[51Cr]EDTA for measuring total and single nephron glomerular filtration rate in the rat

Clearance and micropuncture experiments were performed in halothane anaesthetized rats. The aim was a comparison of paired estimates of glomerular filtration rate (GFR) from the renal clearance of [⁵¹Cr]EDTA (C_[51Cr]EDTA) with simultaneous estimates of polyfructosan ((Inutest) C_In), ³H,- and ¹⁴C-labelled inulin clearance (C_[3H]In and C_[14C]In, respectively) and proximal tubular fluid/plasma concentration ratios (TF/P) of [¹⁵Cr]EDTA and TF/P ratios of ¹⁴C-labelled inulin measured in the same samples. C_[51Cr]EDTA correlated well with, but underestimated C_In by ? 10%. The correlation coefficient (r) was 0.92. C_[51.Cr]EDTA also correlated with, and underestimated C_[14C]In by 6%, r= 0.88, whereas it overestimated C_[3H]In by 5%, still with a close correlation (r= 0.92). Paired data on proximal (TF/P) ratios of [¹⁵Cr]EDTA and [¹⁴C]inulin were collected from early, mid and late proximal convolutions. The data were scattered around the line of identity, r= 0.91. It is concluded that [¹⁵Cr]EDTA is a valid alternative for estimates of total renal and single nephron GFR in rats and has the advantage of being less expensive than [¹⁴C]inulin.     

Absence of capillary recruitment during increased coronary blood flow in the working dog heart

Myocardial plasma flow (MPF) and capillary permeability--surface area product (PS) were determined simultaneously on a regional basis in subendocardial and subepicardial layers of the left ventricular free wall in the working dog heart at control flow rate and during coronary vasodilation. The value for MPF was determined by the radioactive microsphere method and PS was assessed by an integral tissue-uptake method using [51Cr]-EDTA as test molecule. During coronary vasodilation achieved by intra-coronary infusion of adenosine, MPF increased markedly from 101.5 +/- 14.2 to 778.1 +/- 135.2 ml X min-1 X 100 g-1 in subendocardial layers and from 77.7 +/- 10.3 to 635.3 +/- 85.9 ml X min-1 X 100 g-1 in subepicardial layers of the left ventricular wall. Raising MPF by 800% was accompanied by a modest but statistically significant increase in PS[51Cr]-EDTA. In subendocardial layers PS increased from 49.3 +/- 5.0 to 60.0 +/- 3.3 ml X min-1 X 100 g-1 and in subepicardial layers from 43.8 +/- 4.1 to 52.1 +/- 2.4 ml X min-1 X 100 g-1, respectively. Taking into account back-diffusion of the tracer from the tissue to capillary blood which was higher at low flows than at high flows, PS[51Cr]-EDTA showed no increase with an eight-fold increment in flow. This observation rebuts the concept of additional perfusion of capillaries which are devoid of plasma flow under resting conditions during coronary vasodilation.     

Determination of postglomerular permselectivity to neutral dextrans in the dog

The single-pass multiple-indicator-dilution (MID) technique was used to analyze postglomerular capillary permeability. Anesthetized mongrel dogs (n = 13) during mannitol diuresis received a pulse injection of 125I-albumin (plasma reference), [14C]inulin (glomerular reference), creatinine (interstitial reference), and a homogeneous [3H]dextran molecular weight marker 6,000-12,000 dalton in the left renal artery. Simultaneous left renal venous outflow and right and left urine were rapidly sampled. Left urine recoveries of creatinine, [14C]inulin, and [3H]dextran were identical, indicating no glomerular solute flux limitation. Progressive precession of the [14C]inulin and [3H]dextran renal vein curves relative to creatinine indicated increasing postglomerular limitation to solute flux proportional to molecular size. The postglomerular solute extraction (EPG) (renal vein upslope indicator/125I-albumin) varied inversely with postglomerular renal plasma flow (F), indicating diffusion limitation. Ouabain infusion into the left renal artery significantly reduced Na reabsorption but did not alter the EPG of [14C]inulin or [3H]dextran. Permeability-surface (PS) area products calculated from EPG and F ranged from 4.86 +/- 0.89 to 0.97 +/- 0.25 (SD) cm X s-1 X 100 g-1 for indicators 5,000-12,000 dalton. [14C]Inulin PS products remained constant for F greater than or equal to 2.50 ml X s-1 X 100 g kidney-1. PS[3H]dextran/PS[14C]In (n = 20, F greater than or equal to 2.5 ml X s-1) was used to calculate an effective postglomerular capillary pore radius, r = 55.5 +/- 7.6 (SD) A.     

Determination of glomerular permselectivity to neutral dextrans in the dog

The multiple-indicator-dilution (MID) technique was used to separate solute flux (Js) across the glomerular and postglomerular capillaries in vivo. Anesthetized mongrel dogs (n = 20) during mannitol diuresis received a pulse of extracellular indicators including 125I-albumin (plasma reference), [14C]inulin (glomerular reference), creatinine (interstitial reference), and a neutral [3H]dextran (specific mol wt between 10,000 and 24,000 dalton) in the left renal artery. Left renal venous and ureteric outflows were rapidly sampled. 3H-labeled dextrans 10,000-15,500 had renal vein mean transit times (t) greater than those of 125I-albumin, indicating postglomerular extraction. 3H-labeled dextrans greater than 15,500 had t values identical to those of 125I-albumin, indicating only unidirectional glomerular extraction. The glomerular fractional dextran extractions relative to simultaneously injected [14C]inulin (ED/Ei) were calculated from urine and renal vein outflow curves and ranged from 0.98 +/- 0.02 to 0.33 +/- 0.12 (SD) for mol wt 10,000 +/- 24,000. ED/Ei values were quantitatively identical to constant-infusion fractional clearances of the same dextrans. Renal plasma flow (RPF) was then deliberately reduced two-to threefold in the same dog. ED/Ei as measured by the MID technique remained unchanged during graded reduction in RPF. In constant-infusion experiments RPF was reduced from 5.78 to 2.77 ml X s-1 X 100 g-1 and GFR from 50.4 to 36.3 ml X min-1, but the fractional neutral dextran clearances remained constant. The predominance of convective solute flux across the dog glomerulus permitted calculation of glomerular reflection coefficients 0.03 +/- 0.06 to 0.85 +/- 0.03 (SD) for neutral 3H-labeled dextrans 10,000-24,000 dalton.     

Permeability of the sheep placenta to unmetabolized polar non-electrolytes.

1. The rate of appearance in uterine venous blood of radioactively labelled, polar, non-electrolytes has been measured following their injection into the foetal circulation in the chronically catheterized sheep near term. Uterine blood flow was measured by an antipyrine technique. 2. Estimates of a placental permeability constant not corrected for area were 61-2 +/- 5-5 ml. min-1 (mean +/- S.E. of mean) for [14C] urea, 1-85 +/- 0-16 for [14C]erythritol and 0-21 +/- 0-03 for [3H]mannitol. Results are also presented for [14C]ethylene glycol, [14C]L-glucose, [14C]mannitol, [51Cr] EDTA and [3H] and [14C]sucrose. 3. In four sheep, permeability measurements for several solutes were made and the results were analysed in terms of restricted diffusion via cylindrical, water-filled pores. Calculation of pore radius was made by a minimum variance method and values ranging from 0-43 to 0-45 nm were obtained. 4. Stability and absence of protein binding of probe molecules was investigated by gel permeation on Sephadex columns.     

Regulation of spinal cord blood flow in the rat as measured by quantitative autoradiography

Spinal cord blood flow (SCBF) and its response to alterations in blood gases and to systemic hypotension, haemodilution and barbiturate anaesthesia were measured in 47 rats at the level of Th 7-8 by quantitative autoradiography with [14C]iodoantipyrine ([14C]IAP) as tracer. During normocapnia and normoxia the mean SCBF values in the grey and white matter were 94 +/- 21 and 17 +/- 3 ml min-1 100 g-1, respectively. SCBF was highly dependent on PaCO2. Thus in hypercapnic animals (PaCO2 greater than 9 kPa) SCBF was increased in grey and white matter to 228 +/- 22 and 54 +/- 7 ml min-1 100 g-1, while during hypocapnia (PaCO2 less than 3.9 kPa) it was decreased to 64 +/- 14 and 11 +/- 2 ml min-1 100 g-1, respectively. Mean arterial blood pressure (MABP) was reduced by withdrawal of blood to 80 +/- 8 mmHg in a light hypotension group and to 53 +/- 11 mmHg in a severe hypotension group, compared with 126 +/- 13 mmHg in a control group. There was no significant difference in SCBF between the control group and the hypotension groups, suggesting that autoregulation is maintained down to an MABP of at least 50 mmHg. Normovolaemic haemodilution, with a reduction of the haematocrit from 50 +/- 2 to 33 +/- 3, increased SCBF to 113 +/- 9 ml min-1 100 g-1 in grey matter and to 21 +/- 12 ml min-1 100 g-1 in white matter.(ABSTRACT TRUNCATED AT 250 WORDS)     

Calibration of [14C]plastic standards for quantitative autoradiography of [125I]labeled ligands with Amersham Hyperfilm beta-max

The densitometric response of Hyperfilm beta-max (HFBM) to [14C]plastic standards was calibrated to tissue-equivalent concentrations of [125I]. Plastic sections with standard concentrations of [125I] and [14C] were apposed to HFBM for 1, 3, 5, and 9 days, with liver and muscle slices (20 microns thick) labeled with [125I]insulin. The relative optical densities (ROD = log 10 [1/gray level x 256(-1)] produced by [125I]- and [14C]plastic standards were converted to equivalent tissue [125I] concentrations (dpm/mm2). The response of HFBM to the [125I]- and [14C]plastic standards was similar (P less than 0.001). Standard curves of tissue [125I] (dpm/mm2) vs plastic [14C] (microCi/g) concentrations fit second order polynomials (r2 = 0.995-0.999). The results show that [14C]plastic standards are valid for measuring [125I] radioactivity in tissue slices by autoradiography with HFBM.     

ECS, intracellular pH, and electrolytes of cardiac and skeletal muscle.

The extracellular space (ECS) of muscle from each ventricle of the heart (RV and LV), the atria, diaphragm, and quadriceps was estimated in the anesthetized rabbit from the distribution volumes of [14C]insulin, [14C]sucrose, [51Cr]EDTA, and C1--. Whole-tissue electrolytes were measured and intracellular electrolytes calculated. The ECS of the tissues varied, increasing in the order quadriceps less than LV less than RV less than atria. The volume of distribution of [14C]inulin was always less than that of either [14C]sucrose or [51Cr]EDTA which agreed closely, whereas that of C1-- was always greater. There was no difference in intracellular K+ in muscle from each of the cardiac chambers, whereas intracellular Na+ and C1-- varied, increasing in the order quadriceps less than LV less than RV less than atria. Intracellular pH, measured with [14C]DMO did not differ in any of the tissues studied. It is concluded that, in vivo, the estimated ECS incardiac muscle is lower than that reported in vitro, that [51Cr]EDTA is a satisfactory ECS marker, and that differences in intracellular Na+ and C1-- but not K+ or pH exist between muscle from the cardiac chambers.     

Effects of noradrenaline on the transcapillary passage of albumin, fluid and CrEDTA in the perfused rat hindlimb

Isolated rat hindlimbs were artificially perfused with serum solutions, either during maximal vasodilatation induced by papaverine or during infusions of noradrenaline (NA) at concentrations of 0.5-3.5 microM. Transcapillary exchange was followed with three independent techniques: clearance of albumin, measured after tissue accumulation of radiolabelled tracer, capillary filtration capacity (CFC), determined gravimetrically, and the capillary diffusion capacity (PS) for CrEDTA, calculated from venous indicator dilution curves after single bolus injection of dyes. During maximal vasodilation, when resistance to flow was 2.3 +/- 0.1 PRU100, albumin clearance was 0.0241 +/- 0.0012 ml min-1 100 g-1, CFC was 0.0367 +/- 0.0009 ml min-1 mmHg-1 100 g-1 and PS for CrEDTA was 8.2 +/- 0.4 ml min-1 100 g-1. Noradrenaline given before radiolabelled albumin increased vascular tone and reduced all three capillary exchange parameters in parallel. Albumin clearance was reduced also when NA was given after the introduction of radiolabelled albumin. When NA raised vascular tone to a level largely corresponding to that in resting skeletal muscle (PRU100 = 14) albumin clearance was 0.0067 ml min-1 100 g-1, CFC was 0.0141 ml min-1 mmHg-1 100 g-1 and PS for CrEDTA was 2.4 ml min-1 100 g-1. These findings suggest that albumin is transported by convective mechanisms and that the hydrostatic pressures fall in the exchange vessels as a consequence of functional precapillary 'sphincter' activity. Further, albumin clearance seems to be the same in the artificially perfused rat hindlimbs as in intact animals, at comparable vascular resistances, suggesting that capillary permeability is not influenced by the present surgical procedure.     

Reduction of local cerebral blood flow to pathological levels by endothelin-1 applied to the middle cerebral artery in the rat

Endothelin-1 (1 nmol) was applied to the exposed left middle cerebral artery (MCA) in anaesthetised adult male Sprague-Dawley rats. Local cerebral blood flow (1CBF), using [14C]iodoantipyrine and quantitative autoradiography, was measured in 27 anatomically defined structures, 10 min after topical application of endothelin-1. In those areas supplied by the MCA, 1CBF was markedly reduced beyond the threshold for ischaemic damage (e.g. dorsolateral caudate nucleus reduced from 131 +/- 3 to 29 +/- 25 ml.100 g-1.min-1, sensorimotor cortex from 109 +/- 5 to 31 +/- 21 ml.100 g-1.min-1). Distant areas were not affected.     

Renal tubular transport and metabolism of organic cations by the rabbit

The renal tubular transport of the organic cations tetraethylammonium (TEA), N1-methylnicotinamide (NMN), and choline was studied in anesthetized rabbits by the urinary clearance technique. The clearance ratio of [14C]TEA/inulin was 5.72 +/- 0.44 and the clearance ratio of [14C]TEA/p-aminohippuric acid (PAH) was 0.98 +/- 0.02. The clearance ratio of the 14C label/inulin when [14C]NMN was being infused was only 1.31. The clearance ratio of choline/inulin was less than 1 at choline infusion loads from 0 to about 6 mumol . kg-1 . min-1, which produced a plasma choline level of 100 microM. At higher infusion rates the urinary clearance ratio of choline/inulin rose to a maximum of 2 at plasma choline levels of 300-500 microM. Renal metabolism of choline and NMN were revealed by the use of the isolated perfused rabbit kidney. [14C]Choline was extensively metabolized by the kidney into betaine. The renal metabolite of [14C]NMN comigrated with nicotinamide in electrophoresis. The relatively low urinary clearance of the label associated with NMN in the rabbit presents a striking difference from its transport in dog and rat. Studies using isolated perfused segments are done using tissue from rabbits primarily. These data from the intact rabbit kidney may be used to guide future studies of organic cation transport with isolated perfused segments.     

Initial plasma disappearance and distribution volume of [131I]albumin and [125I]fibrinogen in man

The simultaneous plasma disappearance curves of albumin and fibrinogen were recorded in eight normal subjects from 10 to 60 min following intravenous injection. Additional samples were taken at 3, 4, 5, 6 and 7 min. The initial distribution volume (IDV) of albumin calculated by semilogarithmic extrapolation to zero time was 5.56% (range 3.73-8.53) larger than that of fibrinogen, denoting an initial high-rate function of albumin efflux extending from zero to about 10 min after tracer injection. The following slower phase of the albumin curve from 10 to 60 min was found to be similar to the so-called transcapillary escape rate (TER) of single-tracer experiments. By introducing the value Cp(0) (i.e. the estimated curve height at t = 0, from the injected amount of albumin tracer divided by the IDVf), the entire initial part of the albumin curves was analysed. From this analysis the mean value of 0.0135 +/- 0.0038 min-1 was determined for initial slope, corresponding to a whole-body unidirectional albumin efflux [j(0)] of 0.0572 +/- 0.0160 ml 100 g-1 min-1. The result is about 16 times higher than normal estimates of total lymphatic albumin return, indicating a huge backflux of interstitial albumin at the whole-body capillary level. Both phases of efflux seem to reflect uptake in a variety of peripheral tissues, and the hypothesis that the second phase (TER) expresses the initial slope of albumin escape into non-liver tissues is not substantiated. Based on the difference in IDV of the tracers demonstrated, the uncritical use of albumin as a plasma volume marker is not justified.     

A simple and sensitive radioimmunoassay for adenosine.

We developed a simple and sensitive radioimmunoassay (RIA) for adenosine. The RIA is based on the double antibody method with adenosine 2', 3'-0-disuccinyl-3-[125I]-iodotyrosine methyl ester (diSc-adenosine-[125I]-TME) as a tracer. Anti-adenosine antiserum for the RIA was raised in rabbits immunized with diSc-adenosine conjugated to human serum albumin (diSc-adenosine-HSA). All samples and standards were succinylated prior to assay. The present immunoassay allows detection of 6.25-400 pmol/ml of adenosine in sample. Values obtained by the RIA and by a HPLC analysis showed a high correlation with correlation coefficient of 0.997. In order to determine adenosine in plasmas, blood cells must be separated in the presence of 6 mM EDTA, 0.006% dipyridamole (Dip) and 23 microM 2'-deoxycoformycin (dCF) at 2 degrees C. Adenosine in plasma could be accurately determined by the proposed method even without any pretreatments by deproteinizing. The adenosine levels with or without EDTA-treated normal human plasmas determined were 26.2 +/- 7.26 and 100 +/- 3.62 pmol/ml (mean +/- SEM), respectively.     

Uric acid excretion by the rat kidney.

The renal excretion of uric acid was studied in nondiuretic (ND) male Wistar rats and in the same animals subsequently made diuretic (D) by the infusion of hypertonic saline. Clearances of endogenous urate and of inulin, determined chemically, were compared with the simultaneous clearance of 14C infused as [6(-14)C]urate or [2(-14)C]urate. In rats infused with [6(-14)C]urate the isotope/inulin clearance ratios were 0.29 +/- 0.09 (ND) and 0.31 +/- 0.11 (D) ml/min; the simultaneous urate (chemical)/inulin ratios were 0.21 +/- 0.07 (ND) and 0.24 +/- 0.08 (D) ml/min. In rats infused with [2(-14)C]urate the isotope/inulin clearance ratios were 1.02 +/- 0.5 (ND) and 1.13 +/- 0.9 ml/min (D); the simultaneous urate (chemical)/inulin clearance ratios were much lower-0.19 +/- 0.09 (ND) and 0.32 +/- 0.19 (D) ml/min. Thin-layer chromatography of urine after [6(-14)C]urate inl uric acid. In contrast, a similar analysis of urinary radioactivity after [2(-14)C]urate infusion revealed that more than 70% of the 14C was excreted as allantoin and not as uric acid.     

Effects of intraluminal D-glucose and probenecid on urate absorption in the rat proximal tubule.

The in vivo microperfusion technique was employed to examine urate absorption in the proximal convoluted tubule of the rat kidney using [2-14C]urate as the marker for fractional urate absorption. With NaCl as the perfusion solution, water absorption averaged 2.53 +/- 0.16 nl.min-1.mm tubule-1, and the fractional absorption of [2-14C]urate averages 11.6 +/- 1.0%/mm tubule. The addition of D-glucose (50 mg/100 ml) enhanced water absorption to 3.62 +/- 0.19 nl.min-1.mm tubule-1, but inhibited fractional urate absorption to 6.6 +/- 1.2%/mm tubule. Phloridzin (4.4 mg/100 ml), 2-deoxy-D-glucose (45.6 mg/100 ml), and 3-O-methyl-D-glucose (53.9 mg/100 ml) also inhibited the absorption of [2-14C]urate to the same degree as did D-glucose despite differing effects on water absorption. The addition of probenecid (2.8 mg/100 ml) to the NaCl perfusion solution had no effect on water absorption but inhibited [2-14C]urate absorption to 6.4 +/- 0.6%/mm tubule. The addition of both probenecid and phloridzin further reduced [2-14C-A1urate absorption to 3.8 +/- 0.7%/mm tubule. Probenecid alone had no effect on glucose transport. These studies suggest that the presence of either certain hexose sugars, phloridzin, or probenecid in the lumen of the proximal convoluted tubule inhibits the tubular absorption of urate.     

[~(125)I]-(A14)单碘胰岛素在荷人肝癌裸鼠体内的趋瘤特性研究

目的 :观察放射性碘标记胰岛素在荷人肝癌裸鼠体内的趋瘤或亲肿瘤 (tumor-seeking)特性。方法 :采用荷人肝癌裸鼠模型。用 [12 5I]- (A14)单碘胰岛素进行荷人肝癌裸鼠体内分布实验和抑制实验。结果 :体内分布实验显示肝癌组织摄取 [12 5I]- (A14)单碘胰岛素明显高于本底组织 (肌肉 ) ,肿瘤与血和肿瘤与肌肉的放射性比值随时间延长而增高。体内抑制实验发现肿瘤组织于 30min的抑制率为 35 .0 %。结论 :[12 5I]- (A14)单碘胰岛素在荷人肝癌裸鼠体内 ,通过受体介导作用 ,能被肝细胞癌组织特异性摄取。     

An isolated perfused rat kidney preparation designed for assessment of glomerular permeability characteristics

The aim of the present investigation was to modify the widely used isolated perfused rat kidney preparation to make it more suitable for studies of glomerular permeability to macromolecules. Both kidneys were perfused in situ using separate pumps in two of each other independent systems with Tyrode-solution containing human serum albumin (18.2 g 1^-1). Sodium nitroprusside was administered to induce dilatation and to maintain constant vascular resistance (PRU₁₀₀) during the experiments. The addition of sodium nitroprusside decreased vascular resistance from 0.17 ± 0.05 to 0.09 ± 0.02 mmHg min^-l 100 g^-1 ml^-1 and increased urine flow and glomerular filtration rate. The temperature of the perfusate was reduced from 37°C to 8°C to inhibit tubular reabsorption of protein and fluid, resulting in a urine to plasma concentration ratio of [⁵¹Cr]EDTA of 1.26 ± 0.07. Furosemide reduced the urine to plasma concentration ratio for [⁵¹Cr]EDTA further to 1.15 ± 0.02 and increased glomerular filtration rate. Moreover, by performing the studies at low temperatures (8°C) in the presence of sodium nitroprusside and furosemide it was possible to achieve low and stable albumin fractional clearance values close to those prevailing in vivo. Thus, the described technique, allowing simultaneous perfusions of both kidneys with different solutions, pressures and flows, seem to be well suited for studies of macromolecular transport across glomerular capillaries.     

Regional glucose metabolism in the rabbit brain in control and TRH-treated animals

The local cerebral metabolism in urethane anaesthetized control and TRH-treated rabbits was studied with the [14C]2-deoxyglucose method. In the controls, the glucose use was found to be highest in regions known to have a high blood flow and low in regions with low flow. The glucose consumption was, calculated using the constants found by Kennedy et al. in monkeys, 23.5 +/- 6.0 mumol 100 g-1 min-1 in parietal cortex. The TRH was infused at a dose of 0.06 mg kg-1 min-1 which is known to cause vasodilation in the brain. No marked influence of the peptide on the glucose use was detected. It was concluded that the previously reported cerebral vasodilation caused by TRH is not due to an increase in cerebral metabolism.     

Arterio-venous concentration difference of [51Cr]EDTA after a single injection in man. Significance of renal function and local blood flow

The present investigation was undertaken in order to study (1) the difference in arterial (Ca) and venous (Cv) concentration of [51Cr]EDTA (ethylenediaminetetraacetate) after a single intravenous injection, (2) the impact of different physiological variables on this difference, and (3) the error introduced in the measurement of renal plasma clearance and total plasma clearance by using venous blood samples instead of arterial. In 13 patients with GFR ranging from 29 to 150 ml min-1, Ca was higher than Cv immediately after the injection. After mean 38 min (range 12-82 min) the two curves crossed, and 180-300 min post-injection (p.i.) Cv was 5.9% higher than Ca (range 0.5-13.9%, P less than 0.001). The more reduced renal function, the smaller was the concentration difference. The areas under the arterial and the venous plasma concentration curves did not differ significantly at either 0-infinity or 0-300 min p.i. whereas the venous area 0-100 min p.i. underestimated the arterial area in the same period by 4.1% (P less than 0.05). In a computer simulation model, variation in the forearm capillary permeability-surface area product did not have any significant influence on the Cv-Ca difference, whereas the difference was very sensitive to even small changes in forearm blood flow within the physiological range. For measurement of renal plasma clearance it is recommended to use one long period: from the time of injection until 300 min p.i. or longer. If the clearance period is too short, the use of venous samples will overestimate the true renal clearance. Plasma clearance determined by venous and arterial blood samples does not differ significantly as long as the concentration is followed from the time of injection and a long period is applied. When simplified plasma clearance techniques are used, different results may be obtained from venous and arterial samples. The simplified techniques using venous blood samples--which usually include some empirical corrections--should be sufficiently reliable in daily clinical practice provided the forearm blood flow is reasonably high, e.g. exposure to cold should be avoided.     

Permeability of gastric capillaries to small and large molecules

The permeability of capillaries in the stomach to small and large solutes was studied with the double-indicator diffusion technique in the dog stomach and by analysis of steady-state lymph and plasma samples in the cat stomach. The effective pore radius in gastric capillaries determined by indicator diffusion was 53 A, whereas steady-state lymph samples predicted a small-pore radius of 47 A. At the highest plasma flow rates studied (achieved by intra-arterial infusion of isoproterenol), indicator diffusion estimates of the permeability-surface area product for raffinose, inulin, and beta-lactoglobulin A were 140, 70, and 8 ml . min-1 . 100 g-1, respectively. The lymph studies indicate that gastric capillaries are more permeable than capillaries in the intestine and colon to albumin and larger molecules. The calculated effective large-pore radius of gastric capillaries was 250 A. The osmotic reflection coefficients (sigma d) ranged from 0.73 +/- 0.03 for albumin to 0.91 +/- 0.02 for beta-lipoprotein (120-A radius). The sigma d for total plasma protein was 0.78 +/- 0.03, indicating a substantial transcapillary oncotic pressure gradient, despite the greater permeability of these capillaries for macromolecules.