Central ANP administration in conscious dogs responding to dehydration and hypovolemia

Eighteen beagles were chronically instrumented with an anterior third ventricular (A3V) infusion device to analyze, in conscious dogs, the involvement of central atrial natriuretic peptide (ANP) in body fluid and blood pressure control. The dogs' osmotic and body fluid homeostasis was challenged by 24 h water deprivation or blood withdrawal (12 ml/kg body wt) to elucidate possible modifying influences on the release of arginine vasopressin (AVP), angiotensin II (ANG II), and drinking. Three series of experiments were performed: 1) infusion of ANP (500 ng/min) dissolved in artificial cerebrospinal fluid (aCSF) and given for 10 min, 2) infusion of aCSF alone for the same length of time, and 3) time control experiments without infusion. Plasma AVP and ANG II were analyzed by radioimmunoassay, and in several experiments on dehydrated dogs, plasma norepinephrine and epinephrine were additionally determined by high-performance liquid chromatography. Various blood parameters and rectal and ear skin temperatures were measured. Arterial pressure and heart rate were recorded in three animals additionally equipped with carotid loops. Changes in plasma AVP and ANG II induced by dehydration and bleeding were not significantly modified by A3V infusions of ANP and aCSF in comparison to time controls. Blood pressure changes were similar in experiments with A3V ANP infusion and time controls during bleeding and reinfusion. It is concluded that central ANP is not important in the control of vasopressin and renin-angiotensin systems during osmotic and volume challenges in conscious dogs.