Developmental changes in LH secretion by male pituitaries in vitro: from the infantile to adult period

The secretion of LH from the anterior pituitary of male rats was studied at different periods of postnatal development. According to an established cl assification we used rats 14 (infantile), 23 (juvenile), 45 (pubertal) and 90 (adult) days old. By using an in vitro incubation system, both basal and stimulated LH secretion were studied in the same gland. Age-related differ ences were observed in basal LH secretion, with juvenile and pubertal pitui taries showing higher secretion compared with infantile and adult pituitari es. However, the GnRH-induced secretory response was significantly higher i n the infantile rats than in other ages. LH secretion was also studied in p rimary cultures from infantile or adult pituitaries. In 24 and 48 h culture s, infantile cells showed a significantly larger response to GnRH than that of adult cells. In the infantile pituitary LH-inununopositive cells showed differences in size at different locations in the gland. At the periphery of the lobes the predominant cells were smaller and angular shaped, whereas in the center of die gland the majority of the cells were ovoid shaped. In the adult pituitary, the predominant LH-positive cells were ovoid in share and larger in size. Furthermore, 10% more LH-positive cells were observed in infantile pituitaries. On the basis of these data we propose that at the infantile period the male rat pituitary has two populations of LH-secretin g cells, one with adult secretory function and shape and a second with incr eased sensitivity to GnRH and with a morphology atypical of the adult cell. The results presented support the hypothesis that the infantile period is a transitional stage in the rat pituitary development.