Systemic arterial hypertension in rats exposed to short-term isolation; intra-arterial systolic and diastolic blood pressure and baroreflex sensitivity.

A system is described for accurately recording systolic and diastolic blood pressure in conscious, unrestrained rats. The system consists of a portion of flexible intra-arterial catheter joined to a length of rigid plastic tubing which is connected to a transducer via a stainless steel needle and tap. The whole system is filled with degassed saline. Traces obtained on a recording oscilloscope indicate that this system gives a flat response to 35 Hz. With this system we have shown that systolic and diastolic blood pressures are significantly greater in rats which have been isolated for 15--20 days than in group-housed animals, both in the anaesthetized and conscious state. Measurements were made of the pulse-interval response to an increase in systolic blood pressure induced by either a bolus injection or a slow infusion of a vasoconstrictor drug as a means of assessing baroreflex sensitivity. There was a significant reduction of the baroreflex sensitivity of isolated rats compared to grouphoused animals. The present findings indicate that the elevation in blood pressure seen in isolated rats is not a transient response to the stress of the indirect measurement techniques used in previous studies.