The effect of cyclical hormonal changes on erythrocyte electrolyte transport mechanisms

Electrolyte transport characteristics were examined in erythrocytes from 13 normal men and from two groups of women: taking combined oral contraceptive preparations (O/C, n = 10), and ovulatory women (non-O/C, n = 10) pre- and post-ovulation, at the same time intervals (days 7-10 and days 15-18) during a menstrual cycle. With rubidium (86Rb+) used as a potassium analogue, co-transport (ouabain-resistant, frusemide-sensitive 86Rb+ influx) values were found to be lowest in non-O/C women (28 +/- SE 2.5 nmol h-1 10(-9) cells) and highest in men (56 +/- 5.7, P less than 0.001), with results between the two in women taking O/C (42 +/- 4.2, P less than 0.05 vs men, P less than 0.01 vs non-O/C). Passive 86Rb leak (frusemide-and ouabain-resistant) was significantly lower in men (13 +/- 1.6 nmol h-1 10(-9) cells) than in both groups of women (non-O/C 29 +/- 1.8, P less than 0.001; O/C 25 +/- 1.2, P less than 0.001). There was no cyclical variation within either group of women. Maximum ouabain binding (number of NA+,K+-ATPase units) was the same in all groups. Na+,K+-ATPase activity, as determined by ouabain-sensitive 86Rb influx, was the same in men and non-O/C groups, but was significantly suppressed in O/C compared with both men (P less than 0.01) and non-O/C women (P less than 0.05). The differences found were not due to alterations in either progesterone or aldosterone, but could represent an androgenic effect in vivo of the 19-nortestosterone derivatives in combined oral contraceptive preparations.