Recombinant human granulocyte colony-stimulating factor accelerates regeneration after T-2 toxin-induced hemopoietic injury and lessens lethality in mice.

The effects of rhG-CSF on T-2-induced leukopenia and lethal toxicity in mice were investigated. First, T-2 was administered by gavage to adult male mice at a dose of 3 mg/kg b.w. daily for 7 days, and rhG-CSF was given i.p. in daily dose of 10 or 30 micrograms/kg b.w./day, beginning on the 2nd day, for 5 days. The peripheral WBC of mice receiving T-2 alone was decreased to one fourth of control counts, and bone marrow (BM) cell counts were also markedly diminished. The administration of rhG-CSF prevented those T-2-induced depressions. Histologically, the delation of the hematopoietic cells from BM and spleen of mice given T-2 was remarkably counteracted by administration of rhG-CSF. In the other experiment, rhG-CSF was injected i.p. for 5 days beginning on the next day of the 7-day T-2 administration. The recovery of WBC and BM cell counts was hastened by rhG-CSF reaching the control level in 6 days, and differential leukocyte analysis revealed an increase of neutrophils. Furthermore, simultaneous administration of rhG-CSF depressed the T-2-induced lethal toxicity, dose-dependently. The results revealed that rhG-CSF possesses a potent ability to protect T-2-induced leukopenia and lethality in mice, and it could be as an antidote against T-2 and related trichothecene-induced acute intoxication.

Relationship of protein synthesis to mRNA levels in the liver of chicks under various nutritional conditions.

The rate of liver protein synthesis in vivo and hepatic messenger ribonucleic acid (mRNA) levels were measured to examine the mechanisms regulating liver protein synthesis in chicks under various nutritional conditions. Fractional synthesis rate (FSR) of liver protein was measured by using a large dose injection of L-[4-3H]phenylalanine. Poly(A)+RNA was extracted as mRNA from total RNA using poly(U)-Sepharose 4B affinity chromatography. The influence of varying dietary protein levels (0-60%) on protein synthesis and mRNA concentration in the liver of chicks was examined. Both FSR (%/d) and absolute synthesis rate (ASR, mg/d) of liver protein increased with increasing dietary protein levels from 0 to 20% (the dietary protein requirement), whereas when dietary protein increased from 20 to 40%, both rates decreased significantly. This change was accounted for by changes in RNA concentration (RNA:protein ratio) and hepatic mRNA content. Second, the time course of changes in liver protein synthesis and hepatic mRNA content were measured in force-fed chicks that had been deprived of food for 2 d. Liver protein synthesis (FSR) was significantly greater 30 min after refeeding compared with that of unfed chicks. Liver protein synthesis (FSR) correlated with the activity of RNA to synthesize protein (r = 0.61, P < 0.001), and ASR was correlated with hepatic mRNA content (r = 0.37, P = 0.030). Third, experimental diets containing individual nutrients were force-fed to chicks after 2 d of food deprivation. When chicks were refed carbohydrate and protein diets, liver protein synthesis (FSR) tended to be greater by 24% (P = 0.063) and 22% (P - 0.075) at 30 min after refeeding compared with that of unfed chicks, respectively. These findings indicate that changes in the rate of liver protein synthesis in vivo due to the alteration in nutritional conditions are, at least partially, accounted for by not only RNA concentration and the activity of RNA synthesizing protein but also hepatic mRNA levels.

Relationship of protein synthesis to mRNA levels in the muscle of chicks under various nutritional conditions.

The relationship between the rate of protein synthesis and the level of messenger RNA (mRNA) in the breast muscle (pectoralis major) was studied to examine the mechanisms regulating muscle protein synthesis in chicks under various nutritional conditions. The fractional synthesis rate (FSR) of protein was measured by a large-dose injection of L-[4-3H]phenylalanine. Poly(U)-Sepharose 4B affinity chromatography was used to extract Poly(A)+ RNA as mRNA. The first study examined the effect of dietary protein levels (0-60%) on protein synthesis rate and the contents of mRNA and total RNA. The fractional synthesis rate increased with increasing dietary protein levels from 0 to 20%. When chicks were fed high protein diets (40 and 60% of dietary protein), both the FSR and absolute synthesis rate (ASR) of protein were reduced compared with the 20% protein group. Multiple regression analysis indicated that for graded dietary protein levels below the dietary protein requirement, the response of muscle protein synthesis is largely regulated by variation in the ASR per unit RNA (the efficiency of RNA in synthesizing protein). At dietary protein levels above 20%, synthesis rates are also related to changes in the RNA:mRNA ratio (ribosome number relative to mRNA), the mRNA:DNA ratio (mRNA availability) and the DNA:protein ratio (DNA concentration). When chicks were food deprived for 2 d, FSR was reduced to about half that of well-fed controls. Upon refeeding of these chicks with the control diet, the FSR returned to the normal level within 0.5 h. When food-deprived chicks were refed with protein, carbohydrate or fat alone, the FSR returned to the control level within 0.5 h after consumption of each nutrient. The increase in muscle protein synthesis of unfed chicks following refeeding of various nutrients was explained by an increased ASR per unit RNA. Our results suggest that nutrient intake can change muscle protein synthesis rates in chicks largely by altering the ASR per unit RNA, in some cases associated also with changes in the levels of RNA, mRNA and DNA.

The effect of fasting and refeeding on total messenger ribonucleic acid content in the liver of chicks.

1. The effect of 3-days fasting and the subsequent 3-days refeeding on total messenger ribonucleic acid (mRNA) content in the liver of chicks was investigated. 2. Body weight and liver weight were decreased by fasting, and were increased by refeeding to higher than initial values. 3. There was no influence of fasting and refeeding on RNA and mRNA contents per unit liver weight. 4. Total RNA content in the liver was decreased by fasting and was increased by refeeding to higher than the initial level. Fasting tended to reduce total mRNA content in the liver, and the following refeeding increased it significantly up to the initial level.