Effect of contraceptive steroids on gamma-aminobutyric acid metabolism and pyridoxal kinase activity in rat brain

Adult female albino rats were administered oral contraceptive steroids daily for 3 months and γ-aminobutyric acid (GABA) content as well as the GABA metabolizing enzyme(s) activity were assayed. GABA content of the brain was found to be elevated in both estrogenic and progestogenic hormone-treated animals. However, no significant change was observed either in glutamic acid decarboxylase (EC 4.1.1.15) activity or in γ-aminobutyric acid transminase (EC 2.6.1.19) activity of brain tissue in hormone-treated animals. Interestingly, parallel to the increase of GABA content, a concomitant elevation of pyridoxal kinase (PL-kinase) (EC 2.7.1.35) activity was observed. It seems that the increase in the GABA concentration by the contraceptive steroids might have been mediated through an elevated pyridoxal kinase activity of the brain. The possible mechanism and interrelationship between the metabolic activities is discussed.