Simultaneous Mg,Ca, P,K, Na and Cl analysis in rat tubular fluid

Summary The micropuncture recollection technique was used for further analysis of Mg, Ca, P, Na, Cl and K tubular handling during and after acute magnesium plasma loading in the rat. The concentrations of these different ion species in late proximal and early distal fluid samples, ureteral urine and plasma ultrafiltrates were measured using electron probe microanalysis.³H-inulin was used as glomerular indicator.The results indicate that 1, late proximal (TF/P_f)Mg/In values remained proportional to the filtered load (about 80%); 2. part of the filtered Mg was reabsorbed in the loop of Henle by an active and saturable transport mechanism; 3. early distal (TF/P_f)Mg/In values during and after Mg loading were below the corresponding (U/P_f)Mg/In values; this observation might either indicate net Mg tubular excretion by the terminal nephron segments or result from the building up of a medullary Mg ion pool during the loading period; 4. acute hypermagnesemia induced transient calciuria, shown to result from decreased Ca reabsorption in the terminal segments; 5. it enhanced P reabsorption in the terminal segments; the drop in P excretion might have been mediated by decreased PTH release; 6. tubular handling of the other ion species was relatively unaffected by increasing tubular Mg loading.