Calcium metabolism of brain in acute renal failure. Effects of uremia, hemodialysis, and parathyroid hormone.

Studies were carried out to evaluate the changes in content of calcium and magnesium in brain during acute uremia in dogs. Ca content in gray and white matter of brain increased significantly after 3 days of acute uremia and this increment was prevented by thyroparathyroidectomy (TPTX). The administration of parathyroid extract (PTE) to normal dogs and TPTX uremic animals produced a significant rise in brain Ca. These changes were not related to alteration in the concentration of Ca in plasma or cerebrospinal fluid, to changes in calcium-phosphorus product, or to changes in blood pH. Furthermore, the infusion of large amounts of phosphate to vitamin D2-treated animals with suppressed parathyroid gland activity produced marked elevation in calcium-phosphorus product but no significant change in brain Ca. Also, uremia in vitamin D2-treated TPTX dogs failed to increase calcium content in brain despite marked elevation in calcium-phosphorus product. Hemodialysis significantly reduced Ca content of brain but the values were still significantly higher than normal. Mg content increased modestly only in the white matter of uremic dogs with intact parathyroid glands and in normal dogs and TPTX uremic dogs receiving PTE. The results indicate that (a) acute uremia of 3 days is associated with a marked rise of Ca content of brain and modest increment of Mg in certain parts of the brain, and (b) these alterations are not related to uremia, per se, but are dependent on the presence of excess parathyroid hormone. It is suggested that the neurological abnormalities noted in acute uremia may be related in part to the rise in the Ca content of brain.

Effect of parathyroid hormone on rat heart cells.

Myocardiopathy is common in uremia, but its cause in unknown. Excessive entry of calcium in heart cells by catecholamines has been shown to cause necrosis of myocardium. The high blood levels of parathyroid hormone (PTH) in uremia may also enhance entry of calcium into heart cells and exert deleterious effects on the heart. We examined the effect of PTH on rat heart cells grown in culture. Both amino-terminal (1-34) PTH and intact (1-84) PTH, but not the carboxy-terminal (53-84) PTH produced immediate and sustained significant rise in beats per minute and the cells died earlier than control. The effect was reversed if PTH was removed from medium, and was abolished by inactivation of the hormone. There was a dose-response relationship between both moieties of PTH and the rise in heart beats, but the effect of 1-84 PTH was significantly greater than that of 1-34 moiety. PTH stimulated cyclic AMP production within 1 min, and cyclic AMP remained significantly elevated thereafter. The effect of PTH required calcium, was mimicked by calcium ionophore, was prevented by verapamil and was not abolished by alpha- or beta-adrenergic blockers. PTH action was additive to phenylephrine and synergistic with isoproterenol. Sera from uremic parathyroidectomized rats did not effect heart beats, but sera from uremic rats with intact parathyroid glands or from uremic-parathyroidectomized rats treated with PTH had effects similar to PTH. Data indicate that (a) heart cell is a target organ for PTH and may have receptors for the hormone; (b) PTH increases beating rate of heart cells and causes early death of cells; (c) PTH effect appears to be due to calcium entry into heart cells; (d) the locus of action through which PTH induces calcium entry is different from that for catecholamines; and (e) uremic serum has no effect unless it contains PTH. Data suggest that myocardial damage may occur in uremia due to prolonged exposure to very high blood levels of PTH, and assign new dimensions to PTH toxicity in uremia.

Changes in serum and urinary calcium during phosphate depletion: studies on mechanisms.

The changes in serum calcium and the renal handling of this ion were evaluated during phosphate depletion. 96 renal clearance studies were carried out in 10 dogs before and after prolonged phosphate depletion (30-160 days) and after repletion. Depletion was produced by reducing phosphate intake and administering aluminum hydroxide gel while intakes of sodium, calcium, and magnesium were constant. With phosphate depletion, serum phosphorus fell to less than 1.0 mg/100 ml and diffusible serum calcium either remained unchanged or rose transiently. Glomerular filtration rate (GFR) fell by 15 to 53%. Despite the reduced filtered load of calcium, its fractional excretion increased in most experiments. This hypercalciuria was not dependent upon changes in sodium or magnesium excretion, or the urinary concentration of complexing anions, and persisted after sodium restriction. Phosphate repletion reversed the effects on GFR and calcium excretion. The intravenous infusion of small quantities of phosphate (0.04 mmole/min) into either intact or thyroparathyroidectomized (T-PTX), phosphate-depleted animals caused a significant reduction in fractional excretion of calcium, but the intrarenal infusion of 0.02 mmole/min of phosphate into one kidney failed to produce an ipsilateral effect. The administration of parathyroid extract reduced fractional calcium excretion, but the latter remained significantly elevated. After T-PTX, fractional calcium excretion did not increase in the phosphate-depleted animals. Furthermore, serum calcium was normal after T-PTX until serum phosphorus increased slightly, and only then did hypocalcemia develop. These observations indicate that (a) phosphate depletion produces hypercalciuria through a reduction in tubular reabsorption of calcium which is not due to changes in the tubular reabsorption of other ions; this effect is not reversed by the direct intrarenal infusion of phosphate; (b) a state of functional hypoparathyroidsm occurs during phosphate depletion which may, in part, cause reduced tubular reabsorption of calcium; (c) other extra renal mechanism(s), possibly related to events occurring in bone as a result of phosphate depletion, may have an effect on urinary calcium excretion; and (d) in the phosphatedepleted state, parathyroid hormone is not required for the maintenance of a normal level of serum calcium.

Effect of chronic bile duct obstruction on renal handling of salt and water.

Renal sodium reabsorption and the concentrating and diluting abilities of the kidney were evaluated in the same trained mongrel dogs before and after chronic common bile duct ligation (BDL). Glomerular filtration rate (GFR) and C(PAH) were not altered by BDL. The natriuretic response to a standardized infusion of 0.45% solution of NaCl was markedly blunted by BDL (P < 0.01); calculated distal sodium delivery was significantly less in experiments after BDL than in control studies. Furthermore, the fractional reabsorption of sodium at the diluting segment for any given rate of distal delivery was enhanced by BDL. Similarly, C(H2O)/100 ml GFR for a given sodium delivery was higher after BDL than control values. Maximal urinary concentration (Uosm-max) was lower after BDL, and the mean Uosm-max for the whole group of animals was 60% of the control value (P < 0.001). Mean maximal T(H2O)/100 ml GFR after BDL was not different from control values; however, T(c) (H2O)/100 ml GFR for a given Cosm/100 ml GFR was lower after BDL in three dogs only. The sodium content of the inner part of renal medulla after BDL was significantly lower than the values obtained in control animals. The excretion of an oral water load in the conscious state was impaired after BDL; although all animals excreted hypotonic urine, urinary osmolality was usually higher after BDL than in control studies. Maximal urinary concentration and the excretion of an oral water load were not affected by sham operation. These studies demonstrate that chronic, common bile duct ligation is associated with (a) enhanced sodium reabsorption both in the proximal and diluting segments of the nephron, (b) a defect in attaining maximal urinary concentration, (c) diminished sodium content in the renal papilla, and (d) impaired excretion of a water load. The results suggest that decreased distal delivery of sodium may underlie the abnormality in the concentrating mechanism and in the inability to normally excrete a water load. In addition, antidiuretic activity despite adequate hydration, may contribute to the impaired water diuresis. Chronic, common bile duct ligation appears to provide a readily available and reproducible model for the study of liver-kidney functional interrelationship.

Evidence for stimulation of renal gluconeogenesis by catecholamines.

Isoproterenol and norepinephrine (10(-4) M) significantly increased cyclic AMP formation and glucose production by the isolated tubules of the renal cortex of the rat. These effects were abolished by propranolol. Theophylline diminished the effects of the catecholamines on gluconeogenesis despite a marked augmentation in cyclic AMP concentration. In the absence of calcium ion in the incubation medium, isoproterenol stimulates cyclic AMP production, but has no effect on gluconeogenesis. It is concluded that catecholamines enhance gluconeogenesis in renal cortical tubules by the stimulation of beta adrenergic receptors. This effect is probably mediated through adenyl cyclase-cyclic AMP system and requires an adequate level of ATP and the presence of calcium ion.

Osteomalacia and hyperparathyroid bone disease in patients with nephrotic syndrome.

Patients with nephrotic syndrome have low blood levels of 25 hydroxyvitamin D (25-OH-D) most probably because of losses in urine, and a vitamin D-deficient state may ensue. The biological consequences of this phenomenon on target organs of vitamin D are not known. This study evaluates one of these target organs, the bone. Because renal failure is associated with bone disease, we studied six patients with nephrotic syndrome and normal renal function. The glomerular filtration rate was 113+/-2.1 (SE) ml/min; serum albumin, 2.3+/-27 g/dl; and proteinuria ranged between 3.5 and 14.7 g/24 h. Blood levels of 25-OH-D, total and ionized calcium and carboxy-terminal fragment of immunoreactive parathyroid hormone were measured, and morphometric analysis of bone histology was made in iliac crest biopsies obtained after double tetracycline labeling. Blood 25-OH-D was low in all patients (3.2-5.1 ng/ml; normal, 21.8+/-2.3 ng/ml). Blood levels of both total (8.1+/-0.12 mg/dl) and ionized (3.8+/-0.21 mg/dl) calcium were lower than normal and three patients had true hypocalcemia. Blood immuno-reactive parathyroid hormone levels were elevated in all. Volumetric density of osteoid was significantly increased in three out of six patients and the fraction of mineralizing osteoid seams was decreased in all. Evidence for an increase in active lacunae (bone-osteoclast interface) occurred in three out of six patients and in inactive (Howship's lacunae) bone resorption in six out of six. The data indicate that the loss of 25-OH-D in urine of patients with nephrotic syndrome and normal renal function may result in a decrease of blood levels of ionized calcium, secondary hyperparathyroidism and enhanced bone resorption. In addition, the vitamin D-deficient state causes osteomalacia as evidenced by defective mineralization and increased osteoid volume.

The influence of extracellular volume expansion on renal phosphate reabsorption in the dog.

Extracellular volume expansion (ECVE) was produced, by normal saline infusion, in five normal and six thyroparathyroidectomized anesthetized dogs while glomerular filtration rate was reduced by the inflation of an intra-aortic balloon located above the renal arteries. The effect of ECVE on the maximum renal tubular reabsorptive capacity of phosphate (phosphate Tm) was also evaluated in five additional dogs. During ECVE, phosphate excretion increased both in normal and thyroparathyroidectomized dogs, and a direct and significant correlation was found between the fractional excretion of phosphate and sodium. Despite a substantial decrease in filtered phosphate which is produced by the acute reduction in glomerular filtration rate, phosphate excretion, during ECVE, exceeded control values. ECVE was associated with a reduction in phosphate Tm. The results demonstrate that ECVE increases phosphate excretion independent of changes in glomerular filtration rate and parathyroid gland activity. The data indicate that ECVE produced by saline infusion decreases the renal tubular reabsorption of phosphate.

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.

changes in serum and urinary calcium during treatment with hydrochlorothiazide: studies on mechanisms.

Studies were undertaken in man to evaluate the roles of volume depletion and of the parathyroid glands in mediating the changes in serum and urinary calcium which follow the administration of hydrochlorothiazide, 100 mg twice daily, for 4 days, 42 studies were carried out in 16 normal subjects, 9 patients with hyperparathyroidism, and 7 vitamin D-treated subjects with hypoparathyroidism. In six studies in normal subjects, daily sodium losses during thiazide administration were quantitatively replaced, and in six other studies the effect of equivalent sodium losses produced by furosemide was evaluated. Although the magnitude of sodium losses was similar in three groups during therapy with thiazides, urinary calcium fell and urinary phosphorus increased significantly only in normal subjects and those with hyperparathyroidism; no change occurred in patients with hypoparathyroidism. With the replacement of the thiazide-induced sodium losses by NaCl in normals, urinary calcium did not change as urinary sodium increased 4- to 5-fold. Furosemide administration produced similar sodium losses while urinary calcium remained at or above control levels. After correction for changes in plasma protein concentration caused by thiazide-induced hemoconcentration, mean levels of serum calcium were significantly increased only in subjects with hyperparathyroidism and vitamin D-treated patients with hypoparathyroidism. The results indicate that both depletion of extracellular fluid volume and the presence of the parathyroid glands are necessary for the decrease in urinary calcium in response to thiazide therapy. Both the reduction in urinary calcium and increase in urinary phosphate after the use of thiazides may be due, in part, to potentiation of the action of the parathyroid hormone on the nephron. The rise in serum calcium could be due to thiazide-induced release of calcium from bone into extracellular fluid, particularly in states where bone resorption may be augmented, i.e., vitamin D therapy or hyperparathyroidism.

Effect of parathyroid hormone and uremia on peripheral nerve calcium and motor nerve conduction velocity.

Peripheral neuropathy is not an uncommon complication of chronic uremia. Because parathyroid hormone, by raising brain calcium, is partly responsible for central nervous system aberrations in uremia, we studied the relative role of uremia, per se, and(or) parathyroid hormone on peripheral nerve calcium and motor nerve conduction velocity (MNCV). Studies were made in six groups of six dogs each, as follows: (a) normal dogs, (b) thyroparathyroidectomized (T-PTX) animals, (c) dogs with 3 days of uremia produced by bilateral nephrectomy, (d) T-PTX before the induction of acute renal failure, (e) normal dogs receiving 100 U/day of parathyroid extract (PTE) for 3 days, and (f) normal animals receiving 3 days of PTE followed by 5 days without PTE. Calcium content in peripheral nerve (expressed as milligram per kilogram of dry weight) was 252+/-5 (SE) in normal animals and 262+/-4 in T-PTX dogs. It was significantly (P < 0.01) higher in dogs with acute renal failure and intact parathyroid glands (410+/-12) and in normal animals receiving PTE (362+/-7). T-PTX, before acute renal failure, prevented the rise in peripheral nerve calcium (262+/-4) and PTE withdrawal was followed by the return of peripheral nerve calcium to normal (261+/-3). The increments in peripheral nerve calcium were associated with slowing of MNCV. It decreased significantly from 70+/-4 to 43+/-1 m/s after 3 days of acute uremia in dogs with intact parathyroid glands and T-PTX before acute renal failure prevented the fall in MNCV. Administration of PTE to normal animals reduced MNCV from 63+/-3 to 35+/-3 m/s and the withdrawal of PTE restored MNCV to normal (73+/-2 m/s). The results show that (a) excess parathyroid hormone increases peripheral nerve calcium and slows MNCV, (b) T-PTX, previously performed, prevents these changes in acute uremia, and (c) the withdrawal of PTE administration is followed by a reversal of the abnormalities.

Effect of parathyroid hormone on erythropoiesis.

Inhibitors of erythropoiesis have been found in the blood of uremic patients but their nature has not been identified. These patients have excess blood levels of parathyroid hormone (PTH) and it is possible that PTH inhibits erythropoiesis. The present study was undertaken to examine the effect of intact PTH molecules and some of its fragments on human peripheral blood and mouse bone marrow burst-forming units-erythroid (BFU-E), on mouse bone marrow erythroid colony-forming unit (CFU-E), and granulocyte macrophage progenitors (CFU-GM), and evaluate the interaction between PTH and erythropoietin (Ep) on human BFU-E. Intact PTH (1-84 bPTH) in concentrations (7.5-30 U/ml;) comparable to those found in blood of uremic patients produced marked and significant (P less than 0.01) inhibition of BFU-E and mouse marrow GFU-GM, but not of mouse marrow CFU-E. Inactivation of 1-84 bPTH abolished its action on erythropoiesis. Increasing the concentration of Ep in the media from 0.67 to 1.9 U/ml overcame the inhibitory effect of 1-84 bPTH on BFU-E. The N-terminal fragment of PTH (1-34 bPTH) and 53-84 hPTH had no effect on BFU-E. The results demonstrate that (a) either the intact PTH molecule or a C-terminal fragment(s) bigger than 53-84 moiety exerts the inhibitory effect on erythropoiesis, and (b) adequate amounts of Ep can overcome this action of PTH. The data provide one possible pathway for the participation of excess PTH in the genesis of the anemia of uremia.

Central nervous system pH in uremia and the effects of hemodialysis.

Rapid hemodialysis of uremic animals may induce a syndrome characterized by increased cerebrospinal fluid (CSF) pressure, grand mal seizures, and electroencephalographic abnormalities. There is a fall in pH and bicarbonate concentration in CSF, and brain osmolality exceeds that of plasma, resulting in a net movement of water into the brain. This syndrome has been called experimental dialysis disequilibrium syndrome. The fall in pH of CSF may be secondary to a fall of intracellular pH (pHi) in brain. Since changes in pHi can alter intracellular osmolality in other tissues, it was decided to investigate brain pHi in uremia, and the effects of hemodialysis. Brain pHi was measured by evaluating the distribution of 14C-labeled dimethadione in brain relative to CSF, while extracellular space was calculated as the 35504=/4 space relative to CSF. In animals with acute renal failure, brain (cerebral cortex) pHi was 7.06+/-0.02 (+/-SE) while that in CSF was 7.31+/-0.02, both values not different from normal. After rapid hemodialysis (100 min) of uremic animals, plasma creatinine fell from 11.8 to 5.9 mg/dl. Brain pHi was 6.89+/-0.02 and CSF pH and 7.19+/-0.02, both values significantly lower than in uremic animals (P less than 0.01), and there was a 12% increase in brain water content. After slow hemodialysis (210 min), brain pHi (7.01+/-0.02) and pH in CSF (7.27+/-0.02) were both significantly greater than values observed after rapid hemodialysis (P less than 0.01), and brain water content was normal. None of the above maneuvers had any effect on pHi of skeletal muscle or subcortical white matter. The data show that rapid hemodialysis of uremic dogs is accompanied by a significant fall in pH of CSF and pHi in cerebral cortex. Accompanying the fall in brain pHi is cerebral edema.

Changes in the electroencephalogram in acute uremia. Effects of parathyroid hormone and brain electrolytes.

Studies were carried out in order to evaluate the effects of changes in brain calcium and the influence of parathyroidectomy and administration of parathyroid extract on the electroencephalogram (EEG) of normal and uremic dogs. Manual analysis of frequency and power distribution of the EEG in uremic dogs revealed a significant increase in both the percentage distribution and the area or power occupied by frequencies below 5 Hz. In addition, high amplitude bursts of delta activity were apparent in the uremic dog. These changes were largely prevented by parathyroidectomy before the induction of uremia, but the administration of parathyroid extract to either normal dogs, or to previously parathyroidectomized uremic dogs, induced EEG changes similar to those noted in uremic animals with intact parathyroid glands. In all groups of animals which showed EEG changes, brain content of calcium was significantly higher than in either normal dogs or previously parathyroidectomized uremic dogs. Changes in arterial pH and bicarbonate, or in the concentrations of Na+, K+, urea, or creatinine in plasma or cerebrospinal fluid were similar in uremic animals with intact parthyroid glands and in previously parathyroidectomized uremia dogs. The results indicate that the EEG changes found in dogs with acute renal failure require the presence of excess parathyroid hormone in blood, and they may be related to the observed changes in brain content of calcium.

Mechanisms of seizures and coma in hypoglycemia. Evidence for a direct effect of insulin on electrolyte transport in brain.

The mechanisms involved in the production of hypoglycemic coma were studied in rabbits. Measurements were made in brain, cerebrospinal fluid (CSF), and plasma of osmolality, Na(+), K(+), Cl(-), water content, exogenous insulin, glucose, lactate, and glutamate, while pH, Pco(2), Po(2), and bicarbonate were evaluated in arterial blood, 35 min after i.v. injection of insulin (50 U/kg), plasma glucose did not change, but brain K(+) content increased significantly. Grand mal seizures were observed in unanesthetized animals (+/-SD) 133+/-37 min after administration of insulin, at a time when brain glucose was normal, but brain tissue content of Na(+), K(+), osmoles, and water was significantly greater than normal. Coma supervened 212+/-54 min after insulin injection, at which time brain glucose, lactate, and glutamate were significantly decreased. At both 35 and 146 min after insulin administration, exogenous insulin was present in brain, but not in the CSF. After 208 min of insulin administration, animals were given i.v. glucose and sacrificed 35 min later. Most changes in the brain produced by hypoglycemia were reversed by the administration of glucose. Hypoxia (Po(2) = 23 mm Hg) was produced and maintained for 35 min in another group of animals. Hypoxia caused brain edema but did not affect brain electrolyte content. However, brain lactate concentration was significantly greater than normal. The data indicate that the seizures noted early in the course of insulin-induced hypoglycemia are temporally related to a rise in brain osmolality secondary to an increased net transport into brain of Na(+) and K(+), probably caused by insulin, per se. As hypoglycemia persists, there is also depletion of energy-supplying substrates (glucose, lactate, glutamate) in the brain, an event which coincides with the onset of coma. The brain edema observed during hypoxia is largely due to an increase in brain osmolality secondary to accumulation of lactate.

Effect of parathyroid hormone on osmotic fragility of human erythrocytes.

The survival of erythrocytes (RBC) is shortened in uremia, and it has been shown that calcium influx into RBC evoked crenation and increased their rigidity. The high blood levels of parathyroid hormone (PTH) may augment entry of calcium into RBC and hence affect their integrity. We examined the effect of PTH on osmotic fragility of human RBC and investigated the mechanisms through which PTH interacts with RBC. Both the amino-terminal (1-34) PTH and the intact (1-84) PTH, but not the carboxy-terminal (53-84) PTH, produced significant increases in osmotic fragility. This effect was abolished by prior inactivation of the hormone. There was a dose-response relationship between both moieties of PTH and the increase in osmotic fragility. This action of PTH required calcium, was mimicked by calcium ionophore, and was partially blocked by verapamil. PTH caused significant influx of (45)Ca into RBC, which was not associated with potassium leak. The hormone did not affect water content of RBC. Scanning electron microscopy revealed that the incubation of RBC with PTH was associated with the appearance of membrane filamentous extensions, which anchor RBC together. Inhibition of glycolytic activity of RBC with NaF or inhibition of Na-K-activated ATPase with ouabain did not abolish the effect of PTH on osmotic fragility. PTH did not stimulate RBC Na-K-activated ATPase or Mg-dependent ATPase but caused marked and significant stimulation of Ca-activated ATPase. The basal activity of the RBC adenylate cyclase was low and PTH produced only a modest stimulation of this enzyme. Both cyclic AMP and dibutyryl cyclic AMP had no effect on osmotic fragility. THE DATA INDICATE THAT: (a) the RBC is a target organ for PTH, (b) the hormone increases osmotic fragility of RBC, and (c) this effect of PTH is due to enhanced calcium entry into RBC. We suggest that the increased calcium influx may affect the spectrin-actin of the cytoskeletal network of the RBC and may alter the stability and integrity of the cell membrane. This action of PTH on the RBC could be, at least in part, responsible for the shortened survival of RBC in uremia, and assign a new role for PTH in the pathogenesis of the anemia of uremia.

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.

Renal bicarbonate wasting during phosphate depletion. A possible cause of altered acid-base homeostasis in hyperparathyroidism.

With hyperparathyroidism, serum bicarbonate (HCO(3) (-)) is low, urinary excretion of HCO(3) (-) is increased and the apparent T(m) for HCO(3) (-) is reduced. These findings have been ascribed to a direct renal action of parathyroid hormone (PTH). Since hypophosphatemia and phosphate depletion may occur in hyperparathyroidism, it is possible that phosphate depletion could account for the abnormal renal HCO(3) (-) handling. To test this possibility, renal reabsorption of HCO(3) (-) was evaluated in dogs before and after phosphate depletion. Serum HCO(3) (-) was significantly lower in phosphate depleted dogs than in normal animals, and serum HCO(3) (-) was directly related to serum phosphorus. Both the threshold at which HCO(3) (-) appeared in the urine and the T(m) for HCO(3) (-) were reduced during phosphate depletion. Intracellular pH of muscle was significantly higher in phosphate depleted dogs than in normals and the pH returned to normal after phosphate repletion. These data show that phosphate depleted dogs, which probably have physiological hypoparathyroidism, display abnormalities in both serum HCO(3) (-) and its renal handling which are similar to those seen in hyperparathyroidism, supporting the concept that the PTH-induced alterations in HCO(3) (-) homeostasis may be due to phosphate depletion. The latter could alter cell metabolism, resulting in reduced intracellular H(+) concentration, which may then impair H(+) secretion by the renal tubules and decrease their ability to reabsorb HCO(3) (-). Consequently, T(m) HCO(3) (-) and serum HCO(3) (-) fall.

Abnormalities in hepatic lipase in chronic renal failure: role of excess parathyroid hormone.

Post-heparin hepatic lipase activity is reduced in chronic renal failure (CRF). This could be due to reduced synthesis, decreased activity, and/or impaired secretion of the enzyme. Further, the factor(s) responsible for such derangements are not elucidated. We examined hepatic lipase metabolism in normal, 6-wk-old CRF rats, CRF-PTX (parathyroidectomized) rats, and CRF and normal rats treated with verapamil (CRF-V, normal-V) using liver homogenate, hepatic cell culture for 8 h, and in vitro liver perfusion. The Vmax of hepatic lipase in liver homogenate was significantly (P < 0.01) reduced and the Km was significantly (P < 0.01) increased in CRF rats, but the values were normal in CRF-PTX, CRF-V, and normal-V rats. Culture of hepatic cells for 8 h was associated with an increase in hepatic lipase activity but the increment in CRF rats was significantly (P < 0.01) lower than that of normal, CRF-PTX, CRF-V, and normal-V rats. Both parathyroid hormone (PTH)-(1-84) and 1-34 inhibited the production of hepatic lipase in cultured cells from normal, CRF-PTX, CRF-V, and normal-V rats. The expression of the mRNA of the hepatic lipase was significantly reduced in CRF animals with the ratio between it and that of house keeping gene G3DPH being 15 +/-3% compared to 40 +/- 1.3% in normal, 44+/-2.9% CRF-PTX, 44 +/- 5.4% in CRF-V, and 39 +/- 3.9% in normal-V rats. Infusion of heparin to the in vitro hepatic perfusion system increased the activity of hepatic lipase in the effluent in all groups of rat except in CRF animals. Infusion of PTH-(1-34) in dose of 10(-6) M into the liver perfusion system inhibited the increase in post-heparin hepatic lipase activity. The data show that in CRF (a) the mRNA of hepatic lipase is downregulated, and hepatic lipase production, activity and release are impaired, (b) that this is due to the state of secondary hyperparathyroidism of CRF since both acute and chronic excess of PTH were associated with these abnormalities, (c) and that prevention of excess PTH by PTX of CRF rats or blocking the effect of PTH by treatment with verapamil corrected the derangement in hepatic lipase metabolism.

Effect of phosphate depletion on magnesium homeostasis in rats.

The effects of phosphate depletion on magnesium (Mg) homeostasis were evaluated in rats fed a diet containing 0.03% phosphorus for periods up to 8 wk. Plasma phosphorus fell significantly (P < 0.01) from 10.1+/-0.27 (SE) to 5.0+/-0.54 mg/100 ml within 1 day and continued to fall gradually to a level of 1.2+/-0.21 mg/100 ml by the end of the 8th wk. A significant (P < 0.01) increment in urinary Mg excretion (UMgV) from 46+/-2.7 to 126+/-24 mueq/24 h occurred during the 1st day of phosphate depletion; UMgV reached a peak of 300+/-24 mueq/24 h by the 3rd day and remained high ranging between 150-300 mueq/24 h, thereafter. The magnitude of the magnesuria was related to the degree of hypophosphatemia and was not affected by lowering the calcium intake and reducing the hypercalciuria. The concentration of plasma Mg fell significantly (P < 0.01) from 1.2+/-0.02 to 0.79+/-0.10 meq/liter by the 1st day of the study and remained low throughout.Mg balance became negative during the 1st day of phosphate depletion and remained so during the entire study. This occurred despite a significant increment in the fraction of ingested Mg absorbed which became evident by the 3rd wk of phosphate depletion. Mg content of muscle, kidney, and liver were not affected but bone Mg was reduced significantly. The change in bone Mg was not due to an overall reduction in bone mineral content because bone calcium content was not affected. Supplementation of large amounts of Mg (800-1,000 mueq/day) in the drinking water produced a normalization of serum Mg but did not bring about restoration of bone Mg despite a positive Mg balance. The disturbances in Mg metabolism were independent of the age or weight of the animals. Our results indicate that phosphate depletion is associated with (a) magnesuria due to a decrease in the net renal tubular reabsorption of Mg with the main source of the urinary losses being bone Mg; (b) hypomagnesemia secondary to the renal leak of Mg; (c) negative Mg balance; and (d) increase in the intestinal fractional absorption of Mg. The latter was not adequate to compensate for the urinary losses of Mg.

Erythrocyte survival in chronic renal failure. Role of secondary hyperparathyroidism.

The human erythrocyte (RBC) is a target organ for parathyroid hormone (PTH) and the hormone increases RBC osmotic fragility and induces their hemolysis. The present study was undertaken to examine whether elevated blood levels of PTH affect RBC survival, and therefore whether PTH, being an extracorpuscular factor, is responsible for the shortened RBC survival in chronic renal failure. 51Cr-labeled RBC survival was elevated in six normal dogs, in six animals with chronic renal failure and secondary hyperparathyroidism (NPX), and in six thyroparathyroidectomized dogs (NPX-TPTX) with comparable degree and duration of chronic renal failure. In the normal dogs, 51Cr-labeled RBC survival ranged between 22 and 35 (25.6 +/- 1.9) d. In the NPX dogs, 51Cr-labeled RBC survival was shortened and the values ranged between 16 and 20 (18.4 +/- 0.6) d, a value significantly (P less than 0.01) lower than normal dogs. In NPX-TPTX dogs, 51Cr-labeled RBC survival ranged between 20 and 33 (25.2 +/- 1.8) d, a value not different from that in normal dogs but significantly higher (P less than 0.01) than that in NPX animals. Our data demonstrate that excess blood levels of PTH and not other consequences of the uremic state are responsible for the shortened RBC survival in chronic renal failure.