Compensatory development of immature LH cells after long-term gonadectomy: an immunocytochemical, electron microscopic and cell count study.

Following long-term castration of male rats (for 3, 6, 12 and 18 months), some populations of five gonadotroph types, (i.e., immature cell, types III, III/IV, IV and so-called signet-ring cell, appeared in the pituitary glands. Their ultrastructures were electron microscopically observed after immunohistochemical identification of them using anti-rat LH beta serum. In unoperated control rats, 60 days old, the predominant III/IV type was intermingled with some populations of III and IV types, but no immature LH cells or signet-ring cells were detected among them. In the present observation not all of the gonadotroph types turned into signet-ring cells. Immature small LH cells containing a few small secretory granules began to appear (2.0%) at 3 months, and had increased to a maximum (52.5%) at 18 months. The percentage of the signet-ring cells was high (24.1%) at 3 months, but reduced (2.4%) at 18 months. High populations of small, oval and immature LH cells are assumed to occur as a consequence of mitotic division of the most of the immature LH cells. This may compensate for the loss of signet-ring cells in order to maintain the high serum LH and FSH concentrations after long-term castration.