Reproduction and thyroid function in red deer (Cervus elaphus) hinds

Abstract

This experiment was conducted to investigate the effect oestrogens have upon thyroid and pituitary responsiveness to stimulation by thyrothropin-releasing hormone (TRH) in the red deer (Cervus elaphus) hind. The first group of hinds, consisting of three ovariectomized and three entire hinds, were subjected to a TRH challenge (5 µl TRH in 2 ml saline solution) at 0800 h on 17 March 1993. Blood samples were collected at -60, -30, -15, 0, 5, 10, 15, 30, 45, 60, 90 and 120 minutes after the TRH injection. This procedure was repeated on a second group of hinds, consisting of three ovariectomized and three entire hinds, at 0810 h the following day. The entire group of hinds (n=6) exhibited a significantly higher mean plasma T₃ response to the TRH challenge compared with that of the ovariectomized group of hinds (peak values = 2.86 ± 0.55 ng.ml⁻¹ and 2.61 ± 0.55 ng.ml⁻¹ respectively). The ovariectomized hinds had a non-significantly higher mean basal T₃ concentration compared with that of the entire hinds before the TRH challenge (2.32 ± 0.63 ng.ml⁻¹ and 2.18 ± 0.40 ng.ml⁻¹ respectively). The entire hinds also exhibited a significantly higher mean plasma prolactin response compared with that of the ovariectomized hinds (42.70 ± 65.62 ng.ml⁻¹ and 7.33 ± 17.82 ng.ml⁻¹ respectively), however there was no significant difference between the mean plasma basal prolactin concentrations between the two groups before the TRH challenge. There was no significant response of mean plasma LH concentrations in either the ovariectomized or entire group of hinds after the TRH challenge. However there was a small non-significant rise in mean plasma LH concentrations immediately following the TRH injection in both the ovariectomized and entire group of hinds. In conclusion, results from this study demonstrate that oestrogens enhance the thyroid glands and pituitary gland respo~siveness to TRH with respect to T₃ and prolactin release respectively in the red deer hind.