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Summary. Betamethasone

Dairy cows with a variety of clinical conditions were investigated in an attempt to identify the cause(s) of subfertility. Sequential or simultaneous injections of 20 micrograms gonadotrophin-releasing hormone (GnRH), 1 mg oestradiol benzoate and 0.06 mg ACTH(1-24) into five clinical cases of ovarian follicular cysts, two cases of poor body condition and one case of lameness and into control cows revealed a failure in the LH positive-feedback response to oestradiol in all eight clinical cases, but in only two out of twelve control cows. Two of the clinical cases and the two non-responding control cows had high or rising initial progesterone concentrations which would explain the absence of response. All cows studied responded similarly to GnRH and ACTH(1-24). It is suggested that hypothalamus-pituitary control of LH release may involve a rate-limiting step (in the oestradiol positive-feedback system) and that lesions at this point result in subfertility in a variety of clinical situations.

Stress is known to result in lowered female reproductive efficiency. The objective of this study was to examine how increased pituitary-adrenal activity may influence gonadotrophin release in anoestrous ewes. Various doses (0.06-1.0 mg) of a synthetic adrenocorticotrophic hormone (ACTH(1-24)) preparation were injected into ewes 30 min or 3 h before an i.v. injection of 500 ng gonadotrophin-releasing hormone (GnRH). The LH response to GnRH given 30 min after ACTH(1-24) was similar to that after GnRH alone, whereas the response 3 h after ACTH(1-24) was significantly lower, irrespective of the dose of ACTH(1-24). At 30 min and 3 h after ACTH(1-24) the concentrations of cortisol exceeded 50 nmol/l compared with baseline values of less than 10 nmol/l. The effect of ACTH(1-24) on oestradiol-induced LH release was also examined. Those ewes receiving 0.8 mg ACTH(1-24) depot and 50 micrograms oestradiol benzoate simultaneously had a preovulatory-type increase in LH 14-20 h later, similar to when oestradiol benzoate was given alone. None of the ewes receiving an additional 0.8 mg ACTH(1-24) depot 10 h after oestradiol benzoate had increases in LH concentration. The cortisol concentrations in all ewes receiving either one or two injections of ACTH(1-24) were greater than 35 nmol/l at 10 h after the oestradiol injection. However, concentrations of progesterone increased from 0.9 +/- 0.3 (S.E.M.) nmol/l at the time of the second ACTH(1-24) injection to 2.1 +/- 0.3 nmol/l after 2 h.(ABSTRACT TRUNCATED AT 250 WORDS)

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