The effect of hyperthermia on ornithine decarboxylase activity in different rat tissues

Non-thermal exposure to radiofrequency energy from digital wireless phones does not affect ornithine decarboxylase activity in L929 cells

L929 murine fibroblast cells were exposed to radiofrequency (RF) radiation from a time division multiple access wireless phone operating at 835 MHz frequency to determine the effect of RF-radiation energy emitted by wireless phones on ornithine decarboxylase (ODC) activity in cultured cells. Exposure was for 8 h to an average specific absorption rate (SAR) from <1 W/kg up to 15 W/kg. After exposure, cells were harvested and ODC activity was measured. No statistically significant difference in ODC activity was found between RF-radiation-exposed and sham-exposed cells at non-thermal specific absorption rates. At SARs which resulted in measurable heating of the medium, a dose-dependent decrease in enzymatic activity was observed and was shown to be consistent with a comparable decrease caused by non-RF-radiation heating. Thus we observed only the well-known enzyme inhibition due to heating, rather than the previously reported enhancement attributed to RF-radiation exposure.

Effects of potassium deficiency on potassium, polyamines and amino acids in mouse tissues

Sexual dimorphism in potassium content was found in plasma, kidney, heart and skeletal muscle of CD1 mice. We observed that feeding mice with a K(+)-deficient diet had an uneven and gender-dependent effect on organ weight and tissue potassium concentrations. Treatment produced a marked decrease in plasma, pancreas and skeletal muscle K(+) levels in both sexes, and a reduction in kidney, liver and heart potassium concentrations in females. Moreover, K(+) deficiency produced a 2-3-fold increase in the concentrations of cationic amino acids, such as arginine and lysine in both heart and skeletal muscle of the two sexes, a slight increase ( approximately 37%) in renal arginine in the male mice. The concentrations of these amino acids in plasma and other tissues in both sexes remained unaltered. Polyamine levels in heart, liver, skeletal muscle and pancreas from male and female mice were not affected by K(+) deficiency. However, in the male kidney potassium deficiency was accompanied by an increase of putrescine and spermidine concentration, and a reduction of putrescine excretion into the urine, even though renal K(+) concentration was not significantly affected and ornithine decarboxylase activity was dramatically decreased. The general lack of correlation between tissue potassium decrease and the increase in organic cations suggests that it is unlikely that the changes observed could be related with an attempt of the tissues to compensate for the reduction in cellular positive charge produced by the fall in K(+) content. The mechanisms by which these changes are produced are discussed, but their physiological implications remain to be determined.

Inactivation of ornithine decarboxylase by intermediates of tyrosinase-catalyzed reaction

1. Intermediates in the process of melanin synthesis formed through oxidation of catechols by tyrosinase produced the inactivation of ornithine decarboxylase (ODC), a key enzyme in the polyamine biosynthesis pathway. 2. The inactivation was dependent on the substrate used (dihydroxybenzylamine > L-3,4-dihydroxyphenylalanine > L-tyrosine) and on the concentration of intermediate produced rather than on the rate of formation. 3. Sulfhydryl compounds (dithiothreitol and glutathione) or quinone-reducing agents (ascorbic acid) prevented the inactivation of ODC; L-ornithine, but not other amino acids, also protected partially ODC. The results suggest that different cysteine residues in ODC molecule are implicated in the inactivatory event. 4. When 14C-labeled catechols were used, numerous polypeptides resulted labeled, showing that the reactive quinones formed as intermediates in the process of melanin biosynthesis bind covalently to many cellular proteins.

Effects of L-acetylcarnitine (LAC) on the post-injury recovery of mouse spermatogenesis monitored by flow cytometry. 2. Recovery after hyperthermic treatment

It has been demonstrated that L-acetylcarnitine (LAC) can enhance the recovery of spermatogonial cells after X-ray damage. In the present work, the effects of LAC on the recovery processes of mouse spermatogenesis after local acute hyperthermia (42 degrees C, 1 hour) was investigated. LAC was administered i.p. (100 mg/kg body weight) every other day for four weeks after heat treatment. At intervals of 8, 14, 21, 28, 35, 40, 45, and 60 days after hyperthermic treatment, testes were weighed and their DNA content analysed by flow cytometry; the round spermatid fraction was found to be higher at 45 days in the LAC-treated animals than in controls (P less than 0.01). Correspondingly, at the same experimental point, the animals without LAC administration showed a lower testicular weight (P less than 0.05). Combined with histological analysis, these results suggest a more rapid recovery of normal spermatogenesis after physical insult with LAC treatment.

Different turnover of rat fetal and placental ornithine decarboxylases

The half-lives of ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) have been studied in fetuses and placentas from 18-day-pregnant rats. While the turnover of fetal and placental SAMDC were slightly different (t1/2 = 38 and 75 min, respectively) the half-lives of fetal and placental ODC differed markedly. T1/2 of fetal ODC was 15 min, similar to other mammalian ODCs, but placental ODC showed a relatively high half-life, about 160 min. According to that, placental ODC was more resistant than the fetal enzyme to in vivo hyperthermic treatment (40 degrees C, 1 h). Our results suggest that the degradative mechanisms for ODC in rat placenta could be regulated differently to those in other mammalian tissues.

Expression pattern of the genes for different members of the heat-shock protein 70 family, ornithine decarboxylase, and c-Ha-ras during the early stages of hepatocarcinogenesis

Northern blot analysis with specific probes indicates that, in the liver of normothermic rats under the carcinogenic regimen of Solt and Farber (Nature 263:701, 1976), diethylnitrosamine (DEN), 2-acetylaminofluorene (AAF), and partial hepatectomy (PH), either alone or in combination, do not induce the expression of the heat-shock protein 70 (hsp70) gene family. On the contrary, the inducibility of hsp70 mRNAs in the liver of heat-shocked animals is maintained throughout the treatment, as it is in nodules that are found in the liver 2 weeks posttreatment. The steady-state level of the constitutive hsp70-related cognate protein (hsc73) mRNA, which is known to be particularly high in fast-growing cells, increases above the normal level only during liver regeneration, stays at a high level up to 8 days after hepatectomy, independently of any associated exposure to carcinogenic chemicals, and is practically unchanged in the nodules. Ornithine decarboxylase mRNA increases only in livers of normothermic rats at 16 h of regeneration. The expression of the c-Ha-ras oncogene increases slightly, but steadily, during the carcinogenic treatment and persists at a high level when other changes have subsided.

Effect of exertion on the stimulation of ornithine decarboxylase activity by growth hormone in rats

To investigate the effect of stressful stimulation on tissue responsiveness to growth hormone (GH), we examined ODC activity as a measure of hepatic sensitivity to the hormone during forced exertion in rats. GH caused a 15-fold increase in ODC activity in the livers of resting rats at 3 hours after the injection of hormone. Forced walking in a rotating cylinder enhanced the effect of GH on ODC activity by up to 66% above the effect in resting rats, and this enhancement was positively related to the speed of rotation of the cylinder. These results suggest that tissue hypersensitivity to GH stimulation is a consequence of forced exertion. This hypersensitivity to GH would tend to compensate for the inhibitory effects of forced exertion on GH secretion in rats.