FENOBARBİTAL İLE İNDÜKLENMİŞ SIÇAN KARACİĞER MİKROZOMAL MONOOKSİJENAZ ENZİM AKTİVİTELERİNİN GÜNİÇİ DEĞİŞİMLERİ

Amac: Ilac biyotransformasyonunda rol oynayan enzim sistemlerinin aktivi- telerinin biyolojik ritimlerden dolayi gunici (sirkadiyen) degisiklikler gostere- bildigi ve bu durumun ilac alinma zamanina bagli olarak ilac farmakokinetigini degistirebildigi bilinmektedir. Ancak literaturde, enzim induksiyonuna yol acan uygulamalarin aktivite ritimlerini nasil etkiledigi konusunda bir bilgi bulun- mamaktadir. Bu calismada, karaciger mikrozomal enzimlerinden etilmorfin N-demetilaz, 7-etoksikumarin O-deetilaz ve 7-etoksirezorfin O-deetilaz enzim aktivitelerindeki gunici ritmik degisikliklerin fenobarbitalle induksiyonundan sonra nasil degistiginin arastirilmasi amaclanmistir. Materyal ve Yontem: Calismamizda 12 saat aydinlik (0800-2000) ve 12 saat karanlik (2000-0800) olacak sekilde senkronize edilmis 200-250 g agirligindaki erkek sicanlar kullanilmistir. Sicanlar rastgele olarak iki gruba ayrilmis ve bir grubuna 4 gun ustuste fenobarbital (75 mg/kg/gun, gunde tek doz, 10 ml/kg, i.p.) verilerek enzim induksiyonu saglanmis, kontrol grubuna ise es zamanli olarak % 0.9 serum fizyolojik enjeksiyonlari yapilmistir. Sicanlarin gunun 6 degisik saatinde (0900, 1300, 1700, 2100, 0100, 0500) oldurulmesiyle elde edilen karacigerler homojenize edilerek santrifugasyonla postmitokondriyal fraksiyon elde edilmis ve N-demetilaz aktivitesi Hantysch reaksiyonuyla, O-deetilaz ak- tivitesi ise 7-hidroksikumarin ve rezorfin uzerinden fluorometrik olarak olcul- mustur. Bulgular: Incelenen enzimlerden 7-etoksikumarin O-deetilaz ve 7-etoksirezorfin O-deetilaz aktivitelerinde kontrol ve fenobarbital gruplar ara- sinda anlamli gunici fark bulunmustur. Etilmorfin N-demetilaz aktivitesi ise kontrol ve fenobarbital gruplarinda ritmik ozellik gostermemistir. Sonuc: Ilac metabolizmasinda rol oynayan mikrozomal enzimlerin aktivite- sindeki gunici degisiklikler ilgili ilaclarin uygulama zamanina bagli olarak farmakokinetik ozelliklerin degismesine ve dolayisiyla ilac etkinliginde degi- sikliklere neden olabilir. Anahtar Kelimeler: Etilmorfin N-demetilaz, 7-etoksikumarin O-deetilaz, 7-etoksirezorfin O-deetilaz, Fenobarbital, Gunici degisimler. CIRCADIAN VARIATIONS IN PHENOBARBITAL INDUCED RAT LI- VER MONOOXYGENASE ENZYME ACTIVITIES ABSTRACT Purpose: The activities of the enzyme systems which take part in the drug biotransformation is known to exhibit daily variations as a result of the bi- ological rhytms and this situation may alter the drug pharmacokinetics de- pending on the drug taking time. However there is not any publication indi- cating how the enzyme induction mechanisms affect the activity rhytms. In this study it was aimed to investigate the daily rhytmic variations in the acti- vities of some hepatic microsomal drug metabolizing enzymes, namely ethyl- morphine N-demethylase, ethoxycoumarin O-deethylase and ethoxyresorufin O-deethylase, with phenobarbital induction. Materials and Methods: In this study the male rats (weighting between 200-250 g) which were synchronised by 12h light (0800-2000h) and 12h dark (2000-0800h) cycle were used. The rats were randomly divided into two groups and as the phenobarbital and the control. The rats in the phenobarbital group were injected with a single dose of phenobarbital (75 mg/kg/day, 10 ml/kg, i.p.) for 4 successive days in order to induce the enzyme activities. The cont- rol group received 0.9% saline injections simultaneously. The rats were killed by cervical dislocation at six different time points of the day (0900, 1300, 1700, 2100, 0100, 0500) and the liver specimens were homogenized to obtain the post- mitochondrial supernatant fractions. The N-demethylase activity was measured by Hantysch reaction whereas the O-deethylase was measured fluorometrically through 7-hydroxycoumarin and the resorufin. Results: 7-ethoxycoumarin O-deethylase and 7-ethoxyresorufin O-deethylase activities of the control and the phenobarbital groups displayed significant daily rhytmic variations. However, ethylmorphine N-demethylase activities in the control and the phenobarbital groups did not show any circadian rhythm. Conclusion: The daily rhytmic variations in the microsomal enzyme activities which have a role on drug metabolism may affect the pharmacokinetics depen- ding on the time of the day of the drug intake. This situation may lead to the variations on the drug effectiveness. Key Words: Ethylmorphine N-demethylase, 7-ethoxycoumarin O-deethylase, 7-ethoxyresorufin O-deethylase, Phenobarbital, Circadian variations