The effect of experimental cryptorchism on the isozymes of lactate dehydrogenase in mouse testes

Unilateral cryptorchism produced by experimental retention of one testis in the abdomen of the mouse results in a rapid decrease in the weight of that testis. At the same time the specific activity of lactate dehydrogenase (LDH) decreases to 70% of the normal value. The sperm‐specific isozyme, LDH‐X, declines from 41% of the total activity to only 16% after eleven days in the abdomen. All LDH‐X activity is lost by post‐operative day 24. The relative proportion of the other isozymes of LDH increase following the operation. LDH‐5, absent from the mature testis, is detectable in the cryptorchid testis at post‐operative day 28 and represents 15% of the total LDH activity. These observations provide further support of the suggestion that LDH‐X is only found in the testes when meiosis is occurring.