Relationship of the antihypertensive effect of vasopressin withdrawal to sodium excretion in the Doca-salt hypertensive rat.
Arterial pressure, sodium excretion, urine output, and plasma atrial natriuretic peptide (ANP) concentrations were measured before, during, and after a 3-h i.v. infusion of arginine-vasopressin (vasopressin; 20 ng/kg/min) in conscious Doca-salt hypertensive rats. Arterial pressure was 166 +/- 8 mm Hg before the infusion of vasopressin; in comparison, pressure was only 130 +/- 4 mm Hg 5 h after stopping the infusion. The fall in pressure after withdrawal of an equipressor dose of phenylephrine in hypertensive animals was much less. In sham normotensive rats, pressure did not fall below control levels after stopping either the vasopressin or phenylephrine infusion. Sodium excretion rates were higher during infusions of vasopressin than during phenylephrine infusions. However, the elevations observed during vasopressin were similar in the hypertensive (25.3 +/- 4.9 mumol/kg/min) and normotensive (22.9 +/- 2.7 mumol/kg/min) groups. Urinary output increased to a greater extent in the hypertensive rats during the infusions of both vasopressin and phenylephrine, but the increases were similar for the 2 pressor agents. Plasma levels of ANP were elevated during the infusions of vasopressin in the normotensive rats, but not in hypertensive rats. The results indicate that the fall in pressure associated with cessation of a pressor dose of vasopressin appears specific to the hypertensive state, and relatively specific to vasopressin. This withdrawal-induced antihypertensive phenomenon (WAP) does not appear to be due solely to the preceding natriuresis and diuresis during the infusion of vasopressin. However, because the hypertensive animal may be more sensitive to a given degree of sodium loss, the possibility that the natriuresis could play a contributing or permissive role cannot be excluded.
Wang
H
H
Department of Pharmacology, Faculty of Medicine, University of Saskatchewan, Saskatoon.
Wilson
N
N
McNeill
J R
JR
D000818:Animals; D009320:Atrial Natriuretic Factor / Q000097:blood; D001794:Blood Pressure; D003900:Desoxycorticosterone; D006400:Hematocrit; D006973:Hypertension / Q000139:chemically induced / Q000503:physiopathology*; D009318:Natriuresis; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000097:blood; D014667:Vasopressins / Q000008:administration & dosage* / Q000502:physiology
D014667:Vasopressins; D003900:Desoxycorticosterone; D009320:Atrial Natriuretic Factor; D012964:Sodium