Comparison of steroid and LH-RH effects on the responsiveness of hemipituitary glands and dispersed pituitary cells.

We have carried out further in vitro studies on the priming effect of LH-RH and the effect of steroids on pituitary responsiveness to LH-RH. In hemipituitary glands, the priming effect could be elicited only once within an 11-h period and was found to diminish significantly with time after the first exposure to LH-RH. Incubation with oestradiol-17 beta (E2) had no significant effect on the responsiveness of hemipituitary glands to LH-RH. By contrast, E2 increased the responsiveness of dispersed cell system. The presence of hypothalamus or synthetic LH-RH did not facilitate the effects of E2. Testosterone significantly reduced the spontaneous and LH-RH-induced release of LH while progesterone had no effect. Exposure to E2 alone in either of the systems did not produce a consistent increase in the total amount of LH in the system. Synthesis of LH was, however, stimulated by exposure to LH-RH for 48 h but not 12 h. These results demonstrate that there is a marked difference between the mechanisms by which LH-RH and steroids affect the responsiveness of the anterior pituitary gland to LH-RH.