Androgen signalling during downregulation and recovery subsequent to 5-month deslorelin treatment

Slow-release GnRH agonist implants (SRI) are frequently used in small animal medicine to temporarily induce the downregulation of testicular endocrine and germinative function resulting in basal testosterone concentrations and infertility due to the arrest of sper-matogenesis. Treatment-induced effects are fully reversible; tes-tosterone is quickly restored. Recovery of spermatogenesis takes longer, but after 7–10 weeks first sperm are found in the ejaculates. Androgens act via androgen receptors (AR) and altered AR expres-sion might be associated with downregulation due to SRI and sub-sequent recovery. Besides, proteins involved in AR signalling, for example heat shock protein hSP 70 and 90, might be altered due to treatment. To gain further insights, healthy dogs were treated with a deslorelin SRI over 5 months, the SRI was removed surgically at 5 months and 4–5 dogs were castrated at implant removal (week, W 0) or W1, 2, 3, 4, 5, 6, 7, 8 or 10 weeks after SRI insertion. Testes of untreated healthy male dogs served as controls (CG). Gene expres-sions of AR, hSP70, hSP90 and hSPA8 were investigated and group- wise comparison was performed using GraphPad Prism. Expression of AR (ANOVA, p < .0001), hSP70 (Kruskal–Wallis, p < .0001), hSP90 (ANOVA , p < .01) and hSP8A (Kruskal–Wallis, p < .01) differed sig-nificantly with higher AR, hSP70, but lower hSPA8 expression in the down-regulated testis (W0) compared to later time points of recov-ery and CG. Further studies should clarify whether the differences are related to variable tissue composition or truly treatment-related, besides protein expression should be investigated.