Evidence That Endogenous Relaxin Promotes Vaginal Growth and Softening in Pregnant Rats
Zhao, Shuangping
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https://hdl.handle.net/2142/87272
Description
Title
Evidence That Endogenous Relaxin Promotes Vaginal Growth and Softening in Pregnant Rats
Author(s)
Zhao, Shuangping
Issue Date
2000
Doctoral Committee Chair(s)
Sherwood, O. David
Department of Study
Molecular and Integrative Physiology
Discipline
Molecular and Integrative Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Language
eng
Abstract
Rat relaxin is produced and secreted by the ovary throughout the second half of pregnancy. Relaxin promotes growth and softening of the cervix to enable rapid and safe delivery. When this studies were initiated there was no evidence that endogenous relaxin has effects on the vagina, which is linked anatomically to the cervix. There were four objectives. The first was to determine if relaxin promotes vaginal growth. When a monoclonal antibody (MCA1) was injected intravenously to rats daily from days 12--22 of pregnancy, the vaginal wet weight, dry weight, and DNA content were significantly lower than they were in controls. The second objective indicated that relaxin promoted vaginal softening. A fundamental step toward to understanding the mechanism whereby relaxin brings about these effects is to determine the histological changes. Accordingly, the third objective determined vaginal histological changes associated with vaginal growth and softening. Within the stroma relaxin reduced the density of collagen fiber bundles, reduced the length of elastin fibers, and enlarged blood vessels. These changes in the stroma appear to account for the hormone's softening effect on the vagina. Within the epithelium relaxin promoted a two-fold increase in number of cells. The increase in epithelial cells serves to line the enlarged vaginal lumen. The fourth objective provided evidence that relaxin inhibited apoptosis in the vagina. The rates of putative apoptotic cells in the vagina were moderate and steady through day 10, markedly reduced several fold throughout the second half of pregnancy, and then rose to maximal levels after delivery. When rats were made relaxin deficient with MCA1, the rates of apoptotic cells in the epithelium of vaginas were greater throughout the first 24 hours following the initiation of treatment than those from control rats. This study provides evidence that the inhibition of apoptosis is a mechanism whereby relaxin promotes growth of the vagina during the second half of pregnancy.
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