The postnatal ontogeny of gonadotroph cells in the female sheep: Developmental patterns of synthesis, storage and release of gonadotrophic hormones

Abstract

The aim of this study was to determine the developmental changes in the synthesis, storage and release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the hypophyseal gonadotroph cells from infancy to peripuberty of ovine ontogeny. An examination has been made in 15 infantile (12-, 15-week-old) and juvenile (22-, 30-week-old) ovary-intact sheep. Histomorphological and functional changes in the adenohypophyseal population of gonadotrophs were assayed with hybridohistochemistry, immunohistochemistry and radioimmunoassay. The percentage of the adenohypophyseal area (PAA) occupied by gonadotrophs containing LHβ-mRNA or FSHβ-mRNA was highest ( P < 0.05) in the 15-week-old sheep compared with the other stages. The gradual increase in the PAA occupied by immunoreactive (ir)-LHβ-cells from the 12th to 30th week of age was observed ( P < 0.05) and has been interpreted as the increase in the storage of LH. This histomorphological change was accompanied by the gradual increase in the LH pulse frequency from the 15th to 30th week of age ( P < 0.05). The PAA occupied by ir-FSHβ-cells was extremely high in the infantile sheep, and subsequently, low in the juvenile sheep ( P < 0.05). Altogether, similar patterns of pretranslational synthesis of the LHβ- and FSHβ-subunit but clearly different storage patterns of gonadotrophins were observed. The postnatal development of gonadotrophins seems to be determined by the progressive increase in the storage of LH until peripuberty and by the acute decrease in the storage of FSH during the infantile/juvenile shift. These findings imply the different intrahypophyseal regulation of LH and FSH posttranscriptional processing during the period of transition between infancy and peripuberty in female sheep.