Maintenance of normal corneal thickness in the cold in vivo (hibernation) as opposed to in vitro

Abstract

1. Corneal thickness was measured in vivo in normothermic and hibernating (body temperature = 7-10 degrees C) woodchucks and the [Na(+)], [K(+)], [Mg(2+)] and water content of woodchuck and rabbit corneas were determined on freshly isolated tissues.2. Woodchuck eyes from both normothermic and hibernating animals were incubated in moist chambers at 5 or 11 degrees C and the corneal thickness was measured periodically.3. Woodchuck corneas undergo continuous swelling when kept in vitro in a moist chamber at either 5 or 11 degrees C. The rate of this swelling was the same for eyes from active and hibernating animals; it was almost completely reversible upon rewarming at 35 degrees C.4. In the hibernating woodchuck the corneal thickness did not increase measurably, even after several days of hibernation, although the mean corneal temperature was 9.4 degrees C.5. At 7 degrees C, the lactate production of corneas from both hibernating and normothermic woodchucks was reduced to about one fifth its levels measured at 37 degrees C. Oxygen consumption was also greatly reduced in the cold although the endothelial O(2) consumption of corneas from hibernating woodchucks appears to be relatively insensitive to cold.6. It is concluded that removal of the eye and/or the in vitro conditions per se render the cornea more vulnerable to the effects of cold, possibly as a result of the elimination of the influences of orbital tissues and/or secretions or as a result of changes in some intrinsic properties of the cornea due to the elimination of neurohumoural factors or the release of autocoids.7. The finding that normal corneal thickness can be maintained under conditions where the environment is maintained essentially constant for days strongly argues against the validity of the recently proposed nonsteady-state theory of corneal thickness control.