The mammary nipples are vital endocrine target tissues for relaxin in the rat
Kuenzi, Mark James
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Permalink
https://hdl.handle.net/2142/23645
Description
Title
The mammary nipples are vital endocrine target tissues for relaxin in the rat
Author(s)
Kuenzi, Mark James
Issue Date
1994
Doctoral Committee Chair(s)
Sherwood, O. David
Department of Study
Biology, Animal Physiology
Discipline
Biology, Animal 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
In 1991 it was reported that the protein hormone relaxin stimulates growth of the mammary nipples during the second half of pregnancy in the rat. Other than these visual observations, however, nothing was known concerning relaxin's effects on the nipples. Accordingly, the two overall objectives of the thesis were to (1) characterize the effects of relaxin on the structure and function of the mammary nipples and (2) determine if the nipples are endocrine targets for relaxin in the rat.
The first study demonstrated that endogenous relaxin significantly increases length and cross-sectional area of the entire nipple and the cross-sectional area of the lactiferous duct lumen. Furthermore, relaxin promotes disruption of densely packed and well-organized collagen fiber bundles, increased amorphous ground substance, reduced length of elastin fibers, and increased cross-sectional area of blood vessels. Finally, the lactational failure and high incidence of pup mortality that occur in relaxin-deficient rats was demonstrated to be attributable to the inability of the pups to attach to the nipple, stimulate prolactin release, and obtain milk from the dams.
Although it was apparent that endogenous circulating relaxin was essential for both growth and development of the nipples and successful lactation, it was not clear whether relaxin acted directly on the nipples or systemically through effects on other tissues. The second study demonstrated that at least one mechanism by which relaxin stimulates increased lengths and wet weights of the nipples was through direct local actions of relaxin.
In order to firmly establish the mammary nipples as endocrine target tissues for relaxin in the rat, putative relaxin receptors needed to be identified. The third study identified specific relaxin-binding in the epithelium of the lactiferous duct, smooth muscle, and skin of mammary nipples from pregnant rats.
In summary, this work establishes the nipples as vital endocrine targets for relaxin in pregnant rats. Furthermore, it provides insight into the mechanism(s) of relaxin in the nipples by characterizing the relaxin-mediated growth and histological modifications of the nipple as well as identifying those cell types which may initiate these relaxin-mediated effects.
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