Consequence of social isolation on blood pressure, cardiovascular reactivity and design in spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR), which inherently display exaggerated cardiovascular defence reactions to environmental stimuli (Hallbäck and Folkow 1974), and normotensive control rats (NCR) were kept isolated after they were weaned to reduce such environmental influences which normally induce psychological activation. Mean arterial pressure was followed until 7 months of age, when the cardiovascular defence reactions to acute mental stress were compared and an analysis of cardiovascular design was made. The isolated SHR but no the isolated NCR, had significantly lower pressures than their unisolated controls. Likewise, judged by the relative weight of the left ventricle and the hemodynamically evaluated design of the hindquarter resistance vessels, the structural cardiovascular adaptation was about proportionally less pronounced in isolated than in control SHR. However, their cardiovascular responses to acute "psychological stress" were equally intense, and clearly exaggerated when compared with NCR. Thus, a prolonged reduction of excitatory environmental influences implies a relatively less pronounced development of hypertension in SHR, even though an inherent hyperreactivity concerning neurohormonal pressor responses to alerting stimuli is present. These findings tress the importance of interacting intrinsic-hereditary and extrinsic neurogenic influences for the initiation of primary hypertension.