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The ability of RO 23-6457, a retinoid compound with marked in vitro immunosuppressive properties, to prolong vascularized allografts was examined in several in vivo transplantation models. In the murine heterotopic heart model, efficacy was shown in two H-2 incompatible strain combinations, with indefinite graft survival at some doses. In the rat heterotopic heart model, oral administration prolonged Wistar-Furth grafts in Lewis hosts an average of 1 week, with no long-term survivors at a variety of doses. Given subcutaneously, grafts were further prolonged, but the compound proved toxic. In a bilaterally nephrectomized renal transplant model in cynomolgus monkeys treated intravenously at a dose of 2 mg/kg/day, host survival was prolonged to 18, 32, 33, and 74 days, compared with 11, 11, 12, 13, and 26 days in untreated controls (P less than 0.05 by rank-sum testing). The three shorter surviving recipients died from anorexia and weight loss with normal renal function, while the longest survivor rejected its kidney when exhaustion of iv sites precluded further treatment. The toxic effects of the compound resemble the syndrome of hypervitaminosis A. RO 23-6457 will prolong graft survival as a single agent, justifying further preclinical testing and efforts to reduce toxicity.

The effect of cyclosporine (CyS) on survival and function of 250 cm intraabdominal heterotopic small bowel allografts was studied in outbred pigs. Experimental animals received oral CyS alone (25 mg/kg/day), or oral CyS, donor bowel radiation, and recipient splenectomy; controls were untreated. Excluding technical failures, no significant differences in graft survival were observed, although one relatively long-term survivor occurred in each treated group. Rejection was not related to cyclosporine levels. These data show that CyS as a single agent as well as when used with supplemental therapy does not uniformly prevent rejection of small bowel allografts in pigs, although an occasional long-term survivor will occur. The failure to achieve consistently successful engraftment may reflect the large quantity of lymphoid tissue in small bowel. Further experimentation is required before human transplantation is again attempted.

An inbred rat model of small bowel transplantation was used to study the metabolic consequences of systemic venous drainage of the graft. Lewis rats received either Lewis (isograft) or Lewis X Brown Norway F1 (allograft) small bowel grafts. Venous drainage of the isografts was to either the portal vein or the inferior vena cava. Allograft recipients underwent systemic venous drainage and were treated with a 4-week course of tapering cyclosporine. Ammonia levels in systemically drained isografts (108 +/- 5 microM/100 ml) were more than twice those in portally drained isografts (38 +/- 3, P less than 0.001), while amino acid analysis showed significant elevations in glycine, serine, asparagine, histidine, phenylalanine, and tyrosine. Ammonia levels decreased and amino acid alterations were generally corrected when animals were fed a modified protein diet low in aromatic and high in branched chain amino acids. Recipients of both systemically and portally drained isografts grew normally, while weight gain in allograft recipients was impaired. We conclude that systemic venous drainage of small bowel grafts results in altered ammonia and amino acid levels that resemble those found in models of hepatic encephalopathy; these changes can be significantly ameliorated by dietary modification; and the compromised growth seen in systemically drained allografted animals results from chronic rejection and/or cyclosporine rather than the partial porto-systemic shunt.