Hormonal influences on the oviducal lactate dehydrogenase and its isoenzymes.

Changes in the specific activities and distribution of lactate dehydrogenase (LDH) isoenzymes have been studied in the oviduct of intact, ovariectomized and ovariectomized-hormone treated rats. Total LDH and M-subunits were higher in the oviduct during estrus compared to early diestrus phase. Ovariectomy lowered the total activity as well as the proportion of H and M-subunits of LDH, with a total loss of LDH. Treatment of ovariectomized rats with progesterone (2 mg/100 g. body wt/rat/day) and estradiol-17 beta (0.5 microgram/100 g body wt/rat/day) for 7 consecutive days induced marked augmentations in the total activities of this oviducal enzyme. Further, there was a shift in the isoenzyme patterns towards M-type, especially LDH5. Prolactin (400 microgram/100 g body wt/rat/day) depressed the total LDH activity and the distribution of isoenzymes. While LDH4 and LDH5 were very low, LDH1--LDH3, were inclusive, were absent in the oviduct of prolactin-treated group. None of the hormonal replacements could stimulate the LDH4 - subunit. The significance of these changes has been discussed in relation to metabolic activities in the tissue and hormonal influences.