MELATONIN REGULATION IN HUMANS WITH COLOR-VISION DEFICIENCIES

Light can induce an acute suppression and/or circadian phase shift of plasma melatonin levels in subjects with normal color vision. It is no t known whether this photic suppression requires an integrated respons e from all photoreceptors or from a specialized subset of photorecepto rs. To determine whether normal cone photoreceptor systems are necessa ry for Light-induced melatonin suppression, se tested whether color vi sion-deficient human subjects experience light-induced melatonin suppr ession. In 1 study, 14 red-green color vision-deficient subjects and 7 normal controls were exposed to a 90-min, 200-lux, white light stimul us from 0200-0330 h. Melatonin suppression was observed in the control s (t = -7.04; P < 0.001), all color vision-deficient subjects (t = -4. 76; P < 0.001), protanopic observers (t = -6.23; P < 0.005), and deute ranopic observers (t = -3.48; P < 0.05), with no significant differenc e in the magnitude of suppression between groups. In a second study, 6 red/green color vision-deficient males and 6 controls were Exposed to a broad band green light stimulus (120 nm with lambda(max) 507 nm; me an +/- SEM, 305 +/- 10 lux) or darkness from 0030-0100 h. Hourly melat onin profiles (2000-1000 h) were not significantly different in onset, offset, or duration between the two groups. Melatonin suppression was also observed after exposure to the green light source at 0100 h (col or vision deficient: t = -2.3; df = 5; P < 0.05; controls: t = -3.61; df = 5; P < 0.01) and 0115 h (color vision deficient: t = -2.74; df = 5; P < 0.05; controls: t = -3.57; df = 5; P < 0.01). These findings su ggest that a normal trichromatic visual system is not necessary for li ght-mediated neuroendocrine regulation.