Differences in gene expression of the AT(1) receptor and intracellular kinases between WKY and SHR

Phosphorylation is a critical intracellular signal transduction event that occurs following angiotensin receptor (AT1) activation. In the present study we have quantitated the gene expression levels for the AT1, extracellular signal regulating kinases 1 and 2 (ERK1) and (ERK2) and phosphatidylinositol-3 kinase (PI3K) in sites associated with arterial blood pressure control in normotensive and hypertensive rats. Second, we determined if a relationship between gene expression and systolic blood pressure (SBP) existed. Third, we compared the levels of ERK1/2 phosphorylation between normotensive and hypertensive rats within sites investigated. Twenty-week old Wistar-Kyoto (WKY, n=10) and spontaneously hypertensive rats (SHR, n=10) were used. Tissue was isolated from the hypothalamus, rostral ventrolateral medulla, spinal cord, renal cortex, adrenal medulla and celiac ganglion, RNA extracted and reverse transcribed into cDNA. Gene expression levels were quantitated using real time PCR, relative to the expression of a house-keeping gene. AT1, ERK2 and PI3K gene expression levels were significantly higher in all tissue investigated of SHR (except the renal cortex) compared with WKY. For example, in the paraventricular nucleus of the hypothalamus of SHR the level of AT1 was 4 times higher compared with WKY (SHR: 1.40±0.04%; WKY: 0.34±0.06%; P < 0.0001). There was no significant difference in the level of ERK1 gene expression between strains. AT1 and ERK2 gene expression levels were positively correlated with SBPs (tail cuff plethysmography 2 weeks prior to sacrifice) in all central tissue investigated and some peripheral tissue of SHR. Immunohistochemically, there was no difference in the amount of ERK1/2 phosphorylation levels between SHR and WKY in all tissue investigated. Higher levels of AT1, ERK2 and PI3K gene expression in site-specific tissue of SHR seem consistent with the elevated blood pressures observed.