Oestradiol administration raises luteal LH receptor levels in intact and hysterectomized pigs

Summary.Occupied and unoccupied LH receptors in corpora lutea, and LH and progesterone concentrations in circulating plasma, were measured in non-pregnant gilts that had been treated with oestradiol-17β benzoate to prolong luteal function. Oestradiol benzoate (5 mg, administered on Day 12 after oestrus) delayed luteal regression and the decline in LH receptor levels at luteolysis and raised unoccupied receptor levels from 11·8 ± 1·14 fmol/mg protein on Days 10–15 after oestrus to 31·8 ± 3·26 fmol/mg protein on Days 15–21. There was no simultaneous rise in occupied receptor levels and occupancy decreased from 29·8 ± 3·01 to 11·5 ± 1·26%. Basal plasma LH concentrations were unchanged by oestradiol, but mean corpus luteum weight and plasma progesterone concentrations were slightly reduced. Oestradiol benzoate on Day 12 caused a similar increase in unoccupied receptor levels in gilts hysterectomized on Days 6–9 after oestrus, from 17·0 ± 5·83 to 34·5 ±6·00 fmol/mg protein, determined on Days 15–18. Plasma concentrations of LH and progesterone were unchanged by oestradiol. Unoccupied receptor levels in corpora lutea and plasma LH and progesterone were unaltered by hysterectomy in untreated gilts. Occupied receptor levels were not influenced by hysterectomy or oestradiol. It is concluded that oestradiol-17β raises luteal LH receptor levels by a mechanism independent of the uterus.