Estrogen regulates the amount of white adipose tissue (WAT) in females, but its role in males and whether WAT effects involve estrogen receptor-␣ (ER␣) or ER␤ were unclear. We analyzed the role of ER␣ in WAT and brown adipose tissue by comparing these tissues in wild-type (WT) and ER␣-knockout (␣ERKO) male and female mice. Brown adipose tissue weight was similar in ␣ERKO and WT males at all ages. Progressive increases in WAT were seen in ␣ERKO males with advancing age. Epididymal, perirenal, and inguinal WAT weighed 139 -185% more in ␣ERKO than in WT males by 270 -360 days of age. Epididymal and perirenal adipocyte size was increased 20% in ␣ERKO males. Adipocyte number was 82-168% greater in fat pads of ␣ERKO vs. WT males. Compared with WT, 90-day-old ␣ERKO females had increases in fat pad weights (54 -103%), adipocyte size, and number. Both ␣ERKO males and females had insulin resistance and impaired glucose tolerance, similar to humans lacking ER␣ or aromatase. Energy intake was equal in WT and ␣ERKO males, indicating that obesity was not induced by hyperphagia. In contrast, energy expenditure was reduced by 11% in ␣ERKO compared with WT males, indicating that altered energy expenditure may be important for the observed obesity. In summary, ER␣ absence causes adipocyte hyperplasia and hypertrophy, insulin resistance, and glucose intolerance in both sexes. These results are evidence that estrogen͞ER␣ signaling is critical in female and male WAT; obesity in ␣ERKO males involves a mechanism of reduced energy expenditure rather than increased energy intake. O besity is a significant human health problem whose incidence is reaching epidemic proportions in some Western countries. For example, obesity in Americans has risen dramatically in the past 40 years, from 12.8% in 1962 to 22.5% in 1998, and 55% of the population is considered overweight (1). Obesity is associated with increased type II diabetes, heart disease, certain cancers, and other health problems, and obesity is estimated to be responsible for 300,000 deaths͞year in the U.S. (2). Because of these human health concerns, there is intense interest in factors that regulate development and function of white adipose tissue (WAT). In addition, factors regulating WAT in food animals are important because of concerns over excess fat consumption in Western diets, which may contribute to adverse health effects.Evidence from both humans and laboratory animals suggests that estrogen plays an important role in WAT regulation. Ovariectomy of rodents increases WAT, and estrogen replacement decreases WAT (3). Similarly, postmenopausal women have increased WAT, and estrogen therapy decreases WAT levels compared with untreated postmenopausal women (4).Female WAT expresses the classical estrogen receptor, estrogen receptor-␣ (ER␣), as well as the recently described ER␤ (5-8). Although the relative role of ER␣ and ER␤ and the mechanism by which estrogen regulates WAT are unclear, estrogen effects on glucose homeostasis in females may be involved (9). For example, glucose to...

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The sections in this article are: Respiration Circulation Central Command Mechanisms Central Drive of Locomotion Locomotor Pattern Generator Supraspinal Locomotor Sites Central Command Control of Respiration and Circulation in Animals Cerebral Cortex Hypothalamic Locomotor Region Mesencephalic Locomotor Region Amygdala Awake, Exercising Animal Studies Short‐Term Potentiation Respiration Central Command Control of Respiration and Circulation in Humans Respiration Circulation Interactions Between Central Command and Peripheral Feedback Interaction of Central Command with Cardiorespiratory Reflexes Baroreceptor Reflex Hering‐Breuer Reflex Chemoreceptor Reflexes Conclusions

Adipocyte hyperplasia is characteristic of some forms of human obesity, but the role of adipocyte number in obesity and how normal adipocyte number is established are unclear. Preadipocytes proliferate and then differentiate to become mitotically quiescent adipocytes. This involves exit from the cell cycle, a process regulated by cell cycle inhibitors such as the cyclin-dependent kinase inhibitors (CDKIs) p27 and p21. 3T3-L1 preadipocytes show marked changes in p27 and p21 during differentiation, suggesting CDKIs may regulate establishment of adipocyte number in vivo. To study the role of these CDKIs in adipogenesis, we analyzed adult p27 knockout (p27KO), p21 knockout (p21KO), p27/p21 double knockout (DBKO), and wild-type (WT) mice. Adult DBKO mice weighed 100% more and had fourfold increases in body fat percentage compared with WT. Fat pad weights were increased 80, 90, and 500% in p27KO, p21KO, and DBKO mice, respectively, compared with WT. Adipocyte numbers of p27KO, p21KO, and DBKO mice were 1.9-, 1.7-, and 6.1-fold, respectively, that of WT; adipocyte size was not increased. DBKO mice showed glucose intolerance, insulin insensitivity, hepatic steatosis and dyslipidemia; gradations of these effects occurred in p27KO and p21KO mice. In conclusion, p27KO and p21KO mice are obese because of adipocyte hyperplasia, and DBKO mice have further increases in obesity and adipocyte hyperplasia, indicating that their functions in establishing adipocyte number are not redundant. p27 and p21 are major regulators of adipocyte number in vivo, and knockouts lacking one or both of these proteins provide models for producing adipocyte hyperplasia and understanding its metabolic consequences.