Effect of histone H2A on progesterone production by bovine luteal cells.

Histone H2A competitively inhibits binding of GnRH to high affinity rat ovarian receptor sites and blocks gonadotropin-stimulated steroid and cAMP accumulation during culture of rat granulosal or luteal cells. The objective of our study was to examine the progesterone suppressive effects of histone H2A on bovine luteal cells. In the first study, luteal cells were treated at Time = 0 h with a partially purified preparation of bovine ovarian histone H2A (3 ng GnRH equivalents, 800 micrograms protein), equivalent amounts of GnRH (3 ng), or BSA (800 micrograms) and incubated for a total of 4 h. At Time = 2 h, cells were treated with 5 ng bovine LH (bLH) or with medium. Histone H2A completely blocked both basal and LH-induced accumulation of progesterone compared with untreated cultures or cultures treated with bLH. Neither BSA nor GnRH suppressed LH-induced progesterone accumulation. In the second study, histone H2A was added to cultures at Time = 0 h and bovine luteal cells were cultured for 8 h. After 2 h of treatment, histone H2A (3 ng GnRH equivalents) was removed from selected cultures and replaced with fresh medium. Four hours later cultures were treated with 5 ng bLH or medium. LH treatment of cultures from which histone H2A had been removed resulted in an increase in accumulation of progesterone compared with control cultures treated throughout the treatment period with histone H2A. The third study examined the effect of 9-181 pg GnRH equivalents (1.7-34 micrograms protein) of a highly purified preparation of bovine ovarian histone H2A on basal and LH-induced progesterone production during 2 or 3 h of culture.(ABSTRACT TRUNCATED AT 400 WORDS)