Objectives: Five distinct somatostatin receptors (SSTRs) have been cloned, characterized, and designated SSTRs 1 - 5. The role of these receptors in B-cell signaling has not been well characterized.Methods: In the current study, the isolated perfused human pancreas model was used to determine the specific effect of 4 different somatostatin receptor agonists on insulin secretion.Conclusion: We demonstrated that the SSTR 2 agonist and octreotide significantly suppressed insulin secretion. Furthermore, even during the immunoneutralization of endogenous intrapancreatic somatostatin, the SSTR 2 agonist was able to reverse the effect of somatostatin immunoneutralization by suppressing insulin secretion. These results demonstrate that activation of SSTR 2 suppresses insulin secretion in the isolated perfused human pancreas.

Introduction: In this study, immunoneutralization of endogenous insulin, glucagon, and somatostatin with specific antibodies was used in an isolated perfused human pancreas (IPHP) model.Aims: To study intrapancreatic cellular interactions and pancreatic hormonal secretion.Methodology: Randomized, sequential 10-minute test intervals of single-pass per-fusion with each antibody were performed at 3.9 mM or 11.5 mM steady-state glucose concentrations. Somatostatin, insulin, and glucagon levels were measured in the effluent during basal and immunoneutralization intervals.Results: At 3.9 mM glucose concentration, somatostatin antibody (SS-Ab) stimulated insulin and glucagon secretion, insulin antibody (IN-Ab) inhibited glucagon secretion, and glucagon antibody (GN-Ab) stimulated insulin secretion. At 11.5 mM glucose concentration, SS-Ab stimulated insulin secretion, IN-Ab stimulated glucagon and inhibited somatostatin secretion, and GN-Ab stimulated insulin secretion.Conclusion: The variation in hormonal responses to immunoneutralization during stimulated and nonstimulated glucose conditions suggests that a dynamic association exists between the pancreatic cells.

Although basal circulating levels of individual islet cell hormones have been measured, few studies compared the molar ratios of the major hormones secreted by the endocrine pancreas. This study examined the basal levels of four major islet hormones: insulin, C-peptide (C-P), glucagon (G), and pancreatic polypeptide (PP) in normal subjects, in organ donors with brain death, and in the isolated perfused human pancreas. Basal blood samples were taken from normal, fasted control subjects (NCs). Pancreata were obtained from 17 organ donors (ODs) with donor portal vein (DPV) and radial arterial (DRA) blood samples taken before organ procurement. Single-pass perfusion was performed on the procured pancreata, and after rewarming and equilibration, basal samples were collected from the splenic vein (SV) for 30 min. Radioimmunoassays of insulin, C-P, G, and PP were performed on all samples, and basal levels of all hormones were expressed as a common unit, femtomoles per milliliter. The data suggest that in the basal state, these four major islet hormones circulate in a relatively constant molar ratio. The ratio of the hormones is altered in brain death and with in vitro perfusion of the pancreas. The isolated perfused human pancreas secretes a relatively constant molar ratio of these hormones; however, this ratio is markedly different from the circulating ratio seen in either the NC group or the OD group. We conclude that a relatively constant hormonal milieu is secreted from the normal endocrine pancreas, and this hormonal milieu is altered after brain death and with isolation and perfusion of the human pancreas.

Islet amyloid polypeptide (IAPP) and insulin are co-stored and generally secreted in parallel; however, studies have demonstrated that the IAPP/insulin molar secretory ratio may be altered in response to certain stimuli. Because we previously demonstrated that intraislet somatostatin is an inhibitory regulator of basal insulin secretion in the isolated perfused human pancreas, this study was designed to determine the relative influence on the regulation of IAPP versus insulin secretion. Single-pass perfusion was performed in pancreata obtained from cadaveric organ donors with continuous perfusion of a modified Krebs media with the glucose level maintained at constant 3.9 mM. Intraislet somatostatin was immunoneutralized by the infusion of either a highly sensitive monoclonal somatostatin antibody (SAb) or its FAb fragment (SFAb). Sequential test periods separated by basal periods were performed by infusion of either of the following: glucose, SAb, SFAb, or appropriate controls. IAPP/insulin molar secretory ratio decreased by 33% in response to infusion of either SAb or the SFAb, respectively (p < 0.01), and decreased by 67% in response to glucose infusion (p < 0.01). An alteration of the IAPP/insulin secretory ratio is seen in response to infusion of exogenous glucose or in response to the neutralization of intraislet somatostatin.

The present study is to determine if intraislet insulin or somatostatin regulate pancreatic polypeptide (PP) secretion in the isolated perfused rat pancreas by infusing insulin or somatostatin antisera. Isolated rat pancreata were stimulated with either 16.7 mM glucose (G) alone, G with antisomatostatin antibody (G + SA), or G with antiinsulin antibody (G + IA). G inhibited PP secretion -22 +/- 9.5 pM below basal, a decrease of 9 +/- 6.3% (n = 6; p = NS), G + IA inhibited PP secretion -10 +/- 27.2 pM below basal, a decrease of 20 +/- 15% (n = 7, p = NS), and G + SA stimulated PP secretion 18 +/- 7.1 pM above basal, an increase of 26 +/- 5% (n = 6; p < 0.05). G stimulated insulin secretion 3,144 +/- 210 pM above basal (n = 6, p < 0.05), and G + SA stimulated insulin secretion 2,695 +/- 195 pM above basal (n = 7; p < 0.05 vs. baseline, p = NS vs. G alone). G stimulated C-peptide secretion 886 +/- 175 pM above basal (n = 6; p < 0.05), G + SA stimulated C-peptide secretion 847 +/- 102 pM above basal (n = 7; p < 0.05, p = NS vs. G alone), and G + IA stimulated C-peptide secretion 834 +/- 93 pM above basal (n = 7; p < 0.05, p = NS vs. G alone). These data demonstrate that infusion of SA results in significant stimulation of PP secretion during high-G infusion, whereas IA has no effect. Infusions of SA or IA at the doses used have no effect on G-stimulated insulin or C-peptide secretion. This suggests that intraislet somatostatin may be an inhibitory regulator of PP secretion in the isolated perfused rat pancreas.

T o discuss the controversy of the current concept of islet microcirculation, an international symposium was held at the Long Beach Veterans Administration Regional Medical Education Center (Long Beach, C:A) and broadcast over the Internet via the world Wide Web to 14 international stations. Studies concerning three models of islet microcirculation, mantle-to-core, coreto-mantle, and polar, were presented. One presentation, including an interactive question and answer session, was broadcast from the Massachusetts Institute of Technology (Cambridge, MA) and received by the symposium participants in Long Beach, as well as by the 14 stations. The fundamental differences between the models, i.e., the relationship of the microcirculation flow pattern and the islet cell composition, were discussed in an open forum with critiques of techniques, results, and interpretations. Each islet has from one to five arterioles, which penetrate into the islet and divide into numerous capillaries (1-4). The capillaries, resembling a glomerulus, course through the islet in a tortuous fashion that is ideal for cell-blood and bloodcell interactions. The a-, p-, 6-, and PP-cells, which secrete glucagon, insulin, somatostatin, and pancreatic polypeptide, respectively, are nestled between the capillaries and receive their nutrient, hormonal, and neurohormonal regulatory signals across the capillary endothelium, as well as through the interstitial space (5,6). Since the cell types have specific locations within the islet, the pattern of blood flow through the islet should have a significant impact on the ability of cells to intercommunicate within the islet. It is this relationship that represents the controversial topic that was the focus of the symposium. The following is a review of the

The current study was undertaken to determine whether intraislet somatostatin regulates glucagon or pancreatic polypeptide (PP) secretion in the human pancreas. A high-affinity, high-specificity monoclonal somatostatin antibody (CURE.S6) was used to immunoneutralize somatostatin in the isolated, perfused human pancreas. Single-pass perfusion was performed in pancreata obtained from cadaveric organ donors using a modified Krebs media with either 3.9 or 12.9 mM glucose. Sequential test periods separated by basal periods were performed with infusion of either exogenous somatostatin-14 (SS-14), CURE.S6, or a combined infusion. Infusion of SS-14 did not significantly alter glucagon or PP secretion during low-glucose or high-glucose perfusion. Immunoneutralization of intraislet somatostatin with CURE.S6 resulted in a significant increase of glucagon secretion under low-glucose conditions (ΔX=15±3 pM) (p<0.05), but did not significantly effect glucagon secretion under high-glucose conditions (ΔX=−2±3 pM) (p=NS). PP secretion remained unchanged during CURE.S6 infusion. Combined infusion of SS-14 and CURE.S6 did not significantly alter glucagon or PP secretion. The data suggest that intraislet somatostatin may have an inhibitory role in the regulation of glucagon secretion during low-glucose conditions and that intraislet somatostatin does not regulate PP secretion in the isolated, perfused human pancreas.

The present study was undertaken to determine whether there exist specific donor factors which influence the performance of the isolated perfused human pancreas with respect to the sustained level of insulin secretion. Donor factors included age, serum glucose, hospital days, CMV status, RBC transfusion history, and smoking history. Following pancreas procurement, single-pass perfusion was performed in pancreata obtained from 35 cadaveric organ donors using a modified Krebs buffer. Aliquots were collected every 2 min and assayed for insulin concentration. Data was analyzed for 120 min for each pancreas. The mean initial insulin concentration was 2989 ± 383 μU/ml and the insulin concentration at 120 min averaged 1467 ± 338 μU/ml. The mean decay of insulin secretion over time was -13 ± 3.2 μU/ml/min. Multiple regression analysis demonstrated that pancreata from donors who had a smoking history had a faster rate of decay of insulin secretion than pancreata from nonsmokers (P = 0.04). None of the other above mentioned donor factors significantly affected decay of insulin secretion. This analysis suggests that a history of smoking in organ donors results in a significantly faster rate of decay of insulin secretion when the pancreas is utilized for the laboratory model. We conclude that it is important to evaluate specific donor factors of cadaveric organ donors prior to the use of the human organs for experimental purposes.

This study was undertaken to determine whether intraislet somatostatin inhibits insulin secretion in the human islet. A high-affinity monoclonal somatostatin antibody was used to immunoneutralize somatostatin in the isolated, perfused human pancreas. Single pass perfusion was performed in pancreata obtained from cadaveric organ donors using a modified Krebs medium with either 3.9 or 12.9 mM glucose. Sequential test periods separated by basal periods were performed with either somatostatin-14 (SS-14), somatostatin monoclonal antibody (CURE.S6), or a combined infusion. Infusion of SS-14 resulted in inhibition of insulin secretion under both low glucose (delta X = -712 +/- 212 pM) (p < 0.05) and high glucose (delta X = -21,913 +/- 10,003 pM) (p = 0.06) conditions. Immunoneutralization of intraislet somatostatin with CURE.S6 resulted in a significant increase in insulin secretion under both low glucose (454 +/- 162 pM) (p < 0.05) and high glucose (2,177 +/- 829 pM) (p < 0.05) conditions. Combined infusion of SS-14 and CURE.S6 resulted in a reversal of the inhibitory effect of exogenous SS-14. The data suggest that intraislet somatostatin has an inhibitory role in the regulation of insulin secretion in the human islet.

The role of the somatostatin-secreting D cell in the islet remains controversial. The present study was undertaken to determine whether infusion of the Fab fragment of a highly sensitive somatostatin monoclonal antibody into the isolated, perfused human pancreas would influence insulin secretion. Single-pass perfusion was performed in pancreata obtained from cadaveric organ donors using a modified Krebs-media with 3.9 mM glucose. Sequential test periods separated by basal periods were performed with either somatostatin monoclonal antibody Fab fragment (SFab), somatostatin-14 (SS-14), or a combined infusion. Immunoneutralization of intraislet somatostatin with SFab resulted in a significant increase in both immunoreactive insulin (IRI) (1,122 ± 497 pM) (p < 0.05) and immunoreactive C-peptide (IRC-P) secretion (146 ± 53 pM) (p < 0.05). Infusion of SS-14 resulted in inhibition of both IRI secretion (−3,372 ± 1,360 pM) (p < 0.05) and IRC-P secretion (−708 ±220 pM) (p < 0.05). Combined infusion of SFab and SS-14 reversed the inhibitory effect of exogenous SS-14 on IRI and IRC-P secretion. The data suggest that intraislet somatostatin has an inhibitory role in the regulation of B-cell secretion in the human islet and demonstrates that the Fab fragment of the somatostatin monoclonal antibody is an effective tool for immunoneutralization studies in the human pancreas. In addition, immunostaining of the donor pancreata demonstrated the presence of somatostatin-immunoreactive endocrine cells interspersed throughout the islet core and mantle. The demonstrated proximity of somatostatin-immunoreactive endocrine cells to B cells lends anatomic support to the concept that intraislet somatostatin influences insulin secretion in the human islet.

Recent studies suggest that cholesterol gallstone (GS) formation is characterized by altered gallbladder epithelial ion transport and increased gallbladder (GB) luminal Ca2+. Moreover, intracellular Ca2+ has been reported to be an important modulator of intestinal ion transport. The aim of the present study was to determine the effects of Ca2+ channel inhibition on GB ion transport. Prairie dog GBs were mounted in a Ussing chamber and bathed in warm oxygenated Ringer's solution, and short-circuit current (Isc), transepithelial potential difference (Vms), and tissue resistance (Rt) were recorded. Following stabilization, the mucosal surfaces of the GBs were exposed to 1 or 0.1 mM verapamil (VER). Effects on Isc were apparent within 10 sec with nadir values reached in 5 +/- 1 min. Profound (76%) inhibition of Isc was seen with 1 mM verapamil exposure (26 +/- 6 microA.cm-2) as compared to baseline values (170 +/- 6 microA.cm-2) (P less than 0.001). Verapamil exposure (1 mM) also led to a marked inhibition of Vms (P less than 0.001, vs baseline) and a significant increase in Rt (P less than 0.05 vs baseline). Similar trends were seen using 0.1 mM verapamil (Isc nadir 133 +/- 13 microA.cm-2). Verapamil-induced effects on gallbladder electrophysiology were largely reversible (75-90% recovery of baseline Isc after tissue washing). These data suggest that (1) verapamil induces rapid but reversible inhibition of ion transport and (2) Ca2+ channel blockade inhibits ion transport in a dose-dependent fashion. We would propose that intracellular Ca2+ may be a regulator of GB ion transport.