Hemodynamic effect of iopromide in pancreas-duodenum transplanted rats.

BACKGROUND: Radiological contrast media (CM) have been suggested to be able to impair pancreatic microcirculation, especially in acute pancreatitis. PURPOSE: To evaluate the effects of the low-osmolar CM iopromide on total pancreatic and especially islet blood perfusion after whole pancreas transplantation. MATERIAL AND METHODS: Rats receiving a pancreas-duodenum transplantation 2 days earlier, i.e., with graft pancreatitis, were injected with iopromide. Blood perfusion measurements were then made with a microsphere technique. RESULTS: The graft blood perfusion was decreased in control rats when compared to the endogenous pancreas. Administration of iopromide increased both total pancreatic and islet blood perfusion in the grafted pancreas, but not in the endogenous gland. No effects on blood perfusion to either the native or transplanted duodenum were seen after iopromide administration. CONCLUSION: Iopromide increases the blood perfusion of a whole pancreas transplant 2 days after implantation, i.e., when graft pancreatitis is present. The consequences of this CM-induced hyperperfusion for graft pancreatic function remain to be established.Key words: Intravascular contrast media; islet blood perfusion; graft pancreatitis;pancreas transplantation; pancreatic blood perfusion

Radiological contrast media and pancreatic blood perfusion in anesthetized rats.

BACKGROUND: Radiological contrast media (CM) have been suggested to be able to impair pancreatic microcirculation. PURPOSE: To evaluate the effects of an iso-osmolar (iodixanol, 290 mOsm/kg H2O) and a low-osmolar (iopromide, 660 mOsm/kg H2O) CM on total pancreatic and islet blood perfusion. MATERIAL AND METHODS: Thiobutabarbital-anesthetized rats were injected with iodine equivalent doses (600 mg I/kg body weight) of iodixanol or iopromide. Saline or low-osmolar mannitol (660 mOsm/kg H2O) solutions served as control substances. Blood perfusion measurements were then carried out with a microsphere technique. RESULTS: Iso-osmolar iodixanol had no effects on blood perfusion. Low-osmolar iopromide increased total pancreatic blood perfusion, whereas islet blood perfusion was unchanged. No differences were seen when mannitol solutions were given. CONCLUSION: Neither an iso-osmolar nor a low-osmolar CM affected pancreatic islet blood perfusion, whereas the low-osmolar CM increased total pancreatic blood perfusion. The absence of hemodynamic effect of low-osmolar mannitol suggests that the hyperosmolality per se of iopromide versus iodixanol does not induce the hemodynamic effect. The consequences of the effect of iopromide for pancreatic function remain to be established.

Islet capillary blood pressure increase mediated by hyperglycemia in NIDDM GK rats.

This study was performed to measure pancreatic islet capillary pressure under basal conditions and after an acute glucose stimulation of insulin release in normal rats. In addition, the islet capillary pressure was estimated in GK rats, an animal model of NIDDM. Hydrostatic pressure in single pancreatic islet capillaries was determined in vivo by direct measurement using the micropuncture technique. The pancreatic islets were visualized by injection of neutral red. This intravital staining had no effect on islet function, whole pancreatic and islet blood flow, and capillary blood pressure in the exocrine pancreas. Islet capillary blood pressure in normoglycemic Wistar F rats was estimated at 3.1 +/- 0.3 mmHg (n = 15). Administration of D-glucose (1 g/kg) doubled this value, whereas no effect was seen after injection of an equimolar dose of the non-metabolizable glucose-derivative 3-O-methyl glucose. In GK rats, basal islet capillary blood pressure was increased (5.7 +/- 0.4 mmHg; n = 10; P < 0.001) when compared with the control Wistar F rats. Reduction of blood glucose levels in GK rats with phlorizin treatment showed this increased basal islet capillary pressure in GK rats to be glucose dependent and reversible. In the present study, we have for the first time shown that both acute and chronic hyperglycemia augment islet capillary pressure. The effects of a chronically increased islet capillary pressure on long-term islet function remain to be determined.

Capillary blood pressure in syngeneic rat islets transplanted under the renal capsule is similar to that of the implantation organ.

The aim of the present study was to measure capillary blood pressure and interstitial pressure in transplanted pancreatic islets and to correlate these measurements to capillary and tubular pressures in the adjacent kidney. For this purpose, 250 syngeneic islets were implanted under the renal capsule of WF rats and studied 1, 2, or 6 months after transplantation. Some of the animals studied after 1 and 2 months were streptozotocin (STZ)-induced diabetic. Measurements were performed during basal conditions or after an acute glucose-stimulation of insulin release. The hydrostatic pressures were determined in vivo by direct micropuncture. The islet transplant capillary pressure in normoglycemic animals was 6.9 +/- 0.4 mmHg (n = 9), 10.0 +/- 0.8 mmHg (n = 7), and 12.4 +/- 0.8 mmHg (n = 7) when measured 1, 2, and 6 months after implantation, respectively. Previous data from our laboratory showed that the normal capillary pressure of native rat pancreatic islets is approximately 3 mmHg. The blood pressure in kidney peritubular capillaries was 10-12 mmHg in both transplanted and control animals. Islet transplant interstitial pressures were 4-6 mmHg in the normoglycemic recipients at 1, 2, and 6 months after transplantation. Acute glucose stimulation had no effect on islet transplant interstitial pressure or peritubular or transplant capillary blood pressures. Capillary pressures in the islet grafts were slightly increased 1 month after transplantation in STZ-induced diabetic rats, and this was associated with an increased blood perfusion of the transplants. However, 2 months after transplantation there were no differences in transplant capillary blood pressure between diabetic and normoglycemic animals. The graft interstitial pressure was, on the contrary, decreased in the diabetic animals 2 months after transplantation. We concluded that the capillary blood pressure in islets implanted under the renal capsule was similar to that of the implantation organ, which was three to four times higher than that normally found in native islets.

Capillary blood pressure in the endocrine and exocrine parenchyma of rat pancreas transplants.

BACKGROUND: Transplantation of isolated organs or cells leads to a functional denervation of the organ, which may cause a hyperperfusion of blood. The current study evaluated to what extent blood perfusion and capillary blood pressures were affected in the transplanted rat pancreas. METHODS: Inbred, male Wistar-Furth rats underwent transplantation with a syngeneic pancreaticoduodenal graft. Four weeks later, blood flow to the native and transplanted pancreases was measured with a microsphere technique. Capillary pressures were measured by direct micropuncture technique. RESULTS: An increased islet blood flow was consistently observed in the transplanted pancreas as compared with the native organ, while whole pancreatic and duodenal blood flow was similar in the native and transplanted organs. The capillary pressure was twice as high in the exocrine pancreas (6-7 mm Hg) of both the native and transplanted glands when compared with that of the islets (approximately 3 mm Hg). There were no differences in the capillary pressures in either the islets or exocrine gland when native and transplanted pancreases were compared. CONCLUSIONS: We conclude that the transplanted whole pancreas retains a low islet capillary blood pressure after transplantation despite having a higher islet blood perfusion.

Human dentine as a hydrogel.

The pores (tubules) of human dentine in 0.02-cm planoparallel sections of newly extracted permanent teeth were investigated. By the conventional scanning electron microscopy these pores appear empty, but by the newly developed scanning-probe microscopy the presence of a complex matrix could be established. By measuring the transport of neutral myoglobin by diffusion alone and diffusion+bulk flow, the area of dentine occupied by the matrix was calculated to be 1.9 +/- 0.9% and 2.3 +/- 0.5%, respectively. The hydraulic conductivity was surprisingly small, 1.35 +/- 0.55 x 10(-7) ml/(s.cm2 dentine) at a pressure difference of 0.1 kPa across a 1-cm thick section. This suggests a hydrogel with a relatively dense network, the width of meshes estimated at 2 x 30 nm. In line with this concept, enzymatic degradation of the organic matter increased the hydraulic conductivity 3000 times. By studying the transport of negatively charged myoglobin, the matrix was calculated to carry 18 mEq/l of positive charges. Due to the consequent attraction of small, negative ions and thence of water, the pressure within the matrix would be about 1.33 kPa, a force which will act to immobilize the water in the channels. The concept of a hydrogel in the dentine tubules was also supported by the finding that shielding the charges with bathing media of high ionic strength reduced the hydraulic conductivity.

Failure of loop diuretics to improve the long term outcome of ischaemic damage in rat kidneys.

The effects of furosemide administered at the onset of postischaemic renal failure were investigated in Sprague-Dawley rats one month after exposing the left kidney to 45 min of renal ischemia. In the experimental group, 13 mg furosemide was given intravenously both before and a few minutes after induction of the ischaemia and then, by an osmotic pump, in a daily dose of 2-3 mg for the following 7 days. The animals of the control group were treated similarly but with saline alone. After one month, the glomerular filtration rate (GFR) in the damaged left kidneys of the furosemide-treated rats was 0.5+/-0.08 ml/min, which was not significantly different from that in the untreated control rats, of 0.8+/-0.14 ml/min. As expected, the right intact kidneys responded with an increase in GFR to about 2 ml/min. Further effects that were similar in the damaged kidneys of the furosemide-treated and untreated animals were a decrease in potassium secretion and in the urine concentration ability; the urine osmolality in the diseased left kidneys was thus 1000-1500 mOsm/kg, as against over 2000 mOsm/kg in the right, intact kidneys. The function of the individual nephrons in terms of such variables as single nephron filtration rate, fractional fluid reabsorption and tubular and vascular hydrostatic pressures remained unaltered, however. Hence, the severe reduction in whole kidney GFR appeared to be due to a loss of nephrons rather than to an equal decrease in each individual nephron. It is also clear that furosemide did not improve the long-term outcome of acute postischaemic renal failure.

Engraftment and growth of transplanted pancreatic islets.

Transplantation of pancreatic islets may provide a cure for type 1 diabetes. However, this treatment can currently be offered only to very few patients. To improve transplantation success we need to understand better the mechanisms of how the implanted islets survive, grow and/or maintain adequate function. We herein report on our studies to evaluate the factors responsible for the engraftment, i.e. revascularization, reinnervation etc., of transplanted islets and relate these factors to the metabolism and growth of the islets. Graft metabolism can be monitored by microdialysis probes that allow for the measurement of minute amounts of islet metabolites and hormonal products. Growth of the endocrine cells can be stimulated both in vitro before implantation and in vivo post-transplantation. Another problem is rejection of transplanted islets, which may be overcome by the microencapsulation of islets. The knowledge gained by the present studies will enable us to elucidate the optimal treatment of islets to ensure a maximal survival of the transplanted islets, and may be applied also to clinical islet transplantation.

Pancreatic islet blood flow during euglycaemic, hyperinsulinaemic clamp in anaesthetized rats.

AIMS: Previous studies have demonstrated that pancreatic islet blood flow is crucially dependent on blood glucose concentration. Thus, hyperglycaemia increases and hypoglycaemia decreases islet blood perfusion, by a combination of nervous and metabolic signals. The aim of the present study was to evaluate if hyperinsulinaemia, without associated hypoglycaemia, affects islet blood flow. METHODS: Thiobutabarbital-anaesthetized Wistar-Furth rats were subjected to an euglycaemic, hyperinsulinaemic clamp, that is they were infused for 60 min with either saline, insulin (18 mU kg(-1) min(-1)), glucose (27 mg kg(-1) min(-1)) or both glucose and insulin. This was followed by islet blood flow measurements with a microsphere technique. RESULTS: Animals receiving only glucose doubled their blood glucose and serum insulin concentrations, whereas rats receiving only insulin had blood glucose concentrations <2 mmol L(-1) and a 10-fold increase in serum insulin concentrations. Animals given simultaneous glucose and insulin had normal blood glucose concentrations but a 10-fold increase in serum insulin concentrations. Total pancreatic blood flow was unaffected in all animals. Islet blood flow was increased in hyperglycaemic and decreased in hypoglycaemic rats compared with control rats. Islet blood flow did not differ between clamped and control rats. CONCLUSIONS: Serum insulin concentration per se does not affect islet blood flow, whereas the ambient blood glucose concentration is of major importance in this context.

Lymphatic vessels in pancreatic islets implanted under the renal capsule of rats.

Transplantation of pancreatic islets necessitates an engraftment process, including revascularization of the graft. Studies of graft vasculature have demonstrated that islets become revascularized during the first post-transplant week through an angiogenic process. If this also involves lymphatic vessels is unknown. The aim of the present study was to functionally evaluate if lymphatic vessels, which are absent in endogenous islets, form after islet transplantation. To achieve this, inbred Wistar-Furth rats were transplanted with 250 syngeneic islets under the renal capsule. Intra-vital microscopy of the graft in combination with interstitial injection of Evans Blue was performed 1 week, 1 month or 9-12 months later. In all animals studied, there was drainage through intra-graft lymphatic capillaries emptying into larger lymphatic vessels associated with the renal capsule. The number was slightly lower 1 week post-transplantation. Most of the lymphatic capillaries were present in the graft stroma, rather than interspersed among the endocrine cells. In some animals, we were able to demonstrate dye in regional lymph nodes. We conclude that unlike endogenous islets, islet grafts develop a lymphatic drainage. Its functional importance and characteristics remain to be established. However, it can be speculated that immune reactions may be facilitated by the presence of lymphatic vessels.

Intracellular calcium-binding protein S100A4 influences injury-induced migration of white matter astrocytes.

Astrocytes play a crucial role in central nervous system (CNS) pathophysiology. White and gray matter astrocytes are regionally specialized, and likely to respond differently to CNS injury and in CNS disease. We previously showed that the calcium-binding protein S100A4 is exclusively expressed in white matter astrocytes and markedly up-regulated after injury. Furthermore, down-regulation of S100A4 in vitro significantly increases the migration capacity of white matter astrocytes, a property, which might influence their function in CNS tissue repair. Here, we performed a localized injury (scratch) in confluent cultures of white matter astrocytes, which strongly express S100A4, and in cultures of white matter astrocytes, in which S100A4 was down-regulated by transfection with short interference (si) S100A4 RNA. We found that S100A4-silenced astrocytes rapidly migrated into the injury gap, whereas S100A4-expressing astrocytes extended hypertrophied processes toward the gap, but without closing it. To explore the involvement of S100A4 in migration of astrocytes in vivo, we induced focal demyelination and transient glial cell elimination in the spinal cord white matter by ethidium bromide injection in S100A4 (-/-) and (+/+) mice. The results show that astrocyte migration into the demyelinated area is promoted in S100A4 (-/-) compared to (+/+) mice, in which a pronounced glial scar was formed. These data indicate that S100A4 reduces the migratory capacity of reactive white matter astrocytes in the injured CNS and is involved in glial scar formation after injury.

Neuronal nitric oxide synthase and splanchnic blood flow in anaesthetized rats.

AIMS: To evaluate to what extent the neuronal form of constitutive nitric oxide synthase (nNOS) contributes to the blood perfusion of splanchnic organs, including the islets of Langerhans. METHODS: The nNOS inhibitor 7-nitroindazole (300 mg kg(-1) i.p.) was administered to anaesthetized Sprague-Dawley rats, some of which were pre-treated with the ganglionic blocker hexamethonium (20 mg kg(-1) i.v.) The blood perfusion of the splanchnic organs, including the pancreatic islets was then measured with a microsphere technique. RESULTS: Nitroindazole decreased total pancreatic, duodenal and renal blood flow, whereas pancreatic islet, colonic and adrenal blood flows were unchanged. A slight increase in mean arterial blood pressure was seen after nitroindazole treatment. Nitroindazole did not affect blood glucose or serum insulin concentrations. In separate experiments, hexamethonium affected none of the studied blood flow values, suggesting that the effects of nNOS-inhibition were not mediated from the nervous system. CONCLUSION: Nitric oxide derived from the activity of nNOS contributes to the blood perfusion in the upper portions of the gastrointestinal tract, viz. the parts supplied by the cranial mesenteric artery, and the kidneys, whilst no effects are seen on colonic or adrenal blood flow. Pancreatic islet blood flow was unaffected by nNOS inhibition, thereby suggesting that NO derived from the other isoforms of NOS maintains the high basal islet blood perfusion.

The effects of hypothermia on renal function and haemodynamics in the rat.

The effects of 1-2 h of hypothermia at 28 degrees C and rewarming on renal function were investigated in anaesthetized rats, using conventional clearance methods and the micropuncture technique. Renal blood flow (RBF) decreased from 7.3 +/- 0.51 mL min-1 at 37.5 degrees C (control) to 4.0 +/- 0.47 at 28 degrees C, with almost complete restoration to 6.9 +/- 0.59 mL min-1 after rewarming. Systemic blood pressure remained essentially unaltered. The RBF reduction seen during hypothermia was due to a 75% increase in vascular resistance, mainly attributable to constriction of the afferent arteriole and increased blood viscosity. This was accompanied by a decline in glomerular capillary pressure from 56.7 +/- 0.6 to 46.4 +/- 1.3 mmHg, overshooting to 59.0 +/- 0.7 mmHg. The glomerular filtration rate (GFR) decreased from 1.1 +/- 0.08 to 0.6 +/- 0.04 mL min-1, returning to 1.0 +/- 0.07 after rewarming, a pattern also observed for single nephron GFR. This resulted from a decrease in net driving force for glomerular filtration, whereas the filtration coefficient was not affected. Both proximal and distal tubular fluid flow decreased, but fractional reabsorption remained unchanged. In contrast, urine flow increased from 1.8 +/- 0.16 to 5.7 +/- 1.08 microL min-1, returning to 2.1 +/- 0.18, the increase during hypothermia mainly resulting from a disproportionately reduced fluid reabsorption beyond the mid-distal tubule.

A method for studying the effect of vasoactive substances on glomerular filtration without affecting the central haemodynamics.

A method for microcatheterization of rat kidneys was developed. The catheter consists of 50-100 micron thick polyethylene tubes, and is inserted into the interlobular or arcuate arteries via a lumbar artery. The technique makes it possible to perfuse a small number of nephrons with very high doses of vaso active substances without affecting the nephrons in the vicinity or the central haemodynamics. By adding labelled inulin to the perfusate it is also possible to calculate the amount of drug reaching the nephron under study. It was shown that the catheterization and perfusion with Ringer solution per se have no effect on the nephron function. Perfusion with very high doses of acetylcholine was found to have a selective effect on the area perfused but caused no changes in central haemodynamics, or on nephrons in unperfused areas. It is concluded that the technique is suitable for use in studies concerning the handling of high doses of vasoactive substances by the nephron.

Effect of elevated interstitial pressure on the renal cortical hemodynamics.

The influence of renal interstitial pressure on the resistance pattern within the superficial cortical vasculature has been investigated from determinations of 1) the glomerular blood flow eith a modified microsphere technique and 2) the intravascular hydrostatic pressures. Interstitial pressure was monitored via a 50 mum PVC-catheter placed into the subcapsular interstitial space. Two conditions were analyzed viz. a) elevation of uretheral pressure to 20 mm Hg and b) venous stasis to 10-15 mm Hg. Both conditions produced an increase in the interstitial pressure from 1-2 mm Hg to about 5 mm Hg as well as an increased hilar lymph flow and protein flow of about the same size. The vascular reactions were different, however. Uretheral stasis (but not the stasis of a single nephron) produced a decreased resistance in the afferent arteriolae with a concomitant increae in the pressures in the glomerular capillaries, and the peritobular capillary network. In contrast, venous stasis produced only small changes in the parameters studied but for the obvious rise in the peritubular capillary pressure. The results suggest that factors other than the interstitial pressure are governing the afferent vascular tone; the tubular wall tension might be one of these factors.

The adrenal glands as suppliers of plasma L-Dopa and sources of urinary dopamine.

Dopamine (DA) is a natriuretic hormone synthesized in the kidneys by conversion of filtered 3,4-dihydroxyphenylalanine (L-Dopa), and is activated during hypervolaemia and increased dietary sodium intake. The natriuretic activity of endogenous DA is controversial, however, and the regulation of renal DA synthesis has yet to be explained. It has been suggest that the adrenals may be major suppliers of plasma L-Dopa on the basis of their catecholamine biosynthesis. A study was conducted in rats to elucidate the role of the adrenal glands as dynamic suppliers of L-Dopa to plasma, and thereby as sources of urinary DA. Adrenal venous and systemic arterial plasma concentrations and urinary excretion of L-Dopa, DA and sodium were measured before and during acute isotonic volume expansion (VE; 5% of body weight). One group of animals were acutely adrenalectomized (ADX group) to elucidate the ultimate importance of the adrenals in VE-induced renal sodium and DA excretion. In intact animals, the L-Dopa concentration was 62% higher in adrenal venous than in systemic arterial plasma under control conditions, and 42% higher during VE. The adrenaline concentration was 65 times higher in adrenal venous than in systemic arterial plasma before VE and 56 times higher during VE. The L-Dopa concentration in systemic arterial plasma and the urinary L-Dopa excretion were similar in intact and ADX animals. In intact animals, renal sodium and DA excretion during VE increased more than 13-fold and by 42%, respectively. The corresponding values in ADX animals did not differ from those in the intact animals (more than 14-fold and 36%, respectively). It is concluded that the adrenal glands are only minor suppliers of plasma L-Dopa and minor sources of urinary DA. The regulation of plasma L-Dopa remains to be explained.

Characteristics of the glomerular capillary membrane of the rat kidney as a hydrated gel. II. On the validity of the model.

In our gel model applied to the glomerulus, maintenance of membrane integrity is assumed to be preserved not by rigid elements but by the electro-osmotic and balancing hydrostatic pressure offered by negative, fixed charges such that the membrane is able to withstand the external colloid osmotic and hydrostatic forces. Ir a previous study we used micropuncture data to estimate the charge densities required to fulfil this assumption. In the present study the validity of the model was examined from the transport of neutral and negative charged myoglobin as derived from their concentrations in renal venous blood. In order to determine the size of the pores, or rather meshes in the network, the venous concentration of [51Cr]EDTA was also analysed. Based on the ratio between EDTA and neutral myoglobin of 1.08 +/- 0.010 (mean +/- SE, n = 9), the equivalent pore radius was calculated to be approximately 40 A. The ratio of neutral to negative myoglobin in the two series performed was found to be 0.96 +/- 0.018 (n = 8) and 0.97 +/- 0.05 (n = 7), figures which were the same as ratio of 0.97 predicted on theoretical grounds. It is concluded that the experimental data support the hypotheses, although they may also be adapted to the transport in a homogeneously charged membrane; the charge density in this case was estimated at 2.3 mEq L-1. Assuming that the membrane constitutes a network with quadratic meshes, each fibre would seem to carry binding sites approximately 80 A apart and where, in between these binding sites, each fibre was calculated to carry three charges such that the mesh will thus be surrounded by 12 charges.

Dynamics of glomerular ultrafiltration in the neonate kidney.

In the neonate kidney the glomerular filtration rate is generally depressed both in absolute terms and when calculated per gram kidney weight. Micropuncture studies have revealed that this phenomenon is due, not to changes in the driving pressures or the hydraulic conductivity of the glomerular capillary membrane, but to a retarded glomerular blood flow. A retarded flow will thus mean a steep rise in the protein concentration in parallel to the filtration of the protein-free filtrate. The corresponding steep rise of the colloid osmotic pressure will then induce cessation of the filtration in the distal parts of the glomerular capillary. In dehydrated states this phenomenon will be even more aggravated. An extracellular volume expansion with saline induces relaxation of the two arterioles with subsequent rise in the glomerular blood flow. The rise in the colloid osmotic pressure along the capillary is then less and the filtration can proceed along the whole of the glomerulus. Accordingly the glomerular filtration rate will be increased, reaching figures typical of the mature kidney.

TGF-initiated vascular interactions between adjacent nephrons in the rat kidney.

We sought to determine whether tubuloglomerular feedback (TGF), activated from one nephron, affects other arterioles derived from the same cortical radial artery. Surface nephrons supplied by a single cortical radial artery were identified by injecting Ringer solution containing Fast Green from a narrow-gauge polyethylene catheter inserted via a lumbar artery into a renal artery. Stop-flow pressure was measured in an identified nephron from such a grouping. In one series, increasing end-proximal flow rate from 0 to 50 nl/min of synthetic tubular fluid in one member of an identified pair of nephrons reduced stop-flow pressure by 1.3 +/- 0.2 mmHg in the other member. When the nephrons were derived from different cortical radial arteries, the stop-flow pressure changed -0.2 +/- 0.1 mmHg. In another series, increasing flow in the adjacent nephron from 0 to 50 nl/min decreased stop-flow pressure 3.9 +/- 0.9 mmHg, and increasing flow in the adjacent nephron by the same amount when flow in the first nephron was 50 nl/min decreased stop-flow pressure 3.4 +/- 0.7 mmHg. These results indicate the operation of an interaction among nephrons derived from a common cortical radial artery. Such an interaction could produce a cooperative effect larger than that predicted from measured single-nephron responses when systemic arterial pressure changes.