Corticotropin-Releasing Hormone Facilitates Early Survival of Discordant (Bovine-to-Rat) Islet Xenografts R. Lupi, P. Marchetti, A. Coppelli, R. Giannarelli, F. Petraglia, S. Luisi, S. Del Guerra, C. Tellini, P. Florio, A. Genazzani, P. Viacava, and R. Navalesi I N the past few years several reports have described the interactions between the immune and neuroendocrine systems. 1 In particular, the hypothalamus–pituitary–adrenal axis can modulate cell-mediated immune function through the action of corticotropin-releasing hormone (CRH), ACTH, beta-endorphins, and glucocorticoids. Conversely, several cytokines, including interferon-gamma, interleu- kin-1, and interleukin-6 can stimulate the secretion of hypothalamus–pituitary–adrenal axis hormones. More re- cently, CRH has been shown to directly affect lympho- mononuclear cell function, possibly by acting through its binding sites on lymphocytes and monocytes. 2,3 Early failure is a common problem in pancreatic islet xenografts between discordant species. When nonimmuno- suppressed, diabetic rats are chosen as recipients, persistent elevation of blood glucose is observed despite transplanta- tion of either human, dog, or pig islets. The use of silica, antithymocyte globulin, deoxyspergualin, or splenectomy, alone or in varying combinations, can improve discordant islet xenograft survival. 4,5 In the present report, we investi- gated whether hormones of the neuroendocrine system may affect the early engraftment phase of discordant islet xeno- grafts (bovine-to-rat). In particular, we assessed the effect of CRH administration on the survival of islets that were transplanted either within a few days from isolation, or after 4 weeks of culture. MATERIALS AND METHODS Purified bovine pancreatic islets were prepared by collagenase digestion and density gradient purification as described previously. 6 For the purpose of this study we used the islets either within 3 days from isolation (“fresh” islets) or after 4-week culture at 37°C in M199 culture medium (“cultured” islets). In a first set of experiments, thirty nine Lewis rats, aged 8 to 12 weeks, were used as islet xenograft recipients. They received approximately 500 bovine islets under the capsule of the left kidney. The animals were subdivided into several study groups (3 animals per group), as detailed in Table 1. The effect of nicotin- amide (Nic, 500 mg/kg/d SC), gonadotropin-releasing hormone (GnRH, 1 g/d SC), methylprednisolone (MP, 20 mg/kg/d SC) or CRH (1 g/d SC) was evaluated with fresh islets. The effect of MP or CRH was also evaluated with cultured islets. All the compounds were injected once daily between 9 and 10 AM. The islet implan- tation procedures were performed at around 12 PM. Islet survival was assessed at 3 and 7 days from implantation by histology (hematoxylin-eosin staining) and by measuring bovine insulin in the plasma of the transplanted rats by immunoassay (Medgenix, Brussels, cross-reactivity with rat insulin 1%). In a second set of experiments, 13 Lewis rats were made diabetic by IV injection of 65 mg/kg streptozotocin. These animals received either no transplant treatment (n = 3), or bovine islet grafts (approximately 2,000 “fresh” islets under the kidney capsule), without (n = 3) or with MP (n = 3) or CRH (n = 4), at the doses detailed above. Finally, the kinetics of endogenous corticosterone release in response to 1 g CRH SC was also evaluated in 2 normal rats. The peptide was given subcutaneously, and corticosterone levels were From the Catt. Malattie Metaboliche e Ricambio, Ist. Clinica Medica II (R.L., P.M., A.C., R.G., S.D.G., C.T., R.N.),, the Ist. Ostetricia e Ginecologia (S.L., P.F., A.G.),, and Ist. Anatomia Patologica (P.V.), Pisa, Italy and the Cat. Fisiopatologia Riprodu- zione Umana (F.P.), Modena, Italy. Address reprint requests to Dr Roberto Lupi, Department of Metabolic Diseases, via Paradisa 2, Ospedale Cisanello, 56100 Pisa, Italy. Table 1. Experimental Groups (3 rats each) Used in the Present Study Group Islets* Recipient Treatment Histology and Bovine Insulin Measurements (day) 1 Fresh None 3 2 Fresh NIC 3 3 Fresh GnRH 3 4 Fresh MP 3 5 Fresh MP 7 6 Fresh CRH 3 7 Fresh CRH 7 8 Cultured None 3 9 Cultured None 7 10 Cultured MP 3 11 Cultured MP 7 12 Cultured CRH 3 13 Cultured CRH 7 *Fresh islets, transplanted within 3 days from isolation; cultured islets, transplanted after 4 weeks of culture; NIC, nicotinamide; GnRH, Gonadotropin releasing hormone; MP, methylprednisolone; CRH, corticotropin releasing hormone. © 1998 by Elsevier Science Inc. 0041-1345/98/$19.00 655 Avenue of the Americas, New York, NY 10010 PII S0041-1345(98)00696-4 Transplantation Proceedings, 30, 2481–2483 (1998) 2481