Luteinizing hormone has a stage-limited effect on preantral follicle development in vitro

Although it is known that LH receptors are present from the time of thecal differentiation, the role of LH during early follicle development is not ye t clear. The effect of LH on preantral follicle development has therefore b een investigated in vitro using a culture system that supports the developm ent of intact follicles. We have previously shown that although preantral f ollicles 150 mu m in diameter (2-3 granulosa cell layers) do not require LH to proceed through antral development, smaller follicles (1-2 granulosa ce ll layers, 85-110 mu m in diameter) do not develop beyond the large preantr al stage in the presence of only FSH and 5% mouse serum. Follicles of this size were therefore used to determine the effects of LH and serum on their development in vitro. The results showed that although FSH must be continuo usly present, a low concentration of LH together with a slight increase in serum concentration was necessary, specifically during the primary stage of follicle development (from 85 mu m in diameter until the follicles had rea ched 150 pm in diameter) to induce the capacity for subsequent LH-independe nt rapid growth and antral development. The in vitro development of maturab le oocytes with normal spindle and chromatin morphology was also supported. These results indicate that LH probably induces changes in the early diffe rentiating thecal cells, which are critical for the completion of subsequen t follicular and oocyte development.