Effects of Hypothalamic and Hypophysial Estrogen Implants on Pituitary Gonadotrophic Cells in Ovariectomized Rabbits

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Abstract
Minute amounts of estradiol benzoate were implanted into the basal hypothalamus or anterior hypophysis in ovariectomized New Zealand White rabbits. Autopsy was performed 60 days later. For cytologic study of the rabbit anterior hypophysis new modified aldehyde fuchsin (AF) (Halmi) and periodic acid Schiff (PAS)-methyl blue methods were used. Two types of basophils could be differentiated, AF-positive basophils and AF-negative basophils, the latter of which were shown to be gonadotrophs. PAS purple cells were identified as AF-negative basophils in the rabbit. The percentage of AF-negative basophils was 5.26±0.47% in ovariectomized control rabbits with blank tubing implants. When estrogen was implanted in the posterior median eminence-basal tuberal region of the hypothalamus (PME), increase in AF-negative basophils was markedly inhibited, resulting in subnormal numbers (0.66±0.17%). Little inhibition of increase in AF-negative basophils was seen after estrogen implantation into the hypophysis (3.67±0.35%), mammillary body (4.76%) or anterior median eminence (2.93%). Furthermore, PME estrogen prevented hypertrophy of the AF-negative basophils, whereas the direct action of estrogen on the hypophysis failed to prevent these “castration” cells from attaining their characteristic size. The weight of the hypophysis was significantly elevated in the PME-estrogen group, but not in the pituitary- estrogen group. The results indicate that AF-negative basophils are the gonadotrophic cells in the rabbit and that the influence of estrogen on these cells is exerted primarily on PME.