The influence of estradiol and diet on small intestinal glucose transport in ovariectomized rats

Estrogens and the regulation of glucose metabolism

The main estrogens: estradiol, estrone, and their acyl-esters have been studied essentially related to their classical estrogenic and pharmacologic functions. However, their main effect in the body is probably the sustained control of core energy metabolism. Estrogen nuclear and membrane receptors show an extraordinary flexibility in the modulation of metabolic responses, and largely explain gender and age differences in energy metabolism: part of these mechanisms is already sufficiently known to justify both. With regard to energy, the estrogen molecular species act essentially through four key functions: (1) Facilitation of insulin secretion and control of glucose availability; (2) Modulation of energy partition, favoring the use of lipid as the main energy substrate when more available than carbohydrates; (3) Functional protection through antioxidant mechanisms; and (4) Central effects (largely through neural modulation) on whole body energy management. Analyzing the different actions of estrone, estradiol and their acyl esters, a tentative classification based on structure/effects has been postulated. Either separately or as a group, estrogens provide a comprehensive explanation that not all their quite diverse actions are related solely to specific molecules. As a group, they constitute a powerful synergic action complex. In consequence, estrogens may be considered wardens of energy homeostasis.

Estriol blunts postprandial blood glucose rise in male rats through regulating intestinal glucose transporters

Despite increased total food intake in healthy, late-stage pregnant women, their peak postprandial blood sugar levels are normally much lower than the levels seen in healthy nonpregnant women. In this study, we sought to determine whether estriol (E3), an endogenous estrogen predominantly produced during human pregnancy, contributes to the regulation of the postprandial blood glucose level in healthy normal rats. In vivo studies using rats showed that E3 blunted the speed and magnitude of the blood glucose rise following oral glucose administration, but it did not appear to affect the total amount of glucose absorbed. E3 also did not affect insulin secretion, but it significantly reduced the rate of intestinal glucose transport compared with vehicle-treated animals. Consistent with this finding, expression of the sodium-dependent glucose transporter 1 and 2 was significantly downregulated by E3 treatment in the brush-border membrane and basolateral membrane, respectively, of enterocytes. Most of the observed in vivo effects were noticeably stronger with E3 than with 17β-estradiol. Using differentiated human Caco-2 enterocyte monolayer culture as an in vitro model, we confirmed that E3 at physiologically relevant concentrations could directly inhibit glucose uptake via suppression of glucose transporter 2 expression, whereas 17β-estradiol did not have a similar effect. Collectively, these data showed that E3 can blunt the postprandial glycemic surge in rats through modulating the level of intestinal glucose transporters.

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.