progressive deterioration of endocrine function after - diabetes

Progressive Deterioration of EndocrineFunction After Intraportal but Not KidneySubcapsular Rat Islet TransplantationWOLFGANG FA. HILLER, JURGEN KLEMPNAUER, RAINER LUCK, AND BIRTE STEINIGER

In inbred streptozocin-induced diabetic rats, thelong-term function of different endocrine pancreaticisografts was compared. Isolated islets transplantedinto the portal vein showed a progressive deteriorationof function over time. In contrast, islets under thekidney capsule sustained a constant long-termfunction controlling all clinical signs of diabetes.Recipients of kidney subcapsular islets displayednormal growth rate, peripheral serum glucose andinsulin levels, and metabolic parameters. However,their functional reserve was markedly reduced asrevealed by diminished glucose tolerance and reducedinsulin-secreting capacity after an intravenous glucosechallenge. Vascularized whole-organ pancreaticgrafts with portal venous drainage led to completenormalization of all parameters determined in thisstudy. This study showed that the long-term functionof islets transplanted under the kidney capsule issuperior compared with islets transplanted into theportal vein. Diabetes 40:134-40, 1991

In pancreatic transplantation for the treatment of insulin-dependent diabetes mellitus, only the endocrine functionof the graft is required. The pancreas does not need tobe grafted as a vascularized organ; it is also possible to

transplant isolated islets of Langerhans depleted from theexocrine tissue. Due to their small volume, isolated pan-creatic islets can easily be transplanted into different sitesof the organism. Many implantation sites have been usedexperimentally with variable success, e.g., the peritonealcavity (1,2), omental pouch (3), lung (4), cleared mammaryfat pad (5), brain (6), and testes (7). Graft function sufficient

From the Clinic for Abdominal and Transplantation Surgery and Center ofAnatomy, Medical School, Hannover, Germany.

Address correspondence and reprint requests to Dr. Wolfgang FA. Hiller,Klinik fur Abdominal- und Transplantationschirurgie, Medizinische Hoch-schule, Konstanty-Gutschow-Strasse 8, D-3000 Hannover 61, Germany.

Received for publication 24 January 1990 and accepted in revised form28 August 1990.

to restore normoglycemia in diabetic individuals has beendemonstrated best in well-vascularized sites, e.g., thespleen (8,9), the liver via the portal vein (10), and the kidneysubcapsular site (11). The latter two especially have becomestandard sites for islet implantation. Experimental transplan-tation of isolated islets into the portal vein has been per-formed for >15 yr. For years, no further attention was paidto reports on occasional late graft failure in autografts orisografts (12,13). In 1988, the first studies were presentedshowing that this is not a rare phenomenon, but in the rodentmodel, intraportal islet transplantation is regularly associatedwith late deterioration of graft function (14). Late endocrinefailure of islet isografts due to nonimmunological reasons isa potential threat to the whole concept of islet transplantationand warrants further investigation. It is unclear whether thisis a general phenomenon in islet transplantation or dependson the site of implantation. We have therefore performed astudy comparing the long-term endocrine function of isolatedislets of Langerhans transplantated into the portal vein withthose transplanted beneath the kidney subcapsular space.

RESEARCH DESIGN AND METHODSMale Lewis rats, bred under specific pathogen-free condi-tions, were obtained from the central animal laboratory ofHannover Medical School. Rats 8-10 wk old weighing 200-250 g were used in this study. They were kept under con-ventional conditions in fully climatized rooms with constantday and night rhythm and had free access to standard pelletfood and water. Donor operations were performed underfentanyl-fluanisone anesthesia (1 ml/kg body wt equivalentto 0.2 mg/kg fentanyl and 10 mg/kg fluanisone i.m.), andrecipients were anesthetized by ketamine (80-120 mg/kgbody wt i.p.).

Prospective recipients of isolated islets of Langerhans orvascularized pancreas grafts were rendered diabetic by asingle dose of streptozocin (55 mg/kg i.v.) freshly dissolvedin phosphate-buffered saline (PBS) and adjusted to pH 4.5.Diabetes mellitus was confirmed by repetitive nonfastingblood glucose levels >18 mM, polydipsia, polyuria, andweight loss.

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Pancreatic transplantation was performed in three differentmodalities. Isolated islets of Langerhans were transplantedeither into the portal vein (n = 9) or beneath the kidneycapsule {n = 12). A further group of diabetic rats receiveda vascularized whole pancreas (n = 12). The results werecompared with nondiabetic and diabetic controls (n = 12for both groups).

In the donor, the common bile duct was ligated at thepapilla of Vater and cannulated with a catheter (26-gaugeAbbocath, Abbott, North Chicago, IL) proximally at the liverhilus. Type IV cotlagenase (Worthington, Freehold, NJ) wasdissolved in 8 ml Hank's solution (2 mg/ml) and slowly in-jected into the bile duct, thus distending the whole pancreas.The pancreas was removed and incubated in a stationarywater bath at 38°C for 20 min. After three washes in Hank'ssolution, the islets were separated by Ficoll density-gradientcentrifugation at 800 x g for 10 min. Further purification wasobtained by hand picking under a stereo microscope. Islets(n = 1800), isolated from three donors, were then collectedin a 100-|xl syringe.

Intraportal islet transplantation was performed by directpuncture of the portal vein with a small catheter (26-gaugeAbbocath). The cannulation site was oversewn with an 8-0Ethilon suture to minimize blood loss. For kidney subcapsulartransplantation, the catheter was placed transrenally fromthe lower pole of the left kidney ventrally under the kidneycapsule. After injection of the islets, the outlet was electro-coagulated to prevent bleeding and reflux of the islets.

Details of the microsurgical technique for vascularizedpancreas transplantation have been reported elsewhere(15). The arterial blood supply was provided by an aorticsegment carrying the coeliac axis and the superior mes-enteric artery anastomosed end-to-side to the recipient's in-frarenal aorta. Venous outflow of the graft was accomplishedby an end-to-side anastomosis of the donor's to the recipi-ent's portal vein. The exocrine secretion was suppressed byduct ligation.

All animals were followed for 1 yr. Endocrine graft functionwas monitored by daily determination of nonfasting bloodglucose levels and body weight. On days 28, 90, 180, 270,and 360 after transplantation, an intravenous glucose tol-erance test (IVGTT) was performed. After a 6-h fast startingat 0800, glucose (1 g/kg body wt i.v.) was injected. Bloodsamples were taken 10 and 5 min before the injection and2, 5, 10, 20, 40, and 60 min afterward. The K values werecalculated according to the method of Lundbaek (16). Meta-bolic studies on food and water consumption, urine output,and feces production were performed with standard meta-bolic cages 1 wk after each IVGTT. On days 175 and 355,insulin levels in the peripheral blood were measured by ra-dioimmunoassay (Novo, Aarhus, Denmark) as basal levelsand 5 and 40 min after glucose injection (1 g/kg body wti.v.). In recipients of vascularized pancreatic grafts and kid-ney subcapsular islets, a transplantation pancreatectomyand nephrectomy of the islet-bearing kidney, respectively,were performed at day 370 to ensure that normoglycemiawas due to the presence of the grafts.

At the end of the experiment, all grafts were removed,fixed in Bouin's solution for 24 h, and processed for paraffinhistology. Conventional hematoxylin-eosin staining and in-direct immunoperoxidase demonstration of insulin and glu-

cagon- were performed. Deparaffinized sections werepreincubated in 1% H2O2 in PBS for 30 min to block eryth-rocyte hemoglobin. Guinea pig anti-beef insulin serum (65-101, Miles, Munich) was diluted 1:800, and rabbit anti-syn-thetic glucagon serum (64-706-1, Miles) was diluted 1:1000in PBS containing 0.1 % NaN3 and 1 % bovine serum albumin.Sections were incubated overnight with primary antibody at4°C, washed, and covered with either secondary peroxi-dase-conjugated goat anti-guinea pig serum (3-877, Nordic,Tilburg, Netherlands) diluted 1:100 or peroxidase-conju-gated pork anti-rabbit serum (P 217, Dakopatts, Glostrup,Denmark) diluted 1:80 for 60 min at 4°C. Peroxidase wassubsequently revealed by diaminobenzidine reaction.

Results are means ± SD. For statistical evaluation of theresults, one-way analysis of variance and Student's t testwere used. The level of significance was set at P < 0.01.

RESULTSStreptozocin induced stable diabetes in all rats within 2 daysthat lasted throughout the 1-yr observation. Nonfasting bloodglucose levels were persistently >18 mM (Fig. 1). After vas-cularized whole-organ pancreas transplantation, all rats be-came normoglycemic within 8 h. Blood glucose levels wereidentical to those of nondiabetic control rats throughout the1-yr observation. Recurrent hyperglycemia within 24 h aftergraft pancreatectomy proved that normoglycemia had beendue to the existence of a functioning pancreas transplant.

In recipients of isolated islets transplanted under the kid-ney capsule or intraportally, blood glucose levels fell to <8mM within 8 h. In kidney subcapsular graft recipients, theyremained stable thereafter for 1 yr at normoglycemic levels.Again, nephrectomy of the islet-bearing kidney resulted inrecurrent hyperglycemia. In contrast, recipients of islets in-jected into the portal vein had rising blood glucose levelsstarting 6 mo after transplantation. At the end of the study,four of nine rats were frankly diabetic again with blood glu-cose levels persistently >14 mM. The remaining five ratshad nonfasting blood glucose levels that were subnormalbetween 7.5 and 10 mM.

m i0

100 180Days post Tx

FIG. 1. Nonfasting serum glucose in diabetic rats after intraportal(P) or kidney subcapsular (R) islet transplantation compared withnondiabetic (N) and untreated diabetic (D) rats expressed as means ±SD. S, administration of streptozocin; Tx, transplantation; *P < 0.05vs. kidney islet graft recipients. mP < 0.05 vs. diabetic controls.

DIABETES, VOL. 40, JANUARY 1991 135

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ENDOCRINE FUNCTION OF RAT ISLET ISOGRAFTS

All rats suffered weight loss after injection of streptozocin.Diabetic control rats remained underweight compared withnondiabetic rats throughout the observation. After either formof transplantation of the endocrine pancreas, graft recipientsgained weight again and had a normal growth curve (Table1). However, those rats that underwent intraportal islet trans-plantation and became frankly diabetic again suffered fromweight loss when nonfasting blood glucose was >10 mM.

Metabolic studies revealed marked polydipsia, polyuria,and polyphagia in streptozocin-induced diabetic (STZ-D)rats compared with nondiabetic controls throughout the ob-servation. After endocrine pancreatic transplantation, all ofthese metabolic features were completely normalized. Thefour recipients of intraportal islets that became frankly dia-betic again reestablished metabolic signs of diabetes,whereas the five rats remaining nearly normoglycemic withglucose levels <10 mM were undistinguishable from non-diabetic controls with respect to the metabolic parametersas were all recipients of kidney subcapsular islets or vas-cularized pancreatic grafts (Table 1).

After injection of streptozocin, all rats displayed a markedlyreduced glucose tolerance (GT) compared with nondiabeticcontrols. There were no significant changes of the GT overtime. Recipients of vascularized pancreatic grafts showed aperfectly normal GT for 1 yr. Transplantation of isolated isletsof Langerhans into the portal vein or under the kidney cap-sule resulted in a significant amelioration of the GT, whichremained stable in recipients of islets under the kidney cap-sule, although markedly reduced compared with nondiabeticcontrols. In contrast, a deterioration of the GT was noted 3mo after transplantation in recipients of islets transplantedintraportally (Fig. 2). This deterioration of the K values wasnoted in all recipients of intraportal islets, even in those re-maining nearly normoglycemic throughout the whole obser-vation. Nine months postoperatively, there was no longer asignificant difference in GT between recipients of intraportalislets and diabetic controls (Fig. 2). Twelve months aftertransplantation, even the K values of the five rats in the in-traportal group that remained nearly normoglycemic haddropped to levels undistinguishable from untreated diabeticrats (P > 0.35; Fig. 2).

Within 5 min after an IVGTT, the serum insulin levels tripledin nondiabetic rats. Forty minutes after glucose injection,insulin levels were still significantly higher than normal. Theintravenous injection of streptozocin destroyed most of theendocrine pancreas. Basal and glucose-stimulated seruminsulin levels were markedly reduced (Table 2). After vas-

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FIG. 2. Intravenous glucose tolerance measured by K value accordingto Lundbaek (16). Months 1, 3, 6, 9, and 12 posttransplantationcompared with nondiabetic and diabetic controls. Vase, recipients ofvascularized pancreatic grafts; renal, kidney subcapsular islet isograftrecipients; portal, intraportal islet isograft recipients; °P < 0.05 vs.nondiabetic and diabetic controls; mP < 0.05 vs. nondiabetic controls;•P < 0.05 vs. diabetic controls; °P < 0.05 vs. kidney islet graftrecipients.

cularized pancreas transplantation, both basal and peak in-sulin levels were completely normalized. Subcapsular islettransplantation led to long-term normalization of the basalinsulin levels. However, glucose-stimulated insulin secretionwas significantly reduced (Table 2). Peak insulin levels 5 minafter an IVGTT were significantly lower than in nondiabeticrats. After 40 min, the insulin levels were down to valuesmeasured in unstimulated rats. Although basal and glucose-stimulated serum insulin levels remained stable in recipientsof kidney subcapsular islets throughout the whole obser-vation, 175 days after intraportal islet transplantation, basalinsulin levels were significantly lower than normal. They werefurther diminished by day 355. Already by day 175, an IVGTTwas not able to stimulate the insulin output of islets trans-planted into the portal vein (Table 2).

One year after transplantation, duct-ligated whole-pan-creas grafts showed complete atrophy of the exocrine tissue,large numbers of proliferated small ducts with atrophicepithelia, fragmented islets of Langerhans, and persistentlow-grade interstitial infiltration as described previously (17).Interstitial fibrosis was minimal or absent. The fragmentedislets were smaller than normal but consisted of apparently

TABLE 1Weight and metabolic studies at 180 and 360 days posttransplantation

Weight (g) Water (ml/day) Urine (ml/day)

NondiabeticDiabetic

+ Intraportal graft+ Subcapsular graft+ Vascularized pancreas

n

12129

1212

180

404 ±248 ±448 ±460 ±445 ±

3132*542151

360

470 ± 25325 ± 16*447 ± 51515 ± 42446 ± 16

180

23.0 ± 5.3117.1 ± 35.1*31.3 ± 20.420.2 ± 3.821.5 ± 4.4

360

17.7 ± 2.482.6 ± 7.0*29.2 ± 29.118.3 ± 2.927.6 ± 5.2

180

8.5 ± 1.494.5 ± 27.8*25.7 ± 24.19.2 ± 1.29.0 ± 1.4

360

7.7 ± 0.977.5 ± 6.5*24.1 ± 30.19.5 ± 0.99.8 ± 1.6

Values are means ± SD. Groups described in METHODS.*P < 0.01 vs. nondiabetic controls.


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W.F.A. HILLER AND ASSOCIATES

TABLE 2Glucose-stimulated insulin secretion (pM) posttransplantation

Day 175 Day 355

NondiabeticDiabetic

+ Intraportal graft+ Subcapsular graft+ Vascularized pancreas

n

12129

1212

Basal

258 ± 6934 ± 17*

155 ± 69310 ± 103189 ± 69

5 min

809 ± 52121 ± 69*172 ± 103*551 ± 155*792 ± 69

40 min

689 ± 155<15*

69 ± 34*293 ± 138*706 ± 69

Basal

241 ± 103<15*

69 ± 138*258 ± 155224 ± 103

5 min

827 ± 86103 ± 86*241 ± 293*534 ± 172*758 ± 121

40 min

654 ± 172<15*

69 ± 86*327 ± 207*689 ± 138

Values are means ± SD. Groups described in METHODS.*P :£ 0.01 vs. nondiabetic controls.

normal insulin-containing cells. However, the distribution ofglucagon-secreting cells differed from nondiabetic islets.The number of glucagon cells in the islet circumference ap-peared reduced. In some islets, only three to four stainedcells occurred instead of a mostly continuous ring of glu-cagon cells as observed in nondiabetic rat islets. In addition,small isletlike clusters containing only glucagon cells werefrequently present, demonstrating a tendency of insulin- andglucagon-containing cells to separate into distinct histolog-ical structures.

Isolated islets transplanted under the kidney capsuleformed large continuous aggregates 1 yr after transplanta-tion (Fig. 3). They tended to grow into the cortical kidneyparenchyma and were partially situated between the outercortical tubules with direct contact to tubule epithelia. In mostcases, a small layer of fibrotic tissue covered the islet ag-gregates and filled the space between them. Interestingly,mitotic figures of endocrine cells were present in single spec-imens. Most islet cells reacted strongly to insulin. In a fewrats, islet damage had occurred, and strands of dense fi-brotic tissue lay within the islets. In these cases, insulin stain-ing of endocrine cells was of variable intensity. In alltransplanted islets, glucagon-containing cells were markedlyreduced. Some islet aggregates did not contain any glu-

cagon cells in the section plane. Instead, separate isletclumps of glucagon cells were sometimes found, but theywere smaller and less numerous than in duct-ligated whole-pancreas grafts.

None of the islets transplanted intraportally were detectedhistologically after 1 yr. For morphological assessment, twoadditional rats received intraportal islet grafts (Fig. 4). Thelivers of these rats were assessed histologically 180 daysafter transplantation via serial sections. The insulin-contain-ing cells lay in the portal field some distance from the branchof the portal vein and directly contacted periportal hepato-cytes. Fibrous tissue and sometimes small bile ducts hadgrown into the associations of p-cells and hepatocytes. Thus,endocrine cells and hepatocytes were present in isolatedclumps of two to three cells. Glucagon-containing cells wereextremely rare and of reduced size or hormone content. Insome instances, no glucagon cells were found among (3-cells in several section planes. In some portal areas, ac-cumulations of lymphocytes were found surrounding bileducts and vessels.

DISCUSSIONLate graft failure after intraportal islet transplantation hasbeen observed not only in the rodent model but also in larger

FIG. 3. Demonstration of insulin inislet grafts under kidney capsule1 yr after transplantation, x 120.


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FIG. 4. Demonstration of insulin inintraportal islet grafts 180 daysafter transplantation, x 120.

mammals (18). We present evidence that this deleteriouseffect is strongly related to the site of implantation and doesnot occur in kidney subcapsular islet transplantation. Even-tually, all recipients of intraportal islet grafts experienceddeterioration of endocrine function within 1 yr after trans-plantation; four of nine rats even became diabetic again.Those four rats were undistinguishable from untreated dia-betic rats in blood glucose levels, metabolic turnover rates,GT, or insulin response to an IVGTT, The remaining rats (5of 9) were nearly normoglycemic with glucose levels be-tween 7.5 and 10 mM and normal metabolic rates. However,all of them had a markedly deteriorated K value, which wasundistinguishable from diabetic controls, and seven of ninegraft recipients had a poorer insulin response at the end ofthe study. The first sign of graft failure after intraportal islettransplantation was a decrease of the K values in the IVGTTs,which was noted as early as 3 mo after transplantation. Frankhyperglycemia is a late sign of graft failure, which in ourstudy, did not occur before 6 mo after transplantation. Somegrafts were able to protect the recipients from recurrent hy-perglycemia for >1 yr. However, these grafts did not haveany functional reserve as demonstrated by the low K valuecalculated during an IVGTT. Polydipsia, polyuria, and po-lyphagia were also late signs of graft failure and were onlynoted in hyperglycemic rats with nonfasting blood glucoselevels >10 mM.

The exact mechanisms responsible for the progressiveloss of function of intraportal islet grafts are not fully under-stood. In contrast to the early posttransplantation period, 1yr after intraportal transplantation hardly any of the graftedislets could be identified histologically on serial sections;however, the reason for the disappearance remains un-known (19). Three possible causes or a combination thereofhave to be discussed. 1) There is histological evidence forthe development of fibrosis in the periportal fields of the liver,which contain the transplanted islets. This may subsequentlycause an impairment of the blood supply and progressiveloss of endocrine function of the transplanted islets. 2) On

their way from a branch of the portal vein into the portal field,islets have to transmigrate an intact vessel wall. This maycause the disintegration of the islets, which is seen on his-tological sections, or even a destruction of cells, as evi-denced by the remarkable disappearance of glucagon-producing cells. The lack of junction between individual cellswithin the islet may destroy intercellular regulation mecha-nisms and thus cause a breakdown of the islet as a complexorgan. 3) It is also possible that the deterioration of endocrinefunction is a consequence of the intraportal implantation site.It is conceivable that the portal blood, which perfuses theintraportally implanted islets, contains higher concentrationsof glucose than the arterial blood perfusing the kidney andthus islets beneath the kidney capsule. This might lead tocontinuous stress to the intraportal islets, followed by func-tional exhaustion. Furthermore, there is evidence that 2 wkafter transplantation, the replicatory activity of islet cells witha portal venous drainage was impaired compared with kid-ney subcapsular grafts with their systemic venous drainage(20).

Initially, the main advantage of islet transplantation underthe kidney capsule versus the intraportal site was thoughtto be an immunological one. In some rat strains, kidneysubcapsular islets were reported to enjoy a prolonged sur-vival compared with intraportal grafts (11). However, thisdoes not apply to other rat strains (21) or other species (22).Metabolic advantages have been claimed for grafts withportal venous compared with systemic venous drainage(23,24). However, in a study comparing the efficacy of kidneysubcapsular and intraportal islets in normalizing the glucosemetabolism, there was no superiority for either site, which isin agreement with our results (25). No studies have beenreported comparing the long-term function of islets graftedintraportally or beneath the kidney capsule in the absenceof rejection. Our study clearly demonstrates that isletsgrafted into the portal vein had a progressive loss of function,whereas those transplanted under the kidney capsule sus-tained a stable long-term function controlling all clinical signs


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W.F.A. HILLER AND ASSOCIATES

of diabetes. Recipients of kidney subcapsular islets dis-played normal growth rate, peripheral blood glucose, basalinsulin levels, and metabolic turnover rates. However, thefunctional reserve of these grafts was markedly reduced asevidenced by an IVGTT. The relevance of the diminishedcapacity to secrete insulin for the development of the se-quelae of diabetes is still a matter of debate. It has to beremembered that parenteral glucose application is an un-physiologically strong stimulus for insulin secretion. The re-sults of IVGTTs may be of minor clinical importance, becauseexceedingly high nonfasting glucose values were never ob-served in our recipients of kidney subcapsular islet grafts.

The differences of the glucose-induced insulin secretionobserved between islets of Langerhans and the whole pan-creas probably reflect a different mass of insulin-secretingtissue. This is well explained by the loss of viable islets duringtheir isolation from the pancreas. It has been calculated thatthere are 2000-4000 islets in a rat pancreas (26,27), so 1800islets is -50% of the number transplanted along with a vas-cularized pancreas. However, the number of islets alone isnot an adequate criterion for calculating the mass of insulin-producing tissue, which is mainly dependent on the size ofthe harvested islets. Large islets may easily be damagedduring the process of isolation, and therefore, an unpropor-tionally large number of small islets may be harvested. Fur-thermore, not all transplanted islets will eventually vas-cularize in the recipient.

Therefore, it has to be considered whether the late failureof intraportal islet grafts could be due to an insufficient massof insulin-secreting tissue that was transplanted or eventuallyengrafted in these animals. The loss of viable islets is in-herent to the isolation procedure. Thus, especially when hu-man islet transplantation with a one donor-one recipient ratiois to become reality, islet grafts will always have a poorerfunctional reserve compared with vascularized pancreatictransplants. In our model, however, the acute onset of nor-moglycemia within 8 h after transplantation and the normalblood glucose values in nonfasted recipients of isolated is-lets suggest that initially diabetes was adequately controlledin these rats. The amount of p-cells transplanted, as judgedby the identical technique of isolation and the number ofislets injected into the portal vein, did not differ from ratsreceiving kidney subcapsular islet grafts. Furthermore, iden-tical blood glucose levels, GT, and insulin responses afteran IVGTT in both groups receiving isolated islets suggestthat the amount of islets that did engraft was comparableafter portal and kidney transplantation. This leaves the ques-tion open as to why portal islet grafts underwent a progres-sive deterioration of their endocrine function but kidneysubcapsular grafts did not.

In contrast to isolated islets, vascularized whole-organpancreas transplants with portal venous drainage were notonly able to normalize the metabolic features of diabetesmellitus but also led to a normal insulin response after anIVGTT. In a model of STZ-D in rats, it led to a completenormalization of all metabolic parameters measured in thisstudy. In the absence of rejection there was no deteriorationof the graft function with time. These results were in accord-ance with those reported from other laboratories (14).

The rationale underlying pancreas transplantation as atherapeutic procedure in insulin-dependent diabetes melli-

tus is the assumption that the development of the diabeticangiopathy is correlated with suboptimal metabolic controlof the disease. Therefore, the ultimate goal of transplantationof the endocrine pancreas is perfect metabolic restorationin diabetic patients. So far, there are no reports of a completenormalization of the deranged metabolism in diabetes bytransplantation of isolated islets of Langerhans. It remainsto be established whether the functional reserve of the vas-cularized pancreas is necessary to avoid the developmentof the vascular syndrome in diabetes mellitus.

In clinical islet transplantation, adequate long-term func-tion of the graft must be the goal. Our studies show that thisis possible with the kidney subcapsular implantation siterather than the intraportal route. Implantation of islets underthe kidney capsule was only successful when relatively pureislet preparations were used. In the primate, impure pan-creatic fragments failed to vascularize under the kidney cap-sule (28). Unfortunately, in the primate and human pancreas,the islets are surrounded by a fibrous tissue, which makesit difficult to isolate large amounts of pure islet preparations.It should be the aim of future studies to improve the isolationtechniques of human islets to render a kidney subcapsulartransplantation possible.

ACKNOWLEDGMENTSThis work was supported by Deutsche Forschungsgemein-schaft Grants Pi 48/11-1 and Hi 391/1-1.

We gratefully appreciate the skillful technical assistanceof Ralf Nietert, Margot Giesecke, Monika Lohmuller, and Ur-sula Meuer.

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ecember 2021

progressive deterioration of endocrine function after - diabetes

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