The long term goal of this project is to explain the mechanism of hypertonic urine formation in mammals by computer simulation. This goal has been achieved; we have developed a model that represents the structures of the kidney medulla and the membrane transport functions of those structures. The novel feature of this model is the incorporation of the known 3-dimensional structure of the medulla. Inclusion of this feature allows this model to predict concentrating effects in the renal inner medulla consistent with measurements made in experimental animals, and without invoking active transport of solutes from any of the tubules of the inner medulla. The present form of the model represents an hypothesis of hypertonic urine formation; in the next grant period we propose to test this hypothesis. The model solution predicts that there should be gradients of NaCl and urea both in the axial direction, a result extensively documented in the literature, and in the radial direction. The existence of radial NaCl gradients will be tested for by measurements in rats using electron microprobe techniques applied to blood vessels in the inner and outer medulla. Predicted radial gradients of urea in the inner medulla will be tested for by micropuncture; the latter technique will also be used to test for predicted radial NaCl gradients in the inner medulla between tubular fluid and capillary plasma, in instances where electron microprobe analysis would not be reliable. Although the model captures the 3-dimensional ordering of the medulla, it is not fully isomorphic in other respects that could reduce predicted concentrating ability. These effects will be introduced ; they include a) erythrocytes in the blood, b) non-ideal physical chemistry of concentrated NaCl and urea solutions, c) active transport of NaCl from inner medullary collecting ducts, and d) a medullary ray as a transition between the cortex and the outer stripe of the outer medulla. Finally we will continue work on the application of neural network techniques to increase the speed of solution of large nonlinear boundary value problems, like the 3-dimensional kidney model.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
2R01DK033729-07
Application #
3232135
Study Section
Special Emphasis Panel (SSS (E))
Project Start
1984-07-01
Project End
1993-11-30
Budget Start
1990-12-01
Budget End
1991-11-30
Support Year
7
Fiscal Year
1991
Total Cost
Indirect Cost
Name
University of Southern California
Department
Type
Schools of Medicine
DUNS #
041544081
City
Los Angeles
State
CA
Country
United States
Zip Code
90089
Thomas, S R; Wexler, A S (1995) Inner medullary external osmotic driving force in a 3-D model of the renal concentrating mechanism. Am J Physiol 269:F159-71
Holstein-Rathlou, N H; Marsh, D J (1994) Renal blood flow regulation and arterial pressure fluctuations: a case study in nonlinear dynamics. Physiol Rev 74:637-81
Wexler, A S; Kalaba, R E; Marsh, D J (1991) Three-dimensional anatomy and renal concentrating mechanism. I. Modeling results. Am J Physiol 260:F368-83
Marsh, D J; Yip, K P; Kallskog, O et al. (1991) Oscillations and more complex dynamics in tubuloglomerular feedback. Kidney Int Suppl 32:S94-7
Wexler, A S; Kalaba, R E; Marsh, D J (1991) Three-dimensional anatomy and renal concentrating mechanism. II. Sensitivity results. Am J Physiol 260:F384-94
Holstein-Rathlou, N H; Wagner, A J; Marsh, D J (1991) Tubuloglomerular feedback dynamics and renal blood flow autoregulation in rats. Am J Physiol 260:F53-68
Holstein-Rathlou, N H; Wagner, A J; Marsh, D J (1991) Dynamics of renal blood flow autoregulation in rats. Kidney Int Suppl 32:S98-101
Holstein-Rathlou, N H; Marsh, D J (1990) A dynamic model of the tubuloglomerular feedback mechanism. Am J Physiol 258:F1448-59
Cupples, W A; Wexler, A S; Marsh, D J (1990) Model of TGF-proximal tubule interactions in renal autoregulation. Am J Physiol 259:F715-26
Wexler, A S; Kalaba, R E; Marsh, D J (1987) Passive, one-dimensional countercurrent models do not simulate hypertonic urine formation. Am J Physiol 253:F1020-30