Gene expression of ACTH, glucocorticoid receptors, 11βHSD enzymes, LH-, FSH-, GH receptors and aromatase in equine epididymal and testicular tissue

Abstract

Glucocorticoids (GCs) are important mediators of the stress response and have been implicated in the function and regulation of testicular functions in different species. In many tissues, intracellular glucocorticoid activity is controlled by either or both of the two known isoforms of 11β-hydroxysteroid dehydrogenase (11βHSD) type 1 and 2, which interconvert active and inactive GCs. Little is known about the effects of stress on fertility in the equine species. The main objective of the present study was to investigate the expression of receptors for GCs and adrenocorticotropic hormone [ACTH, melanocortin 2 receptor (MC2R)] as well 11βHSD1 and 11βHSD2 in male equine epididymal and testicular tissue. In addition, expression of aromatase P-450 and receptors for luteinizing hormone (LHR), follicle stimulating hormone (FSHR) and growth hormone (GHR) was studied. Reverse transcriptase PCR and quantitative real-time PCR were performed in tissue from the epididymis (caput and cauda) and testes collected from nine healthy mature stallions (age 4-10 years). mRNA for ACTH and GC receptors as well as 11βHSD1 and -2 were found in epididymal and testicular tissue. Expression of the genes studied was always positive in testicular tissue, while it was inconsistent in epididymal tissue. Quantitative gene expression in relation to β-actin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was significantly correlated (R = 0.403, p < 0.001). Quantitative PCR in relation to β-actin revealed significant differences in the gene expression of 11βHSD1, 11βHSD2, LHR, FSHR, MC2R and aromatase between tissue collected from caput epididymidis, cauda epididymidis and testicular parenchyma (p < 0.05). With GAPDH, differences between tissues were significant for 11βHSD1, 11βHSD2 and MC2R (p < 0.05) In addition, high concentrations of mRNA of aromatase and receptors of LH and FSH were found in testicular tissue, while a pronounced expression of GH receptor was present in epididymal tissue. The results support the hypothesis of an interaction between the pituitary-adrenal axis and testicular function in the stallion.