Renal sugar transport in the winter flounder. I. Renal clearance studies

The renal handling of several sugars was examined using clearance techniques in the winter flounder Pseudopleuronectes americanus. The nonmetabolizable sugar alpha-methyl-D-glucoside was extensively reabsorbed, with consequent accumulation in renal tissue to nearly twice plasma concentration. Both glucose and phlorizin abolished reabsorption and reduced tissue-to-plasma ratios (T/P). D-Galactose was reabsorbed. However, the T/P for free galactose was only 0.6 (total sugar was 1.7). Glucose and phlorizin produced only a transient decrease in reabsorption and no change in T/P. 2-Deoxy-D-glucose showed neither net reabsorption nore secretion. Nevertheless, kidney T/P were inexcess of 6 for total sugar and 1.2 for free sugar, indicating entry through the peritubular face of the tubule. Neither glucose nor phlorizin altered 2-deoxy-D-glucose clearance, but both reduced T/P for total sugar (2.4) and free sugar (0.7). Thus, several systems govern the handling of these sugars at the luminal membrane of the renal tubule, just as has been previously demonstrated at the peritubular membrane in this species.

Surface sulphydryl groups and phagocytosis-associated oxidative metabolic changes in human polymorphonuclear leucocytes

The role of surface sulphydryl (-SH) groups of human polymorphonuclear leucocytes on phagocytosis-associated oxidative metabolic changes was studied. p-Chloromercurybenzene sulphonic acid, a surface -SH group inhibitor, had no effect on phagocytosis, superoxide production during phagocytosis, or killing of S. aureus by the leucocytes, while it inhibited phagocytosis-associated stimulation of hexose monophosphate pathway activity and H2O2 production. In contrast, N-ethylmaleimide, which inhibits both intracellular and surface -SH groups, inhibited phagocytosis-associated oxidative metabolic changes. p-Chloromercurybenzene sulphonic acid also inhibited the stimulation of hexose monophosphate pathway activity by exogenous H2O2, suggesting a regulatory role of plasma membrane on the pathway's activity in human polymorphonuclear leucocytes. The results also suggest that: (I) superoxide production is the primary event of oxidative metabolic changes during phagocytosis, (2) superoxide plays an important role in the killing of S. aureus, and (3) the hexose monophosphate pathway plays a primary role in producing NADPH for H2O2 production from superoxide.

Hyporesponsiveness to glucoprivation during postnatal period in the rat

2-Deoxy-D-glucose (2-DG), a glucose analogue, blocks glycolysis and induces intracellular glucoprivation. In the adult rat intraperitoneal administration of 2-DG or its injection into the lateral ventricle (IVT) of the brain induces hyperglycemia which is divorced from a rise in plasma insulin (IRI). In the present study, responsiveness to 2-DG-induced glucoprivation, after central or intraperitoneal injection of the drug, was studied in rats of 7, 14, 21, and 28 days of age and compared to that of the adult rat (50 days old). In 7-, 14-, 21-, and 28-day-old rats, the overall blood glucose (BG) response to IVT-injected 2-DG was equivalent to 4, 3.3, 17, and 33%, respectively, of the BG response present in the adult rat. Following intraperitoneal injection of 2-DG , the BG response evoked in the same age groups corresponded to 27, 31, 41, and 93%, respectively, of the adult response. Base-line plasma IRI levels were significantly lower in pups than in adults and increased progressively with age, but no difference was present in IRI levels between 2-DG-treated and control pups whether the 2-DG was given via the laterl ventricle or intraperitoneally. These results demonstrate the presence in the infant rat of clear-cut hyporesponsiveness to 2-DG-induced glucoprivation. The different response pattern between experiments involving central and peripheral 2-DG administration supports the existence of separate peripheral glucoreceptors for 2-DG and their earlier ontogenic activation. Since the infant mammal glucose is of minor relevance as an energy substrate, an interrelationship appears to be present between requirements for fuel(s) and homeostatic response to fuel deprivation.