In vitro studies suggest that the G protein-coupled receptor (GPR) 30 is a functional estrogen receptor. However, the physiological role of GPR30 in vivo is unknown, and it remains to be determined whether GPR30 is an estrogen receptor also in vivo. To this end, we studied the effects of disrupting the GPR30 gene in female and male mice. Female GPR30((-/-)) mice had hyperglycemia and impaired glucose tolerance, reduced body growth, increased blood pressure, and reduced serum IGF-I levels. The reduced growth correlated with a proportional decrease in skeletal development. The elevated blood pressure was associated with an increased vascular resistance manifested as an increased media to lumen ratio of the resistance arteries. The hyperglycemia and impaired glucose tolerance in vivo were associated with decreased insulin expression and release in vivo and in vitro in isolated pancreatic islets. GPR30 is expressed in islets, and GPR30 deletion abolished estradiol-stimulated insulin release both in vivo in ovariectomized adult mice and in vitro in isolated islets. Our findings show that GPR30 is important for several metabolic functions in female mice, including estradiol-stimulated insulin release.

Estrogen exerts a variety of important physiological effects, which have been suggested to be mediated via the two known estrogen receptors (ERs), and . Three-monthold ovariectomized mice, lacking one or both of the two estrogen receptors, were given estrogen subcutaneously (2·3 µg/mouse per day) and the effects on different estrogen-responsive parameters, including skeletal effects, were studied. We found that estrogen increased the cortical bone dimensions in both wild-type (WT) and double ER knockout (DERKO) mice. DNA microarray analysis was performed to characterize this effect on cortical bone and it identified four genes that were regulated by estrogen in both WT and DERKO mice. The effect of estrogen on cortical bone in DERKO mice might either be due to remaining ER activity or represent an ER /ER -independent effect. Other effects of estrogen, such as increased trabecular bone mineral density, thymic atrophy, fat reduction and increased uterine weight, were mainly ER mediated.

Androgens may regulate the male skeleton either directly by stimulation of the androgen receptor (AR) or indirectly by aromatization of androgens into estrogens and, thereafter, by stimulation of the estrogen receptors (ERs). To directly compare the effect of ER activation on bone in vivo with the effect of AR activation, 9-month-old orchidectomized wild-type and ER-inactivated mice were treated with the nonaromatizable androgen 5␣-dihydrotestosterone, 17␤-estradiol, or vehicle. Both ER␣ and AR but not ER␤ activation preserved the amount of trabecular bone. ER␣ activation resulted both in a preserved thickness and number of trabeculae. In contrast, AR activation exclusively preserved the number of trabeculae, whereas the thickness of the trabeculae was unaffected. Furthermore, the effects of 17␤-estradiol could not be mediated by the AR, and the effects of 5␣-dihydrotestosterone were increased rather than decreased in ER-inactivated mice. ER␣, but not AR or ER␤, activation resulted in preserved thickness, volumetric density, and mechanical strength of the cortical bone. ER␣ activation increased serum levels of insulin-like growth factor I, which were positively correlated with all the cortical and trabecular bone parameters that were specifically preserved by ER␣ activation but not by AR activation, suggesting that insulin-like growth factor I might mediate these effects of ER␣ activation. Thus, the in vivo bone-sparing effect of ER␣ activation is distinct from the bone-sparing effect of AR activation in adult male mice. Because these two pathways are clearly distinct from each other, one may speculate that a combined treatment of selective ER modulators and selective AR modulators might be beneficial in the treatment of osteoporosis. S ex steroids are important not only for the maintenance of the female skeleton, but also for the male skeleton. The relative contribution of androgens versus estrogens in the regulation of the male skeleton is unclear. Testosterone replacement therapy increases bone mineral density (BMD) in hypogonadal men (1), but several clinical studies indicate that BMD is correlated more to serum levels of estradiol than to serum levels of testosterone in males (2-4). A previous clinical study, which directly compared estrogen versus testosterone effects on bone, showed that estrogens play the dominant role in the regulation of bone resorption markers, whereas both estrogens and testosterone contribute to the maintenance of markers for bone formation (5).The effects of testosterone can be exerted either directly by means of the androgen receptor (AR) or indirectly by aromatization to estrogens and further by estrogen receptor (ER)␣ and͞or ER␤. All three sex steroid receptors are expressed both in growth-plate cartilage and in bone (6-11). Functional studies using sex steroid receptor-inactivated animal models have demonstrated that ER␣ but not ER␤ is important for the regulation of appendicular longitudinal skeletal growth in male mice (12-14), and a recent report indicates that AR-inactivate...

To determine the long-term role of ER␤ in the regulation of longitudinal bone growth, appendicular and axial skeletal growth was followed and compared in female ER␤ ؊/؊ , ER␣ ؊/؊ , and ER␣ ؊/؊ ␤ ؊/؊ mice. Our results show that ER␤ inhibits appendicular and axial skeletal growth and has the capacity to induce fusion of the growth plates.