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  • Title: Ontogeny of the inhibitory guanine nucleotide-binding regulatory protein in the rat testis: mRNA expression and modulation of LH and FSH action.
    Author: Eskola V, Rannikko A, Huhtaniemi I, Warren DW.
    Journal: Mol Cell Endocrinol; 1994 Jun; 102(1-2):63-8. PubMed ID: 7926274.
    Abstract:
    The ontogeny of function and mRNA expression of the inhibitory guanine nucleotide-binding regulatory protein (Gi) was studied in the rat testis. Dispersed testis cells of animals aged 8, 15, 20 and 30 days were cultured with or without 100 micrograms/l pertussis toxin (PT) for 24 h. The cells were then cultured for another 24 h with medium only, cholera toxin (CT), PT, or their combination, and the amount of testosterone and cAMP production was measured. PT preincubation increased CT-stimulated cAMP production at all ages, thus indicating the presence of a functional Gi-protein in the postnatal testis. However, when testosterone production was measured, the enhancing effect of PT was absent at the age of 8 days only, indicating that Leydig cells at this age did not have functional Gi-protein. We then cultured 2-day-old and 8-11-day-old testis cells, after 24 h pretreatment with PT, in the presence of ovine follicle-stimulating hormone (FSH) (1 mg/l). The FSH-stimulated cAMP production was enhanced at both ages, thus indicating the presence of a functional Gi-protein in neonatal Sertoli cells. In Northern blot analyses, fetal and postnatal testis tissue had very similar levels of G alpha i2 and G alpha i3 mRNAs; the mRNA level of Gi1 in Northern blots remained low compared to those of Gi alpha 2 and Gi alpha 3. In conclusion, the Gi protein appears in the developing rat testis in utero but the activity first seems to be confined to non-Leydig cells including the Sertoli cell. In Leydig cells, the functional Gi-protein appears between days 8-15 post partum. This finding may be related to the fact that the fetal-neonatal population of Leydig cells possesses a high steroidogenic capacity and an apparent lack of the ability to respond to high gonadotropic stimulation with LH receptor down-regulation and steroidogenic enzyme desensitization.
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