Effect of calyculin-A, phosphatase inhibitor, on 20 alpha-hydroxysteroid dehydrogenase activity in rat luteal cell culture.

Abstract

The effects of calyculin-A (CL-A), a phosphatase inhibitor, on 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD) activity were studied in rat luteal cell cultures to examine whether protein phosphatases were involved in the regulation of the enzyme activity. Luteal cells were harvested from the rats on day 6 of pseudopregnancy. In the absence of prolactin (PRL), the stimulatory effect of CL-A (10(-9) M) on 20 alpha-HSD activity was observed during the first 3 h period of the culture, but was not discernible thereafter. Since the enzyme activity of luteal cells during pseudopregnancy is known to be suppressed by PRL, the results suggest that this effect of CL-A could be manifested only as long as the effect of endogenous PRL was remained. On the other hand, CL-A enhanced the 20 alpha-HSD activity of the cells cultured for 24 h, where a spontaneous increase in 20 alpha-HSD activity was blocked by exogenously supplementing the culture medium with PRL. These results suggest that a CL-A sensitive phosphatase(s) may be involved in the action of PRL in suppressing the increase in 20 alpha-HSD activity in rat luteal cells.