Birgitta Bodin

Multiple Injections of Coloured Microspheres for Islet Blood Flow Measurements in Anaesthetised Rats: Influence of Microsphere Size

We investigated if coloured microspheres could be used for repeated measurements of pancreatic islet blood flow in rats. An initial injection of 1.0-1.5 x 105 microspheres (black colour), with a size of 10 or 15 µm, was made into the ascending aorta, while an arterial reference sample was collected from the femoral artery. Twelve min later, 1 ml of saline or 30% D-glucose was injected intravenously. Three min after this injection a second injection of 10- or 15-µm microspheres (green colour) was given. The animals were then killed, and the pancreas and adrenals were removed and samples (150-200 mg) were secured from the duodenum, ileum, colon, right kidney and liver. The microsphere contents were determined with the aid of a freeze-thawing technique and blood flow values were calculated. Our results suggest that 10-µm microspheres, but not 15-µm microspheres, provide reproducible islet and total pancreatic blood flow measurements when repeatedly injected. Values for the blood flow to the intestines, kidney and liver were less sensitive to the size of the microspheres. We conclude that repeated administration of 15-µm microspheres induces a high risk for erroneous islet and total pancreatic blood flow measurements, whereas two such measurements can be performed if 10-µm microspheres are used.

Pancreatic islet blood flow and its measurement

Abstract Pancreatic islets are richly vascularized, and islet blood vessels are uniquely adapted to maintain and support the internal milieu of the islets favoring normal endocrine function. Islet blood flow is normally very high compared with that to the exocrine pancreas and is autonomously regulated through complex interactions between the nervous system, metabolites from insulin secreting β-cells, endothelium-derived mediators, and hormones. The islet blood flow is normally coupled to the needs for insulin release and is usually disturbed during glucose intolerance and overt diabetes. The present review provides a brief background on islet vascular function and especially focuses on available techniques to measure islet blood perfusion. The gold standard for islet blood flow measurements in experimental animals is the microsphere technique, and its advantages and disadvantages will be discussed. In humans there are still no methods to measure islet blood flow selectively, but new developments in radiological techniques hold great hopes for the future.

A perfusion protocol for highly efficient transduction of intact pancreatic islets of Langerhans.

Aims/hypothesisSuccessful gene transfer to pancreatic islets might be a powerful tool for dissecting the biological pathways involved in the functional impairment and destruction of beta cells in type 1 diabetes. In the long run, such an approach may also prove useful for promoting islet graft survival after transplantation in diabetic patients. However, efficient genetic modification of primary insulin-producing cells is limited by the specific compact structure of the pancreatic islet. We present here a whole-pancreas perfusion-based transduction procedure for genetic modification of intact pancreatic islets.Materials and methodsWe used flow cytometry analysis and confocal microscopy to evaluate the efficiency of in vitro and perfusion-based transduction protocols that use adenoviral and lentiviral vectors expressing green fluorescent protein. Islet cell viability was assessed by fluorescence microscopy and beta cell function was determined via glucose-stimulated insulin secretion.ResultsIn intact rat and human pancreatic islets, adenoviral and lentiviral vectors mediated gene transfer to about 30% of cells, but they did not reach the inner cellular mass within the islet core. Using the whole-pancreas perfusion protocol, we demonstrate that at least in rodent models the centrally located insulin-producing cells can be transduced with high efficiency, while preserving the structural integrity of the islet. Moreover, islet cell viability and function are not impaired by this procedure.Conclusions/interpretationThese results support the view that perfusion-based transduction protocols may significantly improve the yield of successfully engineered primary insulin-producing cells for diabetes research.

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.

KATP Channels and Pancreatic Islet Blood Flow in Anesthetized Rats: Increased Blood Flow Induced by Potassium Channel Openers

K(ATP) channels are important for insulin secretion and depolarization of vascular smooth muscle. In view of the importance of drugs affecting K(ATP) channels in the treatment of diabetes, we investigated the effects of these channels on splanchnic blood perfusion in general and pancreatic islet blood flow in particular. We treated anesthetized Sprague-Dawley rats with the K(ATP) channel openers diazoxide or NNC 55-0118 or the K(ATP) channel closer glipizide. Both diazoxide and NNC 55-0118 dose-dependently increased total pancreatic and islet blood flow in the presence of moderate hyperglycemia, but had no effects on the blood perfusion of other splanchnic organs. Diazoxide markedly lowered the mean arterial blood pressure and thus increased vascular conductance in all organs studied. NNC 55-0118 had much smaller effects on the blood pressure. Glipizide did not affect total pancreatic blood flow, but decreased islet blood flow by 50% in the presence of hypoglycemia. We conclude that K(ATP) channels actively participate in the blood flow regulation of the pancreatic islets and that substances affecting such channels may also influence islet blood flow.

Blood lipids affect rat islet blood flow regulation through beta(3)-adrenoceptors

Pancreatic islet blood perfusion varies according to the needs for insulin secretion. We examined the effects of blood lipids on pancreatic islet blood flow in anesthetized rats. Acute administration of Intralipid to anesthetized rats increased both triglycerides and free fatty acids, associated with a simultaneous increase in total pancreatic and islet blood flow. A preceding abdominal vagotomy markedly potentiated this and led acutely to a 10-fold increase in islet blood flow associated with a similar increase in serum insulin concentrations. The islet blood flow and serum insulin response could be largely prevented by pretreatment with propranolol and the selective β₃-adrenergic inhibitor SR-59230A. The nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester prevented the blood flow increase but was less effective in reducing serum insulin. Increased islet blood flow after Intralipid administration was also seen in islet and whole pancreas transplanted rats, i.e., models with different degrees of chronic islet denervation, but the effect was not as pronounced. In isolated vascularly perfused single islets Intralipid dilated islet arterioles, but this was not affected by SR-59230A. Both the sympathetic and parasympathetic nervous system are important for the coordination of islet blood flow and insulin release during hyperlipidemia, with a previously unknown role for β₃-adrenoceptors.

Changes in Graft Blood Flow early after Syngeneic Rat Pancreas-Duodenum Transplantation

Organ transplantation is associated with changes in graft blood flow, both acutely caused by reperfusion associated phenomena, and chronically due to e.g. denervation. The aim of the study was to investigate regional blood flow early after implantation of a syngeneic pancreas-duodenum transplant in rats, i.e. during reperfusion. Warm ischemia time was 1–2 min and cold ischemia 90 min. Blood flow values were measured with coloured microspheres both 10 and 30 min after implantation in transplanted rats, and at one time point in control rats. A marked decrease in the blood perfusion of the transplanted duodenum compared to the endogenous intestine was seen at both 10 and 30 min. Total graft pancreatic blood flow was increased both 10 and 30 min after implantation, whilst islet blood flow remained unchanged compared to the endogenous gland. We conclude that the blood perfusion of the graft is markedly changed in the immediate post-transplantation period, presumably due to reperfusion. However, islet blood perfusion remains constant, suggesting that islet vasculature is less sensitive to changes induced by the implantation.

Carbon monoxide and pancreatic islet blood flow in the rat : Inhibition of haem oxygenase does not affect islet blood perfusion

Objective. To determine whether carbon monoxide, a known gaseous vasorelaxator, affects pancreatic islet blood flow in rats. Material and methods. Sprague‐Dawley rats were anaesthetized with thiobutabarbital and injected intravenously with the haem oxygenase inhibitor tin‐protoporphyrin IX dichloride (SnPP; 4, 10 or 20 mg/kg body‐weight). After 15 min, blood flow measurements were performed using a microsphere technique. Results. There was a slight increase in mean arterial blood pressure with the highest dose of SnPP. No effects on total pancreatic, islet, duodenal, colonic, renal or adrenal blood flow were seen with any of the applied doses. Conclusions. The findings of this study suggest that the haem oxygenase‐carbon monoxide system is likely to be of limited importance in the regulation of blood perfusion to the pancreas, the islets of Langerhans or any of the other studied organs.

Hyaluronidase Treatment of Graft Pancreatitis in Rats: Marked Effects on the Blood Perfusion of the Transplanted Pancreas

Hyaluronan is known to accumulate in tissues during inflammatory diseases associated with graft implantation and rejection of organ allografts. The aim was to evaluate whether hyaluronidase treatment affected hyaluronan content and blood perfusion in graft pancreatitis. Syngeneic rat pancreatic‐duodenal transplantations were performed. Two days later blood flow measurements were made with a microsphere technique in both grafted and endogenous pancreas in animals treated with daily injections of vehicle or hyaluronidase (20.000 U/kg). Non‐transplanted rats served as controls. Also, samples for analysis of hyaluronan and water content were taken. The hyaluronan content of the pancreatic graft was increased after transplantation. Hyaluronidase treatment markedly reduced total pancreatic and islet blood flow in both grafted and endogenous pancreas, whereas duodenum blood flow was unaffected. No blood flow effects were seen in non‐transplanted control rats. Hyaluronan content was increased in the grafted pancreas, but hyaluronidase treatment decreased it to levels comparable to those of the endogenous gland. There were no differences in hyaluronan content in the endogenous pancreases of transplanted and non‐transplanted rats. Graft pancreatitis after rat pancreas transplantation is associated with an increased hyaluronan content, which can be reduced by treatment with hyaluronidase. Hyaluronidase treatment of the graft recipients effected a 50% reduction in total pancreatic and islet blood flow in the graft, as well as in the endogenous pancreas. The functional importance of this is at present unknown.

Effects of Mn-DPDP and manganese chloride on hemodynamics and glucose tolerance in anesthetized rats

Background Previous studies have demonstrated that magnetic resonance imaging may be a method of choice to visualize transplanted pancreatic islets. However, contrast agents may interfere with microcirculation and affect graft function. Purpose To evaluate the effects manganese-containing contrast media on regional blood flow and glucose tolerance. Material and Methods Anesthetized rats were injected intravenously with MnCl2 (10 µM/kg body weight) or Mn-DPDP (Teslascan™; 5 µM/kg body weight). Blood flow measurements were made with a microsphere technique 10 min later. In separate animals vascular arteriolar reactivity in isolated, perfused islets was examined. Furthermore, an intraperitoneal glucose tolerance test was performed in separate rats. Results Glucose tolerance was unaffected by both agents. No changes in regional blood flow were seen after administration of Mn-DPDP, except for an increase in arterial liver blood flow. MnCl2 increased all blood flow values except that of the kidney. MnCl2, but not Mn-DPDP, caused a vasoconstriction in isolated rat islet arterioles but only at very high doses. Conclusion Mn-DPDP administration does not affect glucose tolerance or regional blood flow, besides an increase in arterial hepatic blood flow, and may therefore be suitable for visualization of islets.