Raul A. Wapnir

Oral hydration solutions: Experimental optimization of water and sodium absorption

Eight solutions of potential efficacy for hydration orally, which differed in composition, osmolality, and pH, were tested in an in vivo perfusion system on rat jejunum to assess the rate of water and sodium absorption or secretion. Optimal results were obtained with a preparation of the type recommended by the World Health Organization, containing 60 mEq/L sodium and 111 mM glucose; there was a maximum influx of both water and sodium, which may be ideal for rehydration. It appeared that the critical factor was the molar relationship between glucose and sodium at a 2:1 ratio. Sodium absorption was inversely correlated with glucose concentration in the perfusates. Osmolality and pH may also have a role in the regulation of fluxes across the mucosa. Citrate at concentrations up to 30 mEq/L did not interfere with water absorption. The data presented may thus contribute to a better rationale for the use of orally administered hydration solutions and guidelines for the preparation of more effective ready-to-use solutions.

Alanine stimulation of water and sodium absorption in a model of secretory diarrhea.

We investigated the effectiveness of L-alanine (Ala) addition to oral hydration solutions (OHSs) during secretory conditions induced by ileal instillation of 10 m M theophylline in anesthetized rats using a perfusion procedure, and monitoring water and sodium transport. Ala was added to two hypotonic OHSs in which the sodium:glucose ratio was 2:1, and compared with the OHS recommended by the World Health Organization (WHO), which has a sodium:glucose ratio of 0.81:1. Theophylline had the expected secretory effect on water and sodium absorption in the WHO-recommended OHS, and on sodium transport in a formula containing 60 m M sodium and 30 m M glucose. However, an OHS with 90 m M sodium and 45 m M glucose canceled the secretory effect of the-ophylline and yielded a greater rate of net water absorption than the WHO formula. Addition to this solution of either 15 or 30 m M Ala enhanced water and sodium absorption of both control and theophylline-treated rats. In the hypotonic OHS with 60 m M sodium and 30 m M glucose, Ala had little effect on both sodium and water transport. Therefore, the data support the view that Ala added to solutions with 90 m M sodium, containing sufficient glucose to maintain a sodium:glucose ratio of not less than 2:1, is most effective at compensating fluid and sodium losses under secretory conditions. Ala presumably exerts its sodium-sparing effect because of its cotransport with sodium and the consequent water influx into the intestinal cells.

Regulation of gluconeogenesis by glycerol and its phosphorylated derivatives

Glycerol, glycerol-3-phosphate (G3P), and dihydroxyacetone phosphate (DHAP) were evaluated as inhibitors of gluconeogenesis on rat liver enzymes in vitro, and for their effects on glucose formation in vivo in well-nourished and malnourished rats. DHAP was more potent as an inhibitor than G3P on fructose-1,6-diphosphatase (FDPase), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G6Pase). The I50 for DHAP was 2, 8, and 9 x 10(-3) M, respectively. No effect was observed on rat liver pyruvate carboxylase (PC). Glycerol was a weak inhibitor of FDPase and PEPCK, but did not inhibit PC and G6Pase. In vivo, when G3P was injected before a parenteral L-alanine (Ala) challenge, it produced a hypoglycemic effect in malnourished rats and a lesser, but noticeable, blood glucose level reduction in well-fed animals. Glycerol caused a smaller reduction in glucose formation from Ala. No comparable effects were observed after a fructose pretreatment. These results underscore the potential hypoglycemic effects of phosphorylated glycerol metabolites and identify the steps in gluconeogenesis where this action is exerted. The study also stresses the nutritional component in the glycerol intolerance syndrome, apparent from the far more severe effects observed in malnourished rats given G3P or glycerol prior to Ala.

Intestinal transport of aromatic amino acids, glucose and electrolytes in a patient with phenylketonuria

Abstract The intestinal transport of aromatic amino acids, glucose and electrolytes was studied with a double lumen transintestinal tube in a phenylketonuric female, when her plasma phenylalanine level was 1.87 mM and at the end of one month on a low-phenylalanine intake when her plasma phenylalanine was 0.84 mM. Three healthy adult volunteers served as controls. Their plasma phenylalanines were below 0.16 mM. Jejunal perfusions were performed using isotonic buffers with either 1, 2 or 5 mM l -phenylalanine, 1 mM l -tryptophan, 1 mM l -tyrosine or one which was amino acid-free. All solutions included 40 mM glucose and 600 mg% of polyethylene glycol mol. wt 3000−3700 as a non-absorable marker. The intestinal absorption rates in the phenylketonuric were significantly below those of the volunteers for l -phenylalanine (−4.3 to −18.1%), l -tryptophan (−9.6%), glucose (−10.3%), and sodium (−40.9%). However, they were higher than in the controls for l -tyrosine and potassium. When circulating phenylalanine was reduced by dietary treatment in the phenylketonuric patient, the transport of l -phenylalanine, l -tryptophan and sodium became at least as high as that in normal individuals. Glucose absorption remained at lower levels.

Glycerol-induced hypoglycemia: A syndrome associated with multiple liver enzyme deficiencies. Clinical and in vitro studies

A 4 10/12 yr-old white male presented with a history of occasional grand mal seizures and hypoglycemic episodes after overnight fasting. Upon evaluation, he became hypoglycemic after 1 g/kg oral glycerol challenge (plasma glucose: 31 mg/dl in 45 min), but had normal glucose, alanine and fructose tolerance tests. He responded well to a glucagon challenge after 11 hr fast but he became hypoglycemic and could not normalize his blood glucose after a 2nd glucagon stimulation test after 17 hr of fasting. Studies conducted on a percutaneous liver biopsy, and compared with 3 non-hypoglycemic controls, showed reduced activities (20%-30% of normal) of alpha-glycerophosphate dehydrogenase, alpha-glycerophosphate oxidase and fructose-1,6-diphosphatase. Alpha glycerophosphate in the patients liver was elevated. Two types of electrophoresis showed absence of one enzymatically active zone and overall decrease of staining intensity for alpha-glycerophosphate dehydrogenase. Other liver enzymes tested were normal. The 50% inhibition of the patients liver fructose-1,6-diphosphatase by alpha-glycerophosphate occurred, in vitro, or lower concentration than in controls (11 versus 22-40 mM). Electron microscopy revealed hepatocytes with moderately swollen mitochondria that very occasionally contained dense inclusions in the inner mitochondrial matrix. After discharge from the hospital, the patient followed a normal course, with a regimen of multiple snacks and avoidance of high-fat food in the morning.

L-phenylalanine interactions with structurally related substances at the intestinal mucosa.

Abstract Ala, Cys, and Ser inhibited rat intestinal transport of 1 m m Phe in vivo when simultaneously present in concentrations of 10 m m or higher. Thi was a more effective inhibitor even at 5 m m levels. l -DOPA caused no effects under the same conditions. The data in these experiments are indicative that Thi may be a competitor for Phes specific translocation mechanism, while Ala, Cys, and Ser would interfere on Phe absorption across the intestine through the transport system common for neutral amino acids.

Alterations in rat brain glutaminase and aldolase induced by lead ingestion following malnutrition

Abstract Ingestion of lead following a period of malnutrition, in rats, has no additional deleterious effects on brain glutaminase and aldolase activities. These enzymes are inhibited following 5 weeks of lead intake, regardless of the previous nutritional history of the animals. Overall brain glycolysis appears not be to affected.

Regulation of hepatic gluconeogenesis and glycogenolysis by phosphorylated glycerol and glycolytic intermediates in diabetic and control Chinese hamsters

Metabolic regulation of gluconeogenesis and glycogenolysis by two phosphorylated derivatives of glycerol, G3P, and DHAP, and by F2,6BP, was assessed in vitro in liver homogenates obtained from Chinese hamsters (C. griseus) of two types: diabetic animals from sublines with consistent glycosuria and hyperglycemia, and normoglycemic controls. Only FBPase was sensitive to inhibition by the phosphorylated metabolites. G3P was weakly inhibitory of FBPase. Addition of 7 X 10(-3) M DHAP halved FBPase activity in the diabetic hamsters and 4 X 10(-3) M DHAP produced the same effect in the controls. The other gluconeogenic enzymes and phosphorylase a were only negligibly inhibited. In contrast, F2,6BP inhibited FBPase at concentrations in the micromolar range. Liver homogenates from diabetic hamsters appeared significantly more sensitive to F2,6BP inhibition of FBPase than those from controls at concentrations 0.6 X 10(-6) M and higher. These data indicate that in well-fed hamsters phosphorylated glycerol derivatives are unlikely to regulate hepatic gluconeogenesis at physiologic concentrations. However, the effects of F2,6BP on gluconeogenesis and glycolysis may be linked to those mediated by insulin. Thus, the deficiency of insulin, elevated end-organ insulin resistance, the alteration in the glucagon-insulin interaction, or a combination of these possible causes can be involved in an abnormal regulation of glycolysis and gluconeogenesis at the FBPase step, associated with changes in F2,6BP concentration.

Glycerol metabolism in experimental malnutrition during lactation

Abstract Malnutrition during lactation could affect glycerol metabolism. This possibility was studied in the rat. The model used consisted of allocating an excessive number of pups (14–16) to dams from the day of birth onward. A marked stunting occurred from Day 2 until Day 21 of life. Alterations in enzymes of glycerol metabolism and its phosphorylated intermediates were apparent, mainly during the second half of lactation. Hepatic, mitochondrial α-glycerophosphate oxidase (GPO) was most severely affected, declining to about one-tenth of the control values at 21 days of life. The same enzyme, in the brain, was reduced to a lesser extent. Brain, muscle, and liver cytosolic α-glycerophosphate dehydrogenase (GPD) was also lower in rats 12 days and older that had been underfed. At the end of the 3-week lactating period, brain α-glycerophosphate (α-GP) was elevated. Changes in α-GP of other organs were less marked. Glycerol kinase (GK) was equally diminished in brain and liver, late in lactation. Hence, nutritional deprivation reduces liver capacity to use glycerol as an energy source. Alterations in stores of phosphorylated glycerol derivatives can alter glycogenolysis and gluconeogenesis, further handicapping glucose homeostasis.

Tyrosine supplementation in chronic experimental uremia

The occurrence of low tyrosine tissue levels in uremic subjects, possibly due to impaired phenylalanine hydroxylation, suggests that tyrosine may be an essential amino acid in uremia. Additional dietary tyrosine may thus re-dress the deficiency. This study examined growth and tyrosine/phenylalanine metabolism in uremic rats during tyrosine supplementation. Rats made uremic (U) by 7/8 nephrectomy were compared to pair-fed (CP) and ad libitum-fed (CA), sham-operated controls. Two sets of each group of rats were studied after 21 days on the respective diets: I = Purina Lab Chow; II = same + 3.5% tyrosine. Plasma tyrosine was below normal in U and CP-fed diet I. With diet II, the tyrosine:phenylalanine ratio in U was lower than both CA and CP. In rats fed diet II, the tyrosine:phenylalanine ratio became indistinguishable among the three groups. Growth parameters in U and CP were similar, regardless of the diet. Body weight gain, tibial length, muscle mass, and tissue protein did not improve in uremic animals supplemented with tyrosine. The specific activity of liver phenylalanine hydroxylase in U was not different from CA or CP. However, loss of cortical renal mass appeared to be the major determinant of decreased kidney phenylalanine hydroxylation in experimental uremia. This alteration is likely to be the greatest contributory factor to the alteration of plasma levels of tyrosine and phenylalanine. The data presented do not support a proposed essentiality of tyrosine in uremia.