Testosterone is an androgenic hormone produced by the testis, ovary and in small amounts by the adrenal gland.
As well as being responsible for male secondary sexual development on reproductive organs, testosterone also is responsible for positive bone, skin and cardiovascular effects
Levels vary with age and season changes, being highest in spring and autumn.
In males, estrogen has a synergistic role critical for proper development and maintenance of testicular function, particularly the regulation of epididymal fluid reabsorption, fluid osmolality and semen pH.
Testosterone levels rise in pre-pubertal male dogs, reaches a peak at puberty (6 - 12 months of age) and subseuqently plateaus for some years, with a general decline toward geriatric age.
The normal testosterone range in male dogs is 0.10 - 0.94 ng/ml.
Testosterone is also converted to the most potent dihydrotestosterone by 5-α-reductase within the prostate and results in prostate enlargement at puberty. Testosterone consequently plays a role in the development of age-related prostate hyperplasia.
Abnormally high levels of testosterone are observed in hyperadrenocorticism, hermaphroditism, persistent Müllerian duct syndrome, cryptorchidism, luteomas, hypospadias (78, XY) and trisomy-X.
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