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D F Mettrick

Publications and source records attributed to D F Mettrick.

At least 55 records · Page 3Linked to original sources
PubMed1979

Net fluxes of electrolytes in the rat intestine infected with Moniliformis dubius (Acanthocephala).

The effect of Moniliformis dubius on fluxes of Na+, K+, Cl-, and HCO3-in the rat intestine was determined using a conventional in vivo single-pass perfusion technique. Results for ion and water movements in the uninfected gut were in agreement with previous studies. In the parasitized intestine the jejunal pH was significantly lower than that in control animals, matching the restriction of the parasites to this region of the small intestine. While parasitism did not affect Na+ transport in the distal ileum, Na+ absorption was reduced (pH 7.0), or secretion enhanced (pH 6.0), in the two proximal regions. Cl-absorption was reduced in the distal ileum, but secretion was enhanced in the other two segments. Parasitism also enhanced K+ secretion in all segments. Net H2O absorption was reduced at pH 7.0; at pH 7.0; at pH 6.0 net secretion was also reduced. These changes clearly indicate that a parasite restricted to the jejunum may significantly affect the absorptive and secretory activity of the intestine distal to the site of infection. The results are discussed in the light of current concepts of electrolyte transport. The effect of the parasites on mucosal function distal to their site of attachment is discussed in terms of the release by the parasite of toxin-like substances, changes in the physical-chemical characteristics of the intestinal lumen, and interference with neurohormonal control of gastrointestinal function.

Animals↗
PubMed1977

The phosphoenol-pyruvate branchpoint in adult Hymenolepis diminuta (Cestoda): a study of pyruvate kinase and phosphoenol-pyruvate carboxykinase.

The properties of pyruvate kinase (PK) and phosphoenol pyruvate carboxykinase (PEP CK), two enzymes that determine the preferrential accumulation of either succinate or lactate as endproducts of carbohydrate metabolism, are described in adult Hymenolepis diminuta. PK activity at Vmax and Km levels of PEP was unaffected by ATP, alanine, FDP4, OR H+ ions, but was inhibited by 50% at 6.3 mM L-lactate and 30 mM HCO3. The addition of 30 mM HCO3 increased the Km(PEP) by 6-fold but did not alter the Vmax. The inhibition of PK by HCO3 cannot be explained entirely by an effect of ionic strength, but probably represents a specific modulator-enzyme interaction. Under similar conditions PEP CK was maximally activated. Although L-lactate inhibited PEP CK (Ki(lac) = 1.8 mM), this effector may play a minor role in regulation of PEP flux. These results implicate the poise of the HCO3-:CO2 system as a major determiner of endproduct accumulation in H. diminuta.

Animals↗
PubMed1977

Proximal-distal absorptive gradients in the in vivo intestine of normal and infected (Hymenolepis diminuta: Cestoda) rats.

Using a single-pass perfusion technique, H2O, Na+, Cl-, HCO3-, and glucose absorption were studied in the jejunum and proximal and distal ileum of rats either uninfected or infected with a tapeworm parasite (Hymenolepis diminuta). The effect of parasitization, region of the intestine, type of buffer, and concentration of glucose in the perfusion fluids on the transport data were analyzed by univariate and multivariate techniques. Proximal-distal flux gradients were observed for water and all the solute species studied, as well as for glucose- and bicarbonate-stimulated salt and water transport; there was a decreasing sensitivity to low pH proceeding distally. The major regional differences occurred between the proximal and distal ileum, with the fluxes in the jejunum being similar to those in the proximal ileum. Na+, H2O, and glucose transport decreased, while Cl- absorption increased, proceeding distally. The parasites diminished the rates of absorption of glucose, salt, and water, and altered the flux gradients, particularly the Na+ and HCO3- transport gradients. The differences in the gradients between control and infected animals were related to differential sensitivity of the different transport systems in the various regions of the gut to parasitism.

Animals↗
PubMed1977

HCO3 transport in rat jejunum: relationship to NaCl and H2O transport in vivo.

HCO3- absorption and its association with Na+ absorption has been studied in the rat jejunum in vivo, using a single-pass perfusion technique. The method of disequilibrium pH, the only valid way of demonstrating jejunal H+ secretion, was used to distinguish between an HCO3- pump and H+ secretion as the mechanism of HCO3- absorption. HCO3- stimulated Na+ absorption; Na+ deletion inhibited HCO3 absorption, decreased luminal acidification, and decreased the level of luminal PCO2. These results confirmed an Na+:H+ cation exchange, the possible mechanism of which is discussed in terms of results using other tissues. Na+-dependent HCO3-absorption made up a larger part of total HCO3-absorption as the luminal HCO3-concentrations diminished, although the precise degree of Na+-dependency could not be determined because of the unstirred layer effect. The mechanism of Na+-independent HCO3-absorption was not established, but it was not affected by PD, Cl-, or H2O movements. Glucose-stimulated and HCO3-stimulated Na+ absorption were less than additive. The physiological importance of HCO3-stimulated Na+ absorption in the acidic postprandial jejunum is probably due entirely to the effect of free CO2 in the lumen.

Animals↗
PubMed1977

HCO3- and H+ secretion in rat ileum in vivo.

Replacing Cl- in the perfusion fluids decreased the luminal pH of rat ileum perfused in vivo. Varying the initial pH in Cl- depletion studies indicated an equilibrium pH near 6.6. Na+ depletion in Cl- deleted fluids partially inhibited luminal acidification. Addition of HCO3- accelerated Na+ absorption and decreased Cl- absorption. Luminal PCO2 was increased using fluids buffered to initial pH 6.6, suggesting secretion of HCO3- rather than OH-. The decreased HCO3- secretion using Cl- depleted fluids was not due to an acclerated rate of H+ secretion. Reaffirmed and expanded in this study is an ileal H+ secretory process that is partially related to Na+ absorption and direct HCO3- secretion that is related to Cl- and Na+ absorption.

Acid-Base Equilibrium↗