Effects of spectral transmittance through standard laboratory cages on circadian metabolism and physiology in nude rats.

Light is potent in circadian, neuroendocrine, and neurobehavioral regulation, thereby having profound influence on the health and wellbeing of all mammals, including laboratory animals. We hypothesized that the spectral quality of light transmitted through colored compared with clear standard rodent cages alters circadian production of melatonin and temporal coordination of normal metabolic and physiologic activities. Female nude rats (Hsd:RH-Foxn1(rnu); n = 6 per group) were maintained on a 12:12-h light:dark regimen (300 lx; lights on, 0600) in standard translucent clear, amber, or blue rodent cages; intensity and duration of lighting were identical for all groups. Rats were assessed for arterial blood levels of pO(2) and pCO(2), melatonin, total fatty acid, glucose, lactic acid, insulin, leptin, and corticosterone concentrations at 6 circadian time points. Normal circadian rhythms of arterial blood pO(2) and pCO(2) were different in rats housed in cages that were blue compared with amber or clear. Plasma melatonin levels (mean ± 1 SD) were low (1.0 ± 0.2 pg/mL) during the light phase in all groups but higher at nighttime in rats in blue cages (928.2 ± 39.5 pg/mL) compared with amber (256.8 ± 6.6 pg/mL) and clear (154.8 ± 9.3 pg/mL) cages. Plasma daily rhythms of total fatty acid, glucose, lactic acid, leptin, insulin, and corticosterone were disrupted in rats housed in blue or amber compared with clear cages. Temporal coordination of circadian rhythms of physiology and metabolism can be altered markedly by changes in the spectral quality of light transmitted through colored standard rodent cages.