Recent studies on M-SHRSP and their crossbred offspring with WKY.

An inbred strain of M-SHRSP was established through successive selective brother-sister breeding of SHRSP for over 20 generations while administering hydralazine hydrochloride. This strain shows blood pressures as high as 250 mmHg or more in males at 12 weeks of age and in females at 15 weeks of age. The incidence of cerebrovascular lesions is over 97%, somewhat higher than that of SHRSP, in both sexes. But there is a remarkable increase in the incidence of multiple small hemorrhages at the base of the brain. Plasma renin activity increases more rapidly than that of SHRSP. Blood pressure of the hybrid (WT) obtained by crossbreeding M-SHRSP and WKY were intermediate to those of the parents. Those offspring obtained by backcrossing WT with WKY for 3 generations were intermediate to those of the parents and had gradually decreased nearly to the level of WKY. Those offspring obtained by backcrossing WT with M-SHRSP for 4 generations were also intermediate to those of the parents and had gradually rose nearly to the level of M-SHRSP. These various M-SHRSP, WKY and hybrid crosses and backcrosses have resulted in rat colonies with eight gradients of blood pressure, ranging from 135 to 250 mmHg.