Abstract
Present study was undertaken to examine the synergistic effect of progesterone and estrogen on the physical properties of the chronically distended rat uterus. Ovariectomy and insertion of a par-affin pellet into a uterine horn were performed within 24 hours after delivery (Day 1). The rats were injected with vehicle alone (Group I), 4 mg progesterone (Group II), 0. 2 μg estradiol-17β (Group III) or both progesterone and estradiol-17β (Group IV) from Day 3 through 7. Stress relaxation curves and passive length-tension curves of the circular uterine strips obtained from rats given no hormonal in-jection on Day 3 (Group V) and from animals injected with vehicle or the hormone on Day 8 were determined.
The stress decline was slower in Group I than in Group V. The stress relaxation in any of the hormone-treated groups was similar to that in Group I. The length of the collagenous framework (Lz) and distensibility (D), which were obtained from the linear part of the passive length-tension curve, were significantly greater, while tnesion at in vivo length (Tv) in passive length-tension curve was smaller, in Group V than in Group I. Lz, D and Tv in Groups II and III were similar to those in Group I. In Group IV, however, Lz was greater, and Tv was smaller, compared with those in Groups I, II and III. Ls and Tv in Group IV were similar to those in Group V. D in Group IV was smaller than that in Group V and significantly greater compared with the value in either Group I or III.
These results suggest that progesterone and estrogen act synergistically in maintaining collagenous framework and distensibility of the distended rat uterus and keep the uterine tension lower.
