Article: PDF OnlyLouis W. J.; Howes, L. G.Journal of Cardiovascular Pharmacology: 1990 - p S1-S5 Free Abstract Summary The spontaneously hypertensive rat (SHR) is the most commonly used animal model of hypertension. For many years, it has been widely accepted that the most appropriate control strain is the Wistar-Kyoto (WKY) rat to which SHR rats are genetically related. However, recent concerns have been raised about genetic differences between the various colonies of SHRs and, in particular, genetic differences between colonies of WKY rats. It has been further emphasized that the only way to establish that a genetic trait is an etiological factor in the development of hypertension is through studies of F2 backcrosses between SHR and WKY rats. The present article details the history of the SHR and WKY strains and demonstrates why there is high likelihood of genetic variability between rats of both strains from different colonies around the world. It suggests that the WKY strain is not the most suitable for backcross studies because of the incidence of spontaneous hypertension and the somewhat higher levels of blood pressure in these rats. A central reference strain is proposed using SHRs inbred at Kyoto University, where brother/sister inbreeding has continued for more than 80 generations. Copyright © 1990 Wolters Kluwer Health, Inc. All rights reserved.