Plasma Concentrations of Luteinizing Hormone and Prolactin in the Ovariectomized Ewe during Induced Hyperthermia

The effect of induced hyperthermia on the basal as well as estradiol-induced secretion of luteinizing hormone (LH) and on prolactin (PRL) secretion was studied in 12 ovariectomized ewes exposed every 14 days to 3 day treatment periods. Ambient conditions of dry bulb and dew point temperatures were adjusted to result in rectal temperatures that were either normal (control) or an average of 1.2°C hyperthermic (experimental). Each ewe served as its own control in a switchback experimental design. On Day 2 of the 3 day treatment period, blood plasma was sampled at 10 min intervals between 0900 and 1300 h to characterize episodic patterns of LH. At 1800 h on the same day, 50 µg estradiol-17β (E 2 β) was injected i.m. to provoke a preovulatory-like surge of LH on Day 3. Plasma concentrations of LH and PRL were determined in samples collected at 60 min intervals between 0800 and 1600 h on Day 3. Induced hyperthermia caused a 4-fold increase in plasma PRL on Day 3 (P