Daily rhythmic variations in phenobarbital-induced rat liver microsonal monooxygenase enzyme activities

43 7. YABANCI DİLDE ÖZET In this study some hepatic microsomal drug metabolizing enzymes, namely ethylmorphine N-demethylase, ethoxycoumarin 0- deethylase and ethoxyresorufin O - deethylase were investigated in male rats (weighting between 200-250 g) subjected to 12h light (0800-2000h) and 12h dark (2000- 0800h) cycle. In order to induce the enzyme activities, the rats in the phenobarbital group were injected with phenobarbital 75 mg/kg daily.The rast were killed by cervical dislocation at 6 different time points (0900, 1300, 1700, 2100, Ol00, 0500) Then, the liver samples were homogenized in the 25% homogenizing medium, and were adjusted to a final concentration of approximately 0.1 g fresh tissue /ml. After that, post-mitochondrial supernatant fraction was prepared by centrifugation at 10000 g average for 20 min at 2-4°C. Post-mitochondrial supernatants were used for measurement of the enzyme activities. The N-demethylation of ethylmorphine result in the formation of formaldehyde which was estimated colorimetrically by means of the Hantysch reaction. The O-deethylation of 7-ethoxycoumarin results in the production of 7-hydroxycoumarin and the O-deethylation of 7- ethoxyresorufm results in the production of resorufin. The last two products were measured fluorometrically.44 The activities of ethylmorphine N-demethylase in the control and the phenobarbital groups did not show a circadian rhythm. However, 7-ethoxycoumarin O-deethylase and 7- ethoxyresorufin O-deethylase activities among the control and the phenobarbital groups showed a circadian rhythm.