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Panminerva Medica 1999 June;41(2):103-8

Copyright © 2000 EDIZIONI MINERVA MEDICA

language: English

The influence of furosemide on free water clearance

Romano G., Bortolotti N., Falleti E., Favret G., Gonano F., Bartoli E.

From the Department of Experimental and Clinical Pathology and Medicine University of Udine, Udine, Italy


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Back­ground. Labor­a­to­ry meas­ure­ments of osmo­lal­ity and elec­tro­lyte con­cen­tra­tions are use­ful as a ­source of clin­i­cal and patho-­phy­sio­log­ic infor­ma­tion on kid­ney func­tion. We ­obtained dif­fer­ent con­di­tions of base­line diu­re­sis in 54 ­rats, ­which ­were ­then treat­ed ­with furos­e­mide 10 mg/kg. ­From meas­ure­ments of plas­ma (P) and ­urine (U) osmo­lal­ity and Na, we cal­cu­lat­ed the ­free ­water clear­ance (CH2O) and the con­tri­bu­tions of Na+ and non-Na+-­solutes to its chang­es dur­ing diu­ret­ic admin­is­tra­tion.
­Results. The ­results ­show ­that furos­e­mide abol­ish­es ­both ­urine dilut­ing and con­cen­trat­ing abil­ity, by reduc­ing the con­tri­bu­tion of non-Na+-­solutes to ­Uosm and the for­ma­tion of CH2O, ­while the con­tri­bu­tion of Na+ to ­Posm ­remains ­unchanged. Dur­ing furos­e­mide the ­urines ­approach iso­smo­tic­ity irre­spec­tive of the base­line ­Uosm ­with an asymp­to­mat­ic func­tion sim­i­lar to ­that ­imposed by osmot­ic diu­re­sis. It is sug­gest­ed ­that the over­flow to the con­cen­trat­ing ­sites of the neph­ron over­whelms ­their nor­mal trans­port capac­ity inde­pen­dent­ly of ­their base­line ­water perme­abil­ity. The dis­rup­tion of the tran­sep­i­the­lial osmot­ic gra­di­ent ­caused by the ­drug ­impairs the tran­sep­i­the­lial osmot­ic ­flow, lead­ing to the excre­tion of iso­smot­ic ­urines.
Con­clu­sions. The ­effect of non-Na+-­solutes in the labor­a­to­ry meas­ure­ment of ­urine con­stit­u­ents can be ­reduced to ­that of plas­ma deter­mi­na­tion by dilut­ing the ­urines accord­ing to empir­ic for­mu­las ­derived ­from the ­present ­data.

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