Kinin B1 and B2 receptor mRNA expression in the hypothalamus of spontaneously hypertensive rats

The central hypertensive effects induced by bradykinin are known to be mediated via B-2 receptors, which are present constitutively in the brain. B-1 receptors are rapidly upregulated during inflammation, hyperalgesia, and experimental diabetes. The hypothalamus plays an important role in the regulation of cardiovascular homeostasis, and all components of kallikrein-kinin system have been identified in this area. Therefore, we analyzed the mRNA expression of B-1 and B-2 receptors in the hypothalamus of spontaneously hypertensive rats (SHR) by RT-PCR. Male SHR were studied at three different ages corresponding to the three phases in the development of hypertension: (i) 3-4 (prehypertensive), (ii) 7-8 (onset of hypertension), and (iii) 12-13 weeks (established hypertension) after birth, and compared with age-matched Wistar-Kyoto (WKY) rats. At all ages tested, B-2 receptor mRNA levels in the hypothalamus of SHR were higher than age-matched WKY rats (p < 0.001). However, the B-1 receptor mRNA levels were higher at the established phase of hypertension only. We conclude that B-1 and B-2 receptor mRNA are differentially expressed in the hypothalamus of SHR and may play different roles in the pathogenesis of hypertension: upregulation of B-2 receptor mRNA from early age may participate in the pathogenesis of hypertension, whereas an upregulation of B-1 receptor mRNA in the established phase of hypertension may reflect an epiphenomenon in essential hypertension.