Reymond M J, Arita J, Dudley C A, Moss R L, Porter J C
Brain Res. 1984 Jun 25;304(2):215-23. doi: 10.1016/0006-8993(84)90324-x.
The effect of aging on the activity of tyrosine hydroxylase (TH) and on the number of TH-positive perikarya in the hypothalamus was studied in old and young female rats. The activity of TH in the mediobasal hypothalamus (MBH) of old rats was significantly (P less than 0.025) less than that in young rats. In old rats, the Km of TH for tyrosine as well as cofactor, 6-methyl-5,6,7,8-tetrahydropterine (6MPH4), was markedly greater than the Km in young rats. The maximal velocity was only slightly reduced in old animals. Contiguous coronal sections of the brain of an old and a young female rat were immunocytochemically stained for TH, and the TH-positive perikarya in the hypothalamus were counted. In the circumventricular region, 6793 TH-positive perikarya were present in the young brain and 6632 in the old brain. In the arcuate region, 2868 and 2760 TH-positive perikarya were counted in the young and old brain, respectively. It is concluded that the reduced TH activity in the MBH of old rats is not a consequence of a reduction in the number of TH-positive perikarya in the arcuate or circumventricular regions of the hypothalamus but is due to a reduction in the affinity of TH for its substrate and cofactor.
研究了衰老对老年和年轻雌性大鼠下丘脑酪氨酸羟化酶（TH）活性及TH阳性核周体数量的影响。老年大鼠中基底下丘脑（MBH）的TH活性显著低于年轻大鼠（P<0.025）。老年大鼠中，TH对酪氨酸以及辅因子6-甲基-5,6,7,8-四氢蝶呤（6MPH4）的米氏常数（Km）明显高于年轻大鼠。老年动物的最大反应速度仅略有降低。对一只老年和一只年轻雌性大鼠大脑的连续冠状切片进行TH免疫细胞化学染色，并对下丘脑的TH阳性核周体进行计数。在室周区域，年轻大脑中有6793个TH阳性核周体，老年大脑中有6632个。在弓状区域，年轻和老年大脑中分别计数到2868个和2760个TH阳性核周体。得出的结论是，老年大鼠MBH中TH活性降低不是下丘脑弓状或室周区域TH阳性核周体数量减少的结果，而是由于TH对其底物和辅因子的亲和力降低所致。
