The Uterine Myometrium Is a Target for Increased Levels of Activin A during Pregnancy

• Published in: Endocrinology (Philadelphia) Vol. 138; no. 7; pp. 3042 - 3046
• Main Authors: Draper, Lawrence B, Chong, Huira, Wang, Eileen, Woodruff, Teresa K
• Format: Journal Article
• Language: English
• Published: Washington Endocrine Society 01-07-1997; Oxford University Press
• Subjects: Activin; Animal models; Binding; In vivo methods and tests; Inhibin; Ligands; Myometrium; Parturition; Pregnancy; Protein folding; Receptors; Uterus
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/endo.138.7.5231

Activin A is a dimeric protein hormone that regulates numerous cellular
functions. A clear physiological role for this molecule in pregnancy is
suggested by previous studies in the human, wherein activin A rises
dramatically as women approach parturition. To determine whether the
rodent is a suitable animal model for further studies of activin action
during pregnancy, the serum concentration of activin A was measured in
pregnant rats. Activin A was detected in the serum of pregnant rats,
beginning on day 12, and the serum concentration rose progressively
through gestation (22-fold) and dramatically (140-fold) in labor. The
potential target tissues for circulating activin were then identified
in two ways. First, iodinated activin was injected into pregnant rats,
and the tissues targeted by labeled ligand were identified in
vivo. A tissue targeted by activin A in the pregnant rat was
the uterine myometrium. To determine the ligand specificity of the
uterine myometrial cells, the uteri of pregnant rats were collected and
analyzed by in situ ligand binding.
125I-activin A binding was specific for the uterus
myometrium, and the ligand binding was competed by unlabeled activin A
but not by inhibin A. This result suggests that the receptor in this
tissue compartment is an activin-specific receptor. The production of
abundant activin A and the ability of exogenous ligand to target the
myometrium of the uterus provides a pathway by which activin could
regulate uterine function during pregnancy.