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PubMed1999

Preventing dehydration in children with cystic fibrosis who exercise in the heat.

PURPOSE: In healthy children who exercise in the heat, the addition of flavor, carbohydrate, and 18 mmol x L(-1) NaCl to water induced a major increase in voluntary drink intake compared with the intake of unflavored water. This increase was sufficient to prevent voluntary dehydration. We hypothesized that, to achieve a similar effect in children with cystic fibrosis (CF), whose NaCl losses in sweat are markedly excessive, the drink should include an NaCl concentration higher than 18 mmol x L(-1). METHODS: Eleven subjects with CF (6 girls, 5 boys, ages 10.9-19.5 yr) attended three 3-h sessions of intermittent exercise of moderate intensity (four 20-min bouts), at 35 degrees C, 50% relative humidity. Either water (W), flavored water (FW), or a 30 mmol x L(-1) NaCl plus 6% carbohydrate solution (Na30) was offered ad libitum, in a counterbalanced sequence. Six subjects performed an additional session in which they drank a 50 mmol x L(-1) NaCl-6% CHO solution (Na50). RESULTS: There was no significant drink effect on body fluid balance, core temperature, heart rate, or serum electrolytes with W, FW, or Na30. Serum osmolality decreased throughout the sessions from 290.6 +/- 1.1 (mean +/- SEM) to 281.3 +/- 1.2 mmol x kg(-1) (P < 0.0005), serum sodium from 143.1 +/- 0.5 to 141.1 +/- 0.7 mmol x L(-1) (P = 0.01) and serum chloride from 109.1 +/- 0.5 to 107.5 +/- 0.5 mmol X L(-1) (P < 0.001). In contrast, the 50 mmol x L(-1) NaCl drink induced a near significant (P = 0.08) higher fluid intake, and it significantly ameliorated the rate of progressive dehydration. CONCLUSIONS: The marked loss of NaCl in the sweat of CF patients may induce an hypo-osmolar state in the serum, even when the drink contains 30 mmol x L(-1) NaCl. This may diminish the thirst drive triggered by hypothalamic osmoreceptors and may lead to voluntary dehydration. A flavored drink with an even higher salt content (50 mmol X L(-1)), however, enhances drinking and attenuates the voluntary dehydration.

Adolescent↗

PubMed1980

A model for the glomerular filter.

The model for the glomerular filter presented here is based on the relationship between basement membrane collagen and fibrillar collagen. The glomerular basement membrane collagen is produced by the epithelial cell and present on its surface in a staggered organization as in fibrillar collagen. Binding and aggregation of the collagen molecules with a matrix protein results in a large (+/- 50 nm) meshwork controlled by collagen molecules and bound to the cell surface. Because the matrix proteins bind GAGs, the aggregates are recognizable as anionic sites. A continued production of glomerular basement membrane material will cause a movement towards the endothelial side accompanied with a degradation. This degradation results in a loss of carbohydrates, digesting of alpha-molecules in the triple helices and a loss of anionic sites. The loss of carbohydrates leads to cross-linking and narrowing of the meshes in the direction of the endothelial side of the GBM. Final digestion results in fragmented helices which will pass the GBM and probably be reabsorbed by the epithelial cells or which will pass the slit diaphragm. The slit diaphragm, a staggered collagen structure in plane, functions as a bridge between the epithelial foot processes and is able to regulate the flow and pressure.

Animals↗