Effects of ovariectomy, gonadal steroid replacement and photoperiod on plasma beta-endorphin in the ewe.
The effects of gonadectomy, photoperiod and ovarian steroid replacement on plasma beta-endorphin concentrations were studied in 2 experiments using mature ewes. In Experiment 1 ovariectomy resulted in an increased plasma beta-endorphin concentration. Changing the photoperiod from long to short daylength had little effect on beta-endorphin, but transfer from short to long photoperiod caused a fall in the beta-endorphin level. In Experiment 2 ovariectomy again caused an increase in plasma beta-endorphin. Treatment with progesterone, estradiol or a combination of both failed to reduce the level to preovariectomy values, although LH concentrations were reduced. No diurnal rhythmicity in beta-endorphin secretion was observed.
Durotoye
L A
LA
Department of Animal Physiology and Nutrition University of Leeds, Leeds LS2 9JT, UK.
Al-Gahtani
S
S
Fordham
D P
DP
Rodway
R G
RG