Effects of confinement stress on episodic secretion of LH in ovariectomized sheep

Episodic secretion of luteinizing hormone (LH) in ovariectomized ewes was evaluated before and during acute confinement and during several days of habituation to the same confinement. Plasma concentrations of LH were quantified in samples collected at 5-min intervals via indwelling jugular vein cannulae. Peaks in each time series of plasma LH were identified by a computer program (Pulsar) developed by Merriam and Wachter. In the first experiment, 6 ewes which had been familiarized with the sampling environment and procedures were abruptly moved into a confinement chamber midway through a 4- to 5-hour sampling. Compared with preconfinement sampling, average plasma LH concentrations as well as the incidence (average frequency) and amplitude of identified peaks of LH decreased. In the second experiment, 10 ewes which had not previously been sampled were transferred from their home pens directly into the confinement chamber for a 3- to 4-hour period of blood sampling. This procedure was repeated with the same 10 ewes on the following 2 days to assess the effect of habituation. The average frequency and amplitude of identified peaks of LH increased (p less than 0.05) in habituated ewes, but average plasma LH concentrations did not change. In summary, episodic secretion of LH was inhibited by the stress of initial confinement, but several days of habituation to the same daily periods of confinement minimized this inhibition and restored the episodic discharges of LH.