Circulating forms of human atrial natriuretic peptide in patients with congestive heart failure

To elucidate the circulating forms of human atrial natriuretic peptide (hANP) in patients with congestive heart failure (CHF), plasma samples obtained from 36 patients with CHF were analyzed and compared with those from normal subjects. Plasma concentrations of hANP-like immunoreactivity (LI) from normal subjects and patients with mild CHF (class I), as classified by the New York Heart Association (NYHA) functional criteria, did not differ (15 +/- 1 vs. 16 +/- 1 pmol/L, mean +/- SE), whereas plasma levels of hANP-LI in patients with moderate and severe CHF significantly (P less than 0.01) increased in relation to the severity of CHF (class II, 44 +/- 4 pmol/L; class III, 116 +/- 24 pmol/L; class IV, 141 +/- 21 pmol/L). Reverse-phase HPLC and gel permeation chromatography coupled with RIA for hANP revealed that the circulating forms of hANP-LI consisted of alpha-hANP, beta-hANP, and gamma-hANP in CHF, whereas alpha-hANP predominated in normal plasma. The percentage of beta-hANP in total hANP-LI as calculated from the chromatograms by gel filtration was greater in severe CHF (NYHA class III and IV) than those in mild CHF (NYHA class I and II), and apparently exceeded those of other forms. Successful medical treatment for CHF resulted in a marked reduction of total plasma hANP-LI levels with a concomitant disappearance or reduction of beta-hANP in 14 patients examined. These data suggest that beta-hANP and gamma-hANP are secreted from the failing human heart, possibly resulting from the augmented synthesis and/or the altered processing of hANP precursor in cardiocytes, and that circulating beta-hANP may serve as a potential marker for the severity of CHF in man.

Plasma endothelin levels in hypertension and chronic renal failure

Endothelin-1 is a novel endothelium-derived vasoconstrictive peptide. Using a highly specific and sensitive radioimmunoassay for endothelin-1, plasma levels of immunoreactive endothelin-1 were measured in 32 research subjects with normal renal function (21 normal subjects and 11 patients with essential hypertension), 24 patients with nondialyzed chronic renal failure, and 51 patients undergoing maintenance hemodialysis. Although there was no significant difference in plasma immunoreactive endothelin-1 levels among the three groups, patients with essential hypertension had significantly higher plasma endothelin-1 levels than normal subjects (2.29 +/- 1.09 vs. 1.41 +/- 0.50 pg/ml, p less than 0.025). When nondialyzed and hemodialyzed patients were divided into hypertensive and normotensive groups, the nondialyzed hypertensive group (n = 17) had higher plasma endothelin-1 levels than the comparable normotensive group (n = 7) (3.08 +/- 3.43 vs. 0.73 +/- 0.34 pg/ml, p less than 0.05), and the hemodialyzed hypertensive group (n = 18) had higher plasma endothelin-1 levels than the comparable normotensive group (n = 33) (2.66 +/- 1.92 vs. 1.35 +/- 0.73 pg/ml, p less than 0.005). Plasma atrial natriuretic factor, arginine vasopressin, renin activity, and aldosterone concentration did not show significant differences between hypertensive and normotensive individuals or a correlation with plasma endothelin-1 levels. These data suggest that circulating endothelin-1 may be partly involved in the development or maintenance of hypertension in humans.

Diabetic hypouricemia as an indicator of clinical nephropathy

We studied the possible association of the low serum uric acid level with incipient diabetic nephropathy in non-insulin-dependent diabetes mellitus (NIDDM). Of 201 NIDDM patients without a diminished glomerular filtration rate, 66 patients (32.8%) showed moderate hypouricemia of less than the mean-1 SD of 201 nondiabetic controls. Thirteen (6.5%) showed marked hypouricemia of less than the mean-2 SD. Hypouricemic patients showed normal daily urinary urate excretion with a markedly elevated urate clearance/creatinine clearance ratio. Most were under poor glycemic control, and presented either negative or intermittent clinical proteinuria. However, neither poor glycemic control, nor the presence of proteinuria or retinopathy alone significantly affected the serum uric acid level of the whole diabetic population. The glomerular filtration rate was determined in comparable groups of diabetic patients with hypouricemia and nonhypouricemic diabetic controls. The hypouricemic group showed a significantly higher endogenous creatinine clearance and lower serum beta-2-microglobulin levels than the nonhypouricemic group. These findings suggest that the hypouricemic group had a higher glomerular filtration rate. Long-term observation of up to 12 years of the above patients revealed that, in most patients, persistent hypouricemia was observed prior to the initial appearance of intermittent proteinuria. We hypothesize that glomerular hyperfiltration also occurs in NIDDM and that it lowers the serum uric acid by increasing the renal clearance of urate. Hypouricemia may also predict the future progression of incipient nephropathy in NIDDM.

Decreased fractional excretion of urate as an indicator of prerenal azotemia

Although the fractional excretion of uric acid (FEUA) is known to reflect extracellular fluid volume changes, the diagnostic significance of decreased FEUA in dehydration has not been previously reported. We studied the possible association between low FEUA and acute prerenal azotemia, and its diagnostic value, compared with other traditional indices, in discriminating prerenal azotemia from renal parenchymal causes of acute renal failure. In 65 chronic renal disease patients, 174 FEUA measurements were obtained from 24-hour urine collections. FEUA levels increased as reciprocal serum creatinine levels decreased. All 8 patients with prerenal azotemia showed significantly decreased FEUA values compared with chronic renal disease patients with a comparable degree of serum creatinine elevation, whereas all 7 patients with acute renal failure had FEUA values higher than those of chronic renal disease patients with comparable creatinine levels. FEUA values in prerenal azotemia were distinctly lower than those in acute renal failure (p less than 0.001). Patients with prerenal azotemia showed a lower fractional excretion of sodium, a lower fractional excretion of chloride and renal failure index, and a higher urine-to-plasma creatinine ratio than those with acute renal failure (p less than 0.05). However, these traditional indices were not useful in discriminating between the two conditions. The urine-to-plasma urea nitrogen ratio and the ratio of plasma urea nitrogen to creatinine showed no statistical difference between prerenal azotemia and acute renal failure. We conclude that, in acute azotemia, a decreased FEUA value may represent a reliable indicator of prerenal azotemia in the differential diagnosis of acute renal failure.

Renal tubular hypouricemia: evidence for defect of both secretion and reabsorption

Two patients had hypouricemia due to increased uric acid clearance. They showed no decrease of urate clearance to creatinine clearance ratio (Cua/Ccr) following pyrazinamide administration, and no increase of Cua/Ccr after probenecid. One patient showed a limited decline in Cua/Ccr after intravenous furosemide. In the other patient, neither acetylsalicylate nor furosemide produced any noticeable change in Cua/Ccr. Both showed a normal diuretic response after intravenous furosemide. The results indicate that they had massive defects in urate transport along the nephron, probably including both secretion and reabsorption.

Fasting plus prandial insulin supplements improve insulin secretory ability in NIDDM subjects

To examine how insulin secretory ability is modified by strict glycemic control in non-insulin-dependent diabetes mellitus (NIDDM) subjects, basal and/or prandial insulin was supplemented for 4 wk in 24 diabetic subjects who were secondary failures to sulfonylurea treatment. One intermediate-acting insulin injection a day (n = 7) failed to suppress the rise in plasma C-peptide after meals and did not improve plasma C-peptide responses during a posttreatment oral glucose challenge. Continuous subcutaneous insulin infusion with a premeal bolus (n = 8) suppressed both fasting and meal-related rises in C-peptide and improved C-peptide response during the posttreatment oral glucose challenge. Daily insulin requirements during the 4 wk of treatment were reduced significantly by 52%. A short-acting insulin injection before each meal (n = 9) without basal supplementation suppressed the prandial rise in C-peptide and was associated with a significant reduction in daily insulin requirements during 4 wk of treatment by 28%. Diabetic subjects whose fasting and prandial hyperglycemia were less than 140 and less than 200 mg/dl, respectively, showed a significantly higher C-peptide response during oral glucose challenge after treatment than those whose insulin treatment only normalized (less than 200 mg/dl) prandial but not basal hyperglycemia (greater than 140 mg/dl). These results suggest that a short-term period of meal-related insulin treatment (which normalized prandial glycemia) increases residual beta-cell function in NIDDM subjects who failed long-term sulfonylurea administration. A basal insulin supplement alone was not effective. The effectiveness of a prandial insulin supplement may have been further improved by a combined basal and meal-related treatment program.

Effectiveness of insulin suppositories in diabetic patients

Experimental insulin suppositories regulated postprandial hyperglycaemia in diabetic patients. The insulin suppositories seemed also to avoid hyperinsulinaemia. The formulation with more rapid dissolution of insulin, which contained a solid dispersed form of insulin, effectively reduced the insulin dose required.

Effect of endothelin-1 on release of arginine-vasopressin from perifused rat hypothalamus

Endothelin-1 (ET-1) is an endothelium-derived vasoconstrictor peptide with potent pressor activity. We studied the effect of ET-1 on release of arginine-vasopressin (AVP) from perifused rat hypothalamus. ET-1 (10(-10) to 10(-8) M) significantly stimulated AVP release. The ET-1-induced AVP release was completely blocked in the presence of nicardipine. Our results suggest a possible involvement of ET in the regulation of AVP release.

Secretion of endothelin and related peptides from renal epithelial cell lines

Using specific radioimmunoassays (RIAs) for endothelin (ET) and big ET, we have studied whether ET and related peptides are secreted from renal epithelial cell lines (LLCPK1 and MDCK) of non-endothelial origin. Dilution curves of extracts of conditioned media from both LLCPK1 and MDCK cell lines were parallel to those of standard porcine (p) ET and big pET in each RIA. Both cell lines incubated in serum-free medium secreted ET- and C-terminal fragment (CTF)-like immunoreactivity (LI) of big ET as a function of time. Reverse-phase HPLC coupled with both RIAs of the extracted media from both cell lines revealed a single component with ET-LI coeluting with pET(1-21) and several components with CTF-LI, one corresponding to the elution position of big pET(1-39), one to its CTF(22-39), and the others eluting earlier than CTF. These data indicate that endothelin and related peptides are synthesized by and secreted from cells other than endothelial cells.

Concomitant secretion of big endothelin and its C-terminal fragment from human and bovine endothelial cells

A specific radioimmunoassay (RIA) for the carboxyl-terminal fragment (CTF) of big porcine endothelin (pET), an intermediate form of pET, was established to characterize big ET-like and its CTF-like immunoreactivity (LI) secreted from cultured bovine and human endothelial cells (EC). The antibody used crossreacted equally with big pET(1-39) and its CTF(22-39), but not with pET(1-21). Serial dilution curves of the culture media from bovine and human EC were parallel to that of standard CTF. Reverse-phase HPLC coupled with RIAs for big ET and ET of the culture media from bovine and human EC revealed essentially the same elution profiles: two major CTF-LI components, one corresponding to big pET(1-39) and the other to its CTF(22-39), in addition to one major ET-LI component corresponding to pET(1-21). The amounts of CTF-LI were almost equal to that of ET-LI on a molar basis. These data suggest that big ET is processed by a putative ET converting enzyme to yield its CTF and the mature ET(1-21) in EC.

Vasoconstrictor-induced heterologous down-regulation of vascular atrial natriuretic peptide receptor

Long-term (24 h) pretreatment of cultured rat vascular smooth muscle cells with 100 nM angiotensin and 1 microM vasopressin induced a marked reduction of the maximal binding capacity of atrial natriuretic peptide (ANP) receptors in a fashion similar to that induced by phorbol ester. The down-regulation of the receptors induced by vasoconstrictors and phorbol ester was concomitantly associated with an attenuation of ANP-stimulated cGMP accumulation. These data suggest that vasoconstrictor-induced activation of protein kinase C is involved in the mechanism of heterologous down-regulation of vascular ANP receptors.

Specific receptor for endothelin in cultured rat cardiocytes

Specific binding sites for the endothelium-derived vasoconstrictor endothelin (ET) and its effect on cytosolic free Ca2+ concentrations [( Ca2+]i) were studied in a primary culture of cardiocytes from neonatal rats. Binding studies using 125I-labeled-porcine ET as a radioligand revealed the presence of a single class of high-affinity binding sites for ET in cardiocytes with an apparent Kd of 6-9 x 10(-10) M and a Bmax of 50,000-80,000 sites/cell. Neither various vasoconstrictors nor Ca2+-channel blockers affected the binding. Pretreatment with ET substantially reduced the total number of ET receptors without changing their affinity. ET dose-dependently increased [Ca2+]i in fura-2-loaded cardiocytes. These data indicate that cardiocytes have specific ET receptors that are controlled by a down-regulation mechanism, and that ET induces a receptor-mediated increase in [Ca2+]i in cardiocytes.

Secondary polycythemia associated with multiple myeloma

A 58-year-old man with polycythemia of more than 8 years duration developed multiple myeloma. Extensive examination indicated his polycythemia to be of a secondary type, but failed to reveal an underlying disorder. To the best of our knowledge, this is the first reported association of multiple myeloma in a patient with definitely-diagnosed secondary polycythemia.

Secretory mechanism of immunoreactive endothelin in cultured bovine endothelial cells

To elucidate the cellular mechanism by which endothelin (ET) is secreted, we have studied the effects of a variety of vasoactive agents on the secretion of immunoreactive (IR)-ET from cultured bovine endothelial cells (EC). Confluent bovine EC cultured in serum-free medium secreted IR-ET as a function of time. Not only thrombin, but also vasoconstrictive hormones, such as arginine-vasopressin (AVP) and angiotensin (ANG) II, dose-dependently stimulated IR-ET secretion, and these effects were completely abolished by V1-receptor antagonist and [Sar1,Ala8]-ANG II, respectively. Protein kinase C (PKC)-activating phorbol ester and Ca2+ ionophore ionomycin had stimulatory effects on IR-ET secretion, and the combination of both compounds had a synergistic effect. These data suggest that AVP and ANG II, like thrombin, stimulate ET secretion from EC by a mechanism possibly involving receptor-mediated mobilization of intracellular Ca2+ and activation of PKC.

Receptor binding activity and cytosolic free calcium response by synthetic endothelin analogs in cultured rat vascular smooth muscle cells

Using a variety of synthetic analogs of porcine endothelin (pET), we have studied the effects of these analogs on receptor binding activity and cytosolic free Ca2+ concentrations ([Ca2+]i) in cultured rat vascular smooth muscle cells (VSMC). Removal of C-terminal Trp21 residue, truncated derivatives pET(1-15) and (16-21), substitution of disulfide bond, Cys(3-11) or Cys(1-15), by Cys (Acm), all resulted in a complete loss of receptor binding activity and [Ca2+]i response, while N-terminal elongation of Lys-Arg residues, but not oxidation of Met7 residue, decreased receptor binding activity and [Ca2+]i response. [Cys1-15,Cys3-11]pET was far more potent than [Cys1-11,Cys3-15]pET in receptor binding and [Ca2+]i response. These data indicate that the C-terminal Trp21 as well as the proper double cyclic structure formed by the intramolecular disulfide bonds of the pET molecule are essential for receptor binding and subsequent [Ca2+]i increase in rat VSMC.

Presence of immunoreactive endothelin in human plasma

A highly specific and sensitive radioimmunoassay has been established for measurement of human endothelin (hET) in human plasma. After extraction of plasma with an octyl-silica column, this assay allowed for detection of immunoreactive (IR) hET as low as 0.2 fmol/ml. In 16 healthy subjects, the mean concentration of plasma IR-hET was 0.6 fmol/ml. Reverse-phase HPLC coupled with radioimmunoassay revealed two major IR-hET components, one corresponding to authentic hET(1-21) and another with more hydrophilicity than hET(1-21). These data indicate that ET is a circulating vasoconstrictor hormone in man.

Degradation of atrial natriuretic peptide in dogs

To clarify the degradation of atrial natriuretic peptide (ANP) in dogs, plasma ANP concentrations in blood samples drawn from the coronary sinus, and in simultaneously collected blood samples of the arteries and veins of the lung, liver, kidney, spleen and cervix, and of the supramesenteric artery and the portal vein, were measured, both when infused with exogenous ANP (280 ng.kg-1.min-1, N = 7) and when not infused (N = 6). Venous ANP concentrations in most organs showed lower values than arterial levels by 11.6 to 33.6%, suggesting degradation during circulation. Exogenous ANP infusion resulted in a 26.0 to 41.9% arterio-venous decrease in ANP levels. These findings suggest that each organ contributes to ANP degradation, and that no specific organ plays a key role. The plasma ANP concentration was not reduced when blood samples were incubated for 60 min at 37 degrees C. The plasma from the coronary sinus and forearm vein contained essentially identical ANP molecular forms, as shown by gel permeation chromatography. Thus, the blood circulation through various organs does not cause high molecular weight ANP to be changed to other forms.

Simultaneous evaluation of insulin secretion and action using a model

For the simultaneous evaluation of insulin secretion and insulin sensitivity, a glucose regulation model has been developed. In order to estimate the parameters of the model, an intravenous glucose infusion test (GIT, 100 mg/kg.min x 2 min and 10 mg/kg.min x 118 min) was carried out on 15 healthy subjects (N), 12 subjects with impaired glucose tolerance (IGT), 20 non-insulin-dependent diabetics (NIDDM) and 13 patients with chronic pancreatitis (CP). The coefficient (microU/mg) for insulin secretion depending on blood glucose concentration in IGT, NIDDM and CP were lower (35.9 +/- 2.7, 24.5 +/- 3.3, 43.1 +/- 3.1) than in N (77.5 +/- 7.9). The coefficients (microU.min/mg) for insulin secretion depending on rate of change in blood glucose concentration in IGT and NIDDM were significantly lower (6.5 +/- 2.1, 3.8 +/- 1.2) than in N (52.8 +/- 8.8). The insulin sensitivity index (ISI; 10(-2) mg/(microU/ml).kg.min) in NIDDM was lower (4.98 +/- 0.75) than in N (11.37 +/- 1.08). Administration of exogenous insulin did not significantly affect the value of ISI in N and NIDDM. ISI showed a tendency to increase (15.09 +/- 1.92) in CP. It was demonstrated that the proposed model which estimates both insulin secretory ability and insulin sensitivity simultaneously is quite useful for analyzing the mechanism of impaired glucose tolerance.

Fail-safe systems for the wearable artificial endocrine pancreas

For the long-term clinical use of the wearable artificial endocrine pancreas, a fail-safe system is an essential mechanism. Several hardware alarm systems have been incorporated for battery-down, and short-run of the pumps. Software alarm systems for overflow or underflow of the AD converter, empty bags, hypoglycemia, hyperglycemia, abnormal values of parameters, and excessive insulin infusion have also been built into the system. The software noise filter was effective in eliminating superimposed artificial noises and the noises induced by muscle exercise. Sudden changes in sensor output during glycemic control of diabetics due to short circuit, or disconnection of the sensor lead, were detected as overflow or underflow of the AD converter. A gradual change in the sensor output was heralded by the hyper- or hypoglycemia alarm sound. These data indicated that the fail-safe system built into the wearable artificial endocrine pancreas is useful for the long-term glycemic control of diabetics.

Brain natriuretic peptide interacts with atrial natriuretic peptide receptor in cultured rat vascular smooth muscle cells

The effect of synthetic porcine brain natriuretic peptide (pBNP), a novel brain peptide with sequence homology to alpha-human atrial natriuretic peptide (hANP), on receptor binding and cGMP generation, was studied in cultured rat vascular smooth muscle cells (VSMC) and compared with that of alpha-hANP. 125I-pBNP bound to the cells in a time-dependent manner similar to that of 125I-alpha-hANP. Scatchard analysis indicated a single class of binding sites for pBNP with affinity and capacity identical to those of alpha-hANP. pBNP and alpha-hANP were almost equipotent in inhibiting the binding of either radioligand and stimulating intracellular cGMP generation. These data indicate that BNP and ANP interact with the same receptor sites to activate guanylate cyclase in rat VSMC.