Lactate and malate dehydrogenases in the muscles and male genital tract of the rabbit.

Average lactate dehydrogenase (LDH) isoenzyme patterns the content of H subunits, total LDH activity, total malate dehydrogenase (MDH) activity and the m- MDH/s-MDH ratio were determined in twelve muscles and the male genital tract of the rabbit. LDH(1) was the predominant form in the heart, soleus and masseter muscles, LDH(3) in the lingual muscles and LDH(5) in the other muscles analysed. In the muscles, an increase in the percentual proportion of M subunits was accompanied, by a proportional increase in total LDH activity and a decrease in total MDH activity, especially m-MDH. LDH isoenzyme patterns and LDH and MDH activities are useful for obtaining some idea about the proportion of individual muscle fibres. Activity accounted for by H subunits was roughly the same in all the muscles analysed, indicating that the synthesis of H subunits is independent of the type of muscle fibre and of the oxygen supply of the muscular tissue, and also that isoenzymes composed chiefly of H subunits are not localized preferentially in the mitochondria. Similar relationships between LDH isoenzymes and LDH and MDH activities were found in the testicular and epididymal tissues. The tests and the head of the epididymis mainly contain LDH isoenzymes composed of H subunits. The total LDH activity in these tissues is relatively low and their MDH activity is relatively high compared with the body and tail of the epididymis. The proportion of H subunits in the ampulla, the seminal vesicles, the coagulating glands and the prostate is also high. Cowper's glands have a high LDH(5) and LDH(4) concentration. One of two LDHx isoenzymes were found in the testes and spermatozoa.