Effects of hypothyroidism on RNA synthesis in the adult rat brain

In this study we investigated the effects of hypothyroidism on adult brain RNA synthesis. Our data show that in the cerebral hemispheres of hypothyroid rats there is a decrease in microsomal RNA content and microsomal [³H]uridine incorporation. Sucrose gradient analysis revealed that these changes are mainly associated with free ribosomes and subunits and reflect changes in rRNA. The above changes are accompanied by a decrease in RNA polymerase I activity. All of the above mentioned changes returned to normal after thyroxine (T₄) treatment. In contrast to RNA polymerase I, RNA polymerase II activity was not affected. However, electrophoretic analysis of the in vitro poly(A)⁺RNA translation products revealed that hypothyroidism affects a few mRNAs. These results indicate that thyroid hormones have a role in adult brain tissue metabolism.     

Inhibition of isoproterenol-induced DNA and RNA synthesis in rat parotid and pancreas following removal of submandibular-sublingual glands

Summary [³H] thymidine incorporation into DNA of the parotid (PA) gland of adult and 20-day-old rats and into DNA of the pancreas (PANC) of 20-day-old rats was increased markedly following a 2-day regimen of isoproterenol (ISO) administration. However, when the submandibular-sublingual (SM-SL) glands had been removed just prior to initiation of the ISO injections, the [³H] thymidine incorporation into PA and PANC was inhibited, and cpm/mg protein of these organs was even lower than that of organs of untreated rats with SM-SL glands present. Removal of the PA glands just prior to initiation of the ISO regimen had no effect on the ISO-induced [³H] thymidine incorporation into DNA of PANC but partially inhibited that of the submandibular (SM) gland. It is suggested that the inhibitory effects on DNA and RNA synthesis that follow removal of SM-SL glands are attributable to the growth factors (epidermal growth factor and nerve growth factor) found in the rat SM gland. These factors appear to regulate normal DNA synthetic activity of exocrine glands as well as ₁-adrenoceptor mediated DNA synthesis. Cellular hypertrophy induced by the ISO was less markedly affected by absence of the SM glands, but a partial inhibition of [³H] uridine incorporation into RNA of PA of adult rats also occurred when SM-SL glands were removed prior to initiation of the ISO-regimen.     

Effects of dietary selenium on biochemical composition of rat testis.

Treatment of rats with selenium (6 and 8 ppm in diet) for 6 and 9 weeks resulted in decrease in testicular protein, phospholipid content and LDH activity and an increase in the lipid, cholesterol content and activity of ACP and ALP. These alterations have been discussed in relation to interference of selenium in various metabolic processes of testis. It seems that selenium affects the oxido-reductase activity of glutathione and resulting in oxidative damage to testis.     

Effects of long-term selenium yeast supplementation on selenium status studied in the rat

To investigate the selenium status during long-term dietary supply of selenium yeast, 30-day-old male rats were fed for 379 days a methionine-adequate low-selenium diet supplemented with 0.2 mg Se/kg (selenium-adequate diet) or 1.5 mg Se/kg (high-selenium diet) in the form of selenium yeast that contained 60% of the element as l-selenomethionine. Their selenium load was determined at several intervals by neutron activation analysis of the selenium concentrations in the main selenium body pools, skeletal muscle and liver. After 64 days the tissue selenium concentrations plateaued in both groups and then stayed at that level. Compared with the selenium-adequate group, elevated tissue selenium concentrations were found in the high-selenium group, but the increase by a factor of 3.5 in the muscle and by a factor of 2.3 in the liver was smaller than the 7.5-fold increase in the selenium intake. In the selenium-adequate group about 50% of the muscle selenium and 30% of the liver selenium and in the high-selenium group about 85% of the muscle selenium and 70% of the liver selenium were estimated to be present in non-selenoprotein forms. During selenium depletion the liver glutathione peroxidase activity in the high-selenium group remained unaffected for 4 weeks and then decreased more slowly than that in the selenium-adequate group. From these results it can be concluded that selenium incorporated from the selenium yeast diet into non-selenoprotein forms can serve as an endogenous selenium source to maintain selenoprotein levels in periods of insufficient selenium supply.     

Effects of selenium on colonic fermentation in the rat

Studies were conducted to determine the effects of dietary selenium (Se) on the hindgut microbial activity in rats. Selenium was fed asl-selenomethionine (SeMet) at either 0 or 2 ppm Se in the presence or absence of wheat bran (WB, 10%), a known substrate for the enteric microflora. Wheat bran feeding caused the greatest fermentation, measured by the production of short-chain fatty acids (SCFAs) along the entire intestinal tract and feces; however, its effects were suppressed by SeMet in the proximal large bowel, cecum, and colon. Selenium significantly enhanced fermentation in the colon and rectum, but not in the cecum or feces. Selenium was found in association with the bacterial cell fractions of gut contents and feces: 40–46% of the total Se was associated with colonic microbes and 58% in fecal microbes. Increased acetate and reduced butyrate production were driven by the addition of Se regardless of whether WB was fed.     

RNA content and RNA synthesis in diapause and non-diapause eggs of Bombyx mori

Changes in amount of RNA and its synthesis were studied in diapause and non-diapause eggs of Bombyx mori. In non-diapause eggs, the amount of total RNA began to increase at the stage of late gastrula and increased constantly thereafter. The synthesis of total and ribosomal RNA commenced at the onset of gastrulation, and after two days it levelled off. In contrast, the amount of total RNA in diapause eggs did not change essentially, and only a low level of total and ribosomal RNA synthesis was detected. On the other hand, if diapause eggs were activated by hot HCl treatment 24 hr after oviposition, the results obtained were essentially similar to those for non-diapause eggs, except that there was a lag of two days after acid treatment. These findings indicate that a significant control of ribosomal and other RNA occurs in relation to diapause and development.     

Ensuring recovery of intact RNA from rat pancreas

The isolation of intact RNA from rat pancreas is compromised by autolysis and by the presence of endogenous ribonucleases. In order to ameliorate recovery we systematically investigated available RNA extraction methods and paid particular attention to the influence of frozen storage and ribonuclease inhibition strategies on overall yield and quality of RNA. Modifications to the basic procedure of Chomczynski and Sacchi (1987) are described which allow, reproducibly, to obtain rat pancreatic RNA suitable for Northern blot hybridization, RT-PCR, and differential display analysis.