Hypothesis. Biochemical changes at the menopause: possible role of the central nervous system.

Some of the biochemical changes which occur at the menopause can be attributed to an increased rate of loss of bone but others cannot be explained in this way. Data, collected through literature search, are presented which suggest that the rise in plasma phosphate concentration at the menopause is not due primarily to increased breakdown of bone but rather to the following sequence of events: progesterone deficiency----respiratory hypoventilation----mild respiratory acidosis and hypoxia----compensatory metabolic alkalosis----altered carbohydrate metabolism----rise in plasma phosphate concentration. Increases in the concentration of many plasma constituents occur at the menopause, which appear to be due to fluid loss and haemoconcentration. A possible cause of these changes is a reduced secretion of vasopressin by the pituitary gland as a result of oestrogen deficiency. Increases in the fasting urinary excretion of phosphate, sodium and magnesium also occur at the menopause. These changes cannot be attributed to increased bone loss but could be due to the effects of oestrogen deficiency on circadian rhythms in the hypothalamus.