| pubmed-article:2686804 | pubmed:abstractText | Simultaneous or sequential injection of 250 ng gonadotrophin releasing hormone (GnRH) and 25 micrograms oestradiol benzoate, with luteinizing hormone (LH) measurements at 0, +20 min (after GnRH) and +16 h (after oestradiol), enabled investigation of the positive feedback effects on the hypothalamus and pituitary. Control ewes had pretreatment LH values of 3.1 +/- 1.2 ng/ml with an increment of 3.2 +/- 2.3 ng/ml 20 min after GnRH. Subfertile ewes, in spite of elevated pretreatment LH concentrations (15.8 +/- 9.5 ng/ml) in eight out of 10 ewes, had increments of 1.4-84 ng/ml after GnRH. Control ewes had LH increments of 3-75 ng/ml 16 h after oestradiol. Subfertile ewes with pretreatment LH concentrations less than 15 ng/ml also responded to oestradiol whereas those with initial LH concentrations 16-40 ng/ml had no further LH increment. Subsequent administration of 1000 iu pregnant mares' serum gonadotrophin (PMSG), with measurement of LH and oestradiol at 0, +24, +30, +48, +54, and +72 h, allowed assessment of ovarian response and hypothalamus-pituitary function. Five control ewes were sampled up to 30 h post-PMSG and only 1 had oestradiol concentrations greater than 10 pg/ml. Sampling up to 72 h in another five control ewes resulted in oestradiol concentrations greater than 10 pg/ml. Increments in LH concentration greater than 3 ng/ml were recorded in control and subfertile ewes with oestradiol concentrations greater than 10 pg/ml. The use of these endocrine challenge tests enabled positive diagnosis of abnormality on 8 out of 10 occasions.(ABSTRACT TRUNCATED AT 250 WORDS) | lld:pubmed |
