The effects of pulsed adrenocorticotropin1-24 administration to one twin on the endocrine and uterine activity changes during twin pregnancy in sheep.

To test the hypothesis that systemic endocrine events are of more importance than local intrauterine endocrine changes in the control of myometrial activity at labor, we examined the endocrine changes and development of uterine activity in chronically catheterized twin fetal sheep during administration of adrenocorticotropin1-24 (ACTH1-24) to one of the twins. Fetal and maternal plasma cortisol, progesterone, estrone, prostaglandin E2 (PGE2) and 13, 14 dihydro 15-keto prostaglandin F2 alpha (PGFM) were measured before and during pulsatile administration of ACTH1-24 (1 microgram infused over 15 min, every 2 h; P-ACTH) to one fetus in each of six twin pregnancies until parturition was initiated. In all cases, each fetus was in a separate uterine horn. The same hormone measurements were made in each co-twin that remained untreated. Intrauterine pressure and electromyographic activity of each uterine horn were monitored continuously throughout the study. In ewes pregnant with twins, the onset of active labor occurred after a mean infusion interval of 204.0 +/- 29.5 h (SEM), which is considerably longer than has been reported for singleton pregnancies. In the P-ACTH-infused twin, birth was preceded by a progressive rise in plasma cortisol beginning 24 h after the start of infusion. This was followed by a later rise in plasma estrone and PGE2, and by a decline in plasma progesterone. In the uninfused twin, delivery was preceded by a small rise in plasma cortisol that was concomitant with a rise in the concentration of cortisol in the maternal circulation. The concentrations of estrone and progesterone in the uninfused twin did not change significantly.(ABSTRACT TRUNCATED AT 250 WORDS)