本研究主要探討膳食中缺鋅對吳郭魚肝臟的細胞色素P450lA (cytochrome, P4501A, CYP1A)活性及表現之影響。吳郭魚隨機分為缺鋅組(zinc-deficiency group)及對飼組（Pair - fed control），分別餵食缺鋅飼料（5 mg Zn / kg飼料）及基礎飼料（46 mg Zn/kg飼料）。 經八週的飼養實驗後，每組各隨機選取6 尾吳郭魚進行分析。發現兩組吳郭魚的增重率、肝體比沒有明顯差異，但缺鋅組之吳郭魚血漿中的鋅濃度則明顯低於對飼組。肝臟中之總CYP 含量及相關之單加氧酶（monooxygenases ）活性亦顯現無差異的情況，說明膳食中缺乏鋅對吳郭魚之肝臟中的總CYP 含量及相關酵素的活性似乎沒有影響。進一步將此二組的吳郭魚分別施打不問劑量之五氯酚( pentachlorophenol , PCP ) ，則發現兩組吳郭魚肝臟中aryl hydrocarbon hydroxylase (AHH)及ethoyresorufin-O-deethylase ( EROD) 之活性均可被PCP 誘發。但在較高劑量的PCP 下，PCP 所誘導的AHH 及EROD 活性，則是缺鋅組比對飼組為低。同時以反轉錄聚合酶連鎖反應檢測(reverse transcription -polymerase chain reaction assay,RT-PCR assay)進行CY P1A mRNA 表現的分析，發現缺鋅組之吳郭魚肝臟CYP1A mRNA 的表現與對飼組比較，缺鋅組之CYP1 mRNA 的表現似乎受到壓抑，顯示鋅似乎在CYP1A 表現的調控上具有特殊之功能其機制為何？有待更進一步的探討。 The present study investigated the effect of dietary zinc deficiency on hepatic cytochrome P4501A ( CYP1A ) activity and expression in tilapia . The fish were given randomly assigned to either a zinc-deficient dietary group ( 5 mg Zn / kg diet ) or a pair-fed control ( 46 mg Zn / kg diet ) . After 8 weeks of the feeding trial, six fish were randomly removed from each dietary group for analysis. Compared with the pair-fed control , zinc deficiency reduced plasma zinc concentration but no effect on the body weight gain , relative liver weight , total CYP content and NADPH-cytochrome C reductase activity in tilapia . CYP-mediated rnonooxygenase activities , which were indicated by aryl hydrocarbon hydroxylase ( AHH ) , ethoxycoumarin-O-deethylase ( ECOD ) , 7-ethoxyresorufin-O-deethylase ( EROD ) , aniline-4-hydroxylase ( A4H ) and aminopyrine-N-hydroxylase ( APNH ) , were also not affected by dietary zinc deficiency . The fish of each dietary group was further injected individually with graded doses of pentachlorophenol ( PCP ) , and levels of hepatic CYP1A mRNA and CYP1A-mediated monooxygenase activities were determined. Hepatic CYP1A-mediated AHH and EROD were significantly inducible by PCP in tilapia from the two groups. When treated with higher doses of PCP, the PCP-induced AHH and EROD activities were decreased in dietary zinc deficient tilapia . Moreover , reverse transcription-polymerase chain reaction assay ( RT-PCR assay ) revealed an inhibition of CYP1A mRNA expression in zinc-deficient tilapia . These results indicate that dietary zinc deficiency reduced the hepatic gene expression of the CYP1A in tilapia.
