Plasma disappearance of albumin and impact of capillary thickness in idiopathic dilated cardiomyopathy and after heart transplantation.

BACKGROUND-The increased plasma disappearance of albumin has previously been described in decompensated congestive heart failure (CHF); this disappearance normalized after diuretic treatment. Cardiac transplantation (HTX) and current medical treatment affect microvascular structure and function. We investigated the plasma disappearance of albumin and the impact of microvascular thickness and electrostatic properties in patients with compensated CHF and after HTX. METHODS AND RESULTS-The fraction of intravascular albumin that passes to the extravascular space per unit time, as determined from the plasma disappearance of intravenously injected (131)I-labeled albumin, was increased to 7.8+/-1.7% in 16 patients with CHF compared with 18 controls (6.5+/-1.9%, P<0.05); these levels normalized after HTX (5.8+/-2.6%, P<0.01, n=17). The change in ratio between (131)I-albumin and simultaneously injected negatively charged glycosylated (125)I-albumin (selectivity index, >1/hour in controls) was lower in patients with HTX (0.993+/-0. 022/hour) than in controls (1.008+/-0.019/hour; P<0.05), which indicated a relatively increased plasma disappearance of negatively charged albumin in HTX patients. Capillary basement membrane thickness was evaluated semiquantitatively from skin biopsies and showed no difference in the 3 groups (control, CHF, and HTX patients). However, in all 3 study groups, subjects with thicker capillary basement membranes had lower albumin escape rates (6.1+/-1. 8%, n=32, versus 7.6+/-2.6% in subjects without thickening of capillary basement membranes, n=19; P<0.05). CONCLUSIONS-The plasma disappearance of albumin increased in patients with compensated CHF and it normalized after HTX. The present normalized capillary basement thicknesses in patients with CHF and the direct association between this parameter and plasma albumin disappearance indicate that previous compensatory microvascular basement membrane growth results in restricted permeability. Microvascular electrostatic properties did not relate to plasma albumin disappearance.

Plasma clearance of polyfructosan and extracellular body fluid distribution in idiopathic dilated cardiomyopathy and after heart transplantation.

The total extracellular fluid volume and distribution in plasma and interstitial spaces, and the microvascular permeability properties were studied in 16 nonedematous patients with congestive heart failure (CHF) due to idiopathic dilated cardiomyopathy and 17 such patients who underwent heart transplantation (HT) by analyzing the 3-hour plasma disappearance curve of polyfructosan. Eighteen healthy subjects served as controls. Polyfructosan (3.5 kD) is an extracellular marker and inulin analog transported almost solely by diffusion. The initial capillary membrane plasma clearance (i.e., the permeability-surface area product), the interstitial plasma clearance determined at 10 minutes (clearance[10), and the extracellular volume were determined from the polyfructosan curves. I-131-albumin was used as a plasma volume reference. Permeability-surface area product was elevated in both patient groups (6.6 +/- 1.9 ml/ kg/min in the CHF group and 6.7 +/- 2.0 ml/kg/min in the HT group vs 5.1 +/- 1.3 ml/kg/min in controls, p <0.01 for both), whereas clearance(10) was normalized in the HT group (4.5 +/- 0.9 ml/kg/min in the HT group, 4.4 +/- 0.7 ml/kg/min in controls vs 5.0 +/- 0.9 ml/kg/ min in the CHF group, p <0.1 and p <0.05, respectively). The normalization of interstitial plasma clearance of polyfructosan was associated with time since HT (r = 0.49, p <0.05). Plasma volumes were similar in all 3 groups (41 +/- 8 ml/kg in controls, 44 +/- 13 in the CHF group and 39 +/- 8 in the HT group). In contrast, total extracellular volume was elevated in both patients groups (177 +/- 27 ml/kg in the CHF group and 173 +/-27 in the HT group vs 152 +/- 12 in controls, p <0.01). The results strongly suggest a microvascular permeability defect in both patient groups that perhaps plays a role in the extravascular distribution of the excess extracellular fluid volume.

Whole body capillary exchange of albumin. Alterations in diabetic microangiopathy.

Until the mid eighties most conceptual knowledge of peripheral transcapillary plasma protein transport has been based on experiments with the lymph collection methods, picturing macromolecular exchange as a slow, mainly unidirectional flux from plasma to lymph. All sieving or restriction is assumed to occur at the capillary membrane level reducing interstitial as well as lymphatic plasma protein concentrations. However, in newer experiments using rapidly resolving tracer techniques, transcapillary albumin fluxes are found 10 to 20 times higher than the lymphatic return. This may imply serial barriers to plasma-lymph transport, i.e. a relatively permeable porous endothelial barrier, and a tight interstitial barrier. The possible outline of this hypothesis and its major implications are discussed. The interstitial barrier is assumed to be formed by the contents of the interstitial space itself, preferentably by the anionic glycosaminoglycanes (GAGs) of the interstitial gel matrix. In the interface between the barriers immediately below the endothelial lining, interstitial plasma protein concentrations may reach close to plasma levels. Thus diseases or conditions that alter plasma protein concentrations, plasma protein fluxes or matrix composition are likely to promote coagulation or precipitation in this interzone. In diabetic microangiopathy loss of fixed anionic charge in the glomerular basal membrane is an important initial step leading to proteinuria. However, the loss of anionic charge seems to be general, afflicting the GAG components of the glomerular membrane, the interstitial matrix, and in the walls of large arteries. By raising the interstitial protein flux as well as by decreasing the antiprecipitating and anticoagulative properties of the matrix, this may lead to increased precipitation. It may therefore be the single pathogenetic factor most likely to explain the perivascular hyalinosis and accelerated atherosclerosis of the disease. Very similar mechanisms may enhance atherosclerosis in nondiabetic patients precipitated by factors like elevated plasma levels of lipoproteins and fibrinogen, aging, and hypertension.

Plasma disappearance and distribution volume of polyfructosan in type 1 (insulin-dependent) diabetes mellitus.

The simultaneous plasma disappearance curves of the extracellular marker polyfructosan and 125I-fibrinogen were recorded for 3 h in 24 male long-term diabetic patients. Eight normal subjects served as a control group. The patients were divided into three groups according to their urinary albumin excretion: Group 1 had normal albumin excretion (< 30 mg/24 h), Group 2 had microalbuminuria (30-300 mg/24 h), and Group 3 had clinical nephropathy (> 300 mg/24 h). Using fibrinogen as a plasma volume reference, the permeability surface product (PdS), the plasma clearance rate at 10 min C1(10), and the extracellular volume (ECV) were determined from the polyfructosan curves. Plasma volume was similar in all groups, and no differences were found between Group 1 and the control group. PdS was higher in the albuminuric groups, but barely to reach significant levels (p = 0.08-0.03), while C1(10) was significantly elevated (p < 0.01). The ECV was also significantly higher in these patients (p = 0.02-0.005), resulting in a marked decrease of the plasma volume to extravascular volume ratio. The results suggest a general degeneration of perivascular resistance components in diabetic microvascular complications, followed by secondary alterations of fluid balance, due to decreasing colloid osmotic counterpressure and eventually increasing transcapillary hydrostatic pressure.

Plasma disappearance of glycated and non-glycated albumin in type 1 (insulin-dependent) diabetes mellitus: evidence for charge dependent alterations of the plasma to lymph pathway.

The fractional plasma escape rates of glycated and non-glycated albumin have earlier been measured in groups of Type 1 (insulin-dependent) diabetic patients and control subjects. The escape of non-glycated albumin was similar in control subjects and normoalbuminuric patients, but elevated in patients with micro or macroalbuminuria. In all groups the escape rate of glycated albumin was lower than that of non-glycated albumin. Glycation increases the anionic charge of albumin. To assay for charge-dependent alterations of transport a selectivity index (non-glycated albumin/glycated albumin transport ratio) was determined from the disappearance data. The index was high in control subjects (1.021 +/- 0.0057 (SEM)). This reflects a mean difference between the two escape rates of 2.1% per hour (for comparison the mean of the fractional escape rate of non-glycated albumin of the normal control subjects was 4.7% per hour). The index was numerically even higher in normoalbuminuric patients (1.031 +/- 0.0047 (SEM)), but reached significantly lower levels in patients with microalbuminuria (1.013 +/- 0.0030 (SEM), p < 0.02). Patients with clinical nephropathy had very low levels indicating loss of selectivity (1.002 +/- 0.0068 (SEM), p < 0.001). This pattern accords well with measurements of renal clearance selectivity indices, suggesting a general, progressive deterioration of anionic perivascular barrier components in diabetic microangiopathy. The structural target for these changes is likely to be the glycosaminoglycans of the glomerular basal membrane and the interstitial matrix.

Transcapillary filtration of plasma protein in long-term type 1 (insulin dependent) diabetic patients.

To study the pathophysiologic mechanism leading to increased transcapillar sieving of albumin in patients with diabetic nephropathy, subcutaneous interstitial concentrations of albumin, transferrin, total IgG and IgG-4 was measured in 30 long-term type 1 diabetic patients using the skin suction blister method. Eight normal subjects served as controls. The patients were divided in groups according to their urinary albumin excretion: normal (n = 11), micro-albuminuria (n = 9), and clinical nephropathy (n = 10). Results were expressed as the blister to serum concentration ratio (Cb:Cs) of each macromolecule. Normoalbuminuric patients had lower Cb:CsIgG ratio than healthy controls (0.28 +/- 0.04 vs. 0.35 +/- 0.09, p = 0.03). The lowest Cb:CsIgG ratio (0.23 +/- 0.07) was found in patients with clinical nephropathy. The same trend could be demonstrated in the other Cb:Cs ratios, but differences there were not significant. No differences related to capillary charge- or size-selectivity could be demonstrated between the groups. The results might reflect an increase of intracapillary hydrostatic pressure or increased capillary hydraulic permeability in the diabetic state per se, augmented during the development of microvascular complications.

Initial plasma disappearance and tissue uptake of 131I-albumin in normal rabbits.

The simultaneous plasma disappearance curves of 131I-albumin and 125I-fibrinogen were recorded in normal rabbits for 1 hr. Using fibrinogen as a plasma reference, the disappearance curves of albumin were shown to contain two separate phases of efflux: one fast from zero to 10 min. comprising 8% of the total tracer; and one slow appearing in the interval of 10 to 60 min. containing another 9% of the tracer. Total albumin escape was analyzed to yield an initial slope of 0.024 +/- 0.004 min-1, corresponding to a wholebody unidirectional albumin clearance (Cl(0)) of 0.090 +/- 0.009 ml(min*100 g)-1. The distribution of efflux was assessed by biopsy uptakes using the same tracers in spleen, kidney, heart, lung, liver, intestine, skin, muscle, and brain. The disappearance curve generally reflects a biphasic pattern of uptake in peripheral tissue, predominantly by muscle and lung. The rapid phase has contributions from the fast near equilibration of liver, and intestine and skin are significant codeterminants of the slow phase. Due to their low body masses highly perfused organs such as kidney, spleen, and heart have little influence on the plasma disappearance. In accordance, the Cl(0) determined for the wholebody was higher than initial clearances found in skin (0.053 ml(min*100 g)-1 and muscle (0.054 ml(min*100 g)-1), but much lower than those found in the highly perfused organs. The initial (unidirectional) rates of peripheral albumin transfer demonstrated, ranged from 10 to 30 times higher than estimates of lymphatic return, suggesting that transcapillary albumin exchange is mediated by high-rate bidirectional diffusion. The rapid decrease of net albumin exchange rates suggests a second, highly significant barrier located within the interstitial matrix, which restricts plasma escape and reduces plasma to lymph albumin transport.

Tissue to plasma capillary permeability of 131I-albumin in the perfused rabbit ear.

The tissue to plasma transfer of 131I-albumin was recorded in perfused rabbit ears (n = 6) following equilibration for 24 hr. 125I-fibrinogen served as the plasma marker, and was introduced intravenously 15 min before clamping. The ears were rollerpump perfused with isotonic diluted plasma at a constant rate of (mean +/- SD) 5.1 +/- 1.5 ml (min.100 g)-1. The mean extravascular albumin distribution volume was 12.4 +/- 1.1 ml.100 g-1, and the fibrinogen volume (plasma volume in tissue) was 3.1 +/- 0.4 ml.100 g-1 as determined from biopsies of the contralateral ear. The initial transfer of albumin was marked, and occurred at rates corresponding to a unidirectional clearance (Cl(0)) of 0.068 +/- 0.012 ml (min.100 g)-1. However, with a reduction of mean interstitial albumin tracer content of no more than 4%, net transport decreased to reach slowly declining levels 5 to 10 times lower within 10 min of continued perfusion. The decrease was considered due to rapid exhaustion of a small interstitial pool of tracer immediately adjacent to the exchange vessel membrane, followed by an increasingly retarded outwash from more distant areas. The results suggest a bimodal structural resistance to albumin movement: a relatively low resistance in the capillary membrane, and a considerable restriction to albumin transport located within the interstitial space.

Whole body capillary exchange of albumin.

Analyzed versus the large plasma marker of fibrinogen, initial albumin plasma disappearance in man or animals is sharply biphasic. Albumin uptake in skin, muscle and viscera follow the same pattern, suggesting serial barriers to albumin efflux in these tissues, i.e., a capillary membrane barrier and an interstitial barrier. The transport across the membrane is rapid, in both directions and probably mediated by diffusion, while interstitial transport may be slow, mainly unilateral and mainly convective. This implies the interstitial barrier and not the capillary membrane to be the rate limiting step of total plasma to lymph albumin transport. The distribution of efflux indicates whole body plasma disappearance to reflect mainly the uptake in muscle, lung, skin, and gut, while the highly perfused tissues of heart, kidney and sinusoid tissue have smaller influence due to their lower body masses.

Metabolism of albumin and fibrinogen in type 1 (insulin-dependent) diabetes mellitus.

The metabolism of albumin and fibrinogen was studied in 24 long-term diabetic Type 1 (insulin-dependent) patients, using a double tracer technique. The patients were divided into three groups according to their urinary albumin excretion. Group 1 had normal albumin excretion (less than 30 mg/24 h), group 2 had persistent microalbuminuria (30-300 mg/24 h), and group 3 had clinical nephropathy (greater than 300 mg/24 h). Eight normal persons served as control subjects. Except for slightly lower distribution fractions of both proteins (intravascular mass/total mass), group 1 did not differ from normal subjects. In groups 2 and 3 the relative catabolism of albumin was increased, as denoted by an increase in the fractional catabolic rate. Albumin synthesis was unaltered, resulting in lower plasma concentrations and lower intravascular and total body masses of albumin. Oppositely, fibrinogen synthesis was augmented, leading to an increase in plasma fibrinogen concentration and total fibrinogen body mass, in spite of increased catabolism. The fractional catabolic rates were unaltered. The study demonstrates that long-term diabetic patients with normal urinary albumin excretion have normal albumin and fibrinogen metabolism, but that grave alterations in plasma protein metabolism are present in patients with only slightly increased urinary albumin excretion.

Central role for sodium in the pathogenesis of blood pressure changes independent of angiotensin, aldosterone and catecholamines in type 1 (insulin-dependent) diabetes mellitus.

We studied 73 Type 1 (insulin-dependent) diabetic patients, 18 to 50 years of age, with a diabetes duration of more than five years. Group 1: normal urinary albumin excretion below 30 mg per 24 h (n = 19); group 2: microalbuminuria, 30-300 mg per 24 h (n = 36); and group 3: diabetic nephropathy, above 300 mg per 24 h (n = 18). Fifteen nondiabetic persons matched for sex and age served as control subjects. The sodium intake evaluated on the basis of 24-h urine sodium excretion was similar in patients and control subjects. Blood pressure in groups 1 and 2 and control subjects was below 160/95 mmHg. The blood pressure was increased in group 3 as compared with the other groups (systolic/diastolic 161 +/- 22/101 +/- 9 mmHg vs 131 +/- 13/84 +/- 10, mean +/- SD, p less than 0.0001). Exchangeable sodium was increased in patients (p less than 0.01) and correlated to the mean blood pressure (n = 70, r = 0.41, p less than 0.01). Extracellular volume was increased in patients (p less than 0.05), whereas plasma volume was normal. Supine serum angiotensin II was suppressed in the patients (p less than 0.001). A negative correlation was found between mean blood pressure and supine serum aldosterone (n = 68, r = -0.24, p less than 0.05), and exchangeable sodium and aldosterone (n = 66, r = -0.36, p less than 0.002) in all patients. The catecholamine levels were also suppressed or normal in the patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Transcapillary escape rate and relative metabolic clearance of glycated and non-glycated albumin in type 1 (insulin-dependent) diabetes mellitus.

The transcapillary escape rate and relative plasma disappearance of glycated and non-glycated albumin were measured in 25 male Type 1 (insulin-dependent) diabetic patients using a double tracer technique. The patients were divided into three groups on the basis of their urinary albumin excretion: group 1, normal albumin excretion (less than 30 mg/24 h) (n = 8); group 2, microalbuminuria (30-300 mg/24 h) (n = 9); and group 3, clinical nephropathy (greater than 300 mg/24 h) (n = 8). Six male age-matched non-diabetic persons served as control subjects. The transcapillary escape rate of glycated albumin was similar in group 1 and control subjects (4.7 +/- 2.1 versus 5.1 +/- 1.7%), but significantly increased in group 2 (7.0 +/- 1.7%, p less than 0.05) and in group 3 (7.9 +/- 3.1%, p less than 0.05). The transcapillary escape rate of glycated albumin was slightly lower than that of non-glycated albumin in all groups, but significant only in normal control subjects. No difference in the catabolic rate of glycated and non-glycated albumin was found. We conclude that the in vivo effects of glycation on the clearance and transcapillary passage of albumin are small and not likely to play any significant role in the development of late diabetic microvascular complications.

Evidence of changes in renal charge selectivity in patients with type 1 (insulin-dependent) diabetes mellitus.

Altered filtration of macromolecules due to decreased electrical charge of the glomerular basement membrane might be the initial step in the development of albuminuria in patients with Type 1 (insulin-dependent) diabetes mellitus. We therefore investigated the selectivity index, i.e. renal clearance of non-glycated plasma albumin/clearance of glycated plasma albumin in 38 patients with Type 1 diabetes mellitus. The two albumin molecules differed slightly in charge, non-enzymatic glycated albumin being more anionic at physiological pH compared with unmodified plasma albumin. Glycated albumin in plasma and urine was determined by a specific, sensitive and highly reproducible chromatographic procedure. In diabetic patients with normal urinary albumin excretion, the selectivity index was increased three-fold compared with that of non-diabetic subjects (2 p less than 0.01). A significant correlation (r = 0.53, 2 p less than 0.01) between haemoglobin A1c and selectivity index was demonstrated in these patients, indicating a change in charge-dependent renal filtration could possibly be attributed to non-enzymatic glycation of components in the glomerular basement membrane and tubuli. Diabetic patients with increased albumin excretion rate had a significantly lower selectivity index compared with patients with normal albumin excretion (2 p less than 0.01). A significant negative correlation (r = 0.85, 2 p less than 0.001, exponential curve fit) was seen between urinary albumin excretion and selectivity index in the diabetic patients, indicating that the capability of differentiating between macromolecules of different charges is again lost with increasing urinary albumin excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of calcium on somatostatin inhibition of insulin release and cyclic AMP production in mouse pancreatic islets.

The effect of somatostatin on glucose-induced insulin secretion and cyclic AMP accumulation in isolated islets from obese, hyperglycemic ob/ob mice was studied in a microperifusion system. The normal biphasic pattern of insulin release as well as the inhibitory pattern of insulin release produced by somatostatin (0.5--1 microgram/ml) was matched by similar changes in the intracellular concentration of cyclic AMP. When islets were stimulated by glucose (3 mg/ml) plus 3-isobutyl-1-methylxanthine (0.1 mM), somatostatin (0.5 microgram/ml) failed to inhibit insulin secretion or cyclic AMP formation in the second phase whereas in the first phase both parameters were significantly reduced by somatostatin (0.5 microgram/ml). In batch-type incubations it was shown that addition of excess calcium (to 6 mM) reversed this inhibition. In the second phase calcium potentiated the (glucose + 3-isobutyl-1-methylxanthine)-stimulated insulin secretion without affecting the cyclic AMP production. This potentiation was inhibited by somatostatin (0.1 microgram/ml). Somatostatin (1 microgram/ml) inhibited adenylate cyclase activity in islet homogenates. No effect of somatostatin on islet glucose utilization could be demonstrated. The results indicate a dual action of somatostatin in the inhibition of insulin release, one involving the islet adenylate cyclase and one affecting the islet uptake of calcium.