1. Renin messenger RNA (mRNA) levels were compared in the kidneys, livers, brains, adrenals, aortae and hearts of spontaneously hypertensive (SHR) and Wistar—Kyoto (WKY) rats at 5 and 12 weeks of age using a ribonuclease-protection technique
2. Relative levels of renin mRNA were increased in the kidney, liver, brain, adrenal and heart of the young SHR compared with the WKY. In the aorta, levels were similar in the two strains at 5 weeks
3. In 12-week-old animals, while increased levels persisted in the liver, brain and adrenal of the SHR, the level in the kidney was now the same in the two strains and the levels in the heart and aorta were lower in the SHR compared with the WKY
4. Renin mRNA levels in the kidneys of SHR and WKY were also compared by Northern blotting and confirmed the observations made with the ribonuclease-protection technique
5. The findings indicate a widespread abnormality of renin gene expression in the SHR which is modulated in some tissues by the development of hypertension
6. While the mechanism(s) for the abnormality remains to be determined, the increased renin mRNA levels in the SHR in several tissues concerned with blood pressure regulation suggests an important role for the renin-angiotensin system in the development and maintenance of hypertension
7. However, the finding of increased renin mRNA in the liver also suggests abnormalities in other, as yet unknown, functions of the renin—angiotensin system in the SHR.