Increased ankle swelling is frequently reported by women during the premenstrual phase of the menstrual cycle. This may represent an increase in permeability of the vessel wall and/or an increase in filtration due to an alteration in the transcapillary hydrostatic pressure. The microvascular filtration coefficient (K_f) has previously been shown to significantly alter during the menstrual cycle in young women taking the oral contraceptive preparation (OCP) or in those with premenstrual syndrome (PMS). However, K_f has not been examined during the menstrual cycle in untreated women without PMS and thus this was the aim of the study. Ethical approval was granted by the Exeter Medical Research Ethics Committee and all subjects gave informed written consent.

Ten healthy females (median age: 32 years, range: 23-43 years) and ten healthy males (median age: 36 years, range: 22-40 years) were recruited for this study. K_f was determined in early follicular phase (day 1 to 7) and late luteal phase (day 20 to 27) in the female subjects, and on two occasions separated by a minimum of 7 days in male subjects. The stage of menstrual cycle was confirmed by serum progesterone and oestradiol levels in female subjects. K_f was assessed in the calf using strain gauge plethysmography (Fitrass 2001, DOMED) and the application of small cumulative pressure steps.

K_f in early follicular phase (median: 2.79 ml min^-1 100 ml^-1 mmHg^-1 X 10^-3; range: 0.9-3.42 ml min^-1 100 ml^-1 mmHg^-1 X 10^-3) was not significantly different from that in late luteal phase (median: 2.72 ml min^-1 100 ml^-1 mmHg^-1 X 10^-3; range: 1.46- 4.38 ml min^-1 100 ml^-1 mmHg^-1 X 10^-3) (P = 0.51, Wilcoxon signed rank test). In the male subjects K_f was not significantly different between the two visits (visit 1 median: 2.91 ml min^-1 100 ml^-1 mmHg^-1 X 10^-3; range: 2.06-5.61 ml min^-1 100 ml^-1 mmHg^-1 X 10^-3; visit 2 median: 3.25 ml min^-1 100 ml^-1 mmHg^-1 X 10^-3; range: 1.70-3.99 ml min^-1 100 ml^-1 mmHg^-1 X 10^-3) (P = 0.72, Wilcoxon signed rank test).

Thus in contrast to findings in women on the OCP or with PMS, K_f does not vary during the menstrual cycle in this study with adequate power to detect similar changes to those previously described. Variations in K_f during the menstrual cycle described in previous studies in healthy women may result from the presence of OCPs per se or be a characteristic of the younger women studied.