[Effects of baroregulation on osmoregulation of arginine vasopressin in rats (author's transl)].

A relationship between blood pressure and the functional character of osmoreceptor controlling vasopressin secretin under usual physiological situations in the rat was studied by employing Na-nitroprusside as depressor agent or norepinephrine as pressor agent and the sensitive and specific radioimmunoassay of arginine vasopressin (AVP). Na-nitroprusside or control saline was given s.c. 15 min after an i.p. injection of 2% (v/w) hyper, hypo or isotonic saline. Norepinephrine or control saline was given s.c. with a concurrent i.p. injection of 2% (v/w) hyper, hypo or isotonic saline. 30 min after this osmotic load, plasma AVP (pAVP) and osmolality (pOSM) were measured on trunk blood as previously described (J. Clin. Invest. 52: 3212, 1973). In rats given Na-nitroprusside, 2 mg/kg body weight, osmotic loading produced a rise in pAVP which correlated relationship (pAVP=1.9 [pOSM-276.6]; N=16; r=0.81) raised significantly (p less than 0.001) to the left of that in the control vehicle (pAVP=1.4[pOSM,-293.8]; N=8; r=0.86). In rats given norepinephrine, 0.1 mg/kg body weight, the regression line generated by osmotic loading (pAVP=1.2[pOSM-229]; N=7; r=0.88) fell significantly (p less than 0.001) to the right of that in the control vehicle (pAVP=1.4[pOSM-202]; N=6; r=0.99). In 4 rats, the same dose of Na-nitroprusside and norepinephrine resulted in a significant (p less than 0.001) decrease (40%) and increase (20%) from the basal level for the same time of osmotic loading in mean arterial blood pressure as measured directly via chronically implanted aorta catheters, respectively. These results indicate that hypotension increases pAVP by lowering the threshold or set and increasing the sensitivity of the osmoregulatory system and hypertension decreases pAVP by raising the threshold or set and reducing the sensitivity of the mechanism without abolishing the system.