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Gestation Length in Rabbits—Effect of Aminoglutethimide Phosphate¹, Dexamethasone, Pregnenolone and Progesterone^{,2, 3, 4,}

University of Wisconsin, Madison 53706

Abstract

Treatment of rabbits on days 25 and 26 of gestation with 900 mg/day of aminoglutethimide phosphate (AGP), an inhibitor of the conversion of cholesterol to pregnenolone significantly shortened the duration of gestation by 4 days (AGP 27 days vs Controls 31).

Dexamethasone, a synthetic glucocorticoid, administered IM on days 25 and 26 of gestation at a dose of 4 mg, also significantly shortened gestation with parturition occurring on day 28. The daily IM injection of 5 mg of progesterone for 10 days starting on day 25 prolonged pregnancy from 30 days in control does to 37 days in treated does. Treatment with progesterone in combination with aminoglutethimide or dexamethasone completely prevented response to aminoglutethimide or dexamethasone and prolonged gestation up to 37 days. Pregnenolone (5 mg) administered IM daily from day 25 onwards failed to prolong gestation length or prevent induction of parturition by aminoglutethimide. Aminoglutethimide phosphate caused a significant increase in the weight of the corpora lutea. Adrenal gland weights were not affected either by aminoglutethimide or dexamethasone treatments. The frequency of nest building was very low for does treated with aminoglutethimide or progesterone but not for does treated with dexamethasone. The percentage of live fetuses was significantly lower in the aminoglutethimide treated animals 23% vs 82% and 94% in the control and pregnenolone treated does, respectively.

¹ Aminoglutethimide Phosphate (Elipten "R") kindly donated by Ciba-Geigy.

² Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison 53706 and Fundacão Ford do Brasil.

³ This investigation was partially supported by Public Health Service Training Grant 5-T-1HD00104-04 from the National Institute of Child Health and Human Development and the Ford Foundation Grant 630-0505A.

⁴ Department of Meat and Animal Science Paper No. 661.

⁵ Permanent address: Departmento de Zootechnia, Univ. Federal de Vicosa-36570-Vicosa-Minas Gerais, Brasil.