Testosterone Pretreatment and the Response of Pituitary LH to Gonadotropin‐Releasing Hormone (GnRH) in the Male Dog

Abstract

To characterize the effects of testosterone (T) pretreatment on the resenous gonadotropin‐releasing hormone (GnRH), intact male dogs were injected subcutaneously with either oil or 500 μMg/kg of T in oil at 1, 3, 6, 12, or 24 hours prior to intravenous GnRH administration (50 ng/kg). The pre‐GnRH levels of plasma LH were reduced in all groups of T‐treated dogs except in animals given T 1 hour before GnRH. The concentrations of plasma LH during both the peak‐response period and the recovery period following GnRH administration in animals injected with T did not differ from those in animals injected with oil. These results indicate that T pretreatment has no effect on the ability of the pituitary to respond to exogenous GnRH at all time periods tested, and imply that direct feedback of T on the pituitary may not be acutely involved in steroid negative feedback in the male dog. Unexpectedly, however, there was some indication that the time of injection of either oil or T could affect the response of the pituitary to GnRH, and this may represent a stress phenomenon.

GnRH in the male dog: dose-response relationships with LH and testosterone

“…Data on the hypothalamus-pituitary-testis (HPT) axis in the dog, however, are scarce (Falvo and Vincent, 1980;. In male dogs a linear trend in LH responses was observed after intra¬ venous administration of GnRH at doses varying from 0.005 to 0.25 µg kg~T (Falvo et al, 1982), but, to our …”

The function of the pituitary‐testicular axis in dogs prior to and following surgical or chemical castration with the GnRH‐agonist deslorelin

“…GnRH (buserelin) administration induced a significant increase in the plasma concentrations of LH, FSH, oestradiol and testosterone in the intact male dogs. Results were largely similar to previously reported data (Falvo et al, 1982 ; Günzel‐Apel et al, 1994 ; Jones et al, 1976 ; Junaidi et al, 2007 ; Knol et al, 1993 ; Purswell & Wilcke, 1993 ), but instead of a short‐lived increase in the plasma LH concentration after GnRH administration that was observed in most other studies, plasma LH was still increased at T = 60 min in the present study, probably caused by the longer half‐life of buserelin relative to native GnRH (Padula, 2005 ). LH is the main regulator of testosterone secretion, and the interval between increase of plasma LH and plasma testosterone has been shown to be 30–60 min in dogs (DePalatis et al, 1978 ; Günzel‐Apel et al, 1994 ; Knol et al, 1993 ).…”

Effects of gonadotropin-releasing hormone administration on the pituitary-gonadal axis in male and female dogs before and after gonadectomy

“…In OVX bitches, GnRH administration is reported to increase only plasma LH and not FSH, estradiol, or progesterone [10,15,22,23]. Similarly, in male dogs with functional gonadal tissue, administration of GnRH causes a rise in plasma LH and testosterone [21,24,25], but not FSH [24].…”