Joseph Seifter

Blood Pressure Control, Proteinuria, and the Progression of Renal Disease: The Modification of Diet in Renal Disease Study

Progressive functional deterioration occurs in most forms of chronic renal disease [1, 2]. Although the mechanisms underlying the progression of renal disease are probably multifactorial [2, 3], both hypertension [3-5] and proteinuria [3, 6-9] may contribute to the progressive loss of renal function. The Modification of Diet in Renal Disease (MDRD) Study compared the rates of decline in glomerular filtration rate in 840 patients with a diverse array of renal diseases who were randomly assigned to either a usual or a low blood pressure goal [10, 11]. In study A (baseline glomerular filtration rate, 25 to 55 mL/min1.73 m2), the intent-to-treat analysis included all patients and showed that the mean decline in glomerular filtration rate was faster in the first 4 months of follow-up and slower thereafter in the low than in the usual blood pressure group [10]. These results suggest that the low blood pressure goal has a long-term benefit. However, the duration of follow-up (0 to 3.7 years) was insufficient to show a difference between the two blood pressure groups in the decline of glomerular filtration rate at the end of the study. In study B (baseline glomerular filtration rate, 13 to 24 mL/min1.73 m2), the decline in glomerular filtration rate was linear and did not differ significantly between the two blood pressure groups. In studies A and B, subgroup analyses showed that baseline proteinuria was a strong predictor of subsequent decline in glomerular filtration rate and that assignment to the low blood pressure goal produced a significantly greater benefit on the rate of decline in glomerular filtration rate in patients with higher baseline proteinuria [10, 12]. We examined the relation of prescribed and achieved blood pressure with decline in glomerular filtration rate, placing particular emphasis on how this relation is affected by proteinuria at baseline. We also evaluated the effect of blood pressure on changes in proteinuria and the relation between changes in proteinuria during follow-up and subsequent decline in glomerular filtration rate. Methods Study Design The MDRD Study consisted of two randomized clinical trials done in a total of 840 patients who had chronic renal diseases of diverse cause [10, 11]. The study protocol was approved by the review boards of the 15 participating institutions. Eligibility criteria included the following: age of 18 to 70 years; serum creatinine level of 1.2 to 7.0 mg/dL for women and 1.4 to 7.0 mg/dL for men or a creatinine clearance less than 70 mL/min1.73 m2; and mean arterial pressure of 125 mm Hg or less [13]. Patients were excluded if they had diabetes requiring insulin, proteinuria of 10 g/d or more, or body weight less than 80% or more than 160% of standard body weight [14]. After a 3-month baseline period, 585 patients who had a glomerular filtration rate of 25 to 55 mL/min1.73 m2, dietary protein intake of more than 0.9 g/kgd, and mean arterial pressure of 125 mm Hg or less were entered into study A. Two hundred fifty-five patients who had a glomerular filtration rate of 13 to 24 mL/min1.73 m2 and a mean arterial pressure of 125 mm Hg or less were entered into study B. Patients in both studies were randomly assigned to either a usual or a low blood pressure goal. The usual blood pressure goal was a mean arterial pressure of 107 mm Hg or less (for patients less than equals 60 years of age) or 113 mm Hg or less (for patients more than equals 61 years of age). The low blood pressure goal was 15 mm Hg lower: It was a mean arterial pressure of 92 mm Hg or less (for patients less than equals 60 years of age) or 98 mm Hg or less (for patients more than equals 61 years of age). Patients in study A were also randomly assigned to receive either a usual protein (1.3 g/kgd) or low-protein (0.58 g/kgd) diet. Patients in study B were assigned to receive either the low-protein or a very-low-protein (0.28 g/kgd) diet supplemented with a mixture of ketoacids and amino acids (0.28 g/kgd; Ross Laboratories, Columbus. Ohio). Results of the dietary interventions have been reported elsewhere [10, 15]. Randomization, done at the Data Coordinating Center, was stratified according to clinical center and average mean arterial pressure at baseline (both studies A and B) and according to the rate of change in serum creatinine levels before study entry (study A only). Additional details about the baseline period have been reported elsewhere [13, 16]. The mean duration of follow-up was 2.2 years. In study A, 553 patients had glomerular filtration rate measurements extending to at least 1 year of follow-up; 381 patients had glomerular filtration rate measurements extending to at least 2 years of follow-up; and 143 patients had glomerular filtration rate measurements extending to at least 3 years of follow-up. In study B, 219 patients had glomerular filtration rate measurements extending to at least 1 year of follow-up; 137 patients had glomerular filtration rate measurements extending to at least 2 years of follow-up; and 62 patients had glomerular filtration rate measurements extending to at least 3 years of follow-up. Antihypertensive Regimens Both nonpharmacologic and pharmacologic interventions were implemented. During the baseline period, antihypertensive regimens were prescribed to achieve the usual blood pressure goal. After randomization, the regimens were modified to achieve either the low or the usual blood pressure goal. Nonpharmacologic therapy included recommendations for regular exercise and for reductions in body weight and intake of alcohol and sodium. Pharmacologic therapy was based on the stepped-care approach defined in the 1988 Report of the Joint National Committee [17]. Use of all antihypertensive drugs was allowed, but angiotensin-converting enzyme inhibitors, with or without a diuretic, were encouraged as the agents of first choice. Calcium channel blockers, with or without a diuretic, were encouraged as the agents of second choice. Blood pressure was measured monthly using a standardized Hawksley random zero sphygmomanometer (Lancing, United Kingdom). Blood pressure regimens were modified monthly; they were modified more often as was necessary to achieve the blood pressure goals. Measurements and Definitions of Variables The primary outcome variable was decline in glomerular filtration rate. This rate was measured as the renal clearance of 125I-iothalamate [18, 19] at the beginning and end of the baseline period and at 2 months, at 4 months, and at every 4 months thereafter during follow-up. Protein intake was monitored by monthly 24-hour urinary urea nitrogen excretion tests [20]. Blood for hematologic and serum tests was obtained at the beginning and end of the baseline period and every 2 months during follow-up. Renal diagnoses were made using medical records and review of available historical information [13]. Each patient was classified as having one of nine renal diagnoses. If patients had baseline proteinuria of less than 3.0 g/d; had presumptive (rather than established) diagnoses of hypertensive nephrosclerosis, tubulointerstitial diseases, or other diseases; and had not had renal biopsy, they were placed in the other or unknown category. Patients with proteinuria of more than 3.0 g/d who had not had renal biopsy and who had the presumptive diagnoses listed above were placed in the glomerular diseases category. Mean baseline blood pressure was defined as the average of the two mean arterial pressure measurements made at the end of the first and second months of the baseline period. Mean follow-up blood pressure was defined as the average of all mean arterial pressure measurements obtained at nonglomerular filtration rate visits beginning at the third monthly follow-up visit (mean arterial pressure during glomerular filtration rate visits was consistently higher than during other visits). Proteinuria was measured monthly during the baseline period and every 2 months during the follow-up period in 24-hour urine samples by using the trichloroacetic acid (Ponceau) technique [21]. Baseline proteinuria was the average of four measurements. In some analyses, patients were classified into subgroups according to whether their baseline proteinuria was 0 to 0.25 g/d; 0.25 to 1.0 g/d; 1.0 to 3.0 g/d; or 3.0 g/d or more. For the analyses reported here, patients were classified as taking a class of antihypertensive agents if they reported taking agents of that class for more than 50% of follow-up visits. This definition was selected because most patients reported taking agents of any particular class for either less than 25% or more than 75% of follow-up visits. Statistical Analysis Hypothesis tests were considered statistically significant if P < equals 0.05, two-sided. No adjustments were made for multiple comparisons. To eliminate positive skewness, proteinuria was log transformed, and changes in proteinuria were expressed as the percentage change from baseline. Baseline characteristics were compared between groups using t-tests, analysis of variance, or chi-square tests, as appropriate. Comparisons of Randomized Groups Mean protein intake was similar in the usual and low blood pressure groups in both study A and study B. The effect of the blood pressure intervention was similar in the usual and low-protein diet groups in study A and in the low-protein and very-low-protein diet groups in study B. The effect of the dietary intervention was not influenced by baseline proteinuria. Consequently, comparisons of the blood pressure groups included all patients, regardless of dietary assignment. In study A, the decline in glomerular filtration rate in the blood pressure groups was compared using a 2-slope model in which each patient was assumed to have an initial rate of decline in glomerular filtration rate during the first 4 months of follow-up and a possibly different slope thereafter [10]. We used a mixed-effects model that allowed different rates of decline for each pat

The effects of meprobamate, barbiturates, d-amphetamine and promazine on experimentally induced conflict in the rat

SummaryConflict behavior was induced in rats by simultaneously rewarding with liquid food and punishing with pain shock every lever response made in the presence of a tone. Meprobamate, phenobarbital and pentobarbital increased the number of shocks a rat would accept in order to obtain the food reward; in contrast, promazine and d-amphetamine decreased the number of shocks taken. The technique thus permits a separation on a behavioral basis of meprobamate, pentobarbital and phenobarbital from promazine and d-amphetamine.

The effects of chlordiazepoxide and chlorpromazine on a punishment discrimination.

SummaryA punishment discrimination was conditioned in laboratory rats by simultaneously rewarding with food and punishing with shock all lever responses made in the presence of a discriminative stimulus (tone). Appropriate setting of the shock intensity resulted in either high or low but stable output of responses during the tone periods. Rats working on a high-shock control baseline were administered CDAP at 7.5, 15.0, and 30 mg/kg. These rats worked during the tone periods and tolerated more shocks in order to obtain food rewards. Rats working on a lowshock control baseline were administered CPZ at 0.25, 0.5, 1.0, 2.0, and 3.0 mg/kg. These rats accepted less shocks during the tone periods. The decrease in shocks taken bears a direct relationship to the increase in dose of the drug. Some preliminary data for a monkey show the reproducibility of the behavior as well as the CDAP effects in another species.

Lipid mobilizer (LM) from posterior pituitary of hogs.

Summary and conclusions 1. Dialyzate of hog posterior pituitary lobe induced hyperlipemia in rats, mice, guinea pigs, dogs and rabbits. 2. The LM activity was indistinguishable from that of plasma dialyzate from cortisonized animals. 3. Neither Pitressin® nor Pitocin® had LM activity. 4. Hog anterior pituitary extracts had no LM activity. 5. LM appears to be a hitherto undescribed hormone either elaborated or stored in the posterior pituitary.

Sodium-hydrogen exchange and glucose transport in renal microvillus membrane vesicles from rats with diabetes mellitus.

Diabetes mellitus is associated with important changes in renal hemodynamics and transport function. Disturbances in solute transport have also been characterized in nonrenal tissues during hyperglycemia and insulinopenia. The purpose of this study was to determine if diabetes is associated with adaptive changes in function of the brush-border membrane of the proximal tubule. We studied Na+ and glucose transport in rat microvillus membrane vesicles isolated from the renal cortex of streptozotocin-induced and BB/W autoimmune diabetic rats. Untreated diabetes was associated with an increase in pH-stimulated total and amiloride-sensitive 22Na+ uptake into vesicles. Insulin treatment returned vesicle 22Na+ uptake to control levels. The increased Na+/H+ exchange was shown to be a result of increased net renal acid production rather than a specific response to insulinopenia because treatment with NaHCO3 also returned 22Na+ uptake to control levels. On the other hand, Na+-glucose cotransport, which was depressed in vesicles from untreated diabetics, returned to control levels with insulin but not NaHCO3 administration. This decreased Na+-glucose cotransport was not secondary to reduction in transport sites in untreated diabetics. These results show that in diabetes mellitus, increased Na+/H+ exchange activity is not the direct result of insulinopenia. However, the diabetic state appears to alter the functioning of the luminal Na+-glucose cotransporter.

Adaptation of Na+-H+ exchange in renal microvillus membrane vesicles. Role of dietary protein and uninephrectomy.

The ablation of renal mass and institution of a high protein diet both lead to renal cortical hypertrophy and increased glomerular filtration rate (GFR). We studied Na+ transport in rat microvillus membrane vesicles isolated from uninephrectomized or sham operated rats fed 6% (low), 24% (standard), or 40% (high) protein diets. The feeding of high protein, as compared with low protein, was associated with a 50% increase in rates of pH-stimulated 22Na+ transport in isolated vesicles from sham and uninephrectomized animals. Values for the standard protein diet were intermediate to values for high and low protein. At each level of dietary protein intake, vesicular Na+ transport was greater in the uninephrectomized than in sham rats. The high protein diet was also associated with increased vesicular 22Na+ flux inhibitable by 1 mM amiloride. Increases in total and amiloride sensitive flux were also noted in the absence of a pH gradient. Conductive Na+ and H+ transport were not altered, nor were sodium-glucose and sodium-alanine cotransport. Kinetic studies revealed evidence for an increased Vmax of Na+-H+ exchange in uninephrectomized animals fed a 40 vs. a 6% protein diet whereas Km was unchanged. Supplements of NaHCO3 in the 40% protein diet, to adjust for an increased rate of net acid excretion, did not prevent the increased rates of Na+-H+ exchange. However, treatment with actinomycin D (0.12 mg/kg) prevented the increased Na+-H+ activity as well as the increased renal mass and GFR noted 24 h after unilateral nephrectomy. Na+-H+ exchange rate was closely correlated with GFR (r = 0.961; P less than 0.005) and renal mass (r = .986; P less than 0.001). These observations provide evidence for modification of the luminal membrane Na+-H+ exchanger in response to changes in dietary protein content and nephron number.

Lipid Mobilization by a Crystalline Peptide Isolated from Plasma of Horses Administered Cortisone.

Summary and conclusions (1) The active hyperlipemia inducing constituent of the dialyzate obtained from the plasma of horses administered cortisone has been crystallized and tentatively identified as a peptide. (2) Injection of 0.02 μg of crystalline material/kg IV induced marked hyperlipemia in intact mice, rats, guinea pigs, rabbits, dogs and humans as well as in hypophysectomized or adrenalectomized rats. (3) The animals used in this study were exposed to potential hepatotoxic agents.

Relation of endocrines and clearing factor inhibitors to hyperlipemia in fasted animals.

Summary 1. LM produced hyperlipemia only in animals primed for lipid mobilization. 2. Intravenous injection of toxic doses of protamine sulfate, convulsant doses of diisopro-pylfluorophosphate and pyrogenic doses of piromen produced hyperlipemia in intact animals. 3. The same doses of these substances injected into adrenalectomized and hypophy-sectomized rats did not produce hyperlipemia. 4. The hyperlipemic action of protamine or DFP is not attributable to direct inhibition of lipoprotein lipase but to a secondary effect mediated through the adrenals and pituitary. 5. The hyperlipemic action of protamine, DFP, pyrogens and possibly other stressors is best explained by release of LM.

Influence of hyaluronidase and steroids on permeability of synovial membrane.

Summary and Conclusions 1. The permeability of the synovial membrane as measured by speed of absorption and excretion into the urine of phenolsulphonphthalein (PSP) instilled into the joint was found to be surprisingly constant in a group of 16 normal rabbits. 2. Hyaluronidase markedly increased permeability of the synovial membrane. The effect was maximal and was not augmented by desoxycorticosterone acetate (DOCA). 3. Adrenal cortical extract decreased permeability of the synovial membrane and an tagonized the effect of hyaluronidase. This effect of adrenal steroids was more pronounced when they were released endogenously by the alarm reaction. Estrone also decreased the permeability of synovial membrane. 4. Desoxycorticosterone increased maximally the permeability of synovial membrane to the same extent as hyaluronidase and could not be augmented by hyaluronidase. 5. It is suggested that the normal permeability of the synovial membrane is in part controlled by the balance between adrenal steroids of the DOCA type and of the Compound E type. 6. These findings are consistent with current views of the etiology of rheumatoid arthritis either by hyaluronidases or from exposure to stressing stimuli. They are also consistent with the therapeutic effects of Compound E or of adrenocorticotrophic hormone in the treatment of arthritis.

Intracellular pH regulation and proton transport by rabbit renal medullary collecting duct cells. Role of plasma membrane proton adenosine triphosphatase.

Proton secretion in the renal medullary collecting duct is thought to occur via a luminal proton-ATPase. In order to determine what mechanism(s) participate in proton transport across medullary collecting duct (MCD) cells membranes, intracellular pH (pHi) regulation and proton extrusion rates were measured in freshly prepared suspensions of rabbit outer MCD cells. Cells were separated by protease digestion and purified by Ficoll gradient centrifugation. pHi was estimated fluorometrically using the entrapped intracytoplasmic pH indicator, 6-carboxyfluorescein. Proton extrusion rates were measured using a pH stat. The resting pHi of MCD cells was 7.19 +/- 0.05 (SE) in a nonbicarbonate medium of pH 7.30. When cells were acidified by exposure to acetate salts or by abrupt withdrawal of ammonium chloride, they exhibited pHi recovery to the resting pHi over a 5-min time-course. Depletion of greater than 95% of cellular ATP content by poisoning with KCN in the absence of glucose inhibited pHi recovery. ATP depletion inhibited proton extrusion from MCD cells. Treatment with N-ethylmaleimide also inhibited pHi recovery. In addition, cellular ATP content was dependent on transmembrane pH gradients, suggesting that proton extrusion stimulated ATP hydrolysis. Neither removal of extracellular sodium nor addition of amiloride inhibited pHi recovery. These results provide direct evidence that a plasma membrane proton-ATPase, but not a Na+/H+ exchanger, plays a role in proton transport and pHi regulation in rabbit MCD.