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Corneal temperature in pigeons during exposure to extreme cold
Author(s) -
Cross Sandra,
Bernstein Marvin H.
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a594-c
Subject(s) - cornea , saline , ophthalmology , chemistry , thermoregulation , hypothermia , zoology , medicine , endocrinology , biology , physiology
Birds endure extreme cold in arctic regions and winter climates, and at high altitudes. This places the corneas at risk of freezing, especially when convection increases during flight. We studied the effect of thermoneutral and cold air on corneal temperature ( T c ) in King Pigeons ( Columba livia , mass 550 g). T c was measured using an infrared thermometer. At T a = 25°C (still air), T c averaged 32°C, 9°C below core body temperature ( T b ). Reducing T a from 25 to −25°C decreased T c from 32 to 15°C. For each 1°C of further T a decrease, T c also decreased by 1°C. By extrapolation, T a could have decreased by an additional 16°C, to −39°C, before the corneas froze, although this remains to be confirmed experimentally. The small decrease in T c , from 32 to 15°C at T a = −25°C, and the resulting 33°C increase in the cornea‐to‐air gradient suggest a sharp increase in ocular blood flow. Indeed, vessels in the iris were visibly engorged. The sympathetic agonist nor‐epinephrine (1 mg in 1 ml saline at 23°C,) was therefore applied topically via the cornea during exposure to T a = −25°C. This reduced T c slightly but significantly, and lessened iridial engorgement, whereas 23°C saline alone had no effect. The results support the hypothesis that increased blood flow in pigeon eyes, in response to extreme cold, prevents corneal freezing. (Supported by APS Frontiers in Physiology Fellowship to SC; NIH grant GM61222.)