Summary. Iodinated FSH was injected to 18- and 36-day-old rats of 3 strains (03, 04 and 12) with different sensitivity to FSH (12 < 03 < 04) and autoradiography was performed on histological sections of the labelled ovaries. Specific labelling was quantified by microphotometry on histological slides, on granulosa cells of individual follicles with different sizes (> 80 μm diameter) and qualities.
In small preantral follicles (< 160 μm diameter) the labelling was low and homogeneous within the granulosa; it increased between 18 and 36 days of age in the 3 strains. At 36 days, ovaries were characterized by the presence of large preantral and antral follicles with a higher labelling in the outer layers of granulosa (near the theca), compared to the inner layers. In definitely atretic follicles, a loss of binding sites was detected in the outer layers. In rats of Strains 03 and 04, the number of binding sites for FSH in the outer layers of granulosa of follicles with a diameter of > 160 μm increased with follicular size; no change was detected in follicles of Strain 12 rats. The low number of binding sites for FSH and the lack of terminal maturation which characterized the follicles of strain 12 rats can be related to the poor and delayed follicular development, the low sensitivity to exogenous FSH and the low fertility of the animals of this strain.
Keywords: FSH binding; granulosa; follicular growth; rat ovary; quantitative autoradiography; strains of rats
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