Cryptorchid testis
Keywords: stallion, equine, testosterone, hCG, cryptorchid, epididymis, testis, histology
A left sided cryptorchid testis from a four year old Quarter horse stallion. Note the small size of the testis (about 20 to 30% of the volume of a normal testis) compared to the normal testis. This is due mainly to the absence of spermatogenesis. Both testes are shown here in their normal orientation. The retained testis lay completely within the abdomen, adjacent to the internal inguinal opening.
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Below. one of two cryptorchid testes, removed from the abdomen, proximal to the inguinal canal. The inset images show histology of tissue sample from the epididymis and the testes; discussed later together with full sized images.
| Spermatogenesis will not occur in most mammals at normal body temperature. Exceptions to this rule includes Cetaceans (whales and dolphins), Sireana (manatees and dugongs) and of course, elephants. The reason for this is not known but most mammals with abdominal testes are marine animals; in that context, elephants are thought to have evolved fairly recently into land dwellers. |
The image below shows seminiferous tubules in a peri-puberal cryptorchid stallion. Interestingly, it is very similar to the situation in a normal peri-puberal stallion, suggesting that increased body temperature only begins to interfere with testis function after puberty; especially with regard to spermatogenesis. There are two types of spermatogonia here, type a (labeled spermatogonia) and b, with type b generally being smaller and having eccentric nuclei. However, one is unable to differentiate with certainty between the two types without immunohistochemistry. In older cryptorchid animals, even the spermatogonia degenerate, resulting in what is known as a "Sertoli-only" syndrome. The basement membrane in this case is already occupied mostly by Sertoli cells.
The author owes a debt of gratitude to Dr Minjung Yoon (mjyoonemail@gmail.com) for his assistance in understanding the cytology in this image.
Although common consideration is given to suppression of spermatogenesis in cryptorchids, there also appear to be detrimental effects of cryptorchidism on the function of Leydig and Sertoli cells. This becomes apparent after experimental cryptorchidism, when there is an increase in both FSH and LH production. Respectively, these are indicators of suppressed Sertoli cell and Leydig cell function. With regard to testosterone production by the Leydig cells, there is considerable overlap between normal and cryptorchid animals but there is to a tendency to decreased testosterone response to hCG stimulation in cryptorchids. Also, there are pathological differences in the ultrastructure of the Leydig cells (cell size, golgi apparatus etc) between normal and cryptorchid animals. Collectively, these findings lend the impression of general compromise in cryptorchid testes.
The image above shows the cauda epididymis in this specimen to be devoid of spermatozoa; just as one would expect in a cryptorchid animal.
Note the stereocilia in the principal cells. These are probably important for sperm transport along the epididymis. Structures known as apical blebs become detached from the luminal surface and as seen here, they form vesicles that burst in the lumen, releasing their products. In fact, more than 200 different proteins are secreted in stallions by these cells. The epididymal epithelium also controls osmotic pressure, ion balance and a supply of androgen-dependent substrates that are essential for sperm survival. Also note the thick layers of smooth muscle in this region of the epididymis. Smooth muscle becomes progressively thicker and more highly innervated by the sympathetic system as one moves from the caput towards the cauda epididymis. Interestingly, it has been shown that temperature affect the function of this muscle as well. In normal animals when body temperature is generally elevated, the smooth muscle layers contract more frequently than otherwise. Therefore more immature sperm are likely to be present in the ejaculate than otherwise.
Selected references
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Cox, J.E. et al 1973. Testosterone in normal, cryptorchid and castrated male horses. Equine Vet. J. 5:85-90
Fouchécourt, S. et al.2000. Stallion epididymal fluid proteome: qualitative and quantitative characterization; secretion and dynamic changes of major proteins. Biol. Reprod. 62:1790-1803
Jones, R. 2004. Sperm Survival Versus Degradation in the Mammalian Epididymis: A Hypothesis.
Biol.Reprod.71:1405-1411
Kerr, J.B. et al 1979. Alterations of the Fine Structure and Androgen Secretion of the interstitial cells in the experimentally cryptorchid rat testis. Biol reprod. 20: 409-422
Lee, P.A. et al. 2001 Inhibin B: Comparison with indexes of fertility among formerly cryptorchid and control men. J Clin Endocrinol Metab.86:2576-2584
Lee, P.A. et al 2002. Leydig cell function after cryptorchidism: Evidence of the beneficial result of early surgery. Pediatric Urology. 167:1824-1827
López, M.L. et al. 1989. Cytochemical and ultrastructural characteristics of the stallion epididymis (Equus caballus).J Submicrosc Cytol Pathol. 1989 Jan;21(1):103-20.
Robaire, B. et al. 2006 Chapter 22. The Epididymis. In Knobil and Neill’s Physiology of Reproduction, 3rd Ed. Ed. Neill, J.D. Elsevier ISBN-13: 978-0125154000 and ISBN-10: 0125154003
Short, R.V. et al. 1967. Male reproductive organs of the African elephant, Loxodonta Africana.
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