In vivo effects of corticotropin-releasing factor in pregnant rats

OBJECTIVES: Our purpose was to study the effects of corticotropin- releasing factor on (1) maternal blood pressure (2) uterine vasculature, and (3) parturition in pregnant rats. STUDY DESIGN: infusion minipumps containing vehicle, corticotropin-releasing factor, or α-helical corticotropin- releasing factor 9-41 (corticotropin-releasing factor receptor antagonist) were inserted subcutaneously in timed pregnant rats on day 16 of gestation. Systolic blood pressure was measured daily by the tail-cuff method. The time of onset of labor was determined and the newborn pups were weighed. Circulating levels of corticotropin-releasing factor were measured in untreated controls by radioimmunoassay. Relaxant responses to corticotropin- releasing factor were studied in isolated segments of uterine artery from late (day 18) and term (day 22) pregnant rats mounted in a wire myograph. RESULTS: The blood pressure was decreased by corticotropin-releasing factor and increased by α-helical corticotropin-releasing factor 9-41 (p<0.05). The time of onset of labor was not affected by either treatment. Pup weight was decreased by corticotropin-releasing factor (p < 0.05). Circulating levels of corticotropin-releasing factor (immunoreactive) were not changed in pregnancy. In vitro, corticotropin-releasing factor caused relaxation of the uterine artery in a concentration-dependent manner and the relaxation was decreased at term compared with late pregnancy (p < 0.05). CONCLUSIONS: Endogenously produced corticotropin-releasing factor lowers blood pressure during pregnancy in rats. It is a relaxant of uterine vasculature and this effect is decreased at term. It does not play an essential role in the initiation of labor in rats.