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Abstract
The spontaneously hypertensive rat (SHR) exhibits cardiovascular (CV) hyperreactivity to environmental stress and behavioral hyperactivity relative to the Wistar-Kyoto rat (WKY). The present study sought to determine whether hyperreactivity in the SHR is related to hypertension or to behavioral hyperactivity. By breeding SHR with WKY, followed by inbreeding, one of us (EDH) has developed two new strains in which the hypertensive trait seems to be separated from the hyperactivity trait: the Wistar-Kyoto Hypertensive (WK-HT) and the Wistar-Kyoto Hyperactive (WK-HA) strains. Conscious SHR, WKY, WK-HT, and WK-HA rats were instrumented with catheters and Doppler flow-velocity probes to record arterial pressure, heart rate (HR), and changes in regional vascular resistances, and subjected to air-jet stress and pharmacological interventions. The hyperactive strains (SHR and WK-HA) exhibited enhanced pressor-, renal-, and splanchnic responses to stress, and higher HRs under all conditions, even after ganglionic blockade (Figure 1).
A second finding of this study was that baroreceptor sensitivity was reduced in the WK-HA relative to the WKY, suggesting that factors in addition to elevated arterial pressure produce resetting of baroreceptor sensitivity.