Testosterone

From Dog

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[1]

In male dogs, testosterone is also responsible for changes within the basolateral nuclear group of the amygdaloid body associated with aggression[2].

Levels vary with age and season changes, being highest in spring and autumn[3].

Testosterone is converted to estrogen in both male and female dogs and regulation of body levels of these androgens is controlled by the pituitary-gonadal axis regulation via GnRH, LH and FSH[4][5].

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[6].

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[7].

The normal testosterone range in male dogs is 0.10 - 0.94 ng/ml.

Low levels of testosterone in male dogs is associated with reduced libido, erectile dysfunction[8], lower sperm production and consequent infertility.

Testosterone is also converted to the most potent dihydrotestosterone by 5-α-reductase within the prostate and results in prostate enlargement at puberty[9]. Testosterone consequently plays a role in the development of age-related prostate hyperplasia[10].

Abnormally high levels of testosterone are observed in hyperadrenocorticism[11], hermaphroditism, persistent Müllerian duct syndrome[12], cryptorchidism[13], luteomas, hypospadias (78, XY)[14] and trisomy-X.

Low testosterone levels in male dogs is commonly observed in neuters, hypothyroidism, hormone-responsive dermatoses, Sertoli cell tumors and with exogenous use of deslorelin[15].

References

  1. Perusquía M & Stallone JN (2010) Do androgens play a beneficial role in the regulation of vascular tone? Nongenomic vascular effects of testosterone metabolites. Am J Physiol Heart Circ Physiol 298:H1301–H1307
  2. Jacobs C et al (2006) Increased number of neurons expressing androgen receptor in the basolateral amygdala of pathologically aggressive dogs. J Vet Med A Physiol Pathol Clin Med 53(7):334-339
  3. Martins MI et al (2002) The effect of season on serum testosterone concentrations in dogs. Theriogenology 66(6-7):1603-1605
  4. Buijtels JJ et al (2012) Disorders of sexual development and associated changes in the pituitary-gonadal axis in dogs. Theriogenology 78(7):1618-1626
  5. de Gier J et al (2012) Effects of gonadotropin-releasing hormone administration on the pituitary-gonadal axis in male and female dogs before and after gonadectomy. Theriogenology 77(5):967-978
  6. Hess RA et al (2011) Estrogen and its receptors in efferent ductules and epididymis. J Androl 32(6):600-613
  7. Pathirana IN et al (2012) Plasma insulin-like peptide 3 and testosterone concentrations in male dogs: changes with age and effects of cryptorchidism. Theriogenology 77(3):550-557
  8. Zhang XH et al (2011) Update on corpus cavernosum smooth muscle contractile pathways in erectile function: a role for testosterone? J Sex Med 8(7):1865-1879
  9. Shidaifat F et al (2009) Age-dependent expression of 5alpha-reductase and androgen receptors mRNA by the canine prostate. Physiol Res 58(1):155-158
  10. Wilson JD (2011) The critical role of androgens in prostate development. Endocrinol Metab Clin North Am 40(3):577-590
  11. Hill KE et al (2005) Secretion of sex hormones in dogs with adrenal dysfunction. J Am Vet Med Assoc 226(4):556-561
  12. Whyte A et al (2009) Malformations of the epididymis, incomplete regression of the mesonephric tubules and hyperplasia of Leydig cells in canine persistence of Müllerian duct syndrome. Anim Reprod Sci 115(1-4):328-333
  13. Tamminen TM et al (2012) A polyorchid dog. Reprod Domest Anim 47(2):e26
  14. Dianovský J et al (2013) Disorder of sexual development in a Yorkshire terrier (78, XY; SRY-positive). J Appl Genet Feb 2
  15. Polisca A et al (2013) Clinical Efficacy of the GnRH Agonist (Deslorelin) in Dogs Affected by Benign Prostatic Hyperplasia and Evaluation of Prostatic Blood Flow by Doppler Ultrasound. Reprod Domest Anim Jan 16