The renal response to vasopressin depends on reproductive status in women (Boyce et al. 2001) as well as in the rat (Forsling et al. 1996). To investigate the possible role of ovarian steroids, the renal response to DDAVP (Ferring AB, Sweden), an agonist at the renal vasopressin receptor (V2), was monitored in women taking a combined contraceptive pill containing 30 mg ethinylestradiol and 150 mg levonorgesterol (Microgynon-30, Schering Health Care).
The study was carried out on 6 women age 19-28 years with local ethics committee approval and informed subject consent. A water load of 750 ml per 70 kg body weight was given between 08.00 and 09.00 h, followed by 0.2 mg oral DDAVP 2 h later. Hydration was maintained by giving the subjects water to drink equivalent to each urine sample passed; blood and urine samples were taken for 6 h for analysis. Subjects were studied on the last pill-free day, taken as day 7, and day 21.
There were no differences in creatinine clearance on the two days and no changes were observed following DDAVP administration. Control urine flow, osmolality and electrolyte concentrations were similar on the two days, but after DDAVP administration urine flow fell to the lower value of 0.69 ± 0.05 ml min-1 on day 21 compared to 0.87 ± 0.07 ml min-1 on day 7 (± S.E.M., P < 0.001, Student’s paired t test), while the urinary osmolality was higher being 785 ± 22 as compared to 721 ± 16 mosmol kg-1 (P < 0.001) Excretion of sodium and potassium was also significantly greater following DDAVP on day 21 (P < 0.005). Plasma osmolality fell on DDAVP administration, the greater drop to 279 ± 1 mosmol kg-1 on day 21 reflecting the greater antidiuresis on that day. The mean plasma sodium and potassium concentrations achieved were also lower on day 21, as was the packed cell volume. Thus the renal responsiveness to vasopressin was greater following 14 days during which an oestrogen and a gestagen were taken than after 7 days during which no ovarian steroids were administered.
Financial support from the Director General Medical Services (Royal Air Force) and the MRC is gratefully acknowledged.