ATRIAL-NATRIURETIC-PEPTIDE AND ITS MESSENGER-RNA IN HEART AND BRAIN OF VASOPRESSIN-DEFICIENT BRATTLEBORO RATS

To understand the secretion and synthesis of atrial natriuretic peptid e we measured immunoreactive atrial natriuretic peptide from plasma, h eart tissues and brain areas, and ANP mRNA was determined from heart a uricles and ventricles of vasopressin-deficient Brattleboro rats (DI) and from desmopressin treated Brattleboro rats (DI+DDAVP). Long-Evans rats (LE) served as controls. DI+DDAVP rats were given for 3 days sc, injections of 0.5 mu g 1-desamino-8-D-arginine vasopressin in 1 mL sal ine twice a day. The rats were housed in single metabolic cages and ur inary output and water intake were measured daily. All the body and or gan weight parameters were similar in the three groups when the rats w ere killed. No change was seen in the plasma ANP level between the gro ups. The right ventricle of DI+DDAVP rats had significantly (P < 0.05) higher concentration of ANP than LE rats (15.8 +/- 4.4 vs. 3.4 +/- 0. 6 ng mg(-1) tissue). The left ventricle of DI and DI + DDAVP had signi ficantly (P < 0.05) lower amounts of ANP mRNA than LE rats (0.5 +/- 0. 2 vs. 1.3 +/- 0.2 and 0.5 +/- 0.1 vs. 1.3 +/- 0.2 arbitrary units). In the hypothalamus, the ANP concentration was significantly (P < 0.05) lower both in DI and in DI+DDAVP rats than in LE rats (9.3 +/- 1.3 vs. 14.5 +/- 1.6 and 6.1 +/- 0.6 vs. 14.5 +/- 1.6 pg mg(-1) tissue). To c onclude, although the water intake and urinary output of DI rats were changed towards normal with desmopressin treatment, the heart ventricu lar and hypothalamic ANP did not parallel the change. Desmopressin inc reased the ANP concentration in the right ventricle of DI rats. Thus t he correction of the complete vasopressin deficiency does not appear t o associate with synthesis or release of atrial natriuretic peptide in heart or hypothalamus.