Effects of the Selective Serotonin Reuptake Inhibitor Fluoxetine on Baroreceptor Reflex Sensitivity and Body Weight in Young and Old Rats

Male F344BNF1 hybrid rats (F1 crosses between female Fischer 344 and male Brown Norway rats) aged 3 or 24 months were treated with vehicle (1 ml water/kg, IP) or fluoxetine (10 mg/kg, IP) once a day for 1 day or 27 consecutive days; body weights were recorded daily. Baroreceptor sensitivity was assessed in conscious unrestrained rats implanted with vascular catheters 24 hours after the single or 27th injection by measuring peak changes in mean arterial pressure (MAP) and heart rate (HR) elicited by graded doses of phenylephrine or nitroglycerin, IV. The results demonstrate that the effects of the serotonin uptake inhibitor fluoxetine, whether administered acutely or for 27 days, are similar in young and old rats: a relative decrease in body weight, a slight decrease in resting MAP without a change in HR, and no effect on baroreceptor sensitivity. In addition, this study in F344BNF1 hybrid rats supports previous reports in inbred rat strains by demonstrating that baroreceptor dysfunction, but not hypertension, is observed in old rats.