Blood pressure and renal haemodynamic response to salt during the normal menstrual cycle

The purpose of the present study was to evaluate prospectively blood pressure and the renal haemodynamic response to salt during the normal menstrual cycle. A total of 35 healthy normotensive young women not on oral contraceptives were enrolled; 17 were studied in the follicular phase and 18 in the luteal phase of the menstrual cycle. The women in each group were then randomly allocated to receive a low-sodium (40 mmol/day) or a high-sodium (250 mmol/day) diet for a 7-day period in two consecutive menstrual cycles. At the end of each dietary period, 24 h ambulatory blood pressure, urinary sodium excretion, plasma renin activity, plasma catecholamine levels and renal haemodynamics were measured. Our results show that the blood pressure response to salt is comparable during the luteal and the follicular phases of the normal menstrual cycle and is characterized by a salt-resistant pattern. In the kidney, effective renal plasma flow was significantly greater and the filtration fraction lower (P<0.05) after salt loading in women studied in the luteal phase compared with women investigated in the follicular phase. This study thus demonstrates that the female hormone status does not affect the blood pressure response to sodium in young normotensive women. However, in contrast with systemic haemodynamics, the renal response to salt varies during the normal menstrual cycle, suggesting that female sex hormones play a role (direct or indirect) in the regulation of renal haemodynamics.