Pituitary and testicular endocrine responses to exogenous gonadotrophin-releasing hormone (GnRH) and luteinising hormone in male dogs treated with GnRH agonist implants

Abstract

The present study tested whether exogenous gonadotrophin-releasing hormone (GnRH) and luteinising hormone (LH) can stimulate LH and testosterone secretion in dogs chronically treated with a GnRH superagonist. Twenty male adult dogs were assigned to a completely randomised design comprising five groups of four animals. Each dog in the control group received a blank implant (placebo) and each dog in the other four groups received a 6-mg implant containing a slow-release formulation of deslorelin (d-Trp6-Pro9-des-Gly10-LH-releasing hormone ethylamide). The same four control dogs were used for all hormonal challenges, whereas a different deslorelin-implanted group was used for each challenge. Native GnRH (5 microg kg(-1) bodyweight, i.v.) was injected on Days 15, 25, 40 and 100 after implantation, whereas bovine LH (0.5 microg kg(-1) bodyweight, i.v.) was injected on Days 16, 26, 41 and 101. On all occasions after Day 25-26 postimplantation, exogenous GnRH and LH elicited higher plasma concentrations of LH and testosterone in control than deslorelin-treated animals (P < 0.05). It was concluded that, in male dogs, implantation of a GnRH superagonist desensitised the pituitary gonadotrophs to GnRH and also led to a desensitisation of the Leydig cells to LH. This explains, at least in part, the profound reduction in the production of androgen and spermatozoa in deslorelin-treated male dogs.

Clinical Use of GnRH Agonists in Canine and Feline Species

“…Although the original stimulating effect causes serum FSH and LH concentrations to rise from 20 min after treatment start, with a peak after 40 min (Junaidi et al. 2007), these values return to normal in the next 5 h then collapse on average 2–9 days later (Vickery et al.…”

“…2007), these values return to normal in the next 5 h then collapse on average 2–9 days later (Vickery et al. 1984; Hoffmann 2005; Junaidi et al. 2007).…”

“…In case of daily administration of the GnRH agonist, FSH and LH levels collapse after 4 days (Vickery et al. 1984; Junaidi et al. 2007).…”

Long-term contraception in a small implant

“…2 This results in a lack of synthesis and/or lack of release of the gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH), inducing temporary infertility in treated individuals. 3 …”

The effects of a slow release GnRH agonist implant on male rabbits

“…As a consequence of reduced testosterone concentrations, testis and prostate volumes are reduced and semen quality is significantly affected with an arrest of spermatogenesis with development not occurring beyond the spermatogonia/spermatocyte stages. Although the available product containing deslorelin is licensed for the temporary suppression of fertility in adult and intact male dogs and male ferrets only (Ema, 2012) and all above described effects are well-known to occur (Trigg et al, 2001;Junaidi et al, 2003Junaidi et al, , 2007Junaidi et al, , 2009aSchoemaker et al, 2008;Romagnoli et al, 2012;Van Zeeland et al, 2014). Offlabel use of sustained released GnRH agonist implants has been effective for temporary hormonal castration in tom cats (Goericke-Pesch et al, 2011a, 2013b, 2014Novotny et al, 2012), boars (Kauffold et al, 2010), and also in model animals such as rats (Grosset et al, 2012;Edwards et al, 2013) or (captive) wildlife animals such as coyotes (Mac Gregor et al, 2013), red pandas (Koeppel et al, 2014), sea otters (Larson et al, 2013) and cheetahs (Bertschinger et al, 2006).…”