The metabolic clearance rate (MCR) of arginine vasopressin (AVP) increases fourfold during human pregnancy. To explore whether circulating vasopressinase may play a role in this change, six women underwent a three-tier infusion clearance study, twice, in random order, to determine the MCRs of either AVP or 1-deamino-8-D-AVP (dDAVP, an analogue resistant to degradation by vasopressinase). [...]

Osmoregulation was studied in eight women during late pregnancy and again 8-10 wk postpartum. Base-line plasma osmolality (Posmol) was significantly lower during (280.9 +/- 2.1 mosmol/kg, SD) than after (289.4 +/- 2.1 mosmol/kg) pregnancy yet 24-h urinary volume and plasma arginine vasopressin (PAVP) measured in vasopressinase-inactivated blood was similar in both groups (pregnancy, 1.39 +/- [...]

Serial studies were designed to characterized changes in osmoregulation throughout gestation. Eight women underwent a 2-h infusion of hypertonic saline before conception, during gestational weeks 5-8, 10-12, and 28-33, and then 10-12 wk postpartum. Basal plasma osmolality (Posmol) was already significantly decreased by 5-8 wk (P less than 0.001) and remained 10 mosmol.kg-1 below nonpregnant [...]

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