Anterior pituitary cell cultures of cows showed a cycle dependent sensitivity to GnRH. The smallest GnRH-inducable LH and FSH secretions were measured during the initial phase of the corpus luteum. During the blossom phase of the corpus luteum the GnRH-inducable LH and FSH secredons were greater. They increased further during the regression phase of the corpus luteum to reach maximal values in the proestrus stage. During the estrus the GnRH induced LH and FSH concentradons decreased again. The anterior pituitary cell cultures of pregnant cows were, with one exception, not sensitive to GnRH.
The cell cultures of 5 out of 7 cows with ovarian cysts secreted only small quantities of LH and FSH following stimulation with GnRH, similarly to the anterior pituitary cell cultures of the cows in the initial phase of corpus luteum. From the remaining two cows with ovarian cysts the cell cultures of the one cow showed a marked LH and FSH secretion already at the smallest GnRH concentration, whereas the cell cultures of the second cow showed a strong LH-, but a minimal FSH secretion. The ratio LH: FSH also changed during the estrus cycle. It was smallest in cell cultures of anterior pituitaries obtained from cows of the corpus luteum regression phase and increased linearly. The greatest ratio LH: FSH was measured during the estrus phase of the cycle. Thereafter it declined again. In anterior pituitary cell cultures of cows with ovarian cysts the ratio LH:FSH was twice that found in anterior pituitary cell cultures of estrous cows.