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Renal function and Magnesium Clearance in Young and Old Cows given Potassium Chloride and Sodium Citrate^1,2,

University of Kentucky³, Lexington 40546

Abstract

Six young (3 yr old) and six old (8 to 11 yr old) cows were used to examine renal function, KC1 and sodium citrate effects on Mg clearance rate and the relation of parathyroid hormone (PTH) to Mg reabsorption. The treatments were 1.5 g KCl/kg body weight (BW) and 1.5 g Na citrate/kg BW. Inulin and paminohippuric acid (PAH) clearance rates were used as measures of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF), respectively, in control cows on each treatment day. Creatinine clearance rate was also used as a measure of GFR in all cows. Magnesium loading (2.4 mg/kg BW) through continuous intrajugular infusion of MgCl₂ facilitated the measurement of changes in Mg clearance rate and reabsorption due to treatment. Inulin and creatinine clearance rates were not different as measures of GFR, and there were no differences in ERPF between young and old cows. Old cows had lower (P<.05) GFR, creatinine to PAH clearance ratios and tubular reabsorption of Mg than young cows. Intraluminal infusion of KC1 and Na citrate increased (P<.05) the GFR. Potassium chloride increased plasma K concentration (P<.001), plasma K clearance rate (P<.002), plasma Na clearance rate (P<.03), plasma Mg concentration (P<.05), net tubular reab sorption of Mg (P<.02), maximum tubular reabsorption of Mg (P<.002) and plasma PTH concentration (P<.03). Plasma Mg clearance rate was increased only by Na citrate (P<.05). These results suggest a possible relationship between age, renal function, Mg antagonists and PTH in Mg homeostasis and in the etiology of hypomagnesemic tetany.

¹ Authorized for publication by the director as Paper No. 81-5-11 in the Journal Ser. of the Kentucky Agr. Exp. Sta.

² Part of the research reported in this paper was presented at the Annu. Meet, of the Southern Sec, ASAS, Atlanta, GA, February 1–4, 1981, and was supported by USDA/SEA—CR GRANT 901-15-161.

² Dept. of Anim. Sci.