Physiological studies on supercooled killifish (Fundulus heteroclitus). 3. Carbohydrate metabolism and survival at subzero temperatures.

Abstract

AbstractThe previously reported hyperglycemia induced in Fundulus heteroclitus by exposure to the subzero cold was investigated in more detail. It was found that the hyperglycemic response was elicited immediately when fish were transferred to water at − 1.5°C and that the striking increase in serum glucose was accompanied by a progressive depletion of hepatic glycogen. Muscle glycogen occasionally, but not always, showed a slight depletion after long exposure to the subzero cold. Serum glucose was not maintained at high levels indefinitely in the subzero cold. After hepatic glycogen was totally depleted, serum glucose levels began to drop. When serum glucose levels fell to normal, the fish began to die. Addition of glucose to the water elevated serum glucose levels and enhanced survival in the subzero cold. Winter fish, which produce higher levels of serum glucose in the subzero cold than do summer fish, survived the subzero cold almost twice as long as did summer fish. Serum nonglucose free carbohydrate levels were unaffected by the length of exposure to subzero temperatures. Liver protein levels were unaffected by temperatures from 20°C to − 1.5°C and muscle protein levels decreased slightly only after long exposure to the subzero cold.