Diabetes insípida perioperatoria secundaria a litio.

La diabetes insípida es una patología caracterizada por la eliminación de volúmenes muy elevados de orina diluida. La hormona antidiurética es la encargada de regular la reabsorción de agua en el túbulo colector. Podemos diferenciar dos variantes, la neurogénica o central y la nefrogénica o secundaria según el nivel que esté afectado. Varios fármacos han sido relacionados con la pérdida de la capacidad concentradora renal de la orina, siendo el litio uno de ellos. Presentamos el caso de una paciente sometida a intervención quirúrgica por estenosis benigna de píloro en tratamiento farmacológico con litio por trastorno bipolar que durante el periodo intraoperatorio comenzó con diuresis elevada sospechándose diabetes insípida. ABSTRACT Lithium-induced Perioperative Diabetes Insipidus–A Case Report Diabetes insipidus is a pathology characterized by the elimination of large amounts of dilute urine. The antidiuretic hormone is responsible of water reabsorption in medullary collecting duct in the kidney. There are two main types of diabetes insipidus, on one hand the neurogenic or central diabetes insipidus and on the other hand the nephrogenic or secondary diabetes insipidus, depending on the level that is affected. Several drugs have been related to loss of renal concentrating mechanism, being the lithium one of them. We present a case report of a patient undergoing surgery for benign pyloric stenosis in pharmacological long-term maintenance treatment of bipolar disorder with lithium. During the intraoperative period the patient began with high urine output and diabetes insipidus was suspected.

Concentration of solutes in the renal inner medulla: interstitial hyaluronan as a mechano-osmotic transducer

Although the concentrating process in the renal outer medulla is well understood, the concentrating mechanism in the renal inner medulla remains an enigma. The purposes of this review are fourfold. 1) We summarize a theoretical basis for classifying all possible steady-state inner medullary countercurrent concentrating mechanisms based on mass balance principles. 2) We review the major hypotheses that have been proposed to explain the axial osmolality gradient in the interstitium of the renal inner medulla. 3) We summarize and expand on the Schmidt-Nielsen hypothesis that the contractions of the renal pelvocalyceal wall may provide an important energy source for concentration in the inner medulla. 4) We discuss the special properties of hyaluronan, a glycosaminoglycan that is the chief component of a gel-like renal inner medullary interstitial matrix, which may allow it to function as a mechano-osmotic transducer, converting energy from the contractions of the pelvic wall to an axial osmolality gradient in the medulla. These considerations set the stage for renewed experimental investigation of the urinary concentrating process and a new generation of mathematical models of the renal concentrating mechanism, which treat the inner medullary interstitium as a viscoelastic system rather than a purely hydraulic system.

The effects of collecting duct active NaCl reabsorption and inner medulla anatomy on renal concentrating mechanism

First, the representation of the inner medulla incorporates an exaggerated radial separation between tubules, vessels, and collecting ducts; and, second, the hydraulic permeability in the upper portion of the inner medullary collecting ducts was erroneously set to zero. In the current work, we explore the role of collecting duct hydraulic permeability and anatomical heterogeneity via mathematical modeling. The model predicts concentrated urine for measured values of the hydraulic permeability and homogeneous lower inner medulla as long as net active NaCl reabsorption is incorporated in the upper inner medullary collecting duct epithelium. This new three-dimensional model results in two recycling paths. The upper portion of the inner medulla recycles NaCl, whereas the lower portion recycles urea.

Inner medullary external osmotic driving force in a 3-D model of the renal concentrating mechanism

The mechanism by which the renal medulla establishes and maintains a gradient of osmolarity along the corticomedullary axis, especially in the inner medulla, where there is no active transmural flux out of the ascending limbs of Henle, remains a source of controversy. We show here that, if realistic values of urea permeability in the inner medullary descending limbs and water permeability in the upper inner medullary section of the collecting ducts are taken into account, even a model including the three-dimensional vascular bundle structures [A. S. Wexler, R. E. Kalaba, and D. J. Marsh. Am. J. Physiol. 260 (Renal Fluid Electrolyte Physiol. 29): F368-F383, 1991] fails to explain the experimentally observed inner medullary osmolality gradient. We show here that this failure can be overcome by application of an external osmotic driving force, an idea recently revived by J. F. Jen and J. L. Stephenson (Bull. Math. Biol. 56: 491-514, 1994) in the context of a single-solute, single-loop central core model. We show that inclusion of such an external driving force with a value equivalent to at least 100 mosM of inner medullary interstitial osmolytes in the three-dimensional model of Wexler et al. accounts for a physiological osmolality gradient, even in the face of realistic permeability values. Furthermore, inclusion of the external driving force makes the model less dependent on the positions of descending and ascending limbs of Henle with respect to the collecting ducts. In an effort to assess whether there is any experimental basis for osmolytes, we show that a significant amount of extra inner medullary interstitial osmolytes is plausible, based on extrapolation from existing experimental data.

August Krogh Lecture. The renal concentrating mechanism in insects and mammals: a new hypothesis involving hydrostatic pressures

Water moves from compartments of higher to compartments of lower water potential. Osmotically active solutes and negative hydrostatic pressure both lower water potential by stretching the hydrogen bonds between water molecules (Hammel-Scholander hypothesis). In trees the negative hydrostatic pressure in the sap is balanced by the osmotic pressure of the leaves. In response to differences in water potential, water flows across biological membranes through water-filled pores. Protein molecules, aquaporins, forming hourglass-shaped pores have been identified, cloned, and located in plasma membranes in mammalian as well as other tissues. Water molecules flow single file through aquaporins. Insects concentrate the urine in the rectum. Mammals concentrate the urine in the collecting ducts in the inner medulla. In both, a compartment with a high osmotic concentration is created through ion transport. Both have a muscular coat surrounding the tissue, which shows peristaltic contractions. In insects it is the muscular layer around the rectum; in mammals it is the renal pelvic wall that surrounds the papilla. Mechanisms are proposed whereby these peristaltic contractions, through the creation of positive and negative hydrostatic pressures in the tissues, can lead to hyperosmotic excreta.