This study was conducted to investigate the involvement of cytochrome P450 3A (CYP3A) in the metabolism of ergotamine in beef liver microsomes. When incubated with liver microsomes, ergotamine was hydroxylated to metabolites M1 and M2. Similarly, its isomer was hydroxylated to M1-Iso and M2-Iso (8-hydroxy-derivatives). Further incubation resulted in a second hydroxylation of M1 and M2 to metabolites M3 and M4 (8,9-dihydroxy derivatives). Maximum formation of metabolites was reached after 20 min, and ergotamine and its isomer were almost totally metabolized after 60 min of incubation. The formation of these metabolites was completely dependent on the presence of NADPH or the NADPH generating system and was also dependent on microsome concentration. Ergotamine was converted at a rate of 2 nM/microgram microsome/min when incubated with bovine liver microsomes to produce a metabolite profile (M1, M2, M1-Iso and M2-Iso) similar to the metabolites produced (2.2 nM/microgram/min) when ergotamine was incubated with liver microsomes of dexamethasone treated rats. This work provides information on the modification of ergotamine in bovine liver microsomes by CYP3A, which is of importance in understanding the detoxification and the clearance of ergotamine and other ergot alkaloids by bovine.
Copyright 2000 Academic Press.