Effect of adrenalectomy on LH release in sheep during the anoestrous season

An experiment was conducted to measure LH pulse frequencies in bilaterally adrenalectomized Ile-de-France ewes during the mid-anoestrous season. Seven ewes were adrenalectomized under general anaesthesia and maintained on daily injections of 3 mg deoxycorticosterone acetate (DOCA). Adrenalectomy did not affect the patterns of LH release and the mean intervals between pulses in the adrenalectomized and sham-operated control ewes were 48 and 52 min respectively. Small implants of oestradiol significantly reduced the frequency of LH pulses in both groups and, in the presence of oestradiol, there were no differences in LH release between adrenalectomized and sham-operated ewes, with the mean interpulse intervals being 91 and 89 min respectively. In a second experiment, designed to assess the effects of DOCA on LH release, the mean interpulse intervals in unoperated control ewes (46 min) and unoperated ewes given daily injections of 3 mg DOCA (47 min) were similar to those observed in adrenalectomized and sham-operated ewes. In the presence of small implants of oestradiol, the combination of DOCA and oestradiol decreased the pulse frequency significantly more than oestradiol alone (mean interpulse intervals of 85 and 65 min respectively) suggesting that DOCA may act as a progestagen in sheep. Thus alternative treatments to DOCA for the maintenance of adrenalectomized sheep must be found for future studies on the role of adrenal steroids in the reproductive system. It appears that adrenal steroids do not play a major role in the seasonal changes in LH release in the ewe.