Burchill S A, Thody A J
J Endocrinol. 1986 Nov;111(2):225-32. doi: 10.1677/joe.0.1110225.
Skin tyrosinase activity increases during hair growth in C3H-HeAvy mice and reaches higher levels in young (30- to 35-day-old) mice when the hair follicular melanocytes synthesize the black pigment, eumelanin, than in older (6-month-old) mice when they produce the golden yellow pigment, phaeomelanin. To examine the regulation of the melanocytes at these different stages we have compared the effect of alpha-MSH and other agents that act, through cyclic AMP-dependent mechanisms, on skin tyrosinase activity in both young and old mice during hair growth, initiated by plucking. Daily administration of alpha-MSH, isoprenaline or theophylline increased coat darkness, and skin tyrosinase activity in the younger mice 7-9 days after plucking, but they were ineffective in the older mice. Similarly alpha-MSH, 8-bromo-cyclic AMP or theophylline increased tyrosinase activity in skin explants from the younger mice incubated for up to 24 h but had no effect in explants from older mice. Cyclic GMP had no effect on tyrosinase activity in skin explants from both young and old mice. It is suggested that whereas cyclic AMP-dependent mechanisms may operate to regulate tyrosinase activity in the hair follicular melanocytes of younger mice that produce eumelanin these systems may not operate in the older mice when these melanocytes synthesize phaeomelanin. Phaeomelanin synthesis, unlike that of eumelanin, may not depend upon tyrosinase and its regulation by cyclic AMP and this could explain the low levels of this enzyme in the skin and its failure to respond to alpha-MSH and other activators of the cyclic AMP system during periods of phaeomelanin production.
在C3H-HeAvy小鼠的毛发生长过程中，皮肤酪氨酸酶活性会增加。当毛囊黑素细胞合成黑色色素真黑素时，年轻（30至35日龄）小鼠的该活性会达到更高水平；而当老年（6月龄）小鼠产生金黄色色素褐黑素时，其活性则较低。为了研究黑素细胞在这些不同阶段的调控机制，我们比较了α-促黑素细胞激素（α-MSH）和其他通过环磷酸腺苷（cAMP）依赖性机制起作用的药物，对拔毛引发毛发生长期间的年轻和老年小鼠皮肤酪氨酸酶活性的影响。每日给予α-MSH、异丙肾上腺素或茶碱可使年轻小鼠在拔毛后7至9天的被毛颜色变深，皮肤酪氨酸酶活性增加，但对老年小鼠无效。同样，α-MSH、8-溴环磷酸腺苷或茶碱可使年轻小鼠的皮肤外植体在孵育长达24小时后酪氨酸酶活性增加，但对老年小鼠的外植体无影响。环磷酸鸟苷（cGMP）对年轻和老年小鼠皮肤外植体的酪氨酸酶活性均无影响。这表明，虽然cAMP依赖性机制可能在产生真黑素的年轻小鼠毛囊黑素细胞中调节酪氨酸酶活性，但当这些黑素细胞合成褐黑素时，这些系统在老年小鼠中可能不起作用。与真黑素合成不同，褐黑素的合成可能不依赖于酪氨酸酶及其cAMP调节，这可以解释在褐黑素产生期间皮肤中该酶水平较低以及其对α-MSH和其他cAMP系统激活剂无反应的现象。
