American Federation for Medical Research

An inactive form of renin has been isolated from human plasma. It has been suggested that this may represent renin precursor secreted from the kidney. However, early studies failed to isolate inactive renin from human renal tissue. In this investigation, rapid processing of human kidney cortex at temperatures below 4 degrees C in the presence of protease inhibitors followed by cibacron-blue affinity chromatography allowed us to extract a totally inactive form of renal renin. Furthermore, we found that in kidney inactive renin constituted from 10 to as much as 50% of the total renin concentration. Biochemical characterization of the inactive renin from plasma and from kidney indicates that they are structural homologues and, when activated, have enzymatic properties that resemble active renal renin. Renal and plasma inactive renin were found to have the following properties in common: (a) a pH optimum of activation of 3.3; (b) reversible activation by acid dialysis on return to pH 7.4, 37 degrees C; (c) pH optima of enzyme activity of 7.8 with sheep angiotensinogen and 5.5 and 6.7 (biphasic) with human angiotensinogen; (d) Michaelis-Menten constants, Km, of 0.29-0.34 microM with sheep angiotensinogen, and 0.99-1.25 microM with human angiotensinogen; (e) an antibody to human renal renin mean inhibitory titer of 1:30,000 with 1 X 10(-4) Goldblatt units of activated renal or plasma inactive renin; (f) gel filtration profiles consisting of two peaks with apparent molecular weights of 56,000 +/- 1,500 and 49,200 +/- 1,000. Activation of plasma and kidney inactive renin by acid plus renal kallikrein was not accompanied by a change in gel filtration elution patterns. To determine whether inactive renin is released by the kidney, we measured inactive renin in samples obtained simultaneously from both the renal veins and inferior vena cava below the origin of the renal veins. In eight consecutive patients, inactive renin concentration was significantly higher in renal venous blood than in inferior vena caval blood. These data indicate that human kidney contains and secretes significant quantities of inactive renin. Thus, the kidney appears to be a major source of inactive renin in human plasma.

Calcium and phosphorus metabolism and balance were studied in 151 patients receiving total parenteral nutrition (TPN). Hypercalciuria was common, with mean (+/- SD) urinary calcium excretion 17.5 +/- 3.9 meq/24 hours (n = 2610). There was a significant positive correlation between urinary calcium excretion and parenteral calcium intake (r = 0.34, p less than 0.001). There was also a positive correlation between calcium balance and parenteral calcium intake (r = 0.61, p less than 0.001) in patients without extra-renal losses. Positive calcium balance was achieved with parenteral calcium intake greater than 15 meq/24 hours. Urinary phosphorus excretion correlated positively with parenteral phosphorus intake (r = 0.50, p less than 0.001). Phosphorous balance also correlated positively with parenteral phosphorus intake (r = 0.78, p less than 0.001). Positive phosphorus balance was achieved with parenteral phosphorus intake above 15 mmol/24 hours. Fifty-three patients received 1,000 IU vitamin D once weekly and showed no significant change in serum calcium. Ninety-eight patients received 1,000 IU vitamin D twice weekly and showed a gradual but significant mean increase over time in serum calcium.

The effects of chronic phosphate depletion on renal tubular function were evaluated by micropuncture and free water clearance studies in the dog. Proximal tubular punctures demonstrated that chronic hypophosphatemia led to a reduction in ratio of tubular fluid to plasma inulin in late superficial tubular from 1.59+/-0.08 in control animals to 1.29+/-0.06 in phosphate-depleted dogs, with proportional inhibition of calcium and sodium reabsorption. The chronic decrease in proximal tubular fluid reabsorption was confirmed by the analysis of sustained water diuresis in conscious, phosphate-depleted dogs, before and after repletion of body PO4 stores, and in control animals. Urine flow rate/100 ml glomerular filtration rate (V/GFR) was significantly higher in PO4 DEPLETION THAN CONTROL (15.8+/-1.1 VS. 10.7+/-0.82). In addition, acetazolamide infusion did not increase V/GFR in phosphate-depleted dogs (15.8+/-1.1 vs. 17.16+/-0.9), supporting the conclusion that inhibition of proximal tubular fluid reabsorption was responsible for the elevated urine flow rate. PO4 repletion over 5 days reduced V/GFR to 9.2+/-0.7 despite no change in urine osmolality and no change in GFR, further suggesting a specific reversible alteration in proximal tubular reabsorption in phosphate depletion. Although hypercalciuria was a constant finding in phosphate depletion (fractional excretion of calcium of 2.04+/-0.4% vs. 0.47+/-0.13% in controls), the enhanced distal delivery of calcium was not a crucial factor; acute phosphate infusion reduced urinary calcium excretion to control values without affecting the reduced proximal tubular reabsorption in either intact or thyroparathyroidectomized phosphate-depleted dogs the change in distal nephron calcium reabsorption was independent of parathyroid hormone (PTH) levels since infusion of PTH failed to alter urinary calcium excretion. We conclude that chronic phosphate depletion leads to a reversible, sustained inhibition in proximal tubular reabsorptive fuction as well as a specific decrease in distal nephron calcium reabsorption. This latter reabsorptive defect is sensitive to phosplate infusion but not corrected by PTH.

Groups of dogs were immunized with sheep erythrocytes administered either directly into the lower respiratory tract (bronchoalveolar spaces) or intravenously. The hemolytic plaque-forming response (Jerne plaque assay) was studied in various canine lymphoid populations (bronchoalveolar cells, hilar lymph nodes, peripheral lymph nodes, and splenic and peripheral blood leukocytes) as a function of time after immunization and as a function of the dose of antigen administered. Serum hemagglutinating antibody titers against sheep erythrocytes were also measured. Intrapulmonary and intravenous administration of sheep erythrocytes to dogs both result in an immune response, the kinetics of which are identical to those observed in other animal species. At equivalent doses, the intravenous route is more efficient than the intrapulmonary route in generating serum hemagglutinating antibodies and antibody-forming cells. Both routes give rise transiently to circulating antibody-forming cells during the primary response; the distribution in tissues of antibody-forming cells is distinctive and unique, depending on the route of immunization. After i.v. immunization, antibody-forming cells are found predominately in spleen, blood, and bronchoalveolar spaces; after intrapulmonary immunization, they are located predominately in hilar lymph nodes, blood, and bronchoalveolar spaces. The reasons for this pattern of distribution are not known. Both routes of immunization are equally effective in populating bronchoalveolar air spaces with antibody-forming cells, which are predominately IgM-secreting and IgG-secreting cells. IgA-secreting cells were not detected.

The acute effects of epinephrine, norepinephrine, and isoproterenol on the plasma immunoreactive parathyroid hormone (iPTH) response were studied in 13 550-600 kg cows. Catecholamines were infused for 7.0 min. During epinephrine infusions at 0.08 mumol/min iPTH increased from 0.48+/-0.12 (mean+/-SE, ng/ml) to 1.09+/-0.18 ng/ml (P < 0.02). Small increases in plasma free fatty acids and glucose could be detected with 0.08 mumol/min epinephrine; the iPTH response to epinephrine was as sensitive as the free fatty acid and glucose responses and possibly of physiological importance. Plasma calcium (total and ionized) and magnesium did not change. The responses were more pronounced at 0.8 mumol/min epinephrine with a mean iPTH increase from 0.49+/-0.16 ng/ml to 1.74+/-0.35 ng/ml (P < 0.01). Small decreases in plasma calcium occurred at 0.8 mumol/min epinephrine, but the plasma magnesium remained unchanged. However, when the plasma calcium was lowered with ethylene glycol bis(beta-aminoethyl ether)-N, N'-tetraacetic acid (EGTA), a much more pronounced lowering of the plasma calcium was required to produce comparable increases of the plasma iPTH concentrations than when epinephrine was infused. It appears that epinephrine has a direct effect on the release of iPTH from the parathyroid glands. Simultaneous infusions of calcium and epinephrine suppressed the stimulation by epinephrine. This points towards a common mechanism of the regulation of parathyroid hormone secretion caused by decreases in the extracellular calcium concentration and/or alterations in the distribution of calcium within parathyroid cells following the administration of epinephrine. The iPTH response to epinephrine was suppressed in the presence of propranolol. Isoproterenol was less active in raising iPTH than epinephrine, and norepinephrine was the least active. The stimulation by isoproterenol and the suppression by propranolol suggest beta adrenergic receptor sites within the parathyroid glands.