungs, while 6PGD enzyme activity was increased by vitamin E, which was not affected by nicotine only. In vitro results correlated well with in vivo experimental results. Our results suggest that vitamin E may favourably increase 6PGD enzyme activity in liver in nicotine treated rats, while it has negligible effects on this enzyme activity in other tissues.     

Effects of nicotine and vitamin E on 6-phosphogluconate dehydrogenase activity in some rat tissues in vivo and in vitro

The aim of this study was to investigate whether nicotine affects 6-phosphogluconate dehydrogenase (6PGD) enzyme activity in some rat tissues, and to see the modulatory effects of vitamin E on this effect in vivo. In addition, the effects of nicotine and vitamin E on 6PGD activity were also tested in vitro. The groups were: nicotine [0.5 mg/kg/day, intraperitoneal (i.p.)]; nicotine + vitamin E [75 mg/kg/day, intragastric (i.g.)]; and control group (receiving only vehicles). There were eight rats per group and supplementation period was 3 weeks. The results of in vivo study showed that nicotine activated the muscle, lungs, and testicular 6PGD enzyme activity but had no effect on heart and liver 6PGD activity. Also, nicotine + vitamin E activated the muscle, testicle, and liver 6PGD enzyme activity, while this combination had no effect on heart, and lungs in vivo. When nicotine is administered with vitamin E the increase in 6PGD enzyme activity in muscle and testicles were lower. On the other hand the increase in 6PGD enzyme activity was eliminated by vitamin E in lungs, while 6PGD enzyme activity was increased by vitamin E, which was not affected by nicotine only. In vitro results correlated well with in vivo experimental results. Our results suggest that vitamin E may favourably increase 6PGD enzyme activity in liver in nicotine treated rats, while it has negligible effects on this enzyme activity in other tissues.     

Glucagon effect on rat liver protein synthesis in vivo

The in vivo effect of glucagon administration on hepatic polyribosomal profiles has been studied. Glucagon did not change significantly total, free or bound polyribosomal fractions 30–45 minutes after its administration. The combined administration of glucagon plus antiinsulin serum failed to show any significant effect of glucagon over the antiinsulin serum treated control. Glucagon increased valine production in the perfused isolated liver. These results suggest that the well known amino acid catabolic action of glucagon may be preferentially mediated through an increased proteolysis. Since it is known that glucagon increases considerably in vivo the liver cyclic AMP levels then its lack of effect on polyribosomal profiles might indicate that the postulated role for the cyclic nucleotide on liver protein synthesis must be taken cautiously.     

The acute effects of N-hydroxy-acetylaminofluorene on rat liver protein synthesis

A single intraperitoneal injection of N-hydroxy-acetylaminofluorene (N-hydroxy-AAF) at a dosage of 30 mg/kg significantly inhibited rat liver protein synthesis within 15 min. Marked alterations in the subcellular distribution of hepatic RNA accompanied the decline in protein synthesis in treated rats. These changes included decreases in nuclear and bound polysomal RNA and increases in free polysomal and non-sedimentable RNA. Heavy polysomal aggregates, both free and bound, were almost completely degraded to monomers and dimers during this period. Sedimentation profiles of total cytoplasmic RNA revealed no evidence of gross RNA breakdown in N-hydroxy-AAF-treated animals. To determine the mechanisms responsible for the inhibition of protein synthesis by N-hydroxy-AAF, cellular components involved in protein synthesis were purified from control and treated animals and examined in two cell-free systems. In a system which measures polypeptide chain elongation and release, the incorporation of amino acids into protein was reduced by 35% using polysomes from N-hydroxy-AAF treated animals compared with controls. By contrast, the function of the pH 5 fraction (containing aminoacylating enzymes and tRNA) from the carcinogen-treated animals was unimpaired. A wheat germ lysate system was used to determine the ability of mRNA to program polypeptide chain initiation and elongation. Cytoplasmic poly(A)⁺ RNA from N-hydroxy-AAF treated rats showed reduced capacity to stimulate protein synthesis in wheat germ lysates compared with similar preparations from DMSO-injected control rats. The rapid inhibition of protein synthesis by N-hydroxy-AAF may be an important contributing factor to other toxic effects of the carcinogen, including the inhibition of rRNA synthesis.     

Effects of nicotine and vitamin E on glucose 6-phosphate dehydrogenase activity in some rat tissues in vivo and in vitro

Effects of nicotine, and nicotine + vitamin E on glucose 6-phosphate dehydrogenase (G-6PD) activity in rat muscle, heart, lungs, testicle, kidney, stomach, brain and liver were investigated in vivo and in vitro on partially purified homogenates. Supplementation period was 3 weeks (n = 8 rats per group): nicotine [0.5 mg/kg/day, intraperitoneal (ip)]; nicotine + vitamin E [75 mg/kg/day, intragastric (ig)]; and control group (receiving only vehicle). The results showed that nicotine (0.5 mg/kg, ip) inhibited G-6PD activity in the lungs, testicle, kidney, stomach and brain by 12.5% (p < 0.001), 48% (p < 0.001), 20.8% (p < 0.001), 13% (p < 0.001) and 23.35% (p < 0.001) respectively, and nicotine had no effects on the muscle, heart and liver G6PD activity. Also, nicotine + vitamin E inhibited G-6PD activity in the testicle, brain, and liver by 32.5% (p < 0.001), 21.5% (p < 0.001), and 16.5% (p < 0.001) respectively, and nicotine + vitamin E activated the muscle, and stomach G-6PD activity by 36% (p < 0.05), and 20% (p < 0.001) respectively. In addition, nicotine + vitamin E did not have any effects on the heart, lungs, and kidney G-6PD activity. In addition, in vitro studies were also carried out to elucidate the effects of nicotine and vitamin E on G-6PD activity, which correlated well with in vivo experimental results in lungs, testicles, kidney, stomach, brain and liver tissues. These results show that vitamin E administration generally restores the inactivation of G-6PD activity due to nicotine administration in various rat tissues in vivo, and also in vitro.     

Effects of nicotine and vitamin E on glucose 6-phosphate dehydrogenase activity in some rat tissues in vivo and in vitro

Effects of nicotine, and nicotine + vitamin E on glucose 6-phosphate dehydrogenase (G-6PD) activity in rat muscle, heart, lungs, testicle, kidney, stomach, brain and liver were investigated in vivo and in vitro on partially purified homogenates. Supplementation period was 3 weeks (n = 8 rats per group): nicotine [0.5 mg/kg/day, intraperitoneal (ip)]; nicotine + vitamin E [75 mg/kg/day, intragastric (ig)]; and control group (receiving only vehicle). The results showed that nicotine (0.5 mg/kg, ip) inhibited G-6PD activity in the lungs, testicle, kidney, stomach and brain by 12.5% (p < 0.001), 48% (p < 0.001), 20.8% (p < 0.001), 13% (p < 0.001) and 23.35% (p < 0.001) respectively, and nicotine had no effects on the muscle, heart and liver G6PD activity. Also, nicotine + vitamin E inhibited G-6PD activity in the testicle, brain, and liver by 32.5% (p < 0.001), 21.5% (p < 0.001), and 16.5% (p < 0.001) respectively, and nicotine + vitamin E activated the muscle, and stomach G-6PD activity by 36% (p < 0.05), and 20% (p < 0.001) respectively. In addition, nicotine + vitamin E did not have any effects on the heart, lungs, and kidney G-6PD activity. In addition, in vitro studies were also carried out to elucidate the effects of nicotine and vitamin E on G-6PD activity, which correlated well with in vivo experimental results in lungs, testicles, kidney, stomach, brain and liver tissues. These results show that vitamin E administration generally restores the inactivation of G-6PD activity due to nicotine administration in various rat tissues in vivo, and also in vitro.     

The synthesis of murine ferrochelatase in vitro and in vivo.

Ferrochelatase (protohaem ferro-lyase, EC 4.99.1.1), the terminal enzyme of the haem-biosynthetic pathway, is an integral membrane protein of the mitochondrial inner membrane. When murine erythroleukaemia cells are labelled in vivo with [35S]methionine, lysed, and the extract is immunoprecipitated with rabbit anti-(mouse ferrochelatase) antibody, a protein of Mr 40,000 is isolated. However, when isolated mouse RNA is translated in a cell-free reticulocyte extract, a protein of Mr 43,000 is isolated. Incubation of this Mr 43,000 protein with isolated mitochondria resulted in processing of the Mr 43,000 precursor to the Mr 40,000 mature-sized protein. Addition of carbonyl cyanide m-chlorophenylhydrazone and/or phenanthroline inhibits this processing. These data indicate that ferrochelatase, like most mitochondrial proteins, is synthesized in the cytoplasm as a larger precursor and is then translocated and processed to a mature-sized protein in an energy-required step.