What are hot flushes?
A hot flush or flash is a very common symptom of menopause. It is described as a feeling of sudden intense internal heat often accompanied by sweating and redness in the face. Hot flushes are caused by a rapid dissipation of heat from the body due to dilatation of peripheral blood vessels close to the skin. Normally the body has a wide range of temperatures, called the thermoneutral zone (TNZ), in which body temperature can be maintained without any metabolic expenditure such as sweating or shivering.
As oestogen levels fall at menopause this contributes to a reduced TNZ such that small increases in core body temperature can trigger responses like flushing and sweating to reduce body heat. This response is thought to be mediated by activation of the central sympathetic nervous system and this in turn is regulated by alpha adrenergic receptors in the central nervous system. The regulation of body temperature is controlled by neurotransmitters like noradrenaline, which causes dilation of peripheral blood vessels.
Oestrogen influences the thermoregulation centres in the hypothalamus of the brain and a fall in oestrogen at menopause is thought to disrupt the regulation by noradrenaline of body temperature. Treatment with an alpha blocking medication like clonidine inhibits release of noradrenaline in the central nervous system and this in turn reduces vasodilation of peripheral blood vessels which helps relieve symptoms of hot flashes
1.
Synthetic hormones for HRT
The synthetic steroid hormone tibolone can be used for HRT to treat symptoms of menopause. Although tibolone itself has no biological activity it is rapidly metabolised into metabolites that have estrogenic, androgenic and progestagenic properties. The active metabolites of tibolone have estrogenic effects on bone and vaginal tissue and function as a progestagen In endometrial tissue, whereas in the brain and liver they have androgenic effects. In breast tissue tibolone blocks the conversion of estrone sulfate to the more active oestrogen oestrodiol, which may reduce the risk of breast cancer
2.
Sequential hormone therapy for HRT
The use of sequential hormone therapy is an alternative form of HRT compared with the more commonly used continuous HRT. The regime for sequential hormone therapy begins with a phase of oestrogen only followed by a combination of oestrogen with progesterone, for the remainder of the cycle, returning to oestrogen only again at the start of the next cycle. For sequential hormone therapy oestrodiol has been combined with cyproterone, a progesterone derivative with weak progestational activity as well as anti-androgen activity and has been found beneficial in relieving symptoms of menopause.
References
- Freedman RR. Menopausal hot flashes: mechanisms, endocrinology, treatment. J Steroid Biochem Mol Biol.2014;142:115-20.
- Modelska K, Cummings S. Tibolone for postmenopausal women: systematic review of randomized trials. J Clin Endocrinol Metab. 2002; 87:16-23.