Influence of nitrate and nitrite on electrolyte transport by the rat small and large intestine

1. The influence of nitrate and nitrite on net absorption of electrolytes (Na+, K+, Cl-) and water from ligated loops was studied at various intestinal sites in rats. 2. Nitrate strikingly reduced Cl- absorption in rat proximal and distal colon, whereas Na+ absorption was reduced only moderately. Nitrite also reduced Cl- absorption in the colon. 3. Nitrate showed no significant effect on electrolyte absorption in the small intestine. 4. The results suggest that Cl-/HCO3- on exchange is the major route of Cl- absorption in the colon, whereas this mechanism seems not to be of importance for Cl- absorption by the small intestine.     

Histophysiological studies on the corpus allatum of Leucophaea maderae

Summary The structural differences between active and inactive corpora allata, visible under the light microscope, become more pronounced under the electron microscope. Aside from differences in cellular and nuclear diameters, and nuclearcytoplasmic ratios, there are qualitative characteristics in ultrastructural organization.The cytoplasm of active corpus allatum cells contains numerous sinuous mitochondria, distinct Golgi elements, ergastoplasmic units with a tendency to form whorls, agranular cytomembranes, and free ribosomes. Pleomorphic inclusion bodies resembling lysosomes are more or less numerous. The plump, ovoid nuclei frequently show two prominent nucleoli whose components may form a meshwork harboring chromatin.The marked reduction in the amount of cytoplasm occurring during the organ's return to inactivity is accompanied by a decrease in the number, and a change in the appearance, of some cytoplasmic organelles. The mitochondria tend to be smaller, and the ergastoplasm is reduced to scattered wisps of ribosome-studded membranes. Nuclei of inactive cells have smaller diameters than those of active ones.In all stages of activity, cell boundaries are clearly visible. As a result, the corpus allatum cell can now be characterized as a discrete unit of epithelioid character and rather complex shape. The plasma membrane may become folded when the cellular content shrinks to the inactive level. Aside from changing outlines, all corpus allatum cells have long, gradually thinning processes. These penetrate deeply into the parenchyma where they interlock with those of other cells; many processes eventually seem to reach the surface of the gland where the secretory products are released into the hemolymph. These have to pass through an acellular connective tissue layer that shares tinctorial and ultrastructural properties with those of a boundary (or basement) membrane.This stromal element forms a sheath and branching processes that extend into and permeate the parenchyma. It seems to represent a system of channels, not only for the release of secretory and other cellular products, but for the entry of nutrients and perhaps chemical messenger substances.Neurosecretory material can be observed in the form of structurally distinctive elements, i.e., as electron-opaque granular inclusions within axon terminals that become contiguous with corpus allatum cells.No definite statement can be made on the basis of the present study about the nature of the corpus allatum hormone or hormones, except that the ultrastructural criteria indicative of proteinaceous secretion, such as the appearance of secretory granules in spatial relation with Golgi elements, seem to be missing in the corpora allata of Leucophaea.Supported by Research Grants A-3984 and B-2145 from the U.S.P.H.S.     

Neurosecretion. XIII. The ultrastructure of the corpus cardiacum of the insect Leucophaea maderae

Summary The corpora cardiaca of Leucophaea maderae contain two classes of intrinsic elements, parenchymal and interstitial cells. The parenchymal cells produce a secretory material first visible in the Golgi zones of the perikarya in the form of distinct electron-opaque granules. These undergo changes (gradual loss of electron-density, emergence of internal structure) as they accumulate in cellular processes.The parenchymal cells are best classified as neuroglandular elements since, in addition to secretory inclusions, they possess characteristics of ganglion cells such as axonlike processes, neurotubules, and sheaths. These covers are provided by branches of the second type of intrinsic elements, the interstitial cells. They are non-glandular structures of considerable morphological complexity. In the manner of glial elements, they permeate the entire organ and encapsulate not only the perikarya of parenchymal cells but cellular processes as well.The cytoplasmic processes include a) relatively short ones belonging to parenchymal cells, and b) long axons whose cell bodies lie within the central nervous system. Many of the latter contain electron-opaque granules of the kind found in electron-micrographs of typical neurosecretory cells. These extrinsic granules represent the second category of secretory products stored within the corpora cardiaca. By comparison with the product of the intrinsic gland cells, the neurosecretory granules seem to be fairly stable. Neither type seems to pass through the connective tissue sheath of the corpus cardiacum in the form of discrete granular entities.This sheath, which sends branches into the interior of the corpora cardiaca, has the properties of a basement membrane. It represents a pathway for the exchange of substances between the cellular components of the corpus cardiacum and the surrounding hemocoele.The dual character of the corpus cardiacum, namely that of a storage and release center for extrinsic neurosecretory substances and of an endocrine organ in its own right, is herewith established beyond doubt. The number of secretory products discernible on the basis of their morphology and localization (two size categories of extrinsic and one intrinsic type of granules) does not match the variety of physiologically active principles known at present. The assignment of specific functions to discrete morphological elements must await further studies.Supported by Research Grants A-3984 and B-2145 from the U.S.P.H.S.     

Active pyrimidine absorption by chicken colon

Pyrimidine absorption by chicken large intestine was investigated employing the everted sac and flux chamber techniques. 3H-labelled uracil was used as substrate. The small intestine and the colon unlike the caecum, transported uracil from the mucosal to the serosal surface against a concentration gradient in the everted sac experiments. Furthermore, there was a net transport of uracil from the mucosal to the serosal side of the colon and jejunum in the flux chamber experiments. Uracil transport by the everted colon sacs against a concentration gradient was inhibited when the purine hypoxanthine was present in the incubation medium. Uracil transport by the everted colon sacs was also inhibited under anaerobic conditions and when 2,4-dinitrophenol was present in the incubation medium. Replacing the Na+ ions of the incubation medium by Li+ ions also caused an inhibition of uracil transport. It is concluded from these results that uracil (and probably other pyrimidines) are absorbed from the chicken colon by a Na+ ion-dependent active transport process having also an affinity for purines.     

Neurosecretion XVII. Experimentally induced release of neurosecretory material by exocytosis in the insect Leucophaea maderae

Summary In the corpora cardiaca of the insect Leucophaea the administration of serotonin elicits ultrastructural features indicative of the extrusion of neurosecretory material by exocytosis. The response to the stimulus and the process of extrusion seem to occur at considerable speed. Nearly all of the 30 test animals, fixed at various intervals starting as early as 3 min after the injection of the drug, show granules captured at the moment of leaving the axon as well as fully exteriorized secretory material. The fact that many of these granules are much smaller than the typical neurosecretory type speaks for intracellular fragmentation of the latter prior to the discharge of this cellular product. After 25 min or more the extruded electron dense structures show signs of breakdown. The apparent speed of these phenomena accounts for the dearth of omega-type configurations observed in unstimulated specimens of this species. The possible relationship between the membrane phenomena involved in exocytosis and the transient protrusions of bounding membranes of neurosecretory granules described in earlier papers remains to be clarified.Supported by N.S.F. research grant BMS 74-12456     

Effects of glutathione and of cysteine on intestinal absorption of selenium from selenite

The influence of glutathione (1 mmol/L) (GSH) on in vitro mucosal uptake and in vivo absorption of⁷⁵Se-labeled selenite (10 μmol/L) was investigated in rat jejunum. For comparison, the effect ofl-cysteine (1 mmol/L) on in vivo absorption of⁷⁵Se-labeled selenite was also studied. In the in vitro, uptake experiments, only the mucosal surface was exposed to the incubation medium for 3 min. For the in vivo experiments, a luminal perfusion technique was employed. GSH inhibited in vitro mucosal Se uptake, whereas absorption in vivo was stimulated by GSH.l-Cysteine also stimulated in vivo Se absorption, confirming former in vitro mucosal uptake experiments. Thus, unlikel-cysteine, GSH affected in vitro and in vivo absorption of Se from selenite differently. Enzymatic cleavage of products of the reaction of selenite with GSH occuring more efficiently under in vivo than in vitro conditions may be a prerequisite for the stimulatory effect of GSH on Se absorption. This apparently does not apply to the stimulatory effect of cysteine. Since, GSH occurs in the intestinal lumen under physiological conditions, it may contribute to the high bioavailability of Se from selenite.     

Stimulation of mucosal uptake of selenium from selenite by some thiols at various sites of rat intestine

The influence of several thiols (conc. 1 mmol/L) on mucosal uptake of⁷⁵Se from⁷⁵Se-labeled selenite (conc. 10 μmol/L) across the brush border of rat jejunum and cecum was investigated in vitro using a short-term uptake technique.l-Cysteine (l-Cys) stimulated⁷⁵Se uptake in the mid- and distal jejunum and cecum, but not in the proximal jejunum. The effect was maximal in the distal jejunum.d-Cys was less effective in the jejunum and similarly effective in the cecum.l-Leucine (l-Leu) andl-glutamic acid significantly reduced the stimulatory effect ofl-Cys on Se uptake in the distal jejunum, whereas the respective effect ofd-Cys was not diminished byl-Leu. Cysteamine stimulated mucosal⁷⁵Se uptake at all intestinal sites tested, whereas the effect of mercaptopyruvate was restricted to the distal jejunum. Thioglycolate also enhanced⁷⁵Se uptake in the distal jejunum. The stimulatory effects ofl-Cys, mercaptopyruvate, and thiologlycolate were Na⁺-dependent, whereas the effect of cysteamine also occurred in the absence of Na⁺. Mercaptosuccinate,d-penicillamine, ergothioneine, and thiosulfate did not enhance mucosa⁷⁵Se uptake. It is concluded from these findings that the reaction of some thiols with selenite results in Se compounds that are rapidly absorbed by the intestinal epithelium through various Na⁺-dependent and Na⁺-independent, mechanisms. The high bioavailability of Se from selenite found by others might thus be the result of the presence of thiols in the gastrointestinal tract.     

Endogenous amylin contributes to the anorectic effects of cholecystokinin and bombesin

Previous studies indicated that amylin contributes to the anorectic effects of cholecystokinin (CCK) and bombesin (BBS), possibly by enhancing the release of pancreatic amylin or by modulating their anorectic actions within the central nervous system (CNS). To elucidate the interaction between amylin and CCK or BBS, respectively, we investigated the influence of an IP injection of CCK or BBS on feeding in amylin-deficient mice (IAPP(-/-)). The anorectic effects of CCK and BBS were nearly abolished in IAPP(-/-) mice compared to wildtype (WT) mice (e.g. 20 microg/kg CCK, 1-h food intake: WT/NaCl 0.53 +/- 0.03 g; WT/CCK 0.16 +/- 0.03 g (P < 0.001); IAPP(-/-)/NaCl 0.49 +/- 0.05 g; IAPP(-/-)/CCK 0.39 +/- 0.04 g). Acute amylin replacement restored the anorectic effect of CCK in IAPP(-/-) mice.To find out whether CCK or BBS enhance the feeding-induced release of pancreatic amylin, we injected rats with CCK-8 (0.5-50 microg/kg) or BBS (5 microg/kg) and measured plasma amylin levels after injections. Neither CCK nor BBS increased the plasma amylin level in rats. We suggest that the mediation of the anorectic effects of CCK and BBS by amylin is not dependent on a CCK- or BBS-induced release of pancreatic amylin, but may rather be due to a modulation of their effects by amylin within the CNS.     

Über sekretorisch tätige Zellen im Thalamus von Fundulus heteroclitus L. (Untersuchungen über das Zwischenhirn der Fische II)

Ohne Zusammenfassung     

Absorption of electrolytes and water by the jejunum and colon in milk-fed lambs

Net absorption of electrolytes (Na, Cl, K, Ca) and water from ligated loops was studied at various intestinal sites in milk-fed lambs. The unidirectional fluxes of Na across the intestinal mucosa were also investigated using 22Na. Net Na and water absorption in the mid-jejunum were about two-fold higher than in the proximal and distal jejunum and the colon descendens. With the exception of the proximal jejunum, Na and Cl absorption did not differ significantly. The unidirectional Na fluxes in both directions were much higher in the proximal and mid-jejunum than in the distal jejunum and colon descendens. K was also absorbed most efficiently from the mid-jejunum. In the colon descendens mean net K absorption was about zero. Ca absorption in the upper and mid-jejunum exceeded that of the distal jejunum and colon descendens, where the values were close to zero. The results show that in the whole jejunum of young milk-fed lambs net absorptive fluxes of Na, Cl, K, Ca and water occur, whereas the colon descendens appears to play a role only in Na, Cl and water absorption.