The suppression of nocturnal pineal melatonin in the Syrian hamster: dose-response curves at 500 and 360 nm

It has recently been shown that wavelengths in the near-UV range (UV-A, 320-400 nm) are capable of influencing pineal melatonin content in the hamster. The purpose of this study was to compare the capacities of monochromatic visible and UV radiation for suppressing nocturnal pineal melatonin. Groups of male Syrian hamsters adapted to a 14-h light, 10-h dark cycle (lights on, 1700-0700 h) were exposed to irradiances of 500 or 360 nm light for 5 min during their dark phase. Both wavelengths suppressed pineal melatonin in a dose-related manner. The resultant fluence-response curves were similar in shape, although their corresponding threshold irradiances were markedly different. The calculated ED50 values for 500 and 360 nm light were 0.022 microW/cm2 (1.66 X 10(13) photons/cm2) and 0.306 microW/cm2 (1.66 X 10(14) photons/cm2), respectively. These data show that the induction of a 50% depression of pineal melatonin requires 10 times the number of 360-nm photons compared to 500-nm photons at the level of the cornea. Despite this difference in sensitivity to wavelength, environmental irradiances of UV-A are well above the threshold for melatonin suppression in the hamster. These results thus demonstrate the importance of considering UV-A, in addition to the visible wavelengths, in the regulation of hamster pineal physiology.     

Endometriosis of the liver containing mullerian adenosarcoma: case report

We present a case of a liver endometrioma in a postmenopausal woman. After failed management with leuprolide acetate, the mass was resected and contained focal areas of mullerian adenosarcoma. This is a rare case of mullerian adenosarcoma that appeared to arise within an endometrioma of the liver.     

Metabolic consequences of anoxia in the isolated, perfused guinea pig heart: anaerobic metabolism of endogenous amino acids

The metabolic consequences of anoxia in the isolated, perfused guinea pig heart were examined by 13C NMR spectroscopy of 13C-labeled metabolites in situ. Upon addition of [3-13C]pyruvate to the perfusate during normoxic conditions, label is detected in several metabolites, including alanine (C3), glutamate (C2, C3, and C4), and aspartate (C2 and C3), reaching steady state levels 10-15 min after the labeled precursor reaches the heart. During anoxia, the label in glutamate and aspartate decreases and label appears in C2(3) of succinate. This real-time observation demonstrates that in the isolated intact heart, anaerobic metabolism of the amino acids aspartate and glutamate to succinate occurs. These pathways, which were first noted to occur in skeletal muscle of diving mammals, may provide a mechanism supplemental to glycolysis for the production of nucleoside triphosphates during periods of anoxia.     

Growth and fatty acid metabolism of human breast cancer (MCF-7) xenografts in nude rats: impact of constant light-induced nocturnal melatonin suppression

The nocturnal melatonin (MLT) surge is a relevant oncostatic signal for a variety of experimental malignancies. Population studies support the hypothesis that exposure to light at night may represent a new risk factor for breast cancer possibly through the suppression of pineal MLT production and/or circadian disruption. We tested the ability of constant light exposure to suppress MLT production in female nude rats and stimulate the growth of tissue-isolated MCF-7 human breast cancer xenografts via increased tumor linoleic acid (LA) metabolism. Rats maintained on an alternating light/dark cycle (L:D group) exhibited a robust circadian MLT rhythm that was abolished following constant light exposure. During the exposure of animals bearing tissue-isolated human MCF-7 breast cancer xenografts to constant light, the rate of tumor growth markedly increased relative to the L:D group. Tumor LA uptake and its metabolism to the mitogen 13-hydroxyoctadecadienoic acid (13-HODE) were also substantially higher under constant light conditions. This is the first biological evidence for a potential link between constant light exposure and increased human breast oncogenesis involving MLT suppression and stimulation of tumor LA metabolism.     

Suppression of pineal melatonin in Peromyscus leucopus by different monochromatic wavelengths of visible and near-ultraviolet light (UV-A)

The purpose of this study was to examine the effects of monochromatic visible and near-ultraviolet radiation (UV-A) on pineal melatonin suppression in the white-footed mouse, Peromyscus leucopus. To this end, mice were entrained to a daily cycle 8 h of light and 16 h of darkness. During the night when pineal melatonin contents were high, mice were individually exposed for 5 min to specific wavelengths of monochromatic light (10 nm half-peak bandwidths). Control animals received the same handling conditions but no experimental exposure. Pineal glands were collected from animals 18 min after the 5 min experimental exposure and were later assayed for melatonin content. In groups of animals exposed to equal photon densities (2.64 × 10¹⁵photons/cm²) of either 320, 340, 360, 500, or 560 nm, mean pineal melatonin content was significantly suppressed as compared to the unexposed control animals. The 640 nm wavelength (red) at the same photon density did not suppress pineal melatonin. These experiments are the first to demonstrate light-induced suppression of pineal melatonin in Peromyscus leucopus. In addition, these data reveal a novel finding: the suppression of pineal melatonin content by ultraviolet wavelength as low as 320 and 340 nm.     

The influence of different light spectra on the suppression of pineal melatonin content in the syrian hamster

The purpose of this study was to test the capacity of different visible wavelengths of light to suppress nocturnal levels of pineal melatonin in hamsters. It was found that the visible wavelengths vary in their ability to perturb pineal melatonin. During the period of peak pineal melatonin production, animals were exposed to fluorescent light sources having half-peak bandwidths of 339–371 nm (near-ultraviolet), 435–500 nm (blue), 510–550 nm (green), 558–636 nm (yellow) and 653–668 nm (red). In each experiment, animals were exposed to equal irradiances of each light source. The different irradiances used were 0.928, 0.200, 0.186, 0.074 and 0.019 μW/cm². The resultant data demonstrated that blue fluorescent light was the most efficient in suppressing pineal melatonin. Green fluorescent light was found to be the next most efficient light for inhibiting pineal melatonin followed by yellow fluorescent light. Near-ultraviolet and red light were the least capable of suppressing pineal melatonin. These observations suggest that the retinal photopigment responsible for mediating the pineal gland's response to light in the hamster may be either rhodopsin or another blue-sensitive chromophore.     

Characterization and use of a digital light projector for vision research

For creating stimuli in the laboratory, digital light projection (DLP) technology has the potential to overcome the low output luminance, lack of pixel independence, and limited chromaticity gamut of the cathode ray tube (CRT). We built a DLP-based stimulator for projecting patterns on the in vitro primate retina. The DLP produces high light levels and has good contrast. Spatial performance was similar to that of a CRT. Temporal performance was limited by the refresh rate (63 Hz). The chromatic gamut was modestly larger than that of a CRT although the primary spectra varied to a small degree with light output and numerical aperture.