Subcutaneous and intrabursal administration of an LRH agonist to the pregnant hemicastrated rat during preimplantation.

A single injection of the LRH agonist, Wy-40,972, under the right ovarian bursa (IB) on any individual day (D) 1-7 in the pregnant rat increased still further the compensatory ovarian weight gain produced by hemicastration (HC) alone. Conversely, a single subcutaneous (sc) injection during the same period abolished the compensatory hypertrophy and reduced the weight of the remaining ovary to that of the ovary of the intact rat and below. The single sc or IB injections of Wy-40,972 were most effective in delaying implantation when administered on D3-4 or 4, respectively. Subcutaneous administration on D5, 6, or 7 produced an antifertility effect, whereas IB administration on any of these 3 days failed to modify the pregnancy. These data demonstrate that the LRH agonist, Wy-40,972, acts directly on the ovary with regard to both weight increase and delay of blastocyst implantation. The results are discussed in relation to hormonal requirements for implantation and desensitization of the ovary.