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Objective High blood pressure in spontaneously hypertensive rat (SHR) is associated with increased sympathetic innervation of key tissues, possibly as the result of increased nerve growth factor (NGF). The aim of this study was to test for genetic linkage of the NGF gene to high blood pressure.Design We studied NGF gene expression in young SHR and examined linkage of the NGF locus to mean arterial pressure in genetically segregating crosses of SHR and normotensive Donryu (DRY) rats.Methods NGF mRNA was measured by Northern blot, and a restriction fragment length polymorphism of the NGF gene revealed after digestion with the Nsil restriction enzyme was used to study inheritance.Results Levels of NGF mRNA were detected easily in the kidneys of 2-, 4- and 10-week-old SHR but not in agematched DRY rats. In an F2 population, the blood pressure of rats homozygous for the DRY NGF allele was 6mmHg less than in heterozygotes and 8mmHg less than in rats homozygous for the SHR NGF allele (analysis of variance, P< 0.004). In backcross rats the blood pressure of NGF heterozygotes was not significantly different from that of SHR homozygotes.Conclusion These results indicate differences in renal NGF mRNA in SHR during the development of hypertension and suggest that a genetic locus in or near the NGF gene contributes in a Mendelian dominant pattern to a significant increment in blood pressure in SHR.