The proliferation of gonadotropes in the anterior pituitary of the castrated male rat was examined immunohistochemically after colchicine treatment. The results show a more than 10-fold increase in mitotic frequency in gonadotropes 1 or 2 weeks after castration, as compared with controls. This result explains the increase in the population of immunoreactive LH cells in castrated male rats. The gonadotropes decreased significantly 1 month after castration. The mitotic activity of gonadotropes was almost completely suppressed in castrates implanted with a silastic tube filled with testosterone.
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