Biomedical subjects

J P Gassée

Publications and source records attributed to J P Gassée.

13 recordsLinked to original sources

PubMed1977

[Current concept of the mechanism of proteinuria].

Plasma proteins cross the glomerular basement membrane in inverse proportion to their molecular dimension; molecules larger than serum albumin are completely excluded from the glomerular filtrate. This filtration, which is purely passive, also depends of the electrical charge of the proteins; negatively charged proteins are indeed repelled by the negatively charged layer of sialogylcoproteins present along the outer surface of the epithelial cell membrane and extending to the glomerular basement membrane. The filtered proteins are selectively absorbed by the proximal tubular cells and are hydrolyzed by lysosomal enzymes. This results in a renal catabolism of proteins the importance of which depends on their ability to cross the glomerular barrier. In renal disease, proteinuria results either from an increased permeability of the glomerular basement membrane (selective or non-selective glomerular proteinuria) or from a diminished tubular reabsorption of normally filtered proteins of low molecular weight (tubular proteinuria).

Blood Proteins↗

PubMed1976

Determination of glomerular intracapillary and transcapillary pressure gradients from sieving data. 3. The effects of angiotensin II.

The effects of the intrarenal infusion of synthetic Asn1, val 5 angiotensin II (AII) (from 0.38 to 1 mug min-1) on the determinants of glomerular filtration have been studied. The intracapillary and transcapillary pressure gradients along the capillaries, together with 2 parameters characterizing the porosity of the membrane in terms of pore theory (r, radius of the pores and Ap/1, total pore area per unit of path length) were calculated from the analysis of the sieving curve of I125 PVP molecules (polyvinylpyrrolidone) according to a biomathematical model previously described. AII increased PGC, the intracapillary hydrostatic pressure, but more at the efferent end of the capillaries. Filtration pressure equilibrium was maintained. AII also decreased the water permeability coefficient, Kf. by decreasing Ap/1, r remaining constant. Our results were compared to those obtained from the direct measurements of PGC, using micropuncture techniqles in hydropenic and plasma loaded rats. The complete agreement between the two approaches confirms the validity of the method based on the analysis of the sieving data of neutral macromolecules to calculate the determinants of GFR.

Angiotensin II↗

PubMed1976

The participation of the renal tubules to the metabolism of insulin.

The role of renal tubules was explored by two kinds of experiments: (1) inhibition of the tubular reabsorption of insulin by induced polyuria; (2) suppression of insulin filtration by ureter clamping; 1. Anaesthetized dogs maintained in normoglycaemia by glucose compensation were infused with crystalline and 125I-insulins. Polyuria was induced by: (1) saline-bicarbonate infusion; (2) furosemide with saline-bicarbonate infusion to replace urine losses; (3) massive infusion of mannitol. Inulin and paraminohippuric acid were used to estimate the glomerular filtration rate and the renal plasma flow. The permeability of the glomerular wall (pore radius and total area of the pores per unit of path length) was determined by measuring the sieving curve of 131I-polyvinyl-pyrrolidone fractions during basal and treatment periods. Mannitol infusion was able to bring the insulin/inulin clearance ratio up the values of the sieving coefficient of insulin (insulin filtration rate) without modifying the permeability of the glomerular wall; saline infusion displayed a similar effect; furosemide, only a minute one although it induced a more marked polyuria. 2. Clamping of the left ureter was performed on dogs with catheters inserted into the artery, the left renal vein, the pelvis and a renal lymphatic vessel. Almost complete suppression of the glomerular filtration was achieved. It slightly increased the high insulinic concentration of the renal lymph, entailed a 1/3 decrease in the extraction ratio of insulin and reduced by half its renal clearance. In conclusion, the tubules participate to the catabolism of insulin by two different mechanisms: (1) an uptake from the tubular fluid which can be inhibited by diuretics exerting their main action on the proximal tubules; (2) a direct catabolism from the interstitial fluid resulting from the large permeability of the peritubular capillaries to insulin.

Animals↗

PubMed1976

[Effects of angiotensin II on the parameters determining glomerular filtration].

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Angiotensin II↗

PubMed1975

Determination of glomerular intracapillary and transcapillary pressure gradients from sieving data. II. A physiological study in the normal dog.

The two theoretical models proposed previously to calculate the intracapillary and transcapillary glomerular pressure gradients from the sieving of macromolecules such as PVP have been used to analyse in 22 normotensive dogs the sieving curve relating the sieving coefficients, phi, to molecular size (phi: glomerular clearance of PVP fractions/GFR). Neither the "local c2" model-filtrate unmixed at the outer face of the capillaries walls--nor the constant c2 model-filtrate well mixed--allowed to obtain realistic values for the hemodynamical parameters. Indeed with the local c2 model, the best fit between calculated and experimental sieving curves could be obtained only by reversing the intracapillary pressure gradient; conversely the constant c2 model obliged to decrease the intracapillary pressure so abruptly along the capillaries, that retrofiltration took place in the distal parts of the vessels. This difficulty has been overcome by combining the two models; the so-called "hybrid model" considers that the filtrate is well mixed in the vicinity of the urinary pole only. The following results were obtained: 1. PGCa and PGCe (intracapillary pressures at the afferent and efferent extremities of the capillaries) equal to 49.7 +/- 1.03 and 41.8 +/- 1.00 mm Hg respectively. 2. Pressure equilibrium is generally reached at the efferent extremity of the vessels. 3. The slope of PGC (see article) varies inversely to FF. (filtration fraction). 4. The model, however, does not allow to rule out the possibility of retrofiltration.

Animals↗

PubMed1975

Determination of glomerular intracapillary and transcapillary pressure gradients from sieving data. I. A mathematical model.

Determination of glomerular intracapillary and transcapillary pressure gradients from sieving data. A biomathematical model is described to calculate the intracapillary and transcapillary glomerular pressure gradients from the sieving coefficients (phi: fractional clearances/GFR) of macromolecules such as polyvinylpyrrolidone (PVP). Two differential equations have been developed. The first one calculates local values for GFR in terms of local values for PGC (intracapillary hydrostatic pressure) and pi (oncotic pressure). The second equation calculates the clearance of PVP equimolecular fractions, the sieving equations previously described (24) being used to derive the concentrations of PVP in the filtrate (c2). Two variants of the second equation have been considered, assuming the filtrate in contact with the membrane either "well stirred" or "unstirred" (constant c2 and local c2 gradient models respectively). Computer simulations have been used to illustrate how the sieving curve is modified when the five parameters on which depends the shape of the curve are changed one by one. The sieving curve relates phi to a(s) (hydrodynamically equivalent molecular radius). The determining parameters are: GFP, the mean effective glomerular filtration pressure, epsilon, the slope of the intracapillary pressure, FF, the filtration fraction, Cp0, the protein concentration in arterial plasma and r, the pore radius which is the only structural parameter involved when one assumes the glomerular membrane crossed by cylindrical pores of uniform size and length. The shape of the sieving curve is modified significantly enough by changing GFP, FF and r within reasonable limits, to make it possible to derive GFP and r from experimental sieving data for macromolecules such as PVP or dextrans.

Capillaries↗

PubMed1975