%0 Journal Article
%T Binding characteristics of the ovine membrane progesterone receptor alpha and expression of the receptor during the estrous cycle
%A Ryan L Ashley
%A J Alejandro Arreguin-Arevalo
%A Terry M Nett
%J Reproductive Biology and Endocrinology
%D 2009
%I BioMed Central
%R 10.1186/1477-7827-7-42
%X Binding studies were performed using crude membrane fractions from CHO cells expressing the mPR-alpha. Using quantitative Real-time PCR we determined the expression pattern of mRNA for the ovine mPR-alpha during the ovine estrous cycle in tissues known to express the mPR-alpha. Jugular blood samples were also collected and analyzed for serum concentrations of P4 to ensure ewes were at the appropriate stage of their cycle.Only progesterone, 20alpha-hydroxyprogesterone and 17alpha-hydroxyprogesterone were able to displace binding of 3H-P4 (P < 0.001) to membrane fractions from CHO cells expressing ovine mPR-alpha. The average B-max and Kd values for three separate experiments were 624 +/- 119 fmol/micro gram protein and 122 +/- 50 nM, respectively. Significant changes in expression of mRNA for the mPR-alpha during the estrous cycle were noted in the corpus luteum and uterus.The mPR-alpha specifically binds progestins and its expression was correlated to progesterone secretion during the ovine estrous cycle. Results from the present studies suggest that mPR-alpha may have an important physiological role during the ovine estrous cycle.Progesterone (P4) is a steroid hormone produced primarily by the ovary with the amount of P4 secreted depending on the level of gonadotropin stimulation and the physiological status of the ovary. Granulosa cells, theca/stromal cells and luteal cells all secrete P4 albeit at different levels [1-3]. Progesterone has many biological effects in a variety of tissues, and as such considerable research has focused on the mechanisms through which P4 mediates its actions. Many physiological effects of P4 are mediated through gene regulation by the nuclear P4 receptors (nPR) that function as ligand-dependent transcription factors. More recently, P4 also has been shown to evoke rapid stimulatory effects through a variety of signal transduction molecules and pathways (reviewed in [4]) and it is thought that these non-genomic effects are the result of
%U http://www.rbej.com/content/7/1/42