A Study of Spermatogenesis in the Dog, With Specific Reference to the Role of the Leydig Cell

The work included in this thesis describes studies in the spermatogenic process in the dog, and the approach used was to attempt supression of LH and testosterone in the testis and study the mechanisms affected by this interference to the normal testicular environment. The first two dogs were treated with an unsuccessful progesterone implant and then with subcutaneous injections of Medroxyprogesterone acetate, the results did not show an effect in the circulating blood plasma levels of either LH or testosterone, or in the testicular tissue. However it appeared to have an effect at epididymal level as seen by changes to the epithelium and the spermatozoa found in this section. Therefore GnRH agonists were considered. A Nafarelin derivative administered by osmotic subcutaneous pumps was used in two dogs, however, due to problems with the pumps, the treatment was ineffective until changed to daily subcutaneous injections. The results of this treatment showed that it did produce testicular changes which were reflected on the supression of LH but more so of testosterone. There was a length of treatment related change in the testicular tissue, as evidenced by the partial or total elimination of germ cells from the seminiferous tubules. To further study the changes at testicular level, the isolation, purification and culture of Leydig cells was also undertaken. For this purpose testicular tissue from dogs, rats and mice was used. The results indicated that the procedure for handling the cells was producing viable cells capable of responding to exogenous treatments when assessed by their testosterone producing capacity. Subsequently the techniques thus developed were applied to the Leydig cells that were obtained from dogs and mice that were treated with daily subcutaneous injections of Nafarelin acetate. As far as the testosterone produced by the Leydig cell cultures from the two treated dogs the results were inconclusive as they had opposite responses to what was expected. However the results on the detection of testicular GnRH-like receptors suggests that the GnRH agonist acted directly on the pituitary and not in the gonad as is the case in the rat. It was concluded that a larger animal sample is required to further understand the mechanisms involved in testicular function in the dog