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Endocrinology Vol. 139, No. 8 3534-3541
Copyright © 1998 by The Endocrine Society

ARTICLES

Pancreatic Islet Blood Perfusion in the Nonobese Diabetic Mouse: Diabetes-Prone Female Mice Exhibit a Higher Blood Flow Compared with Male Mice in the Prediabetic Phase1

Per-Ola Carlsson, Stellan Sandler and Leif Jansson

Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden

Address all correspondence and requests for reprints to: Per-Ola Carlsson, M.D., Department of Medical Cell Biology, Biomedical Center, P.O. Box 571, S-75123 Uppsala, Sweden.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
The present study tested the hypothesis that changes in pancreatic islet blood flow correlate with the difference in diabetes incidence between male and female nonobese diabetic (NOD) mice. The blood flows were determined by a microsphere technique. In animals aged 10 and 14 weeks, the islet blood perfusion was 3-fold higher in female NOD mice compared with that in either age-matched male NOD mice or age- and sex-matched control ICR mice. At 5 weeks of age islet blood flow was similar in all groups. No differences between male and female NOD mice in whole pancreatic, duodenal, ileal, or colonic blood flows were observed at any time point. Administration of a bolus dose of aminoguanidine (a blocker of inducible nitric oxide synthase) to 10-week-old animals selectively and markedly decreased islet blood flow in female NOD mice, whereas islet blood flow in ICR mice and male NOD mice remained unaffected. Aminoguanidine did not affect mean arterial blood pressure or whole pancreatic blood flow in any of the groups. Injection of NG-methyl-L-arginine, an unspecific inhibitor of both constitutive and inducible nitric oxide synthase, markedly decreased whole pancreatic and islet blood flow to the same level in both male and female NOD mice. These combined findings suggest that diabetes-prone female NOD mice have an increased islet blood flow, which is mediated by an excessive production of nitric oxide formed by inducible nitric oxide synthase. The islet blood hyperperfusion may augment homing to the pancreatic islets of inflammatory cells and soluble factors involved in ß-cell destruction during the development of insulin-dependent diabetes mellitus in this animal model. The presently observed gender difference in the blood flow response could, therefore, at least partially explain why female NOD mice are more prone to develop hyperglycemia than the males.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
IT IS KNOWN that an infiltration of inflammatory cells into the islets, i.e. insulitis, precedes ß-cell destruction both in human subjects with insulin-dependent diabetes mellitus (IDDM) (1, 2, 3) and in animals with spontaneous autoimmune diabetes, such as the nonobese diabetic (NOD) mouse (4, 5, 6) and the BioBreeding rat (BB) rat (7, 8).

Accumulating evidence suggests that the vascular endothelium is of crucial importance for the development of inflammatory reactions (9, 10). Several studies have focused on the endothelial and leukocyte surface receptors that are involved in the homing of mononuclear inflammatory cells to pancreatic islets, with the aim to evaluate their role for the origin of insulitis and IDDM (11, 12, 13, 14, 15). Furthermore, changes in vascular permeability in islet blood vessels during the development of IDDM have been described in both BB rats (16, 17) and chemically induced diabetes in mice (18, 19, 20). Despite this interest in the islet vascular system in diabetes, there has been no quantitative studies to date on the blood flow through the pancreatic islets during the development of insulitis and overt IDDM.

The NOD mouse strain, originally derived from outbred ICR mice, is characterized by a spontaneously developing diabetes that bears much resemblance to human IDDM (4, 5, 21). Thus, the pancreatic islets of the mice become infiltrated with mononuclear cells, followed by ß-cell destruction. This mononuclear cell infiltration commences at 4–5 weeks of age. A major feature of this syndrome that is as yet not well understood is that female NOD mice are much more prone to develop hyperglycemia than the males in most colonies (22).

The aim of the present study was to evaluate to what extent changes in pancreatic islet blood flow in the prediabetic phase occur in NOD mice. Locally produced high levels of the vasoactive free radical nitric oxide (NO), catalyzed by inducible NO synthase (iNOS), have been suggested to be of major importance during development of IDDM (23, 24, 25). Furthermore, islet blood flow is known to be very sensitive to the vasodilatory actions of NO (26, 27). We therefore decided to evaluate if iNOS activity may influence islet blood flow in the prediabetic period in this animal model of IDDM. For this purpose, we administered aminoguanidine (AG), an inhibitor of this enzyme (28, 29, 30), and NG-methyl-L-arginine (NMA), which is an unspecific inhibitor of both iNOS and constitutive NOS (cNOS) (29). The blood perfusions of the whole pancreas and the intestines were determined to evaluate the specificity of AG for iNOS inhibition and to exclude any general gender differences in mesenteric perfusion in the NOD mouse strain.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Animals
Inbred male and female NOD mice were obtained from a local colony established at the Biomedical Center, Uppsala University (Uppsala, Sweden), in 1988. Originally, three breeding pairs of inbred NOD mice were obtained from the Clea Co. (Aobadi, Japan). The colony was rederived by caesarean delivery in 1992 due to a decreasing diabetes incidence and infection with mouse hepatitis virus. The colony has subsequently been maintained barrier bred under pathogen-free conditions. The cumulative diabetes incidence is now 74% in the females and less than 10% in the males at 30 weeks of age. Barrier-bred male and female ICR mice were purchased from Taconic Farms (Germantown, NY). All animals had free access to autoclaved tap water and pelleted food throughout the course of the study. The experiments were approved by the local animal ethics committee at Uppsala University.

Blood flow measurements and assessment of islet volume
Male and female NOD and ICR mice, aged 5, 10, and 14 weeks, were used in these experiments. Blood flow measurements were performed with a microsphere technique as previously described and extensively evaluated in mice (31). Briefly, the animals were anesthetized with an ip injection of 0.02 ml/g BW Avertin [a 2.5% (vol/vol) solution of 10 g 97% 2.2.2-tribromoethanol (Sigma Chemical Co., St. Louis, MO) in 10 ml 2-methyl-2-butanol (Kemila, Stockholm, Sweden)] and placed on an operating table maintained at body temperature (38 C). An injection of 200 IU heparin (5000 IU/ml; Lovens Lakemedel Malmo, Sweden) was given in the left jugular vein. Polyethylene catheters were inserted into the ascending aorta, via the right carotid artery, and into the right femoral artery. The former catheter was connected to a pressure transducer (PDCR 75, Druck, Groby, UK) to allow continuous monitoring of the mean arterial blood pressure. When the blood pressure had remained stable for 10–15 min, the mice were given an iv injection of 0.1 ml saline, AG (10 mg/kg; Sigma) or NMA (25 mg/kg; Sigma) dissolved in saline 15 min before the blood flow measurements. Approximately 9 x 104 nonradioactive microspheres (NEN-Trac, DuPont Pharmaceuticals, Wilmington, DE) with a diameter of 11 µm were injected during 10 sec via the catheter with its tip in the ascending aorta. Starting 5 sec before the microsphere injection and continuing for a total of 60 sec, an arterial blood reference sample was collected by free flow from the catheter in the femoral artery at a rate of approximately 0.10 ml/min. The exact withdrawal rate in each experiment was confirmed by weighing the sample.

Arterial blood was then collected from the catheter in the femoral artery for determination of blood glucose concentrations with test reagent strips (ExacTech, Baxter Travenol, Deerfield, IL) and for serum insulin determinations with RIA (Insulin RIA Kit, Pharmacia-Upjohn Diagnostics, Uppsala, Sweden), using a rat insulin standard (Novo Research Institute, Bagsvaerd, Denmark).

The animals were killed, and the whole pancreas, the adrenal glands, pieces of the duodenum (proximal part), ileum (distal part), and colon (descending part) were carefully dissected free from fat and lymph nodes, blotted, weighed, and placed between object slides. Before placement between object slides, each pancreas was cut into 20–24 pieces. The slides were then placed at -20 C for at least 24 h. This enables the visualization of both islets and microspheres, as the exocrine parenchyma becomes transparent when viewed after thawing in a microscope equipped with darkfield illumination (32). The percent islet volume was determined by a point-counting method (31, 33). For this purpose, the number of intersections overlapping islets was counted at a magnification of x400 in a stereo microscope equipped with both dark- and brightfield illumination (Wild M3Z, Wild Heerbrugg, Heerbrugg, Switzerland). Approximately 20–24 different fields were counted in each mouse pancreas (corresponding to {cong}2400 points).

The total contents of microspheres in the exocrine and endocrine parts of the pancreas; in the pieces from duodenum, ileum, and colon; and in the adrenal glands were then counted under the stereo microscope (32). The number of microspheres in the arterial reference sample was determined by transferring the blood to glass microfiber filters with a pore size of 0.2 µm (Whatman, London, UK) and counting the microspheres in a microscope equipped with transmitted light.

The blood flow values were calculated according to the formula Qorg = Qref x Norg/Nref, where Qorg is organ blood flow (milliliter per min), Qref is withdrawal rate of reference sample (milliliter per min), Norg is number of microspheres present in the organ, and Nref is number of microspheres present in the reference sample. The microsphere contents of the adrenal glands were used to confirm that the microspheres were adequately mixed in the arterial circulation. A difference less than 10% in numbers of microspheres between the right and left adrenal gland was taken to indicate sufficient mixing. When the islet blood flow was expressed per islet weight, to correct for differences in size of the islet organ, the latter was estimated by multiplying the pancreatic weight with the islet volume fraction of the whole pancreas in each animal.

Estimation of degree of insulitis
Separate male and female NOD and ICR mice aged 5, 10 and 14 weeks were used for histological evaluation of the degree of insulitis. Blood glucose concentrations were determined in each animal from the cut tip of the tail by test reagent strips (ExacTech) immediately before the animals were killed by cervical neck distension. The pancreatic glands were removed, fixed in a 10% formalin solution, and embedded in paraffin. Sections, 5 µm thick, were cut and stained with hematoxylin and eosin. Pancreatic islet histology was ranked according to an arbitrary scale as illustrated previously (34). Rank A denotes normal islet structure; B denotes mononuclear cell infiltration in the periinsular area; C denotes heavy mononuclear cell infiltration into a majority of islets, i.e. insulitis; D denotes the presence of only a few residual islets, showing an altered cellular architecture and pyknotic cell nuclei. The pancreatic sections were evaluated by an examiner unaware of the origin of the sections.

Statistical analysis
Values are expressed as the mean ± SEM. Multiple comparisons between data were performed using ANOVA and Fisher’s protected least significant difference test (StatView, Abacus Concepts, Berkeley, CA). When only two groups were compared, probabilities of differences were calculated using Student’s unpaired t test. Coefficients of correlation were obtained by simple linear regression, and the statistical significances of correlations were evaluated by ANOVA (StatView).


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Pancreatic islet morphology
A majority of the NOD mice of both sexes showed normal pancreatic islet morphology at 5 weeks of age (Table 1Go). However, some of the 5-week-old NOD mice had developed periinsulitis or even insulitis. At 10 and 14 weeks of age, most islets of the male and female NOD mice exhibited inflammatory changes, which seemed more pronounced in the females at both time points (Table 1Go). Normal pancreatic islet morphology was seen in all groups of male and female ICR mice (Table 1Go). In animals used for evaluation of islet morphology, blood glucose concentrations did not differ among any of the groups (data not shown).


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  		Table 1. Pancreatic islet morphology of NOD and ICR mice of different ages and sexes

 
Pancreatic islet volume
Using the freeze-thawing technique (32), the total islet volume as a percentage of the total pancreatic volume was estimated to assess the extent of progressive islet destruction. Pancreatic islet volume decreased with age in both male and female NOD mice (Fig. 1AGo). At 10 and 14 weeks of age, female NOD mice had a smaller total pancreatic islet volume than the age-matched male NOD mice. In male ICR mice, the islet volume increased between 5 and 10 weeks of age, but no further increase was found between 10 and 14 weeks of age (Fig. 1BGo). In female ICR mice, an increase in islet volume was seen between 10 and 14 weeks of age (P < 0.001). At 14 weeks of age, female ICR mice had a larger total islet volume than males of the same age.



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  		Figure 1. Percent volume of islet mass in relation to the pancreatic volume in male (gray bars) and female (hatched bars) NOD (A) and ICR (B) mice at different ages. Values are the mean ± SEM for 8–20 mice. *, {dagger}, and {ddagger}, P < 0.05, P < 0.01, and P < 0.001 (vs. corresponding male mice). §, ||, and ¶, P < 0.05, P < 0.01, and P < 0.001 (vs. 5-week-old mice of the same gender). All comparisons were performed by ANOVA and Fisher’s protected least significant difference test.

 
Mean arterial blood pressure, blood glucose, and serum insulin concentrations
In anesthetized animals used for the blood flow measurements, mean arterial blood pressure was lower in NOD mice and male ICR mice at 5 weeks of age compared with that in corresponding 10-week-old animals (Table 2Go). No differences could be seen among the different groups of mice when 10- and 14-week-old animals were compared. Administration of AG (10 mg/kg BW) to 10-week-old NOD and ICR mice did not significantly change their mean arterial blood pressure. However, administration of NMA increased blood pressure by approximately 25% in both male and female NOD mice aged 10 weeks (data not shown). The blood glucose and serum insulin concentrations were similar in all groups, including mice treated with AG (Table 2Go) and NMA (data not shown).


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  		Table 2. Mean arterial blood pressure (MAP), blood glucose, and serum insulin concentrations after treatment with saline or aminoguanidine (AG) in NOD and ICR mice of different ages and sexes

 
Pancreatic and islet blood flows
The weights of the pancreatic glands were similar in all animals. Whole pancreatic blood flow increased between 5 and 10 weeks of age in both male and female NOD mice (Table 3Go). In the females it then decreased between 10 and 14 weeks of age (P < 0.01), whereas no corresponding change in whole pancreatic blood flow was seen in the male NOD mice in this time interval. In ICR mice, whole pancreatic blood flow did not change with age. Injection of AG did not affect whole pancreatic blood flow in any of the mouse strains (Table 3Go). Administration of NMA markedly decreased whole pancreatic blood flow compared with the corresponding values in saline-treated NOD mice shown in Table 3Go (0.53 ± 0.10 (n = 9) and 0.53 ± 0.10 (n = 11) ml/min·g pancreas in male and female NOD mice aged 10 weeks; P < 0.001 and P < 0.01, respectively, by Student’s t test).


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  		Table 3. Whole pancreatic blood flow (PBF) and islet blood flow (IBF) after treatment with saline or aminoguanidine (AG) in NOD and ICR mice of different ages and sexes

 
Islet blood flow, when expressed per islet tissue weight, was markedly increased in 10- and 14-week-old female NOD mice compared with that in 5-week-old female NOD mice (Table 3Go). An increased islet blood flow could also be seen at 10 weeks of age in male NOD mice compared with that in 5-week-old male NOD mice, but this increase was less marked than in the females (Table 3Go). At 10 and 14 weeks of age, islet blood flow per islet tissue weight was 3-fold higher in female NOD mice than in the males, whereas at 5 weeks of age islet blood flow did not differ between male and female NOD mice (Table 3Go). When islet blood flow was expressed as flow to the whole islet organ (per g pancreas), similar findings were observed (Table 3Go). Due to the marked decrease in islet volume with age, islet blood flow per pancreatic weight decreased between 10 and 14 weeks in female NOD mice (P < 0.001). In ICR mice, no differences in islet blood flow between any of the groups were seen (Table 3Go).

When examined at 10 weeks of age, islet blood flow (when expressed per islet tissue weight or per pancreatic weight) was unaffected by AG in ICR mice or in male NOD mice (Table 3Go). However, in female NOD mice, islet blood flow was markedly decreased and did not differ from the islet blood flow in male NOD mice after the administration of AG (Table 3Go).

Administration of NMA markedly decreased islet blood flow compared with the corresponding values in saline-treated NOD mice given in Table 3Go (4.54 ± 0.91 and 4.66 ± 1.17 µl/min·g pancreas in male and female NOD mice, aged 10 weeks; P < 0.001 for both comparisons, by Student’s t test). This decrease was also seen when islet blood flow was corrected for estimated islet weight compared with the corresponding values in saline-treated NOD mice given in Table 3Go (0.49 ± 0.08 and 0.52 ± 0.15 µl/min·mg estimated islet weight in male and female NOD mice, aged 10 weeks; P < 0.001 for both comparisons, Student’s t test).

When individual islet blood flow values were correlated to the islet volume, we found that an islet volume decrease was accompanied by an increase in islet blood flow per estimated islet weight in 10- and 14-week-old saline-treated female NOD mice (Figs. 2AGo and 3AGo). No such correlations were seen in saline-treated male NOD mice (Fig. 2BGo and 3BGo), in AG-treated (Fig. 2Go, C and D), NMA-treated (data not shown) male or female NOD mice of the same age, in 5-week-old NOD mice, or in ICR mice of any age (data not shown).



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  		Figure 2. Pancreatic islet blood flow in relation to estimated total islet weight in 10-week-old female and male NOD mice injected iv with 0.1 ml saline or AG (10 mg/kg) dissolved in saline 15 min before the blood flow measurements. A, Saline-injected female mice (n = 10): y = 19.608 - 9.6929x (r = 0.760; P = 0.011). B, Saline-injected male mice (n = 10): y = 3.7620 - 0.5632x (r = 0.320; P = 0.370). C, AG-injected female mice (n = 9): y = -0.5398 + 1.6145x (r = 0.50; P = 0.155). D, AG-injected, male mice (n = 10); y = 1.3354 + 0.0755x (r = 0.024; P = 0.950).

 


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  		Figure 3. Pancreatic islet blood flow in relation to estimated total islet weight in 14-week-old female and male NOD mice injected iv with 0.1 ml saline 15 min before the blood flow measurements. A, Saline-injected female mice (n = 12): y = 13.896 - 8.1142x (r = 0.650; P = 0.022). B, Saline-injected male mice (n = 10): y = 2.5954 - 0.0371x (r = 0.010; P = 0.980).

 
Duodenal, ileal, and colonic blood flows
No differences between male and female NOD mice in intestinal blood flows were observed at any time point (data not shown). With the exception of the ileal blood flow in male ICR mice after AG administration, intestinal blood flows in NOD and ICR mice were not affected by AG administration (data not shown). NMA did not affect intestinal blood flow values in 10-week-old NOD mice.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
The present study comprises the first direct, quantitative measurements of changes in islet blood flow in relation to the development of IDDM. A 3-fold increase in islet blood perfusion per islet weight in 10- or 14-week-old diabetes-prone female NOD mice compared with that in age-matched, less diabetes-prone, male NOD mice as well as with that in control ICR mice was seen. The augmented blood flow within the islets may enable increased migration of leukocytes and transport of cytokines to the islets as discussed further below.

In contrast to the present findings, several previous morphological studies of the islet vasculature have suggested that islet blood perfusion may be decreased due to vasoconstriction or destruction of islet capillaries during the development of IDDM (35, 36, 37, 38, 39). An explanation for the discrepancies between these morphological findings and the increased islet blood flow seen in the present study may be that the number of blood microvessels within an organ does not necessarily reflect the blood perfusion of that organ, as the flow in single capillaries varies considerably. This means that even if a reduction in capillary area in islets of female NOD mice occurs (39), this may be compensated for by an increased flow in the remaining capillaries. The microsphere technique, which previously has been evaluated for use in mice (31), does not enable us to determine if this is the case.

Progression of insulitis in NOD mice does not seem to be uniform, as islets free of lymphocyte infiltration coexist with those of severe insulitis (4). As the NOD mice grow older, the proportion of intact islets decreases with a concomitant increase in the number of islets showing severe insulitis (4). By using the lightfield illumination when examining the freeze-thawed preparations used for blood flow determinations in our study, abnormal islet morphology could be seen as gray patches, with a peri- or intrainsular location. Such islet abnormalities were observed solely in NOD mice, preferentially in mice 10 or 14 weeks of age, suggesting that they represent infiltration of inflammatory cells. Unfortunately, the degree of islet infiltration, i.e. insulitis, in these preparations was difficult to determine with accuracy for individual islets. A correlation between the degree of insulitis and blood perfusion in individual islets could, therefore, not be determined with certainty. Nevertheless, islets from 10- and 14-week-old female NOD mice with signs of insulitis appeared more perfused than the rest of the islets. Furthermore, most islets of these animals showed signs of insulitis, and the remaining islets were mainly small in size. As the blood flow distribution within the islet organ is heterogeneous, with a higher blood perfusion of larger islets (40), it is, therefore, reasonable to consider the presently observed islet blood flows in 10- and 14-week-old NOD mice as the blood perfusion of islets with insulitis.

It is known that vasodilation decreases shear stress and causes margination of leukocytes, which may enhance the accumulation of inflammatory cells. However, in the present study infiltration of inflammatory cells occurred before any changes in islet blood perfusion were observed. This means that the observed changes in islet blood flow are not responsible for the initial recruitment of inflammatory cells to the islets in NOD mice. However, after initiation of the islet blood flow increase, the islet vasodilation may contribute together with signals from inflammatory cells to an increased expression of endothelial surface molecules, e.g. integrins, which are necessary for the adhesion of leukocytes to the endothelium and the subsequent transmigration into tissues (9, 10). It can also be envisaged that blood hyperperfusion may increase the local concentrations of ß-cell-suppressive cytokines within the islets.

NO is a highly reactive free radical, participating in both physiological and pathophysiological processes (41, 42). It is a potent vasodilator important for regulation of arterial blood pressure and local blood flow in its role as the main endothelium-derived relaxation factor (41). Furthermore, NO is known to strongly influence islet blood flow (26, 27). The endothelium-derived relaxation factor action is due to NO produced by a calcium-dependent cNOS (43). NO can also be produced by a NOS that is induced by immunological stimuli in a number of cells (iNOS) (25, 44). A markedly increased production of NO, in potentially ß-cytotoxic concentrations, has been shown to occur in islets exposed to cytokines in vitro (25, 45, 46, 47). Nevertheless, evidence demonstrating up-regulation of iNOS expression or high levels of NO in pancreatic islets in situ in conjunction with the development of IDDM is scarce. In female NOD mice, mononuclear leukocytes freshly isolated from pancreatic islets have recently been shown to have an increased iNOS expression compared with mononuclear leukocytes in the less diabetes-prone males and a control strain (48). However, a study of iNOS gene expression in isolated islets failed to detect any difference between female and male NOD mice (49).

In the present study, administration of AG selectively decreased the high islet blood flow in female NOD mice, without affecting islet blood flow in male NOD mice or in male and female ICR mice. AG has been suggested to be a fairly selective iNOS inhibitor due to its hydrazine moiety (28, 29, 30), although the substance is pleiotropic and has several physiological effects. However, in view of the short time between the administration of AG and the blood flow measurements, we think that other effects of the drug, such as prevention of protein glycation, are unlikely to be of importance. We chose a dose previously shown to have no effect on islet blood flow in normal rats (50) and no (50) or minor effects (51) on mean arterial blood pressure. In this study, AG lacked effects on mean arterial blood pressure in both male and female NOD and ICR mice. As no, or minor (ileal blood flow in male ICR mice), effects on the blood flow values of the intestines and the whole pancreas were seen, only marginal effects of AG on cNOS occurred.

Inhibition of both cNOS and iNOS with NMA caused a marked decrease to the same level of both whole pancreatic and islet blood flow in male and female 10-week-old NOD mice. This once again underlines the exquisite sensitivity of the islet blood perfusion to NO, as previously described in rats (26) and mice (27). After treatment, there were no differences in either whole pancreatic or islet blood flow between the genders. Taken together, the present results suggest that the increased islet blood flow seen in female NOD mice at 10 and 14 weeks of age is due to increased iNOS activity in these animals. Interestingly, only one main difference between the subpopulations of inflammatory cells invading the islets in male and female NOD mice has been observed to date, namely the presence of BM8+ macrophages only in islets of female NOD mice from 7 weeks onward (6). These cells, therefore, may produce, or by their cytokine production cause, the excess of NO in islets of female NOD mice. Alternatively, the presence of a larger quantity of specific inflammatory cells in islets of female than male NOD mice may be responsible for the detected differences in sensitivity to AG between the sexes.

As shown in previous studies (4, 5, 21), the islet volume was preferentially decreased in female NOD mice, most markedly between 10 and 14 weeks of age. Interestingly, in saline-treated 10- and 14-week-old female NOD mice, an inverse correlation was seen between the islet volume (islet weight) and the islet blood perfusion. This correlation was abolished after AG or NMA treatment. It should be noted that at a given islet weight in the 10- and 14-week-old saline-treated female NOD mice, respectively, the islet blood flow values were higher in the 10-week-old animals. One possibility is that a higher islet blood flow in the younger age group is suggestive of a more rapid islet destruction. This would mean that animals with the highest islet blood perfusion are more prone to develop diabetes. However, it could also be an unrelated epiphenomenon or perhaps secondary to the smaller size of the islets in the female NOD mice.

In conclusion, we herein describe for the first time an increased islet blood perfusion in the prediabetic phase of autoimmune diabetes. Furthermore, there is strong evidence to suggest that this increase in islet blood flow is due to excessive production of NO caused by increased iNOS activity. The increased islet blood flow seen in the diabetes-prone female NOD mice may augment homing to the pancreatic islets of inflammatory cells and soluble factors involved in ß-cell destruction during the development of IDDM in this animal model.


   Acknowledgments
 
The skilled technical assistance of Astrid Nordin and Eva Törnelius is gratefully acknowledged.


   Footnotes
 
1 This work was supported by grants from the Swedish Medical Research Council (12X-109, 12X-8273, and 12P-10739), the Novo Nordic Fund, the Swedish Diabetes Association, the Family Ernfors Fund, the Juvenile Diabetes Foundation International, the Göran Gustafsson Foundation, and the Åke Wiberg Fund. Back

Received February 18, 1998.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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