In explanation of premenstrual fluid retention, previous studies reported higher capillary filtration coefficients in women in the luteal phase of the menstrual cycle than at other times (e.g. Tollan et al. 1993). In contrast, Gooding et al. (2002) found no cycle-related differences. The discrepancy may relate to use of a single large venous congestion pressure step to measure filtration in the first studies as opposed to small incremental pressure steps in the second since only the former triggers a local veni-arteriolar vasoconstrictor reflex (Gamble et al. 1993). This has been shown to be attenuated in the luteal phase in skin when activated by venous distension on limb dependency (Hassan et al. 1990), and reduced ability to regulate precapillary resistance could contribute to increased capillary pressure and higher filtration values. This study aimed to examine changes in filtration capacity during the cycle and investigate whether local vasoconstriction in the whole limb is altered between phases.

With local University of Birmingham ethical approval and informed consent, calf microvascular filtration capacity (K_f) was assessed in thirteen healthy women (18-22 years) with normal menstrual cycles and not taking oral contraceptives, by applying small cumulative increases in pressure to a thigh cuff and measuring calf swelling by mercury-in-silastic strain gauges. K_f was significantly lower in the early luteal (4.65 ± 0.50 X 10^-3 ml min^-1 100 ml^-1 mmHg^-1, mean ± S.E.M.) than in the menstrual, early follicular or late luteal phases (5.99 ± 0.76, 6.56 ± 0.78, 6.67 ± 1.29 X 10^-3 ml min^-1 100 ml^-1 mmHg^-1, respectively, P < 0.05, repeated measures ANOVA). Mean arterial pressure and resting calf blood flow were unchanged through the cycle. Calf blood flow was also measured by further brief venous congestion when the thigh cuff had been inflated to 50 mmHg for 7-10 min, as in the single step filtration method. Venous distension led to a reduction in flow of 49 ± 9 % in the menstrual phase but changes in flow (-11 ± 17 %) were non-significant in the early luteal phase.

The limb vasoconstrictor response to venous distension is clearly attenuated in the early luteal phase of the cycle, which could underlie the higher limb filtration capacity values measured with a large single step venous congestion method. The reason for lower early luteal K_f values with small venous congestion steps remains to be determined.