Telemetric monitoring of cardiovascular parameters in conscious spontaneously hypertensive rats.

We compared cardiovascular values obtained with a telemetric system simultaneously with those recorded by an externalized catheter in spontaneously hypertensive rats (SHR). We also tested the hypothesis that telemetric monitoring reduces the amount of stress associated with performance of cardiovascular studies. Femoral arterial and venous catheters were implanted under methoxyflurane anesthesia in male SHR previously implanted 38 +/- 7 days earlier with radiotelemetric devices. Rats were then allowed 1 day to recover before undergoing experimentation. Baseline blood pressure (BP) and heart rate (HR) values obtained with the telemetric system and with the femoral arterial catheters were similar, and intravenous (i.v.) administration of phenylephrine (PE), angiotensin I (ANGI), acetylcholine (ACh), or nitroglycerin (NTG) evoked similar changes in BP and HR. Hemodynamic responses evoked by i.v. administration of nifedipine were also similar as recorded by telemetric monitoring and the femoral arterial cannula. Baseline cardiovascular parameters measured in SHR instrumented only with telemetric devices consistently yielded BP and HR values significantly lower than those recorded by tail-cuff or femoral catheters. In addition, SHR subjected to the tail-cuff procedure responded to oral administration of captopril with a greater degree of hypotension. These studies demonstrate that telemetric monitoring of cardiovascular parameters in conscious rats is a sensitive, accurate, and flexible method. The lower basal cardiovascular values and the insensitivity to the hypotensive effects of angiotensin-converting enzyme (ACE) inhibition, suggest that a decreased level of stress is associated with performance of cardiovascular studies by a radiotelemetric system.