PROSSEB 



Changes in lipids have been reported. Acclimation of goldfish to 

 cold was accompanied by increased unsaturation of tissue lipids and 

 acclimation to heat by a decreased unsaturation (Hoar and Cottle, 

 1952). In cold the tissue phospholipids of goldfish increased in re- 

 lation to cholesterol, but no consistent correlation was observed be- 

 tween the ratio of cholesterolto phospholipid and thermal resistance. 

 Also no good correlation was found between dietary lipid unsaturation 

 and thermal resistance, although a high cholesterol diet increased 

 resistance to both heat and cold (Irvine etal., 1957). Preliminary ob- 

 servations indicate a higher percentage of stearic and palmitic acids 

 in liver of 30 C- acclimated than of cold- acclimated goldfish 

 (Murphy and Johnston, 1961). Liver of goldfishfrom 5 C had 1.76% 

 lipid, from 30 C had 3.97% lipid. The iodine numbers were as fol- 

 lows: 30 C, 97.7; 15 C, 100.3; 5 C, 102.3; hence the liver lipid is 

 more unsaturated in the cold-acclimated state. Similar changes were 

 noted by Hoar and Cottle (1952). In view of the central nervous 

 changes to be reported below, it is likely that numerous changes in 

 the lipids of cell membranes will be found. 



What mechanisms underlybiochemical changes? Changes in lip- 

 ids must depend on differences in some synthetic enzymes. As stated 

 above, there is no evidence for involvement of the adrenal cortex and 

 conflicting evidence for involvement of the thyroid in temperature 

 acclimation of poikilothermic vertebrates. Much more work should 

 be done on possible hormonal regulation of metabolism. However, 

 present evidence favors a direct effect of temperature. This could 

 occur in several possible ways; (1) In the cold, the total metabolism 

 is lower than at high acclimation temperatures ; hence metabolic sub- 

 strates in general may accumulate, and these may induce more in- 

 termediary enzymes at several levels. (2) an intermediate such as 

 pyruvate (or lactate) may accumulate because its degradative en- 

 zymes have a higher Q than those enzymes forming it, and thus 

 this intermediate may reach concentrations which induce an alternate 

 path. If B>-C, in the system: 



A ^i^ B ^i^ C 



n 



D 

 has a highQ , B accumulates and may induce the enzyme catalyzing 



22 



