Hormone Replacement Therapy, Insulin Sensitivity, and Abdominal Obesity in Postmenopausal Women

The purpose of this study was to determine whether insulin sensitivity differs between postmenopausal women taking estradiol, women on estrogen plus progesterone hormone replacement therapy (HRT), and women not on HRT and whether differences are explained by the differences in total and/or abdominal adiposity and fat deposition in the muscle. We studied 28 obese, sedentary postmenopausal Caucasian women. Women taking oral estrogen (n = 6) were matched for age (57 +/- 3 vs. 58 +/- 2 years), weight (87.9 +/- 6.0 vs. 83.0 +/- 3.9 kg), and BMI (33.9 +/- 1.7 vs. 33.9 +/- 1.9 kg/m(2)) with women not on HRT (n = 6). Eight women taking oral estrogen plus progesterone were matched with eight different women not on HRT for age (59 +/- 2 vs. 60 +/- 2 years), weight (82.8 +/- 3.7 vs. 83.7 +/- 4.1 kg), and BMI (30.7 +/- 1.0 vs. 29.9 +/- 1.3 kg/m(2)). VO(2max) (maximal aerobic capacity), percentage of fat, total body fat mass, and fat-free mass (FFM) were similar between groups. Visceral fat, subcutaneous abdominal fat, sagittal diameter, and mid-thigh low-density lean tissue (intramuscular fat) did not differ by hormone status. Basal carbohydrate and fat utilization was not different among groups. Fasting plasma glucose and insulin did not differ by hormone use. Glucose utilization (M) was measured during the last 30 min of a 3-h hyperinsulinemic-euglycemic clamp (40 mU. m(2). min(-1)). Postmenopausal women taking oral estrogen had a 31% lower M than women not on HRT (42.7 +/- 4.0 vs. 61.7 +/- 4.7 micromol. kg(FFM). min(-1), P < 0.05). M was 26% lower in women taking estrogen plus progesterone (44.0 +/- 3.5 vs. 59.7 +/- 6.2 micromol. kg(FFM). min(-1), P < 0.05) than women not on HRT. M/I, the amount of glucose metabolized per unit of plasma insulin (I), an index of insulin sensitivity, was 36% lower in women taking estrogen compared with matched women not on HRT (P < 0.05) and 28% lower in women taking estrogen plus progesterone compared with matched women not on HRT (P < 0.05). Postmenopausal women taking oral estrogen or those taking a combination of estrogen and HRT are more insulin-resistant than women not on HRT, even when women are of comparable total and abdominal adiposity

Deceleration of the E1P-E2P Transition and Ion Transport by Mutation of Potentially Salt Bridge-forming Residues Lys-791 and Glu-820 in Gastric H+/K+-ATPase*

A lysine residue within the highly conserved center of the fifth transmembrane segment in PIIC-type ATPase α-subunits is uniquely found in H,K-ATPases instead of a serine in all Na,K-ATPase isoforms. Because previous studies suggested a prominent role of this residue in determining the electrogenicity of non-gastric H,K-ATPase and in pKa modulation of the proton-translocating residues in the gastric H,K-ATPases as well, we investigated its functional significance for ion transport by expressing several Lys-791 variants of the gastric H,K-ATPase in Xenopus oocytes. Although the mutant proteins were all detected at the cell surface, none of the investigated mutants displayed any measurable K+-induced stationary currents. In Rb+ uptake measurements, replacement of Lys-791 by Arg, Ala, Ser, and Glu substantially impaired transport activity and reduced the sensitivity toward the E2-specific inhibitor SCH28080. Furthermore, voltage clamp fluorometry using a reporter site in the TM5/TM6 loop for labeling with tetra-methylrhodamine-6-maleimide revealed markedly changed fluorescence signals. All four investigated mutants exhibited a strong shift toward the E1P state, in agreement with their reduced SCH28080 sensitivity, and an about 5–10-fold decreased forward rate constant of the E1P ↔ E2P conformational transition, thus explaining the E1P shift and the reduced Rb+ transport activity. When Glu-820 in TM6 adjacent to Lys-791 was replaced by non-charged or positively charged amino acids, severe effects on fluorescence signals and Rb+ transport were also observed, whereas substitution by aspartate was less disturbing. These results suggest that formation of an E2P-stabilizing interhelical salt bridge is essential to prevent futile proton exchange cycles of H+ pumping P-type ATPases