Long‐term Treatment with Antihypertensive Drugs in Spontaneously Hypertensive Rats (SHR). Effects on Blood Pressure, Survival Rate and Cardiovascular Design

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Abstract
Three age groups of SHR were treated orally with hydralazine and guanethidine. The first “prehypertensive” group was treated from 2.5 until 8 months of age, and thereafter pressure was followed for another 6 months. A delayed and quite modest pressure increase then occurred and average life span was prolonged compared with untreated SHR or SHR treated only from 12 months of age. ‐ The second, 8 months old group, representing “established” hypertension, was treated for 5, 10 or 20 weeks, the last subgroup being followed for another 2 weeks without treatment. Arterial pressure, left ventricular weight and design of the resistance vessels as explored by quantitative hemodynamic analyses, were studied at these intervals. After 5 weeks pressure was normalized with some regression of hypertrophic vascular changes, particularly in females, though the increased wall/lumen ratio appeared to remain and heart weight was only slightly reduced. After 20 weeks with and 2 weeks without treatment, cardiac and vascular design were still the same as during treatment but pressure had now risen considerably. ‐ The third, 14 months old group with “advanced” hypertension was treated for 13 weeks, causing only modest pressure reduction and vascular regression. ‐ This suggests that early treatment has great advantages, that females exhibit more regression of vascular structural changes than males and that late treatment gives less regression, presumably due to addition of less reversible wall components like collagen.