D, Day giaocam Co tron mCilchth~n
1.3. Sinh t6ng hop va chuyen hoa cua cac chat d~n truy~n thftn kinh
1.3.1. Sinh tong hlJpva chuyen hoa catecholamin Sinh to'nghop
Tien than cua cac catecholamin la acid amin ·va tyrosin. Qua trinh t6ng hop catecholamin duoc thuc hien qua vai giai doan (so d6 4.1).
- Too DOPA: d:1utien tyrosin duoc hydroxyl hoa d vi tri meta nho tyrosin hydroxylase tao thanh 3,4- dihydoxyphenylalalin (DOPA). Giai doan nay duoc thuc hien trong bao tuong d sci sau hach giao cam.
- Tqo dopamin: DOPA duoc decarboxyl hoa d~ tao thanh dopamin nho L- aromatic aminoacid decarboxylase.Qua trinh nay ciing di€inra d bao tuong,
- Tqo noradrenalin (norepinephrin): dopamin duoc ~- hydroxyl hoa nho dopamin-~- hydroxylase tao thanh noradrenalin. Sau do noradrenalin duoc du trfr d ngon sci sau hach giao cam.
- Tqo adrenalin (epinephrin): noradrenalin duoc methyl hoa tao thanh adrenalin nho enzym phenethanolamin- N- methyltranferase. Qua trinh nay xay ra dtuyen tuy thuong than.
Chinh vi the, ngon sci sau hach giao cam chu yeu tiet ra noradrenalin chi co m9t luong nho adrenalin. Nguoc lai, d tuyen thuqng th~n tiet ra ca adrenalin va noradrenalin (trong do 80% la adrenalin).
Cac catecholamin bi chuy~n hoa va mat ho:;tt tinh bdi catechol
oxymethyltranferase (COMT)va monoamin oxidase (MAO).
Chuyi'n hoa
Trong cd th~ cac catecholamin deu bi chuy~n hoa bdi 2 lo:;tienzym la COMT (catechol oxymethyltranferase) va MAO (monoamin oxidase) (Sdd6 4.2).
COMT tac d9ng vao nhom -OH d vi tri meta. COMT tham gia vao chuy~n hoa cac catecholamin d tU:1nhoan nhieu hdn d te bao. Vi v~y, khi dung thuoc lic che COMT thudng lam keo dai tac d\lng cua catecholamin ngo:;tilai.
MAO tac d9ng vao vi tri amin d chu6i ben t:;tochat chuy~n hoa la acid 3- methoxy 4- hydroxy mandelic (con g9i la acid vanyl mandelic- VMA). MAO co nhieu d ty th~ nen tham gia chuy~n hoa cac catecholamin trong te bao nhieu hdn d tU:1nhoan. Khi dung thuoc lic che MAO lam tang catecholamin n9i sinh nhieu hdn.