Effects of methotrexate on biopterin levels and synthesis in rat cultured pineal glands.
Culture of rat pineal glands in methotrexate (0.5, 5, or 10 microM) for 6 or 24 h did not alter pineal tetrahydrobiopterin (85-90% of total biopterin in cultured glands), except for a decrease of 30% after 24 h culture in 10 microM methotrexate. However, pineal dihydrobiopterin and/or biopterin (10-15% of total biopterin) was increased by methotrexate up to 2.5-fold. Biopterin detected in the culture medium following pineal culture was also increased to a similar extent after methotrexate treatment and appeared to represent leakage of pineal dihydrobiopterin and/or biopterin. Culture of glands in 5 microM methotrexate did not alter the conversion of [U-14C]-guanosine to [14C]biopterin, suggesting that pineal tetrahydrobiopterin synthesis was not altered by methotrexate. Complete inhibition of dihydrofolate reductase activity measured in pineal homogenates was obtained following culture of glands in all concentrations of methotrexate studied. Therefore, dihydrofolate reductase and dihydrobiopterin do not appear to be involved in a major biosynthetic pathway for pineal tetrahydrobiopterin from GTP, although they may have a minor role in tetrahydrobiopterin synthesis.
D000818:Animals; D001708:Biopterins / Q000096:biosynthesis / Q000378:metabolism*; D002478:Cells, Cultured; D006151:Guanosine / Q000378:metabolism; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D008727:Methotrexate / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010870:Pineal Gland / Q000187:drug effects / Q000378:metabolism*; D011621:Pteridines / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism
D011621:Pteridines; D006151:Guanosine; D001708:Biopterins; D007770:L-Lactate Dehydrogenase; D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate