| effect of polar day on plasma profiles of melatonin, testosterone, and estradiol in high-arctic lapland longspurs. | in polar habitats, continuous daylight (polar day) can prevail for many weeks or months around the summer solstice. in the laboratory, continuous light conditions impair or disrupt circadian rhythms in many animals. to determine whether circadian rhythms are disrupted under natural polar day conditions in a species that is only a summer resident in polar regions we analyzed diel rhythms in plasma concentrations of melatonin, testosterone (t), and 17-beta estradiol (e(2)) during the summer solsti ... | 2002 | 11944971 |