VIP has powerful stimulatory effects on both endocrine and exocrine pancreas but its localisation within the gland has not been established. In this study, human pancreas was obtained fresh at surgery (eleven) or within four hours of death (seven). The pancreas was also removed from rats (twenty-two). Immunocytochemical staining showed VIP to be present in fine nerve fibres in all areas of the pancreas. Many fibres were seen in the exocrine pancreas, running between the acini, and around ducts and blood vessels. In addition, dense networks of fibres were observed forming meshes around islets and occasional ganglia were found containing immunoreactive cell bodies. In general, there were fewer VIP fibres in the rat pancreas than in the human, but overall distribution was identical. The mean VIP content of whole human pancreatic tissue was 42 +/- 10 pmol/g wet weight (38 +/- 9 pmol/g in head, 49 +/- 6 pmol/g in body and 42 +/- 11 pmol/g in tail). Whole rat pancreatic tissue contained 28 +/- 7 pmol/g wet weight while preparations of isolated islets were found to contain 374 +/- 30 pmol/g. It is possible that the heavy VIP innervation of the islets described here indicates a role in the regulation of islet hormone release.

Our observations that opioid peptides have direct effects on islet insulin secretion and liver glucose production prompted a search for endogenous opiates and their receptors in these peripheral tissues. ,u-, 6-and K-receptor-active opiates were demonstrated in brain, pancreas and liver extracts by displacement studies using selective ligands for the three opiateReceptor-active opiates in brain extracts exhibited a stronger preference for 6-opiate-receptor sites than for Iu and K sites. Pancreatic extract opiates demonstrated a similar activity at , and 6 sites, but substantially less at K sites. Liver extracts displayed similar selectivity for all three sites. The affinities of the receptor-active opiates for,u-, 6-and K-receptor subtypes displayed a rank order of potency: brain > pancreas > liver. Total immunoreactive f-endorphin and[Met5]enkephalin levels in liver and hepatocytes were greater than those in brain. Immunoreactive [MetI]enkephalin levels in pancreas were similar to, but /J-endorphin levels were substantially higher than, those in brain. 6 and K opiate-binding sites of high affinity were identified in crude membrane preparations of islets of Langerhans, but no specific opiate-binding sites could be demonstrated in liver membrane preparations. Immunoreactive dynorphin and /J-endorphin were demonstrated by immunogold labelling in rat pancreatic islet cells. No positive staining of liver sections for opioids was observed. These results suggest that the tissue content of opiate-receptor-active compounds in the pancreas and the liver is very significant and could contribute to the regulation of normal blood glucose levels.

Glucose-induced insulin secretion from islets cultured in the presence of interleukin-6 (IL-6) for 12-24 h was inhibited to a similar extent as when islets were treated with interleukin-1 beta (IL-1 beta). However, unlike IL-1 beta, IL-6 did not potentiate insulin secretion during an acute (30 min) exposure of islets to the cytokine, nor did it inhibit DNA synthesis during a 24 h culture period. A 12 h pretreatment of islets with tumour necrosis factor-alpha (TNF-alpha) combined with IL-1 beta potentiated the inhibitory effect of IL-1 beta on secretion, such that 20 mM-glucose-induced insulin secretion was abolished. No synergistic inhibition of secretion was observed with TNF-alpha and IL-6. However, IL-1 beta and IL-6 were found to inhibit insulin secretion in an additive manner. These results suggest that IL-6 inhibits insulin secretion in a manner distinct from that of IL-1 beta, and that IL-6 is unlikely to mediate the inhibitory effects of IL-1 beta or TNF-alpha on rat islets of Langerhans.

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1. Incubation of islets of Langerhans in vitro in the presence of colchicine produced a progressive inhibition of the insulin-secretory response to glucose, which was dependent on the time of incubation. 2. The uptake of [3-H]colchicine by islet cells was a rapid process, equilibrium being reached in less than 30 min. Part of the colchicine taken up was bound to protein material, which was recovered largely in a post-microsomal supernatant fraction prepared from the islets. In contrast with this rapid uptake, the binding of colchicine by islet-cell proteins in intact islets or in islet homogenates was a slow process, and equilibrium was not reached for 60-90 min. After an initial 30 min delay, the time-course of the binding of [3-H]colchicine to islet-cell proteins paralleled that for the inhibitory effect of colchicine on insulin release. 3. Some purification of the colchicine-binding material present in islet homogenates could be achieved by precipitation of the protein with 2mM-CaCl2 (2.8-fold). However, ion-exchange chromatography on DEAE-Sephadex produced a further 27-fold purification on elution with 0.6M-NaCl. 4. Colchicine-binding protein prepared from islets by ion-exchange chromatography showed an intrinsic association constant for colchicine of 1.4muM and an apparent molecular weight on gel filtration of 110000. 5. These results suggest that colchicine-binding protein in islet cells closely resembles tubulin extracted from the other tissues. The delayed effectiveness of colchicine in inhibiting insulin secretion is not due to poor penetration of colchicine into the cells but rather to slow binding of the alkaloid to islet-cell tubulin. It seems likely that, as in other tissues, this binding prevents polymerization of the tubulin into microtubules, and thus interferes with the release process.