Glucocorticoid metabolism and action in the rat epididymis
Date of Award
Doctor of Philosophy
School of Exercise and Health Sciences
Faculty of Computing, Health and Science
Dr Peter Roberts
Dr Peter Burton
Glucocorticoid hormones are known to be essential for numerous physiological processes and are released in response to stress, via negative feedback mechanisms on the HPA axis. In humans the main glucocorticoid is cortisol and in rats, corticosterone. Glucocorticoid levels in target tissues are regulated by the glucocorticoid receptor (GR), cortisol-binding globulin (CBG) and the two 11β -hydroxysteroid dehydrogenase enzymes (11 β-HSD-1 and 2) that interconvert active and inactive glucocorticoids. The 11 β-HSD-1 enzyme acts both as a reductase ( converting inactive cortisone to cortisol in humans and 11- dehydrocortisone to corticosterone in rats) and a dehydrogenase (inactivating glucocorticoids), although largely functions as a reductase in vivo. In contrast, 11 β-HSD-2 acts exclusively to inactivate excess cortisol or corticosterone allowing aldosterone to bind to the mineralocorticoid receptor (MR) in specific tissues.
Stress-related increases in active glucocorticoids may negatively affect male reproduction by decreasing testosterone levels in Leydig cells. Glucocorticoids have been suggested to have both pro-oxidative and anti-oxidative properties and oxidative stress is reported to contribute to impaired sperm maturation and infertility. Sperm mature and reach full fertilising potential as they pass through the epididymis and cells comprising the epididymal epithelium have essential roles in maintaining an optimal luminal fluid environment.
The 11 β-HSD-1 and 2 enzymes have been localised in the adult rat epididymis, suggesting that corticosterone may influence sperm maturation, however a precise role for glucocorticoids in the epididymis has not previously been investigated. Therefore, the aims of this thesis were to examine the postnatal developmental localisation of 11β-HSD-1 and 2, GR, MR and Na+K+-ATPase in the rat epididymis and investigate both a possible role for glucocorticoids in mediating oxidative stress during sperm maturation and the regulation of 11 β-HSD- 1 and 2 in the adult rat epididymis.
The results from the first study demonstrated 11 β-HSD-1, the GR and MR localisation in the epididymal epithelium from postnatal day 1 (pnd 1) and 11β HSD-2 and Na+K+-ATPase reactivity from pnd 15. At pnd 28 there was maximal immunoreactivity for both the GR and MR and 11β ~-HSD-1 and 2, coinciding with the differentiation of epididymal principal and basal cells and the preparation for the arrival of sperm in the lumen at puberty (pnd 40). Relative mRNA levels of 11β ~-HSD-1 and 2 were compared at pnd 28 and 75. Levels of 11β ~-HSD-1 mRNA were higher at pnd 75 than at pnd 28 (pp+K+-ATPase ), leading to epithelial cellular deterioration. In the epididymis this could disrupt ion and fluid transport and damage tight junctions forming the blood-epididymis barrier, having deleterious effects on sperm maturation. All treatments increased the absolute intensity (Al) of 4-HNE immunoreactivity (p+K+-ATPase Al (p
Collectively, the results suggest that an intricately regulated and finely balanced level of glucocorticoids are maintained, both during postnatal maturation of the rat epididymis and in the adult epididymis, to regulate epididymal cell differentiation and maturation, preserve appropriate ion and fluid transport processes and mediate levels of reactive oxygen species (ROS) required for normal sperm maturation. Furthermore, at excess levels, glucocorticoids may be detrimental to normal epididymal maturation and function, possibly causing epithelial oxidative stress and impaired sperm maturation.
LCSH Subject Headings
Glucocorticoids -- Physiological effect
Edith Cowan University. Faculty of Computing, Health and Science -- Dissertations
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Gladstones, G. H. (2009). Glucocorticoid metabolism and action in the rat epididymis. Retrieved from http://ro.ecu.edu.au/theses/1825