Prolonged survival of rat cardiac allografts by donor pretreatment with methotrexate. Enhancement by combined immunosuppressant treatment of the recipient.

Using an intraabdominal heterotopic cardiac transplant procedure, we determined that the Fischer 344 rat (donor)/Long Evans rat (recipient) combination provides a suitable model for studying acute rejection of cardiac allografts. Rejection time was 9.7 +/- 0.2 days. With this model we investigated the effect of donor pretreatment with methotrexate on allograft survival. Methotrexate injection at a single optimum dose of 100-200 mg/kg, i.p., resulted in a 55-60% increase in allograft survival with indefinite survival of some allografts. The optimum time for methotrexate administration was found to be 3-24 hr before transplant, indicating the clinical feasibility of this approach. Combining methotrexate with different recipient treatments (cyclosporine, methylprednisolone, or methylprednisolone plus azathioprine) resulted in significantly longer allograft survival than with any treatment alone. We have demonstrated a novel and clinically feasible approach to the treatment or prevention of acute allograft rejection. Such a treatment could allow reduction in the dose of immunosuppressant drugs to the recipient and thus lessen the toxicity of immunosuppressant therapy.

Improved survival of heterotopic cardiac allografts in rats with dietary n-3 polyunsaturated fatty acids.

A heterotopic cardiac transplant model, with male Fischer 344 rats as donors and Long Evans rats as recipients, was utilized to investigate the effect of dietary n-3 polyunsaturated fatty acids on acute rejection. Both donor and recipient rats were fed purified diets high in either n-3 polyunsaturated fatty acids (from concentrated n-3 ethyl esters [EE] or fish oil [FO]) or n-6 polyunsaturated fatty acids (from corn oil [CO]) for either 2-3 or 3-4 weeks before transplant. The recipient rats continued on their diets until rejection. The AIN-76A-based diets (with 30% of calories as fat) had adequate essential fatty acids and were balanced for sterols and antioxidants. Allograft survival was significantly increased by 45% when recipient rats were fed EE as compared to the control (CO diet fed to both donor and recipient), regardless of the diet fed to the donor. There was a slight but significant increase in allograft survival when only donor rats were fed the EE diet 2-3 weeks before transplant. With the FO diet (containing one third of the n-3 fatty acids in the EE diet), only the group fed FO to both donor and recipient (starting 2-3 weeks before transplant) showed a significant increase in allograft survival over the control. However, if the FO diets were fed for 3-4 weeks before transplant, increased survival was seen in groups fed FO to either the donor or recipient alone. In this case, allograft survival with FO feeding to both donor and recipient was not different from recipient treatment alone. In all the studies there was a significant and direct correlation between allograft survival and the donor heart phospholipid n-3/n-6 fatty acid ratio and the n-3 fatty acid content (at rejection). There was an indirect relationship with the n-6 fatty acid content. There was no detectable 20:3 (n-9) in the cardiac phospholipids, indicating the absence of essential fatty acid deficiency. Recipient diets were the strongest determinant of the fatty acid composition in the transplanted donor heart. The data indicate that providing dietary n-3 polyunsaturated fatty acids before and after cardiac transplant to recipient animals provides a significant protection against acute rejection.