Micropuncture study of composition of loop of Henle fluid in desert rodents

Gottschalk, Carl W.; Lassiter, William E.; Mylle, Margaret; Ullrich, Karl Julius; Schmidt‐Nielsen, Bodil; O'Dell, Roberta; Pehling, Gundula

doi:10.1152/ajplegacy.1963.204.4.532

Cited by 79 publications

(27 citation statements)

References 1 publication

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“…An osmolality of the fluid at the bend of the long loops nearly identical to that in the fluid at the terminal end of the CDs is also observed in hamsters (10,11). The interstitial fluid osmolality predicted by the model for the papillary tip (1,353 mosmol/kgH 2 O) is similar to that predicted for the urine.…”

Section: Comparison With Experimental Measurementssupporting

confidence: 62%

A mathematical model of the urine concentrating mechanism in the rat renal medulla. I. Formulation and base-case results

Layton

2011

American Journal of Physiology-Renal Physiology

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Layton AT. A mathematical model of the urine concentrating mechanism in the rat renal medulla. I. Formulation and base-case results. Am J Physiol Renal Physiol 300: F356 -F371, 2011. First published November 10, 2010 doi:10.1152/ajprenal.00203.2010.-A new, region-based mathematical model of the urine concentrating mechanism of the rat renal medulla was used to investigate the significance of transport and structural properties revealed in anatomic studies. The model simulates preferential interactions among tubules and vessels by representing concentric regions that are centered on a vascular bundle in the outer medulla (OM) and on a collecting duct cluster in the inner medulla (IM). Particularly noteworthy features of this model include highly urea-permeable and water-impermeable segments of the long descending limbs and highly urea-permeable ascending thin limbs. Indeed, this is the first detailed mathematical model of the rat urine concentrating mechanism that represents high long-loop urea permeabilities and that produces a substantial axial osmolality gradient in the IM. That axial osmolality gradient is attributable to the increasing urea concentration gradient. The model equations, which are based on conservation of solutes and water and on standard expressions for transmural transport, were solved to steady state. Model simulations predict that the interstitial NaCl and urea concentrations in adjoining regions differ substantially in the OM but not in the IM. In the OM, active NaCl transport from thick ascending limbs, at rates inferred from the physiological literature, resulted in a concentrating effect such that the intratubular fluid osmolality of the collecting duct increases ϳ2.5 times along the OM. As a result of the separation of urea from NaCl and the subsequent mixing of that urea and NaCl in the interstitium and vasculature of the IM, collecting duct fluid osmolality further increases by a factor of ϳ1.55 along the IM. countercurrent system; NaCl transport; urea transport; kidney DURING PERIODS OF WATER DEPRIVATION, the mammalian urine concentrating mechanism, which is localized in the renal medulla, stabilizes the osmolality of blood plasma by producing a urine that has an osmolality that substantially exceeds that of blood plasma. However, despite decades of sustained experimental and theoretical investigation (24,37,54,58), the nature of the urine concentrating mechanism in the inner medulla (IM) of the mammalian kidney remains controversial.Anatomic studies have revealed a highly structured organization of tubules and vasa recta in the outer medulla (OM) of some mammalian kidneys (2, 29), with tubules and vessels organized concentrically around vascular bundles, tightly packed clusters of parallel vessels, and tubules containing mostly vasa recta. Recent studies of the three-dimensional architecture of the rat IM and expression of membrane proteins associated with fluid and solute transport in nephrons and vasculature have revealed transport and structural properties that likely impact th...

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Section: Comparison With Experimental Measurementssupporting

confidence: 62%

A mathematical model of the urine concentrating mechanism in the rat renal medulla. I. Formulation and base-case results

Layton

2011

American Journal of Physiology-Renal Physiology

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“…Changing the bath and perfusion fluid to the sodium-free, choline-chloride solutions reduced the PD slightly to 3.27±0. 19. The fact that the PD fell slightly with removal of sodium could represent the contribution of localized sodium concentration gradients to the overall transtubular PD.…”

Section: Resultsmentioning

confidence: 99%

“…Tissue analysis have shown that the greatest osmotic gradient is generated between the cortex and outer-inner medullary junction with subsequent further rise in the interstitial NaCl and urea concentrations as one progresses towards the papillary tip (16)(17)(18). That active NaCl transport exists somewhere along the ascending limb of Henle has been established with the demonstration that the fluid in the early distal tubule is hypoosmotic to plasma, while the fluid obtained from the bend of the loop is hyperosmolar (19). These and subsequent micropuncture studies have not been able to further elucidate the mechanism of this NaCI transport in view of the inaccessibility of the thick ALH to micropuncture techniques.…”

Section: Resultsmentioning

confidence: 99%

Sodium Chloride and Water Transport in the Medullary Thick Ascending Limb of Henle. EVIDENCE FOR ACTIVE CHLORIDE TRANSPORT

Rocha¹,

Kokko²

1973

J. Clin. Invest.

400

163

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A B S T R A C T Transport of NaCl and water was examined in the rabbit medullary thick ascending limb of Henle (ALH) by perfusing isolated segments of these nephrons in vitro. Osmotic water permeability was evaluated by perfusing tubules against imposed osmotic gradients. In these experiments the net transport of fluid remained at zero when segments of thick ALH were perfused with isotonic ultrafiltrate in a bath of rabbit serum in which the serum osmolality was increased by the addition of either 239±8 mosmol/liter of raffinose or 232±17 mosmol of NaCl indicating that the thick ascending limb of Henle is impermeant to osmotic flow of water. When these tubules were perfused at slow rates with isosmolal ultrafiltrate of same rabbit serum as used for the bath, the effluent osmolality was consistently lowered to concentrations less than the perfusate and the bath. That this decrease in collected fluid osmolality represented salt transport was demonstrated in a separate set of experiments in which it was shown that the sodium and chloride concentrations decreased to 0.79+0.02 and 0.77±0.02 respectively when compared with the perfusion fluid concentrations. In each instance the simultaneously determined transtubular potential difference (PD) revealed the lumen to be positive with the magnitude dependent on the perfusion rate. At flow rates above 2 nl -min1, the mean transtubular PD was stable and equal to 6.70+0.34 mv. At stop-flow conditions this PD became more positive. Ouabain and cooling reversibly decreased the magnitude of this PD. The transtubular PD remained positive, 3.3+ 0.2 mV, when complete substitution of Na by choline was carried out in both the perfusion fluid and the bathing media. These results are interpreted to indicate that Dr. Rocha is

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“…Numerous investigators (12)(13)(14)(15) have found that the osmolality of the intratubular fluids becomes progessively hyperosmotic from the corticomedullary junction to the papilla. Disagreement, however, has arisen as to whether this occurs primarily by abstraction of fluid or by influx of solute.…”

Section: Resultsmentioning

confidence: 99%