Effects of oestrogen-only and oestrogen-progestogen replacement therapy upon circulating angiotensin I-converting enzyme activity in postmenopausal women.

Objective: Levels of angiotensin I-converting enzyme (ACE) in blood are associated with variation in cardiovascular disease risk. Serum ACE activity in women may be reduced by combined oestrogen-progestogen hormone replacement therapy (HRT). However, the relative contribution of each hormonal component to this observation is uncertain. We investigated ACE activity in two groups of healthy postmenopausal women receiving HRT regimens.
Design: The first group received placebo or oestrogen-only HRT randomly (oral conjugated equine oestrogens or transdermal 17 beta-oestradiol). The second group was treated with oestrogen-only HRT (oral 17 beta-oestradiol) followed by sequential oestrogen-progestogen HRT (17 beta-oestradiol and dydrogesterone).
Measurements: Assay of blood for soluble ACE activity before and whilst receiving HRT.
Results: In the first group, oral conjugated equine oestrogens significantly reduced (P < 0.01) ACE activity by 18% on average relative to pretreatment whereas non-significant changes of -9% and +7% were seen with transdermal 17 beta-oestradiol or placebo treatment, respectively. In the second group oestrogen-only HRT significantly reduced (P < 0.001) ACE activity by 15% on average. The reduction during both the oestrogen-only and combined phases of sequential treatment was 12% and 19%, respectively, compared with pretreatment values (P < 0.01 and P < 0.001). ACE activity also differed significantly (P < 0.05) between the two phases of sequential treatment.
Conclusions: Both oestrogen-only and oestrogen-progestogen HRT may reduce ACE activity in blood. Oestrogen and progestogen may exhibit additive effects on blood ACE activity.