Hyperresponsivitiy of spontaneously hypertensive rat to indirect measurement of blood pressure.

A chronic, indwelling, tail arterial cannula was implated in conscious undisturbed rats for measurement of blood pressure and heart rate and for obtaining blood samples. As an index of sympathetic activity, plasma levels of catecholamines in arterial blood of conscious animals were assayed by a radioenzymatic, paper-chromatographic procedure. Blood pressures of unrestrained spontaneously hypertensive (SHR) rats in their home cages (161 +/- 3/141 +/- 4 mmHg) were not different from those of pentobarbitol-anesthetized, hypertensive animals but were about 25 mmHg lower than awake animals during the restraint required for the tail-cuff procedure. Basal levels of plasma catecholamines in awake, undisturbed or in pentobarbital-anesthetized animals were similar in age-matched SHR and normotensive Wistar-Kyoto (WKY) rats. SHR rats were shown to have greater increase in plasma catecholamines than WKY rats during forced immobilization or restraint for indirect measurement of blood pressure.