CASTRATION INDUCES TIME-DEPENDENT CHANGES IN THE FOLLICLE-STIMULATING-HORMONE BETA-SUBUNIT MESSENGER RIBONUCLEIC ACID-CONTAINING GONADOTROPE CELL-POPULATION

We have previously observed 3- to 10-fold increases in pituitary LH β -subunit mRNA levels in the rat 28 days after castration. These changes correlate with increases in percentages and areas of cells that bear the LHβ mRNA and with the amount of label for mRNA per cell. In contrast, FSHβ mRNA levels increase 2.5- to 4-fold 7-14 days after castration, decline to near-intact levels 28 days postcastration, and rise 4.5-fold by 96 days postcastration. The purpose of this study was to determine morphological correlates of these changes in FSHβ mRNA levels. Dispersed pituitary cells from intact and castrated rats were analyzed for FSHβ and LHβ mRNAs and protein by in situ hybridization techniques and immunocytochemistry, respectively. In intact animals over 79% of pituitary cells labeled for FSHβ mRNA were small (area <150 μm2). However, 7 days after castration, the average area of labeled cells increased 4fold (80% were over 200 μm2in area), without a significant change in percentages of FSHβ mRNA-containing cells. The amount of mRNA per cell (as measured by area of label per cell) increased 6-fold. Fourteen days after castration, the average area of cells containing FSHβ mRNA decreased to 2 times that in intact rats (48% were >200 μm2). The percentage of labeled cells increased from 11% (intact) to 20%. Furthermore, the dual labeling studies showed that 37% of these FSH cells were monohormonal (detected by FSHβ mRNA, but not LHβ antigen) compared with 23% in intact rats. At this same time, the FSH cells exhibited a decrease in the amount of mRNA per cell. In 21- to 84-day castrates, average areas of FSHβ mRNA remained at 2-2.5 times the areas of cells from intact rats. In addition, 21 days after surgery the percentages of labeled cells and amount of FSHβ mRNA per cell declined to those in intact rats. A greater proportion was multihormonal (only 15% expressed FSHβ mRNA but not LHβ antigens). At 84 days there were 2fold increases in the percentages of labeled cells and the density of label, which correlate with the recovery in mRNA levels assayed at 96 days. Thus, factors that contribute to the early rise in FSHβ mRNA include increases in the amount of mRNA per cell, which coincides with increased cell area. Factors that contribute to the decline in FSHß mRNA include decreases in the percentages and area of labeled cells and the amount of mRNA per cell. The increase in the percentage of small cells bearing oniy FSHβ mRNA (monohormonal) at 14 days suggests that small cells may proliferate or be recruited to provide a continued supply of mature FSH-secreting gonadotropes. This, in turn, supports the high FSH secretory activity assayed after castration. © 1990 by The Endocrine Society.