Importance of Adaptive Changes in Vascular Design for Establishment of Primary Hypertension, Studied in Man and in Spontaneously Hypertensive Rats

Experiments are surveyed which deal with the background of the raised resistance in primary hypertension, as studied in man and, particularly, in spontaneously hypertensive rats (SHR). When exposed to frequent neurohormonal pressure rises, resistance vessels adapt structurally within a few weeks with a thickening of the media which encroaches upon the lumen, thus raising the wall/lumen ratio. This structural adaptation, implying both a raised resistance even at complete smooth muscle relaxation and potentiated resistance increases to given smooth muscle activation, appears to be so pronounced in primary hypertension, both in man and SHR, as to account almost alone for the raised “resting” resistance.

Concerning hereditary elements, SHR respond to graded environmental stimuli with exaggerated heart rate and pressure rises that are primarily central in origin. These responses, again, serve to trigger a gradual structural adaptation of both the resistance vessels and the left heart which, in turn, seems to be somewhat more pronounced than in controls for a given pressure “load”.

Early pharmacological interference in SHR with neurohormonal pressor influences can largely prevent the structural vascular adaptation and, hence, prevent hypertension. Moreover, once established, the structural changes can show considerable and rapid regression if the pressure load is effectively kept lowered by pharmacological means.