Bidirectional transport of glutamine across the cell membrane in rat liver.

Hepatocytes isolated from fed rats were used to investigate glutamine transport. Glutamine transport appears as a composite process involving at least two saturable components. The Na+-dependent component probably represents the entry through the N system. The Na+-independent component was also inhibited by histidine and exhibited trans-stimulation, suggestive of a facilitated diffusion process. Kinetic parameters for both systems suggest that facilitated diffusion only plays a minor role in glutamine influx. In contrast, the Km for glutamine efflux was consistent with a physiological role of the facilitated-diffusion component in glutamine release. In Na+ medium, relatively constant distribution ratios (about 8) between intra- and extra-cellular concentrations were observed, with external glutamine ranging from 0.5 to 5 mM. The present observations suggest that glutamine influx might largely be mediated by the N system, whereas facilitated diffusion allows hepatocytes to release glutamine when intracellular concentrations are elevated. The physiological consequences of this bidirectional transfer of glutamine across the liver cell membrane is discussed.     

Regulation of lipogenesis in vivo by glucose availability and insulin secretion in maternal and foetal tissues during late gestation in the rat. Effect of glucose intubation, streptozotocin-induced diabetes and starvation.

Administration of an oral load of glucose did not change the rate of lipogenesis in maternal liver during late gestation. However, streptozotocin-induced diabetes or starvation decreased maternal liver lipogenesis at 20-22 days of gestation. Glucose intubation, on the other hand, increased foetal lipogenesis at 21-22 days. In addition, maternal starvation decreased foetal lipogenesis and plasma insulin concentration. However, chronic hyperglycaemia induced by streptozotocin administration to the mother did not change foetal liver lipogenesis.     

Energy metabolism of medium-chain triglycerides versus carbohydrates during exercise

Medium-chain triglycerides (MCT) are known to be rapidly digested and oxidized. Their potential value as a source of dietary energy during exercise was compared with that of maltodextrins (MD). Twelve subjects exercised for 1 h on a bicycle ergometer (60% VO2 max), 1 h after the test meal (1MJ). The metabolism of MCT was followed using 1-13C-octanoate (Oc) as tracer and U-13C-glucose (G) was added to the 13C-naturally enriched MD. After MCT ingestion no insulin peak was observed with some accumulation of ketone bodies (KB), blood levels not exceeding 1 mM. Total losses of KB during exercise in urine, sweat and as breath acetone were small (less than 0.2 mmol X h-1). Hence, the influence of KB loss and storage on gas exchange data was negligible. The partition of fat and carbohydrate utilization during exercise as obtained by indirect calorimetry was practically the same after the MCT and the CHO meals. Oxidation over the 2-h period was 30% of dose for Oc and 45% for G. Glycogen decrements in the Vastus lateralis muscle were equal. It appears that with normal carbohydrate stores, a single meal of MCT or CHO did not alter the contribution of carbohydrates during 1 h of high submaximal exercise. The moderate ketonemia after MCT, despite substantial oxidation of this fat, led to no difference in muscle glycogen sparing between the diets.     

Vasopressin-immunoreactive cells in the dorsomedial hypothalamic region,medial amygdaloid nucleus and locus coeruleus of the rat

Summary Recently, the existence of a vasopressin-immunoreactive cell group was described in the bed nucleus of the stria terminalis (van Leeuwen and Caffé 1983). In the present investigation additional nuclei containing vasopressin-immunoreactive cells were found, after colchicine pretreatment, in the dorsomedial hypothalamus, medial amygdaloid nucleus and the locus coeruleus.Vasopressin-immunoreactive cells in the dorsomedial hypothalamus and medial amygdaloid nucleus are small (8–14 m and 10–14 m, respectively), while those in the locus coeruleus are medium-sized (20–25 m). Incubation with anti-bovine neurophysin II and anti-rat neurophysin revealed staining of the same cell group in the above-mentioned areas. None of these cell groups show stained cells after incubation with anti-oxytocin and anti-bovine neurophysin I. When sections of the homozygous Brattleboro rat, which shows a deficiency in vasopressin synthesis, are incubated with anti-vasopressin, anti-bovine neurophysin II, or anti-rat neurophysin, no immunoreactivity can be observed in these brain regions.The above-mentioned cell groups may contribute to the vasopressinergic innervation of brain sites that have been reported to persist after lesioning of the suprachiasmatic, paraventricular and bed nuclei of the stria terminalis.     

The cell coat of the olfactory epithelium proper and vomeronasal neuroepithelium of the rat as revealed by means of the Ruthenium-red reaction

Summary The apical cell coat of the olfactory epithelium proper and the vomeronasal neuroepithelium of the rat was investigated electronmicroscopically by means of the Ruthenium-red reaction. In the olfactory epithelium proper, the cilia of receptor cells and microvilli of supporting cells possess a cell coat measuring approximately 10 nm in thickness. In the vomeronasal neuroepithelium, the apical cell coat is thicker than in the olfactory epithelium proper. On microvilli of vomeronasal receptor cells the cell coat varies in thickness from 15 to 20 nm, and on microvilli of supporting cells it measures approximately 75 nm. The functional implications of these findings are discussed.A portion of this study was presented at the 6^th European Anatomical Congress in Hamburg. This publication is dedicated to Prof. E. KlikaSupported by the Deutsche Forschungsgemeinschaft (Br 358/5-1).     

Lambda Ig constant region genes are translocated to chromosome 8 in Burkitt''s lymphoma with t(8;22)

By in situ hybridization of normal human chromosomes with a cloned genomic probe specific for the constant region of the lambda immunoglobulin genes, band 22q11 was preferentially labelled. In two cell lines with t(8;22) derived from Burkitt's lymphoma a strong signal was noted on the 8q+ chromosome derivative, indicating that the constant region of the lambda Ig gene cluster was translocated from chromosome 22 to chromosome 8. In addition, the signal observed on the 22q- derivative chromosome was stronger than the background in one of the two cell lines tested, but not in the other. The implications are that the break point in chromosome 22 in some cases lies within the Ig gene itself or between clusters of such genes, and that different cases have different break points.