Renal handling of phosphorus in oliguric and nonoliguric mercury-induced acute renal failure in rats

The renal handling of phosphorus was evaluated in rats with acute renal failure (ARF) induced by injection of mercuric chloride (HgCl(2)). Clearances of endogenous creatinine (Ccr) and of phosphorus (Cp) were measured in the following groups: 1. Intact animals (control); 2. Parathyroidectomized rats (PTX) with normal kidney function (PTX control); 3. Animals with mercury-induced acute renal failure (Hg-ARF); 4. PTX rats with Hg-ARF; 5. Rats with Hg-ARF maintained normophosphatemic with dietary phosphate restriction; 6. Animals with oliguric ARF following renal artery constriction; 7. Rats with unilateral Hg-ARF. In addition, radioinulin clearances were measured in 6 normal and in 14 azotemic animals and correlated with simultaneously recorded endogenous Ccr. Radioinulin clearance was also used as an estimate of GFR (glomerular filtration rate) in the animals of group 7. The Cp/GFR in the intact animals (group 1) was 0.25 +/-0.06 (mean +/-SD). PTX (group 2) caused a subsequent decrease in Cp/GFR to 0.11 +/-0.04 P < 0.0005. The ARF animals in group 3 were classified either as oliguric (U(vol) [urine volume] <2 ml/24 hr, Ccr 0.008 +/-0.005 ml/min) or nonoliguric (V(vol) >2 ml/24 hr, Ccr 0.136 +/-0.12). The Cp/GFR in the oliguric animals (0.16 +/-0.09) was lower than that in group 1, P < 0.0005, and failed to increase following administration of exogenous parathyroid hormone. The Cp/GFR in the oliguric animals in groups 5 and 7 was also lower than the clearance ratio in group 1, 0.030 +/-0.08 and 0.077 +/-0.006, respectively. In the nonoliguric ARF animals of group 3 the Cp/GFR (0.94 +/-0.29) was higher than that in group 1, P < 0.0005. In the nonoliguric ARF animals of group 4 the Cp/GFR 0.27 +/-0.08 did not differ from the clearance ratio in group 1, however it was higher than that in the PTX animals (group 2) P < 0.0005. Cp/GFR in the nonoliguric animals of group 5 was not different from that in the nonoliguric rats of group 3. In the animals with nonoliguric unilateral Hg-ARF Cp/GFR on the affected side 0.51 +/-0.16 was higher than that on the control (contralateral) side, 0.23 +/-0.07, P < 0.0005. These results indicate that the low Cp/GFR observed in the oliguric ARF animals was not related to the level of circulating parathyroid hormone nor to the presence or absence of azotemia but probably was due to a reduced renal cortical perfusion. The high Cp/GFR in the nonoliguric ARF animals could be explained by secondary hyperparathyroidism and impaired phosphorus reabsorption due to tubular injury.

The clinical physiology of calcium homeostasis, parathyroid hormone, and calcitonin. I

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Evidence for suppression of parathyroid gland activity by hypermagnesemia

The effect of hypermagnesemia, produced by MgCl(2) infusion, on the activity of parathyroid glands, as assessed by changes in levels of serum calcium (S(Ca)) and in the fraction of filtered phosphate excreted (C(P)/C(Cr)), was studied in 11 intact and 4 thyroparathyroidectomized (T-PTX) dogs. To exclude the effect of diurnal variation in C(P)/C(Cr) on the results, studies were initiated in both morning and afternoon hours and each study with MgCl(2) infusion was paired with a control experiment in the same dog not receiving MgCl(2). During MgCl(2) infusion, serum phosphorus rose progressively. Despite this rise, the levels of C(P)/C(Cr) fell in all experiments and were significantly different from values observed at the same time of the day in the paired control experiments. The concentrations of total S(Ca) fell by 1.0-2.4 mg/100 ml with a proportional decrease in the levels of the diffusible and ionized fractions. The pattern of the fall in C(P)/C(Cr) during MgCl(2) resembled that observed after CaCl(2) infusion (seven dogs) and that which acutely followed thyroparathyroidectomy (seven dogs). When parathyroid extract was given to dogs receiving MgCl(2) infusion both C(P)/C(Cr) and S(Ca) rose, and MgCl(2) infusion did not affect C(P)/C(Cr) and S(Ca) in T-PTX dogs. These results indicate that hypermagnesemia suppresses the activity of the parathyroid glands, probably, by inhibiting production and (or) release of the hormone, without interfering with end-organ response. An increase in serum magnesium of 1.7-2.0 mg/100 ml was capable of producing the suppressive effect. Evaluation of the effect of simultaneous modest hypocalcemia and hypermagnesemia suggests that a decrease in the level of serum calcium is more potent than an increase in the concentration of serum magnesium in the regulation of parathyroid activity.

Divalent ion excretion in chronic kidney disease: relation to degree of renal insufficiency

1. The excretory patterns of sodium, calcium, magnesium and phosphorus were evaluated in seventy-eight patients with varying degrees of renal insufficiency, and in twelve normal subjects.

2. In mild renal failure the fractional excretion of filtered sodium, magnesium and phosphorus are significantly higher while that of calcium is significantly lower than values seen in normals. In advanced renal failure the fractional excretions of the filtered loads of all these ions increase steeply. These patterns are not influenced by the type of renal disease.

3. The fractional excretions of filtered sodium and calcium, calcium and magnesium, and sodium and magnesium were plotted against each other. The analysis of the plots showed that the fractional excretions of their filtered loads correlate poorly in patients with mild and moderate renal insufficiency, but closely in patients with severe renal failure.

4. These results indicate that the relation between the renal handling of divalent ions is not uniform at all levels of renal insufficiency. The dissociation between the excretory patterns observed in patients with early renal failure is consistent with the concept that different mechanisms may influence each individual ion separately. This is in contrast to the close association which exists between the excretory patterns of these ions in patients with advanced renal disease, and in which a single common mechanism may underlie the renal handling of these ions.