Prolongation of rat heart allograft survival by a synthetic progestogen (melengestrol acetate) and ara-cytidine acylates.

Immunosuppressive effects of newly developed synthetic progestins, melengestrol acetate (MGA), and three pyrimidine analogs, ara-cytidine (Ara-C), Ara-C 5'-benzoate and octanoate, were investigated on the heart allograft survival in the rat. MGA at the dose of 25 mg/kg given every 3rd day starting 1 day before the grafting through day 20 prolonged the graft survival significantly without toxic effects (80.2 +/- 40.2 days versus control 7.0 +/- 0.1 days). The high dose (50 mg/kg/day) was more effective (137.4 +/- 26.6 days) but a high incidence of multiple abscesses (37%) was also noted. The other three agents were either highly toxic or not immunosuppressive.