The Role of Magnesium in the Pathogenesis of Azotemic Hypothermia

Abstract

Hypermagnesemia has been observed in patients with uremia, since 1934 when Hirschfelder pointed out the dangers of Epsom salt purgation in patients with nephritis (1). It has been subsequently demonstrated that the hypermagnesemia associated with uremia is primarily due to decreased urinary excretion of this cation (2, 3). Another manifestation of uremia is decreased body temperature. This aspect of renal failure was mentioned by Bourneville in 1873 (4), and hypothermia due to experimental uremia was reported in 1892 (5). The clinical importance of uremic hypothermia was stressed by Schreiner and Maher (6) in their monograph on uremia. The cause of uremic hypothermia, however, is still unknown.

In this study, we investigated hypermagnesemia as the potential cause of uremic hypothermia. Was there any reason to suspect this possibility, aside from the fact that hypermagnesemia is common in uremia? We believe so. Hypermagnesemia has been observed in a number of hibernating animals, i.e., groundhog (7), hedgehog (8), bat (9), and ground squirrel (10). Furthermore, the parenteral injection of magnesium salts in both rabbits and dogs leads to decreased body temperature (11, 12). Finally, it has been suggested that the antipyretic effects of salicylic acid may be due to increased blood magnesium (13).

The questions investigated were: (1) Does azotemia produced by ureteral ligation lead to hypothermia in the rat? (ii) Is azotemic hypothermia accentuated by hypermagnesemia? (iii) Does azotemic hypothermia occur in the absence of hypermagnesemia?

Methods. Forty female Sprague-Dawley rats weighing approximately 200 g, were randomly divided into control and test groups. The animals were pair fed a synthetic caseinbase diet containing negligible amounts of sodium, potassium, magnesium, chloride, and phosphorus. Electrolytes were provided in a gavage solution by means of an automatic refilling syringe pipet; each 5 ml contained 1.25 mEq of Na, 2 mEq of K, 2.5 mEq of Cl, 1.25 mEq of Mg, and 0.75 mM P. Magnesium was eliminated from the gavage solution of the test animals (groups III and IV). Deionized water was allowed ad libitum.