Our research plan is summarized in Figure D$3-1.$ We will study $13$ groups of subjects: $2$ groups ofpremenopausal, healthy lean women $($n$=10$ per group$)$; $2$ groups of young, healthy obese women $($n$=10$ pergroup$),1$ group of premenopausal, obese women with OSA $($but not PCOS; n$=20),1$ group ofpremenopausal, obese women with PCOS $($but not OSA; n$=20),4$ group of healthy lean and obesepostmenopausal women without OSA $($n$=60),1$ group of obese postmenopausal women with OSA $($n$=20),1$ group of obese men without OSA $($n$=20),$ and $1$ group of obese men with OSA $($n$=20)$ to address ourthree Specific Aims. All subjects will participate in two lipid metabolism studies $($see D$3\mathrm{.}4.$ Lipid metabolismstudy$)$: one at the beginning of the study, to determine basal, postabsorptive lipid kinetics at baseline, andanother after various interventions $($see D$3\mathrm{.}5.$ Interventions$).$ Briefly, $60$ obese subjects with OSA $(20$ obesemen, $20$ obese premenopausal and $20$ obese postmenopausal women$)$ will be studied again after treatmentwith continuous positive airway pressure $($CPAP$)$; $10$ lean and $10$ healthy obese women and $20$ obese menwill be studied again after glucocorticoid treatment with dexamethasone; $20$ lean or obese premenopausalwomen with PCOS and $20$ lean or obese postmenopausal women will be studied again after progesteronetreatment; $10$ lean women, $10$ obese premenopausal women and $10$ lean or obese postmenopausal womenwill be studied again after testosterone treatment; $20$ lean or obese postmenopausal women will be studiedagain after estrogen treatment; $10$ lean or obese postmenopausal women will be studied again up to $10$weeks later with no treatment intervention. All studies will be performed in the CRU at WashingtonUniversity School of Medicine.The primary study endpoints will be: i$)$ the rates of hepatic VLDL$-$TG and VLDL$-$apoB$-100$ secretion and theVLDL$-$TG plasma clearance rate $($assessed by using stable isotope labeled tracer methods$)$; ii$)$ theconcentrations of total plasma TG and VLDL$-$TG $($assessed by using spectrophotometric analysis$)$; and iii$)$the concentrations of VLDL$-$apoC$-$II$,$ VLDL$-$apoC$-$III, and VLDL$-$apoE $($assessed by using immunoturbidityassays$).$ To help interpret the results from these measurements and to better understand the potentialmechanisms responsible for the proposed differences between groups and treatment effects on VLDL$-$TGmetabolism, we will also measure: i$)$ plasma glucose and insulin concentration; ii$)$ the rate of appearancePrincipal Investigator$/$Program Director $($last$,$ First, Middle$)$: MITTENDORFER, BettinaPHS $398($Rev$.04/06)$ Page $28$ Continuation Format Page$($Ra$)$ of FFA in plasma $($by using stable$-$isotope labeled tracer techniques$)$; iii$)$ the relative contribution ofsystemic plasma FFA and non$-$systemic fatty acids to total VLDL$-$TG secretion $($by using stable isotopelabeled tracer techniques$)$; iv$)$ whole$-$body fat oxidation $($by using online gas$-$exchange analysis$)$; v$)$ the Raof $-$hydroxybutyrate in plasma $($by using stable isotope labeled tracer techniques$)$; the Ra of glucose inplasma $($by using stable isotope labeled tracer techniques$)$ and the hepatic insulin resistance index$($calculated from the glucose Ra and plasma insulin concentration $(124))$; and vi$)$ muscle and adipose tissueLPL protein mass $($by using the Western blot technique$).$ FFA Ra in plasma is an index of the release ofFFA from adipose tissue into the systemic circulation $(107)$ and represents a major source of fatty acidprecursor for VLDL$-$TG synthesis in the liver; ~$2/3$ of fatty acids in VLDL$-$TG are derived from systemicplasma FFA $(26$; $57$; $102$; $104).$ The remaining fatty acids in VLDL$-$TG are derived from non$-$systemic fattyacid pools; i$.$e$.,$ fatty acids that are not labeled with tracer during the infusion period, which includes: a$)$ fattyacids released from pre$-$existing lipid stores in the liver and retroperitoneal fat depots, b$)$ fatty acids derivedfrom lipolysis of plasma lipoproteins taken up by the liver, and c$)$ fatty acids resulting from hepatic de novolipogenesis. The Ra of $-$hydroxybutyrate in plasma provides an index of hepatic fatty acid oxidation $(125).$Muscle and adipose tissue LPL protein mass provides information concerning the amount of LPL present inthese tissues. We will measure both total LPL protein mass and heparin$-$releasable LPL protein mass $($i$.$e$.,$the amount of LPL associated with endothelial cells$)$ because LPL requires translocation from the cytosol tothe site of action, the endothelial cell barrier $(27$; $29$; $30).$

What will happen in this dtidy