Urea Excretion

Schmidt‐Nielsen, Bodil

doi:10.1007/978-1-4614-7545-3_10

Cited by 2 publications

(2 citation statements)

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“…The renal handling of urea in many species has been thoroughly studied and its potential importance in the concentrating process emphasized among others by Bonventre et al (1980) and Schmidt-Nielsen (1987). It has long been recognized that in the mammalian kidney, urea is utilized in the process of water conservation (Gamble et al 1934).…”

Section: Potential Role Of Urea and The Two-compartment Modelmentioning

confidence: 99%

Two fluid compartments in the renal inner medulla: a view through the keyhole of the concentrating process

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Shohet

2006

Phil. Trans. R. Soc. A.

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Approximately four decades ago, the countercurrent theory became influential in studies on the concentrating process in the mammalian kidney. The theory successfully represented the concentrating process in the outer medulla, but the problem of the concentrating mechanism in the inner medulla, as defined by Homer Smith has remained essentially intractable. In a recent comprehensive review by Knepper and coworkers of various theories and models, attention was refocused on the possible role of hyaluronate (HA) in the inner medullary concentrating process. The authors proposed a hypothesis that HA can convert hydrostatic pressure to concentrating work.Here, we briefly survey the earlier ideas on the role imputed to HA and present a new hypothesis which is different from that of Knepper and coworkers. We estimate that the hydrostatic pressures available in the inner medulla can account only for a very small fraction of the concentrating work. We hypothesize that the role of HA is tied up with extravasated plasma albumin and suggest that owing to the property of HA solutions to exclude other macromolecules, extravasated plasma albumin and HA constitute two fluid compartments in the interstitium in the inner medulla. In this proposed two-compartment model, the Gibbs-Donnan distribution influences the movement of ions and water between the HA and the extravasated albumin compartment. To relate the hypothetical role of HA to the concentrating process, we briefly describe new results obtained by other investigators on the accumulation of urea in the inner medulla. This subject has been critically reviewed recently by Yang & Bankir.Many processes have been identified as contributing to the concentrating process in the mammalian inner medulla. We speculate that among these many processes, the primary responsibility for the final concentration of the excreted urine may be portioned out differently in different mammalian species.

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Section: Potential Role Of Urea and The Two-compartment Modelmentioning

confidence: 99%

Two fluid compartments in the renal inner medulla: a view through the keyhole of the concentrating process

Pinter

Shohet

2006

Phil. Trans. R. Soc. A.

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“…That is why we include the endogenous urea as a first member of group of endogenous beta-adrenergic receptor antagonists (EBARA) (1)(2)(3)(4)(5)(6)(7)(19)(20)(21). Taking into account the nonspecific beta-adrenergic receptor antagonistic activity of endogenous urea, we propose a new classification:  endogenous nonspecific beta-adrenergic receptor antagonists (ENBARA), including urea, manganese ions, hydrogen peroxide, and L-taurine (reviewed in 6,7), and   endogenous specific beta-adrenergic receptor antagonists (RESBARA), incluing beta-arrestin 1 and 2 being cofactors of five isolated beta-adrenergic receptor kinases (6,7,20,(22)(23)(24)(25)(26)(27)(28) (see the Figure).…”

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confidence: 99%

Endogenous urea as endocoid: an extrarenal focus

Temnyalov

2004

Biomedical Reviews

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Until now the attention of the investigators in the field of biomedical aspects of urea (carbamide) was concentrated on its functions at renal level. However, the functional significance of endogenous urea at extrarenal level in mammalian organism (1) has not been satisfactory elucidated yet. Therefore a new principal question arises: which are the signals realized by endogenous urea in living animals and humans-extrarenally? Here we discuss some data obtained with urea used at concentrations corresponding to physiological (1.0-8.3 mmol/L) and pathological (10-160 mmol/L) ones, in animal and human organism-at extrarenal level. Based on previous work of our research group, we have shown for the first time that endogenous urea is able (in 4-fold elevated concentration, via infusion) to antagonize dose-and time-dependently some postsynaptic cardiovascular beta-1,2-adrenergic responses (positive chronotropic and vasodepressor effects of isoproterenol at 1, 2, and 4 nmol/kg intravenously) in anesthetized mongrel cats and dogs of

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Urea Excretion

Cited by 2 publications

References 91 publications

Two fluid compartments in the renal inner medulla: a view through the keyhole of the concentrating process

Two fluid compartments in the renal inner medulla: a view through the keyhole of the concentrating process

Endogenous urea as endocoid: an extrarenal focus

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