Arginine vasopressin in primigravid human pregnancy. A prospective study.

The relationship between plasma osmolality (Posm) and plasma arginine vasopressin (Pavp) was determined in: (1) 62 normal primigravidas (P) at various stages of gestation and 35 nonpregnant, healthy volunteers (NP) under conditions of normal hydration or water deprivation, and (2) a separate group of 29 normotensive primigravidas during both the second and third trimesters under normal hydration. Pavp was similar in the P and NP groups, and Posm and Pavp were correlated significantly in both groups, but the osmotic threshold was lowered by 11 mosm/kg in primigravidas. In the prospective study, Pavp and Posm were correlated significantly at both stages. Pavp rose between trimesters, as did plasma volume and plasma renin activity, but urine volume and osmolality and Posm did not change significantly. These data confirm that resetting of the osmostat is operative in primigravid pregnancy and extend these observations by demonstrating that this phenomenon is established at least as early as mid-pregnancy. Furthermore, the osmoregulatory system does not appear to be altered by changes in plasma volume or plasma renin as pregnancy progresses.

Changes in body water and plasma constituents during bullfrog development: effects of temperature and hormones.

The osmoregulatory responses to warmer temperatures and hormone treatment in cold-adapted (5 degrees C) Rana catesbeiana tadpoles and newly metamorphosed frogs were examined. Tadpoles transferred to 11 degrees C and 18 degrees C and left for 5 days lost 7% and 10% of their body weight. Plasma [Na+] was elevated 28% and 21%, respectively. Control (5 degrees C) animals maintained their body weight and plasma [Na+] constant. Daily treatment with either ovine prolactin (oPRL) or ovine growth hormone (oGH) prevented the weight loss and the increase in extracellular [Na+] that occurred when tadpoles were transferred to 18 degrees C. Neither propylthiouracil (PTU) nor arginine vasotocin (AVT) were effective in countering temperature-induced weight loss in tadpoles. Newly metamorphosed frogs transferred to 18 degrees C also lost weight; this was not prevented by daily treatment with saline, oPRL, oGH or PTU. However, in frogs treated daily with AVT, initial BW was regained by day 6. When warm-adapted (18 degrees C) tadpoles were treated daily for 18 days with saline, bPRL, bGH, thyroxine (T4), ergocornine, cortisol, or cortisol + T4, bPRL was most effective in retarding weight loss and maintaining body water content, whereas T4 + cortisol caused the greatest loss of weight and body water. By day 20, the correlations between weight loss and both body water content and hematocrit were highly significant. These data suggest that reported increases in plasma solute concentrations in larval amphibians may actually reflect decreases in extracellular fluid volume, rather than increased amounts of solutes, per se.