Sympathetic nervous system and blood pressure maintenance in the Brattleboro DI rat

Experiments were performed to determine the functional role of the sympathetic nervous system (SNS) in blood pressure regulation in Brattleboro diabetes insipidus (DI) rats and to determine the effects of synthetic arginine vasopressin (AVP) on sympathetic function in DI rats. The experiments were conducted in male age-matched Long-Evans (LE) and DI rats in the conscious unstressed state. Mean arterial pressure (MAP) and heart rate were similar in conscious unstressed LE and DI rats, but basal plasma concentrations of norepinephrine (NE) and epinephrine (E) were elevated in DI rats compared with LE rats. An intra-arterial bolus injection of hexamethonium (30 mg/kg) resulted in greater reductions of MAP in DI rats (-62 +/- 5 mmHg) than in LE rats (-42 +/- 7 mmHg; P less than 0.05). Administration of AVP to DI rats by osmotic minipump reduced plasma NE concentration in DI rats to a level not different from that in LE rats, but E concentration remained elevated. AVP administration to DI rats also reduced the hexamethonium-induced fall in MAP in these animals (-47 +/- 7 mmHg) to a level not different from that in LE rats. We conclude that the SNS plays a greater role in blood pressure maintenance in conscious DI rats than in LE rats and that AVP administration can normalize plasma NE concentration and the contribution of the SNS to blood pressure maintenance in these animals.