No abstract

During four days of fasting in rats skeletal muscle protein synthesis fell progressively, whereas skeletal muscle protein breakdown was unchanged until the third and fourth days when it rose dramatically. In contrast, the synthetic rate of smooth muscle protein was unchanged during three days of fasting despite a loss of protein content, indicating an abrupt rise in protein breakdown in this tissue on the first day of fasting which was sustained thereafter. Urinary excretion of N tau-methylhistidine was significantly increased throughout fasting. The concentration of free N tau-methylhistidine in plasma and in muscle tissue was elevated throughout the period of fasting. This elevation was not caused by reduced renal clearance, but appears to have been mainly the result of increased breakdown of N tau-methylhistidine-containing proteins in tissues other than skeletal muscle.

No abstract

Transport of glutamine and other neutral amino acids across the blood-facing membranes of isolated, dually perfused rat jejunum was measured using a paired-tracer isotope-dilution technique. Glutamine, asparagine, histidine, alanine, and leucine showed mutual inhibition of transport. The major component of physiological glutamine transport was saturable (Km = 0.88 +/- 0.15 mM, Vmax = 454 +/- 49 nmol.g-1.min-1; mean +/- SE), stereospecific and Na-independent and appeared to exhibit symmetry of glutamine transport; it most resembled system L. The minor Na-dependent component of glutamine transport resembled system A, i.e., it transported N-methylaminoisobutyric acid (Km approximately equal to 10 microM, Vmax approximately equal to 1.2 nmol.g-1.min-1). At 0.5 mM glutamine transport was insensitive to insulin and glucagon and was unaffected by perfusate pH (7.0-7.8). Glutamine extracted by the jejunum is rapidly utilized; at physiological blood glutamine concentrations the basolateral glutamine-transporter flux may thus not only restrict intestinal glutamine catabolism but also the consequent release of glutamine-derived ammonia (a substrate and stimulant of ureogenesis) into the portal circulation.

Oestrogens protect against ischaemic heart disease in the post-menopausal female by increasing serum concentrations of apolipoprotein (apo) AI and the abundance of high-density lipoprotein particles. In men and experimental male animals, the administration of oestrogen has variable effects on apo AI expression. As the major mode of oestrogen action on target genes involves regulating promoter activity and hence transcription, oestrogen is expected to alter transcription of the apo AI gene. To test this hypothesis, the effect of 17 -oestradiol (E 2 ), on rat apo AI promoter activity in male hepatoma HuH-7 cells, was tested by cotransfecting a reporter template, pAI.474.CAT containing 474 to 7 of the rat apo AI promoter and an oestrogen receptor (ER) expression vector, pCMV-ER. Transfected cells exposed to E 2 showed a dose-dependent decrease in chloramphenicol acetyltransferase (CAT)-activity, with a maximum 91 1·5% reduction at 1 µM E 2 . Deletional analysis of the promoter localized the inhibitory effect of ER and E 2 to site B ( 170 to 144) with an adjacent 5 contiguous motif, site S ( 186 to 171) acting as an amplifier. HuH-7 cell nuclear extracts showed binding activities with both sites S and B, but recombinant human ER did not. Furthermore, nuclear extracts from E 2 -treated HuH-7 cells showed weaker binding activity to site B, but not to site S. In summary, the inhibitory effect of ER and E 2 on rat apo AI gene activity is mediated by a promoter element, site B. This inhibitory effect arises from a mechanism that does not involve direct ER binding to the B-element. The conclusion that E 2 inhibits apo AI transcription was confirmed in vivo. Treatment of male adult Sprague-Dawley rats with up to 200 µg E 2 for 7 days decreased apo AI protein and hepatic mRNA by 72 21% and 68 1·4% respectively. Results of 'run-on' transcription of the apo AI gene in isolated hepatic nuclei showed a 55% decrease in hormone-treated male rats. These findings suggest that E 2 exerts primarily an inhibitory effect within male hepatic nuclei.