PRITCHARD, HUNTER, and LASKER: EXERCISE AND BIOCHEMICAL CHANGES 



For lactate measurements muscle was quickly 

 cut into small pieces, weighed, and homogenized 

 in 10% trichloroacetic acid in prechilled tubes. 

 Proteins and cellular debris were spun down in 

 a clinical centrifuge. Aliquots of the protein- 

 free supernatant fluid were analyzed for lactate 

 enzymatically using the test reagents supplied 

 by SIGMA Chemical Company.'' The test is 

 based on the conversion of nicotine adenine nu- 

 cleotide (NAD) to the reduced form (NADH) 

 as lactate is converted to pyruvate by lactate de- 

 hydrogenase. All readings were made at 340 m/jL 

 on a Beckman DU spectrophotometer. Results 

 are expressed as mg of lactic acid per 100 g wet 

 weight muscle tissue. 



Muscle and liver samples for glycogen de- 

 terminations were drojiped into preweighed 

 graduated centrifuge tubes containing 3 ml of 

 30% potassium hydroxide. Glycogen was pre- 

 cipitated with alcohol and determined according 



' P.O. Box 14508, St. Louis, Mo. 63178. Reference 

 to commercial products does not imply endorsement. 



to the method of Montgomery (1957) . All read- 

 ings were made at 490 m/^ on a Beckman DU 

 spectrophotometer. Results are expressed as 

 mg glycogen (as glucose) per 100 g wet weight 

 in the case of muscle, and as percent glycogen 

 in the case of liver. 



Muscle tissue was dried in an oven at 60° C 

 to constant weight for fat analysis. Fat was 

 removed by a soxhlet extraction with chloro- 

 form-methanol (2: 1, v: v) . After the extraction 

 the solvent in the tissue was evaporated and 

 the difference in weight of the tissue recorded 

 (Krvaric and Muzinic, 1950). 



RESULTS 



Fish that swam continuously for 6 hr at the 

 subthreshold speed of 98 cm/sec and at the 

 threshold speed showed no difl'erence in the gly- 

 cogen content of the white muscle from the 

 controls (Table 1). On the other hand, in fish 



Table 1. — Glycogen in red and white muscle, and liver of jack mackerel following various forced swimming con- 

 ditions. Red and white muscle glycogen in mg per 100 g wet weight; liver glycogen is percent of wet weight. -- in- 

 dicates measurement was lost during analysis. 



1 Differed from the controls, P ^ 0.05, Mann Whitney U test (Siegel, 1956). 



381 



