Relationships Between Uterine Blood Flow, Peripheral Sex Steroids, Expression of Endometrial Estrogen Receptors and Nitric Oxide Synthases During the Estrous Cycle in Mares

Abstract

Abstract. The objective of this study was to investigate the relationships between uterine perfusion and estrogen, progesterone and the uterine nitric oxide synthase (NOS) system in five trotter mares during the estrous cycle. Color Doppler sonography for measurement of uterine blood flow and collection of blood for determination of plasma estrogen and progesterone concentrations were performed on days 0 (= ovulation), 1, 5, 11 and 15 and daily during estrus (days -1 to -4) of one estrous cycle; endometrial biopsy collection for mRNA expression analysis of NOS and estrogen receptors was performed on days 0, 1, 5, 11, 15 and -3. Blood flow in each uterine artery was assessed by calculating the mean time-averaged maximum velocity (TAMV) and the pulsatility index (PI). Plasma concentrations of estrogen and progesterone were determined using specific enzyme immunoassays. The mRNA expressions of endothelial NOS (eNOS), inducible NOS (iNOS) as well as estrogen receptors α (ERα) and β (ERβ) were quantified using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. The TAMV and PI had a biphasic pattern during the estrous cycle (P<0.05), with maximum and minimum, respectively, values on days 5 and -4. Estrogen receptor mRNA concentrations increased significantly during days 15 (ERα) and -3 (ERβ). Transcript expression of eNOS, but not iNOS, had a biphasic pattern during the cycle (P<0.05) with maximum levels on days 5 and -3 and correlated positively with TAMV (r=0.81, P=0.05). We infer that the uterine NOS system, especially eNOS, plays an important role in the regulation of uterine blood flow during the estrous cycle in mares. Key words: Endometrial messenger RNA expression, Estrous cycle, Nitric oxide synthases, Steroid hormones, Uterine perfusion (J. Reprod. Dev. 57: [43][44][45][46][47][48] 2011) haracteristic uterine blood flow patterns have been reported during the estrous cycle in mares based on color Doppler sonography [1,2]. Uterine perfusion had a wave-shaped profile throughout the cycle, showing maximal blood flow during estrus and the early luteal phase [1][2][3][4]. Variations in uterine blood flow in cycling mares have been attributed to changes in circulating estrogen concentrations. However, due to a weak correlation between the resistance to uterine blood flow and plasma estrogen concentrations, other factors may also regulate uterine blood flow [2].Changes in uterine blood flow during the estrous cycle in many species are mediated mainly by estrogens [5]; although flow was enhanced by high plasma estradiol concentrations [6,7] and decreased during the luteal phase [8,9], the mechanisms involved have not been elucidated. Estrogens appear to act via two pathways: the genomic and non-genomic pathways [10]. Briefly, in the classical genomic pathway, estrogens bind to their nuclear receptors, subsequently regulating the transcription of target genes. For example, administration of estradiol increased estrogen receptors within 48 h in cyclic ewes [11]. Furthermore, a non-genomic pathway wit...

Expression of receptors for ovarian steroids and prostaglandin E2 in the endometrium and myometrium of mares during estrus, diestrus and early pregnancy

“…Previously, a positive correlation between endometrial transcripts of ESR1 and ESR2 were observed throughout the equine estrous cycle (Honnens et al, 2011). In addition, there were effects of estrous cycle day on the expression of ESR1 and ESR2 (Honnens et al, 2011).…”

“…Previously, a positive correlation between endometrial transcripts of ESR1 and ESR2 were observed throughout the equine estrous cycle (Honnens et al, 2011). In addition, there were effects of estrous cycle day on the expression of ESR1 and ESR2 (Honnens et al, 2011). Since we compared ESR2 during the preovulatory period, late diestrus and early pregnancy in postmortem specimens, and did not evaluate its expression at other time points of the estrous cycle, we could therefore have missed differences in ESR2 mRNA expression across different days of the reproductive cycle.…”

“…It plays a major role in the uterotrophic effects of estrogen, as evidenced by a loss of cellular proliferation and secretory protein production in the uterus of adult female ER-␣ knockout mice (Lubahn et al, 1993). Estrogen receptor ␤ (ER-␤) has a high degree of sequence homology with the classical ER-␣ (Hiroi et al, 1999) and has been described in the uterus of women (Matsuzaki et al, 1999), mice (Weihua et al, 2000), and more recently the horse (Honnens et al, 2011). Adult female ER-␤ knockout mice were infertile or had signs of subfertility, demonstrating that this receptor is important in female reproduction (Weihua et al, 2000).…”

Dual effect of hormones on mare reproductive physiology and dysfunction

“…In fact, in the mare endometrium, during estrus, high levels of ovarian steroid receptors, such as ER , ER and PR mRNA and protein have been detected in luminal and glandular epithelia, as well as in stromal cells (Watson et al 1992, Gebhardt et al 2012, Silva et al 2014. In addition, a positive correlation between mRNA expression of ER and ER has been reported in mare endometrium (Honnens et al 2011). In the luteal phase, when circulating P4 levels are high, endometrium expression of ER and PR are inhibited.…”

Preovulatory Dominant Follicular Size and Serum Nitric Oxide Can Predicate the Conception Rate after Foaling Heat in Straight Egyptian Arabian Mares

“…In mares, NO seems to be implicated in both in follicular growth and ovulation (Pinto et al, 2002) and is also a potential mediator of luteal development and maintenance, angiogenesis, and blood flow (Ferreira et al, 2011). Also, Honnens et al, (2011) found that NO regulates uterine blood flow during the estrous cycle in mares. Therefore, the present study aimed to evaluate ovarian changes and its relation to oxidative stress during early postpartum period in Arabian horses.…”