Effects of aminoglutethimide on cervical dilatability and serum immunoreactive relaxin in pregnant rats.

Administration of aminoglutethimide (AG) at a daily sc dose of 20 mg/kg to rats from the 10th to 20th days of pregnancy resulted in fetal wastage, increased placental weights, and decreased placental alkaline phosphatase. In an effort to determine the endocrine problems relating to these abnormalities, serum relaxin (R) and progesterone (P) levels were determined by RIA and cervical distensibility was measured: All three parameters were subnormal in AG-treated rats. Therapy with estrogen (E) or (P) failed to correct any of the physiological problems associated with AG treatment, but a combination of these steroids increased fetal survival to control levels. However, cervical dilation in preparation for parturition failed to occur. Relaxin therapy alone increased cervical dilation but did not enhance fetal survival. A combination of E, P, and R maintained a normal complement of fetuses and provided normal cervical dilation. None of the treatments prevented placental enlargement but P treatment tended to maintain normal placental alkaline phosphatase.