The Influence of Oral Contraceptives on Diurnal Urine Regulation

Hypothesis / aims of study Sex hormones have a pronounced effect on arginine vasopressin (AVP), and therefore on the diurnal water homeostasis. The structural resemblance of oxytocin to AVP has likewise led to speculations of a possible additive antidiuretic effect of oxytocin (1). Prostaglandin E2 (PGE-2) counteracts the effect of AVP on water reabsorption and will be elevated when the concentration of estrogen is above normal range (2). In consequence of these relationships, it seems reasonable to assume that the endpoint, the diurnal urine production, would be influenced by the concentration of sex-hormones. Since the ethinyl estradiol of oral contraceptives (OC) is much more potent than the endogenous estrogens, ingestion of OC can, therefore, be expected to exaggerate diurnal variations in urine flow. This study therefore aims to elucidate the influence of oral contraceptives (OC) on diurnal urine regulation. We hypothesized that: 1) combined oral contraceptives decrease AVP concentration and diminish the circadian profile of AVP. 2) The high content of ethinyl estradiol in the pills increases the level of oxytocin and will lead to an oxytocin-induced antidiuresis. In addition we determined renal prostaglandins to clarify whether they were involved in the diurnal urine regulation in females taking oral contraceptives.