Effects of hormone replacement therapy on insulin-like growth factor (IGF)-I, IGF-II and IGF binding protein (IGFBP)-1 to IGFBP-4: Implications for cardiovascular risk

Abstract

OBJECTIVE: Hormone replacement therapy (HRT) in postmenopausal women is controversial, with an elevated cardiovascular event rate for combined estrogen-progestogen but no adverse cardiovascular effect and possible cumulative benefit for estrogen alone. Here we measured the effects of differing estrogen/progestogen combinations on the insulin-like growth factor (IGF)/IGF binding protein (IGFBP) system which has been implicated in the pathophysiological mechanisms underlying cardiovascular disease, higher IGFBP-1 levels having been linked with a reduced cardiovascular risk. DESIGN: Oral conjugated equine estrogens (CEE) alone, or in combination with the increasingly androgenic progestogens medroxyprogesterone acetate, desogestrel or norethisterone, were given in a randomized triple crossover fashion to 35 healthy postmenopausal women. Serum concentrations of IGFs and the principal circulating IGFBPs were measured. RESULTS: Circulating IGF-I, IGFBP-3 and IGF-I/IGFBP-3 molar ratio were significantly reduced by CEE. These effects were reversed by progestogens according to their androgenicity. Plasma IGFBP-1 concentration increased from baseline to CEE alone. This rise was opposed by progestogens of increasing androgenicity. IGFBP-2 levels fell and IGFBP-4 increased with CEE, with no further change with addition of progestogens. CEE increased the proportional contribution of IGFBP-1 and IGFBP-4 to total IGFBP binding and decreased the IGFBP-3 contribution. This was reversed by progestogens. CONCLUSION: There are marked changes in molar ratios of the IGFBPs in relation to estrogen/progestogens in HRT. The effect of progestogens on IGF bioavailability could be an important determinant of the longer-term risks of specific HRT preparations by opposing the potentially beneficial effects of CEE alone on cardiovascular risk.