Okolo, Stanley O.; (1995) Effects of age and sex steroids on the circulation in women. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

Female sex hormones are presumed responsible for the relative cardiovascular youth of premenopausal women compared with men. It is unclear how these hormones achieve this effect, but suggested mechanisms include lipoprotein metabolism, release of vasoactive substances, and direct effects on vascular smooth muscle. Information on female cardiovascular physiology is very scanty, and results of studies performed in men are usually extrapolated to women. I, therefore, investigated the circulatory effects of age and the characteristic sex hormones in women. Limb blood flow, measured by venous occlusion plethysmography and blood pressure, monitored with an automatic device were relatively unchanged in successive age decades until the age of 64 when they increased. This pattern differs from that in men. In individual subjects limb blood flow was proportional to systolic pressure, but not to age. Peripheral vascular reactivity, as indicated by the reactive hyperaemic response, decreased abruptly after the age of 64, and was inversely related to time since menopause. Resting forearm flow fell, without any change in blood pressure, in the mid-luteal phase of menstrual cycles, and after oral micronized progesterone therapy in postmenopausal women. Transdermal 17β-oestradiol therapy, which produces physiological oestrogen levels, increased forearm flow in non-flushing postmenopausal women but reduced flow in flushers. Stroke distance, stroke volume and left ventricular contractility, measured by Doppler echocardiography increased but frontal cerebral flow, measured by 133Xenon inhalation technique fell. Addition of cyclical progestogen caused no further vascular change over eight weeks. Subcutaneous oestradiol implants, however, increased resting forearm flow, irrespective of flushing frequency. The vascular changes observed with age provide essential reference ranges for assessment of circulatory responses in women. The cardiovascular effects of oestradiol may contribute to the cardiovascular superiority of younger women and the vasoconstrictor action of progesterone might be clinically relevant to disturbances such as menstrual migraine or pelvic pain syndrome.

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