Variations in mucosal water and sodium transfer associated with the rat oestrous cycle

Sexual Dimorphism in Colon Cancer

A higher incidence of colorectal cancer (CRC) is found in males compared to females. Young women (18-44 years) with CRC have a better survival outcome compared to men of the same age or compared to older women (over 50 years), indicating a global incidence of sexual dimorphism in CRC rates and survival. This suggests a protective role for the sex steroid hormone estrogen in CRC development. Key proliferative pathways in CRC tumorigenesis exhibit sexual dimorphism, which confer better survival in females through estrogen regulated genes and cell signaling. Estrogen regulates the activity of a class of Kv channels (KCNQ1:KCNE3), which control fundamental ion transport functions of the colon and epithelial mesenchymal transition through bi-directional interactions with the Wnt/β-catenin signalling pathway. Estrogen also modulates CRC proliferative responses in hypoxia via the novel membrane estrogen receptor GPER and HIF1A and VEGF signaling. Here we critically review recent clinical and molecular insights into sexual dimorphism of CRC biology modulated by the tumor microenvironment, estrogen, Wnt/β-catenin signalling, ion channels, and X-linked genes.

Estrogen and estrogen receptors in the modulation of gastrointestinal epithelial secretion

Gastrointestinal (GI) epithelial ion transport is physiologically important in many aspects of humans, such as in maintaining fluid balance of whole body, and also plays a role in the development and progression of common GI disease. Estrogen and estrogen receptors have been shown to modulate the activity of epithelial ion secretion in GI tract. This review aims to address the current state of knowledge about the role of estrogen and estrogen receptors in modulation of GI epithelial secretion and to elucidate the underlying mechanisms. We highlight the recent findings regarding the importance of estrogen and estrogen receptors in GI epithelia protection and body fluid balance by modulation of gastrointestinal epithelial HCO₃^- and Cl^- secretion, especially current information about the regulatory mechanisms of duodenal HCO₃^- secretion based on our study in this field. Since there are no reviews on this topic but only few papers to address the main issues, we hope to timely provide new perspectives for the association between estrogen and GI disease.

Estrogen increases ENaC activity via PKCδ signaling in renal cortical collecting duct cells

The most active estrogen, 17β‐estradiol (E2), has previously been shown to stimulate a female sex‐specific antisecretory response in the intestine. This effect is thought to contribute to the increase in whole body extracellular fluid (ECF) volume which occurs in high estrogen states, such as in the implantation window during estrous cycle. The increased ECF volume may be short‐circuited by a renal compensation unless estrogen exerts a proabsorptive effect in the nephron. Thus, the effect of E2 on ENaC in kidney cortical collecting duct (CCD) cells is of interest to understand estrogen regulation of ECF volume. Previous studies showed a rapid stimulatory effect of estrogen on ENaC in bronchial epithelium. In this study we examined if such a rapid effect on Na⁺ absorption could occur in the kidney. Experiments were carried out on murine M1‐CCD cell cultures. E2 (25 nmol/L) treatment caused a rapid‐onset (<15 min) and sustained increase in the amiloride‐sensitive Na⁺ current (I_Na) in CCD monolayers mounted in Ussing chambers (control, 1.9 ± 0.2 μA/cm²; E2, 4.7 ± 0.3 μA/cm²; n = 43, P < 0.001), without affecting the ouabain‐sensitive Na⁺/K⁺ pump current. The I_Na response to E2 was inhibited by PKCδ activity antagonism with rottlerin (5 μmol/L), inhibition of matrix metalloproteinases activity with GM6001 (1 μmol/L), inhibition of EGFR activity with AG1478 (10 μmol/L), inhibition of PLC activity with U‐73122 (10 μmol/L), and inhibition of estrogen receptors with the general ER antagonist ICI‐182780 (100 nmol/L). The estrogen activation of I_Na could be mimicked by the ERα agonist PPT (1 nmol/L). The nuclear excluded estrogen dendrimer conjugate (EDC) induced similar stimulatory effects on I_Na comparable to free E2. The end target for E2 stimulation of PKCδ was shown to be an increased abundance of the γ‐ENaC subunit in the apical plasma membrane of CCD cells. We have demonstrated a novel rapid “nongenomic” function of estrogen to stimulate ENaC via ERα‐EGFR transactivation in kidney CCD cells. We propose that the salt‐retaining effect of estrogen in the kidney together with its antisecretory action in the intestine are the molecular mechanisms causing the expanded ECF volume in high‐estrogen states.

Estrogen stimulates sodium absorption in kidney cells. This rapid “nongenomic” response to estrogen is transduced via estrogen receptor transactivation of the epidermal growth factor receptor. The ER‐EGFR transactivation triggers a protein kinase signaling cascade which culminates in the insertion of sodium channel subunits into the cell membrane. Estrogen is a novel salt‐retaining hormone with proabsorptive effects in kidney and antisecretory actions in intestine.

Estrogen regulation of epithelial ion transport: Implications in health and disease

Estrogen, 17β-estradiol (E2), has been shown to modulate the activity of ion channels in a diverse range of epithelial tissues. The channel activation or inhibition responses to E2 are often rapid, occurring in seconds to minutes, independent of protein synthesis and gene transcription ('non-genomic' response). These rapid effects of E2 require activation of specific protein kinases or changes in intracellular calcium and pH which in turn modulate the conductance, open probability or number of channels in the plasmamembrane. Estrogen has also been shown to affect the expression of ion transporters over days ('genotropic' response) causing long-term sustained changes in transepithelial ion transport. It is now accepted that so called non-genomic responses are not stand-alone events and are necessary to prime the latent genomic response and even be critical for the full latent response to occur. In a number of epithelia the non-genomic and genotropic responses to estrogen are sex-specific and variable in potency and sensitivity to E2 depending on the stage of the estrous cycle. Of increasing interest is the effect these rapid and latent actions of E2 on ion transporters have on the physiological functions of epithelia. For example, estrogen regulation of a class of voltage-gated K(+) channels (KCNQ1) can determine the rate of Cl(-) secretion in the intestine. In whole-body terms, the combined effects of estrogen on a variety of ion channels which control fluid and electrolyte transport in the kidney, intestine and lung may be necessary for endometrial expansion and implantation of the blastocyte.

Estrogen and its role in gastrointestinal health and disease

INTRODUCTION

While the concept of a role of estrogen in gastrointestinal (in particular, colonic) malignancy has generated excitement in recent years, no review has examined the role of this potent and omnipresent steroid hormone in physiological states or its contribution to the development of benign pathological processes. Understanding these effects (and mechanisms therein) may provide a platform for a deeper understanding of more complex disease processes.

METHODS

A literature search was conducted using the PubMed database and the search terms were "estrogen," "estrogen AND gastrointestinal tract," "estrogen AND colon," "estrogen AND esophagus," "estrogen AND small intestine," "estrogen AND stomach," "estrogen AND gallbladder," and "estrogen AND motility." Bibliographies of extracted studies were further cross-referenced. In all, 136 full-text articles were selected for review. A logical organ-based approach was taken to enable extraction of data of clinical relevance and meaningful interpretation thereof. Insight is provided into the hypotheses, theories, controversies, and contradictions generated over the last five decades by extensive investigation of estrogen in human, animal, and cell models using techniques as diverse as autoradiographic studies of baboons to human population analysis.

CONCLUSIONS

Effects from esophagus through to the colon and rectum are summarized in this first concise collection of data pertaining to estrogenic actions in gastrointestinal health and disease. Mechanisms of these actions are discussed where possible. Undoubtedly, this hormone exerts many actions yet to be elucidated, and its potential therapeutic applications remain, as yet, largely unexplored.

Novel female sex-dependent actions of oestrogen in the intestine

The intestine is an oestrogen responsive organ and circulatory oestrogens suppress Cl(-) secretion across the epithelium of the colon to promote fluid retention at the luteal stage of the menstrual cycle. Ion transporters in the colon which are involved in Cl(-) secretion show differential expression between males and females as do the signalling protein kinase intermediates involved in acutely regulating these transporters. Work from our laboratory has identified the KCNQ1/KCNE3 channel as one of the principal targets for oestrogen-induced signalling cascades in the distal colon. Through inhibition of the KCNQ1 channel, basolateral K(+) recycling is decreased so reducing the favourable electrochemical gradient for Cl(-) extrusion at the apical membrane. The actions of oestrogen on non-reproductive tissues such as the colon, kidney, lung and sweat gland will affect whole body electrolyte and fluid homeostasis and also have consequences for reproductive potential.

Female gender-specific inhibition of KCNQ1 channels and chloride secretion by 17beta-estradiol in rat distal colonic crypts

The estrogen sex steroid 17beta-estradiol rapidly inhibits secretagogue-stimulated cAMP-dependent Cl(-) secretion in the female rat distal colonic crypt by the inhibition of basolateral K(+) channels. In Ussing chamber studies, both the anti-secretory response and inhibition of basolateral K(+) current was shown to be attenuated by pretreatment with rottlerin, a PKCdelta-specific inhibitor. In whole cell patch-clamp analysis, 17beta-estradiol inhibited a chromanol 293B-sensitive KCNQ1 channel current in isolated female rat distal colonic crypts. Estrogen had no effect on KCNQ1 channel currents in colonic crypts isolated from male rats. Female distal colonic crypts expressed a significantly higher amount of PKCdelta in comparison to male tissue. PKCdelta and PKA were activated at 5 min in response to 17beta-estradiol in female distal colonic crypts only. Both PKCdelta- and PKA-associated with the KCNQ1 channel in response to 17beta-estradiol in female distal colonic crypts, and no associations were observed in crypts from males. PKA activation, association with KCNQ1, and phosphorylation of the channel were regulated by PKCdelta as the responses were blocked by pretreatment with rottlerin. Taken together, our experiments have identified the molecular targets underlying the anti-secretory response to estrogen involving the inhibition of KCNQ1 channel activity via PKCdelta- and PKA-dependent signaling pathways. This is a novel gender-specific mechanism of regulation of an ion channel by estrogen. The anti-secretory response described in this study provides molecular insights whereby estrogen causes fluid retention effects in the female during periods of high circulating plasma estrogen levels.

Neuroendocrine mechanisms mediating fluid intake during the estrous cycle

Gonadal steroids appear to influence fluid-electrolyte homeostasis through behavioral as well as renal mechanisms. The marked fluctuations in drinking behavior observed during the estrous cycle of the female rat may be due to an interaction between estrogen and the dipsogenic peptide hormone, angiotensin II, at the level of basal forebrain receptors. The preoptic region in particular may play an important integrative role in the maintenance of extracellular fluid balance in synchrony with the estrous cycle, since it contains receptors for angiotensin and estrogen. Prolactin may also directly participate in mechanisms of extracellular thirst, while an exact role for vasopressin has yet to be established. Recent studies also suggest that estrogens may influence body fluid regulation by interacting with several neurotransmitters, including serotonin, dopamine and noradrenaline.

Effects of estrogen and testosterone on specific prolactin binding in the kidneys and adrenal of rats

The effects of estradiol benzoate in the female rat, testosterone propionate in the male rat, and castration in both sexes on specific prolactin binding sites in the particulate membranes of the kidneys and adrenals were studied. Castration resulted in a significant increase in PRL binding activity in the kidneys of both males and females, and in a significant increase in PRL binding activity in the adrenals of the females. The increase in PRL binding with castration and the decrease seen with testosterone treatment were similar in both immature and mature rats. Progesterone administration to castrate females failed to alter PRL binding in both tissues. The present results suggest that estrogen and testosterone participate in the PRL osmoregulatory system in rat.