We investigated the relationship between gap junction formation and the sex steroids testosterone, progesterone and 17β-estradiol in the anterior pituitary glands of castrated male rats and ovariectomized female rats. Male and female 30-day-old Wistar-Imamichi strain rats were castrated or ovariectomized, and 30 days later they were subcutaneously injected with the above sex steroids. They were divided into six groups according to the injected materials: sesame oil (control), testosterone, progesterone, 17β-estradiol, testosterone with 17β-estradiol, and progesterone with 17β-estradiol. Five rats from each group were sacrificed 1, 2, 3, 4 and 5 days after the injections, and the anterior pituitary glands were prepared for observation by transmission electron microscopy. We quantified the number of follicles and gap junctions and calculated the rate of occurrence of gap junctions as the ratio of the number of gap junctions existing between folliculo-stellate cells per intersected follicle profile in electron photomicrographs. The administration of testosterone to castrated male rats increased the rate of gap junctions between folliculo-stellate cells; however, progesterone and 17β-estradiol did not affect the formation of gap junctions. The administration of progesterone to ovariectomized female rats increased the rate of gap junctions between folliculo-stellate cells; this progesterone effect was prevented by the simultaneous administration of 17β-estradiol, which by itself did not affect the rate of gap junctions between folliculo-stellate cells. These observations indicate that the formation of gap junctions within the anterior pituitary gland is regulated differently by sex steroids in castrated male and ovariectomized female rats.
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