The activity of lactate dehydrogenase (LDH) and the pattern of its isoenzymes (LDH-1,-2,-3,-4, and-5) were investigated in normal and malignant mammary tissues in Sprague-Dawley rats. The total LDH activity was measured by a colorimetric method with the use of pyruvate as the substrate. LDH isoenzymes were separated by acrylamide gel electrophoresis and were measured by densitometry. Isoenzyme LDH-1 was designated as the band migrating farthest in the gel toward the anode. Mammary glands of nulliparous animals had low LDH activities, which later increased progressively during pregnancy and lactation and which were accompanied by a concurrent shift of isoenzyme pattern toward a predominance of muscle-type subunits. Involution of the mammary gland resulting from the cessation of lactation was associated with a return of LDH activities and isoenzyme patterns to the original stage. Actively growing mammary tumors induced by 7, 12-dimethylbenz[a]anth-racene showed an extremely high activity of LDH and an elevated proportion of the muscle-type subunits. Ovariectomy in the tumor-bearing animals resulted in tumor regression, which was accompanied by a reduction in LDH activity and a relative decrease in percent of the muscle-type subunits. Furthermore, unlike the normal mammary gland, in both growing and regressing mammary tumors, LDH-1 was consistently undetectable under the present experimental conditions despite a tenfold concentration of the tissue extracts. Results of this study indicated that both the LDH activity and the pattern of isoenzymes in normal and malignant mammary tissues showed characteristic changes under various endocrine states of the hosts and that the malignant transformation resulted in a loss of LDH-1 in the tissue. These characteristic LDH parameters can, therefore, be utilized as biologic markers for normal and neoplastic mammary tissues at various stages of development.
ASJC Scopus subject areas
- Cancer Research