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Microheterogeneity of pituitary follicle-stimulating hormone in male rats: differential effects of the chronic androgen deprivation induced by castration or androgen blockade

M. Simoni, G. F. Weinbauer, R. K. Chandolia, and E. Nieschlag

ABSTRACT

Testicular androgens are known to influence not only the secretion but also the bioactivity and molecular composition of pituitary FSH. In the present study, we investigated the effects of chronic androgen blockade and castration on the molecular heterogeneity of the gonadotrophin. Groups of male adult rats (five animals per group) received one of the following treatments: vehicle, the non-steroidal anti-androgens casodex (20 mg/kg per day) or flutamide (20 mg/kg per day), or castration. After 8 weeks, the animals were killed and individual pituitary homogenates fractionated by isoelectric focusing (IEF) on sucrose density gradients in the pH range 2·5–8. FSH was measured by radioimmunoassay (RIA) in the individual fractions and by in-vitro bioassay (Sertoli cell aromatase bioassay) in pools of fractions which were combined according to pH intervals of 0·5 units. Bioactive and immunoreactive FSH were also measured in sera and unfractionated pituitary extracts. Testosterone and inhibin were assayed in sera by RIA.

A significant increase in serum immunoreactive and bioactive FSH was demonstrated in flutamide-treated and castrated animals, whereas the pituitary content of bioactive FSH remained unchanged in the four groups. Serum testosterone and inhibin were undetectable in castrated animals and significantly increased in those treated with flutamide. By RIA, the IEF profiles of the flutamide-treated and castrated rats showed a significant reduction of the FSH isoforms with 3·5<pI<4, with a significant increase in the isoforms with pI>4 only in the castrated group. By bioassay, there was a significant decrease in the isoforms with 3·5<pI<4 in both casodex- and flutamide-treated animals, with no significant differences between the two groups. Castration caused a further significant shift in the relative distribution of FSH isoforms towards the less acidic components, with a significant increase in the isoforms with 5<pI<5·5 not attained by androgen blockade alone.

These results suggest that the effects of long-lasting castration on pituitary FSH heterogeneity cannot be entirely reproduced by the androgen blockade. Since inhibin, eliminated by castration but not by androgen blockade, is a major regulator of FSH in the male rat, we speculate that it might not only influence FSH secretion but also modulate its qualitative properties.

DOI:
https://doi.org/10.1677/jme.0.0090175
Volume 9: Issue 2,
Pages:
175–182 (8 total)
Free access

Chorionic gonadotrophin beta subunit mRNA but not luteinising hormone beta subunit mRNA is expressed in the pituitary of the common marmoset (Callithrix jacchus)

T Muller, M Simoni, E Pekel, CM Luetjens, R Chandolia, F Amato, RJ Norman, and J Gromoll

The pituitary gonadotrophins LH and FSH are responsible for regulation of gametogenesis in the testis and ovary. Chorionic gonadotrophin (CG), a third closely related glycoprotein hormone derived by gene duplication of the LHbeta gene and secreted by the placenta in primates, is essential for the rescue of the corpus luteum and maintenance of pregnancy. We have recently shown that marmoset (m) CGbeta mRNA is highly expressed in the pituitary of the common marmoset (Callithrix jacchus) and that LH is less active than human CG in activating the human LH receptor lacking exon 10. To investigate further which gonadotrophin is the actual ligand of the LH receptor (LHR) of the marmoset monkey that naturally lacks exon 10, we identified and characterised the genomic organisation of the mLHbeta gene and its expression. Intergenic PCR amplification of the region encompassing the mLHbeta and the mCGbeta genes revealed that, surprisingly, mCGbeta is located 20 kbp upstream of the LHbeta gene, whereas in other species the intergenic distance is approximately 2-3 kbp. Sequence analysis of the mLHbeta coding region showed 70% identity to mCGbeta and 90% identity to human LHbeta at the amino acid level. Both gonadotrophin beta subunits are present at the genomic level, but RT-PCR of pituitary and placental total RNA using specific oligonucleotides for mCGbeta and mLHbeta showed high expression of mCGbeta mRNA in both tissues, whereas LHbeta was expressed neither in the pituitary nor in the placenta. Thus mLHbeta mRNA is lacking in the marmoset pituitary. Immunohistochemistry of marmoset pituitaries showed that mCG was confined to the gonadotrophes, and partly co-localised in cells stained positively for FSH. Western blot analysis confirmed the presence of mCG in the pituitary. Northern blot analysis using mCGbeta as a probe displayed one transcript of 0.7 kb in the pituitary and detected two transcripts of 1.1 kb and 2 kb in the marmoset placenta. Our results suggest that, in the common marmoset, CG is the only gonadotrophin with luteinising function that is present in the pituitary. We postulate that, owing to an unknown mutational event in evolution, expression of mLH was completely abolished, and CG - which, unlike LH, acts normally even when exon 10 is missing from the LHR - took over its function.

DOI:
https://doi.org/10.1677/jme.0.0320115
Volume 32: Issue 1,
Pages:
115–128 (14 total)