Hormonal Regulation of Natriuretic Peptide System during Induced Ovarian Follicular Development in the Rat1

Abstract

All components of the natriuretic peptide (NP) system have been found in the ovary. The purpose of this study was to determine the hormonal regulation of the NP system during follicular growth and ovulation induced by gonadotropins eCG and hCG. Ovarian membrane binding, before and after treatment, revealed the presence of guanylyl cyclase-type receptors exclusively. Equine CG treatment increased Bmax from 225 +/- 50 fmol/mg protein in control animals to 354 +/- 51 fmol/mg protein, and additional hCG treatment increased it further to 492 +/- 130 fmol/mg protein (p < 0.05), without changing receptor affinity. The increased binding was consistent with increased ability of atrial natriuretic peptide (ANP) to activate guanylyl cyclase in the ovarian cells obtained from hormone-treated animals. In confirmation, autoradiography of 125I-tyroCNP and 125I-ANP binding to the rat ovary showed that both guanylyl cyclase GC-A and GC-B receptor subtypes are localized to the granulosa cells of antral follicles. Quantitative analysis of GC-A and GC-B receptors by reverse transcription-polymerase chain reaction showed that the expression level of both receptors started to increase at 2 h and reached maximal levels at 6 h following eCG treatment. Increased levels of GC-B mRNA were also observed 12 h after eCG injection. At 24 and 48 h the receptor levels were below basal. Stimulation of NP receptors by eCG was paralleled by activation of both ovarian ANP and C-type natriuretic peptide (CNP) gene expression. ANP mRNA increased as early as 1 h after eCG injection and remained elevated up to 6 h. CNP mRNA increased at 2 h after eCG injection, peaked (5-fold) at 6 h, and remained elevated 48 h later, a stage at which follicular maturation continues. Incubation of ovaries with ANP significantly decreased eCG-induced estradiol level, indicating the functionality of the ovarian NP system. These results implicate the NP system in the induction and maintenance of fluid balance in the rapidly developing ovarian follicle.

Pregnancy alters nitric oxide synthase and natriuretic peptide systems in the rat left ventricle

“…Measurement of cGMP concentration has already been described (Gutkowska et al 1999). Briefly, the dissected tissues were cut into small pieces and homogenized in 5 vol of ice-cold 5% (v/v) trichloroacetic acid (TCA).…”

“…Because of their contribution to ANP and NO release in the cardiovascular system, estrogen and oxytocin receptors (OTR) were also evaluated (Gutkowska et al 1999, Jankowski et al 2001, Mukaddam-Daher et al 2001, Wang et al 2003). Our results demonstrate that cGMP concentration in the rat LV is controlled by both NOS and natriuretic peptides, but their inverse expressions at different stages of gestation suggest distinct roles in the control of physiologic cardiac hypertrophy.…”

Molecular characterisation and functional interrogation of a local natriuretic peptide system in rodent pituitaries, αT3-1 and LβT2 gonadotroph cells

“…As well as the profound effects on endochondral ossification, these models of disrupted CNP/GC-B pathways suggest potentially important roles of this system in pituitary and gonadal tissues as Npr2 K/K mice are GH deficient and exhibit female infertility (Tamura et al 2004). Further support for CNP as a regulator of reproductive function comes from several studies that have shown CNP to potently stimulate cGMP production in GNRH neurons (Olcese et al 1994), pituitary gonadotrophs (McArdle et al 1993), and endocrine cells of the testis, ovaries, placenta and uterus (Khurana & Pandey 1993, Huang et al 1996, Middendorff et al 1996, Acuff et al 1997, Jankowski et al 1997, Gutkowska et al 1999, Stepan et al 2001, Walther & Stepan 2004, implicating CNP function at all levels of the hypothalamo-pituitarygonadal (HPG) axis. Furthermore, cGMP is a useful pharmacological target in the treatment of male reproductive disorders (Rosen & McKenna 2002, Christ & Hodges 2006.…”

Dephosphorylation and inactivation of NPR2 guanylyl cyclase in granulosa cells contributes to the LH-induced decrease in cGMP that causes resumption of meiosis in rat oocytes

“…Gene expression analysis and enzyme assays have indicated that other guanylyl cyclases are present at levels much lower than those of NPR2 . NPR2 is located throughout the granulosa cells of the follicle, in both the mural granulosa and the cumulus cells directly surrounding the oocyte; it is not expressed in the oocyte (Gutkowska et al, 1999;Zhang et al, 2010). The agonist of NPR2, C-type natriuretic peptide (CNP, released from a precursor protein that is encoded by the Nppc gene) is produced only in the mural granulosa cells (Zhang et al, 2010).…”