What Happens in Male Dogs after Treatment with a 4.7 mg Deslorelin Implant? I. Flare up and Downregulation

Abstract

Although registered since 2007, knowledge about changes in testosterone concentrations (T), testicular and prostatic volumes (TV, PV) and semen quality, as well as the time point of infertility following treatment with a 4.7 mg deslorelin (DES) slow-release implant, is limited. Therefore, seven sexually mature male dogs were treated with DES (TG); three male dogs treated with saline served as controls (CG). The study assessed local tolerance, TV, PV, semen parameters and T subsequent to GnRH/hCG stimulation in regular intervals. Local tolerance was good. In TG, T was increased right after treatment, but decreased four hours afterwards. Subsequently, TV, PV, semen quality and T decreased over time in TG, but not CG. T was basal (≤0.1 ng/mL) from D28 onwards. Response to GnRH/hCG stimulation was variable, with two TG dogs having increased T post-stimulation on all study days independent of pre-treatment concentrations. A(zoo)spermia in TG was observed from D35–D77 in all seven dogs. Whereas treatment was still effective in six TG dogs five months after implant insertion, it was fully reversed in one dog in terms of T and spermatozoa on the last examination. These results indicate high variation in individual dogs, necessary to consider when advising dog owners.

What Happens in Male Dogs after Treatment with a 4.7 mg Deslorelin Implant? II. Recovery of Testicular Function after Implant Removal

“…We recently presented the results of the first five months after treatment until implant removal [ 10 ], whereas the results obtained after implant removal are included in the current paper. All of the methods were described in detail recently [ 10 ].…”

“…Whereas the initial period subsequent to treatment with a 4.7 mg deslorelin implant was recently characterized in detail [ 10 ], until now, the restart and recovery of endocrine and germinative testicular function following treatment are not well characterized. Whereas very few studies are available in dogs, all either referring to the 6 mg deslorelin [ 11 ] or to other GnRH agonist SRIs [ 2 , 12 , 13 ], indicating the full reversibility of treatment-induced effects on testicular endocrine and germinative function, some information about the reversibility of 4.7 mg deslorelin induced effects is available in male and female cats [ 14 , 15 , 16 , 17 , 18 , 19 ].…”

The use of a 4.7 mg deslorelin slow release implant in male dogs in the field

“…Preparation of testicular tissues was as previously described [5,15,16]. Briefly, the testes were cut longitudinally immediately after removal and approximately 0.5 cm 3 parenchyma samples were taken from the area between the tunica albuginea and the mediastinum testis.…”

“…Following an initial short-term stimulation of gonadotropin secretion, sustained exposure to GnRH reduces GnRH-stimulated gonadotropin secretion through GnRH receptor down-regulation, internalization, and signal uncoupling [1][2][3][4]. As a consequence of treatment, testicular endocrine and germinative function is downregulated with basal testosterone concentrations, a significant reduction in testicular and prostatic volume and infertility due to an arrest of spermatogenesis resulting in azoospermia or even aspermia [5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”

“…Although the 4.7 mg deslorelin SRI was registered already in 2007 and 2 recent studies described in detail the effects on pituitary-testicular axis and germinative testicular function during 5 months of treatment [16] and subsequent implant removal and recovery of testicular function [15] in 7 male Beagle dogs, but data in larger field populations are still missing in the literature and currently limited to the data from the registration studies [7]. Besides, although confirming the suitability of the 4.7 mg deslorelin-containing SRI as a reversible alternative to surgical castration in general, a considerable variation in terms of onset and duration of effect was identified even in this homogenous Beagle population [15,16]. This clearly supports the need for a larger field study including dogs of different breeds and body weights aiming to the parameters were significantly reduced compared to pre-treatment in the respective dogs.…”