Publications

Although increased G(i) signaling has been associated with dilated cardiomyopathy in humans, its role is not clear. Our goal was to determine the effects of chronically increased G(i) signaling on myocardial function. We studied transgenic mice that expressed a G(i)-coupled receptor (Ro1) that was targeted to the heart and regulated by a tetracycline-controlled expression system. Ro1 expression for 8 wk resulted in abnormal contractions of right ventricular muscle strips in vitro. Ro1 expression reduced myocardial force by >60% (from 35 +/- 3 to 13 +/- 2 mN/mm(2), P < 0.001). Nevertheless, sensitivity to extracellular Ca(2+) was enhanced. The extracellular [Ca(2+)] resulting in half-maximal force was lower with Ro1 expression compared with control (0.41 +/- 0.05 vs. 0.88 +/- 0.05 mM, P < 0.001). Ro1 expression slowed both contraction and relaxation kinetics, increasing the twitch time to peak (143 +/- 6 vs. 100 +/- 4 ms in control, P < 0.001) and the time to half relaxation (124 +/- 6 vs. 75 +/- 6 ms in control, P < 0.001). Increased pacing frequency increased contractile force threefold in control myocardium (P < 0.001) but caused no increase of force in Ro1-expressing myocardium. When stimulation was interrupted with rests, postrest force increased in control myocardium, but there was postrest decay of force in Ro1-expressing myocardium. These results suggest that defects in contractility mediated by G(i) signaling may contribute to the development of dilated cardiomyopathy.

OBJECTIVE

Most observational studies suggest that postmenopausal women taking hormone replacement therapy have a reduced risk of radiographic knee and hip osteoarthritis (OA). There are no randomized trial data on the association of hormone treatment with knee or hip OA, and no studies have been published regarding the relationship of hormone treatment to knee or hip symptoms. This study examined the association of hormone treatment with prevalent knee symptoms and disability related to knee pain as assessed at the final visit of the Heart and Estrogen/Progestin Replacement Study (HERS).

METHODS

The HERS was a 4-year randomized, double-blind, placebo-controlled trial of estrogen plus medroxy progesterone acetate for prevention of coronary heart disease in postmenopausal women with documented coronary disease. Participants in this substudy on knee pain were 969 postmenopausal women, with a mean age of 66 years and mean body mass index of 28.6 kg/m2, attending the final visit at 9 clinical centers. Frequent knee symptoms were assessed by interview and the severity of knee pain and disability related to knee pain were determined using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Knee symptoms and disability were compared between women assigned to receive hormones and those assigned to receive placebo.

RESULTS

Frequent knee pain was reported in 24.1% of women assigned to receive hormone therapy versus 26.1% of those assigned to the placebo group, a difference of -2.0% (95% confidence interval [95% CI] -7.4% to 3.5%). Among women with knee pain, there were no differences in the severity of pain (score difference -0.2, 95% CI -1.2 to 0.8) or disability (score difference -0.7, 95% CI -3.8 to 2.4) as assessed on the WOMAC. All results were similar for women whose body mass index was either above or below the median.

CONCLUSION

In a group of older, postmenopausal women with cardiac disease, we found no significant effect of 4 years of estrogen plus progestin therapy compared with placebo on knee pain and related disability. Our findings may not apply to other groups of women or to the effect of hormone therapy on the structural changes of knee OA.