ObjectiveTo investigate the role of the renin gene in the hypertension of the spontaneously hypertensive rat (SHR) of the Okamoto strain.MethodsWe determined whether the SHR renin allele was cosegregated with high blood pressure in 137 F2rats derived from inbred SHR and Wistar–Kyoto rats. Systolic blood pressure in conscious rats was measured by the tail-cuff method, whereas mean arterial pressure was determined from an indwelling catheter in the left carotid artery. Renin genotypes of F2rats were determined using a SHR-specificBglIIrestriction fragment length polymorphism that we have previously described.ResultsThe SHR renin allele was cosegregated significantly with higher systolic blood pressure in male F2rats aged 8–24 weeks and in females aged 12–24 weeks. The greatest differences in blood pressure between SHR renin allele homozygotes and Wistar–Kyoto rat renin allele homozygotes were 35 mmHg for males and 17 mmHg for females aged 24 weeks. The SHR renin allele was also associated with a higher mean arterial pressure in rats aged 24 weeks and cosegregated with higher body weight of male F2rats aged 12–24 weeks but not with that of the females. In contrast to the relationship with blood pressure, the SHR renin allele was segregated with lower plasma renin concentrations in rats aged 24 weeks.ConclusionThese results are consistent with the SHR renin gene being one of the loci determining high blood pressure in rats of this strain, possibly through action at some extra-renal site subserving control of blood pressure.