Influence of starvation, surgery, and sepsis on cardiac protein synthesis in rats: effects of parenteral nutrition, glutamine, and growth hormone

Investigation of the cardiotoxic effects of parenteral nutrition in rabbits

INTRODUCTION

Parenteral nutrition (PN) is used for the intravenous delivery of nutrients to patients who cannot take food orally. However, it is not clear whether PN also negatively impacts cardiac tissue. The present empirical study investigated the cardiac effects of PN in rabbits.

METHODS

The effects of PN were examined in three groups of rabbits: animals in the PN + fasting group (n = 14) had been fully fasted before receiving a full PN dose via an intravenous central catheter; the PN + oral feeding group (n = 14) received half of the daily calorie requirement as a half dose of PN via an intravenous central catheter; the third group consisted of controls (n = 14) with full enteral feeding and full enteral fluid intake with no PN and no central venous catheter. At the end of the 10-day study period, the rabbits were subjected to echocardiographic examination and euthanized. Blood and tissue samples were obtained from all groups. DNA was isolated from nucleated blood cells. Tissue samples were examined by both light and electron microscopy, relative telomere length was determined from DNA, and blood samples were analyzed biochemically.

RESULTS

At the end of the study, there were no statistically significant differences in weight change between the three groups. Echocardiography revealed minimally impaired diastolic function in the PN + fasting group compared to the other groups. Biochemical and histopathological analyses, relative telomere length determination, and electron micrographs showed significant cardiac damage in the PN + fasting group but not in the PN + oral feeding group or the control group. The blood biochemical analyses showed hyperglycemia and a low insulin level in the PN + fasting group but not in the other two groups.

CONCLUSIONS

A combination of PN and fasting may damage the cardiac muscle cells of rabbits via a mechanism involving hyperglycemia and oxidative stress. Additional enteral feeding may protect against the destructive effects of PN on cardiac tissue.

The combined effects of glutamine and growth hormone on intestinal anastomosis in the rat intra-abdominal sepsis model

AIM

Intestinal anastomoses are always risky in patients who develop intra-abdominal sepsis. In this study, the effects of combined glutamine and growth hormone (GH) on healing of intestinal anastomosis following intestinal repair in the rat intra-abdominal sepsis was induced.

MATERIAL AND METHODS

Forty Sprague Dawley Albino rats at 10 weeks weighing between 180 and 240 g were included in the study. All the animals were divided into five groups comprising eight rats each. In the control group, no treatment was given in addition to the routine oral nutrition before and after surgery. In the other groups, following surgery, oral glutamine was given at a dose of 1 mg/kg/d in the glutamine group, subcutaneous GH was given at a dose of 1 mg/kg/d in the GH group, and combined glutamine and GH were administered at the same doses in the glutamine + GH group. In rats, a clinical model mimicking intestinal fistula was generated and fistula repair was performed, and the bursting pressure of the repair area and tissue hydroxyproline level of the repair area were calculated.

RESULTS

Compared with the control group, glutamine, GH, and combined groups displayed significantly higher mean bursting pressures and tissue hydroxyproline levels.

CONCLUSION

In order to decrease the risks originating from impaired mechanisms due to intra-abdominal sepsis, and to make anastomosis safer, combined use of glutamine and GH increases the bursting pressure of anastomosis. While the use of either of these two substances alone is effective, combined use makes this effect more prominent.

Effects of endotoxaemia on protein metabolism in rat fast-twitch skeletal muscle and myocardium

BACKGROUND

It is unclear if the rat myocardium undergoes the same rapid reductions in protein content that are classically observed in fast-twitch skeletal muscle during endotoxaemia.

METHODOLOGY/PRINCIPAL FINDINGS

To investigate this further, and to determine if there is any divergence in the response of skeletal muscle and myocardium in the mechanisms that are thought to be largely responsible for eliciting changes in protein content, Sprague Dawley rats were implanted with vascular catheters and administered lipopolysaccharide (LPS; 150 microg kg(-1) h(-1)) intravenously for 2 h, 6 h or 24 h (saline administered control animals were also included), after which the extensor digitorum longus (EDL) and myocardium were removed under terminal anaesthesia. The protein-to-DNA ratio, a marker of protein content, was significantly reduced in the EDL following 24 h LPS administration (23%; P<0.05), but was no different from controls in the myocardium. At the same time point, a significant increase in MAFbx/atrogin-1 and MuRF1 mRNA (3.7+/-0.7- and 19.5+/-1.9-fold increase vs. controls, respectively; P<0.05), in addition to protein levels of alpha1-3, 5-7 subunits of the 20S proteasome, were observed in EDL but not myocardium. In contrast, elevations in phosphorylation of p70 S6K residues Thr(421)/Ser(424), and 4E-BP1 residues Thr(37)/Thr(46) (P<0.05), consistent with an elevation in translation initiation, were seen exclusively in the myocardium of LPS-treated animals.

CONCLUSIONS/SIGNIFICANCE

In summary, these findings suggest that the myocardium does not undergo the same catabolic response as skeletal muscle during early endotoxaemia, partly due to the absence of transcriptional and signalling events in the myocardium typically associated with increased muscle proteolysis and the suppression of protein synthesis.

The effect of protein malnutrition on the capacity for protein synthesis during wound healing

OBJECTIVES

It has been shown that wound healing in the rat is associated with increased protein synthesis at the site of the wound 48 hours after surgical trauma. The aim of the current study was to examine the effect of protein malnutrition prior to abdominal surgery on the capacity for muscle protein synthesis both at the site of the wound and in undamaged abdominal muscle.

DESIGN AND MEASUREMENTS

Thirty-two rats were randomly assigned to a low or high protein diet (3% and 20% casein respectively). After two weeks, half the rats in each group underwent abdominal surgery. Forty-eight hours after the operation all the animals were killed and tissues were analysed for RNA and protein contents.

RESULTS

The capacity for protein synthesis, as indicated by the RNA:protein ratio, was increased at the site of the healing wound. The low protein diet caused a decrease in the capacity for protein synthesis in unoperated animals but did not prevent the increase associated with wound healing.

CONCLUSION

The capacity to increase protein synthesis during wound healing is protected against the effects of malnutrition, indicating that it has a high biological priority.

Glutamine and acute illness

This is a literature review over a time period of the past 2 years concerning glutamine in clinical nutrition. Emphasis is put upon studies of glutamine in clinical settings, but a brief overview of the large range of literature over the role of glutamine in various experimental settings is also included. The most interesting concept for the past 2 years is the suggestion to use plasma glutamine concentration at admission to the intensive care unit as a prognostic marker and as a possible indicator for indication of glutamine supplementation.