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A Journal on Internal Medicine

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

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


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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