Radiotelemetric versus externalized catheter monitoring of blood pressure:Effect of vasopressin in spontaneous hypertension

The changes in arterial pressure that follow withdrawal of a 3-h intravenou s infusion of arginine vasopressin (AVP; 20 ng/kg/min) in spontaneously hyp ertensive rats (SHR) were monitored by radiotelemetry or conventional exter nalized femoral arterial catheters connected to pressure transducers. Basel ine control arterial pressure was lower in the telemetry group compared to the externalized group. After withdrawal of the AVP infusion, blood pressur e fell below preinfusion levels in both groups but the decrease was much le ss in the telemetry group. Strikingly, absolute blood pressure values recor ded both during and after the vasopressin infusion were remarkably similar in the two groups. Responses in rats with externalized catheters implanted 7 days before infusion of AVP, a protocol similar to the telemetry group, w ere similar to those in rats with catheters implanted 24 h earlier. Blood p ressure remained decreased in SHR infused with AVP for several days with co mplete recovery requiring 6-7 days. In contrast, physical activity decrease d only on the first day following withdrawal of the infusion. Thus, the mec hanism accounting for the blood pressure decrease must be of a long duratio n and unrelated to a change in gross physical activity. The results emphasi ze the value of radiotelemetry for recording blood pressure responses. (C) 1999 Elsevier Science Inc.