Serotonin infusion via the iPrecio® micro infusion pump results in repeated reductions in blood pressure in the normotensive Sprague Dawley rat.

Chronic serotonin (5‐hydroxytryptamine; 5‐HT) infusion causes a prolonged fall in blood pressure (BP) in the Sprague Dawley (S.D.) rat. We have previously studied the hypotensive effects of 5‐HT using an infusion rate of 25μg/kg/min, administered s.c. continuously via osmotic pump for 7 days. We hypothesized that increasing delivery rates of 5‐HT to the S.D. rat would result in progressively greater reductions in BP. 5‐HT or Vehicle (Veh) were administered s.c. via the iPrecio® micro infusion pump for 48 hrs at an initial rate of 5μg/kg/min. The pumps were stopped for 48 hrs and then increasing rates of 5‐HT or Veh were delivered in increments of 10μg/kg/min to achieve a final rate of 45μg/kg/min. Delivery intervals were followed by an interval in which the pumps were stopped for 48 hrs. Mean arterial BP was monitored (DSI radiotelemetry). BP prior to 5‐HT infusion was 101 mm Hg, while BP prior to Veh infusion was 99mmHg. BP values during infusion of 5‐HT at rates of 5μg/kg/min, 15μg/kg/min, 25μg/kg/min, 35μg/kg/min, and 45μg/kg/min were 88 ± 1.6 mmHg, 76 ± 7.0 mmHg, 84 ± 5.8 mmHg, 86 ± 7.5 mmHg, and 88 ± 6.6 mmHg, respectively. BP did not change in Veh infused rats. This study demonstrates that a smaller rate of 5‐HT than we have previously employed is required to elicit a hypotensive effect in the S.D. rats. This is the first study to utilize the iPrecio® micro infusion pump to deliver 5‐HT chronically at increasing rates to the S.D. rat.