Arterial Nerve Growth Factor (NGF) mRNA, Protein, and Vascular Smooth Muscle Cell NGF Secretion in Hypertensive and Hyperactive Rats

Elevated levels of nerve growth factor (NGF) protein and NGF mRNA have been reported in the vessels of spontaneously hypertensive rats (SHR: hypertensive, hyperactive) compared to Wistar-Kyoto (WKY) rats. Elevated NGF may be involved in the development of hypertension in SHRs. We examined vascular NGF mRNA and protein content and the regulation of NGF secretion by vascular smooth muscle cells (VSMCs) from two inbred strains (WKHT: hypertensive; WKHA: hyperactive) derived from SHRs and WKYs. Our goal was to determine if receptor-mediated defects in NGF regulation play a role in increased secretion of VSMC NGF from hypertensive animals. Tissue NGF mRNA content was determined by competitive, quantitative RT-PCR. Tissue NGF and NGF content in cultured VSMC-conditioned medium was quantified using a two-site ELISA. Tail artery NGF mRNA was elevated in WKHTs compared to WKHAs. Tissue NGF protein was elevated in WKHT aorta, mesenteric, and tail artery compared to WKHAs. Pharmacologically induced increases in NGF output were blocked with inhibition of transcription or protein synthesis. Basal NGF secretion by WKHT VSMCs was significantly higher than WKHAs. The observed increases in VSMC NGF output in SHRs over WKYs in response to β-adrenergic agents are not preserved in the WKHT:WKHA comparison. Protein kinase C-dependent increases in SHR VSMC NGF appear in both WKHTs and WKHAs. In contrast, elevated NGF levels due to disturbances in α-adrenergic, peptidergic, and purinergic control of NGF output are features common to both genetic models of hypertension (SHR and WKHT). These results suggest that the defect in smooth muscle NGF metabolism observed in SHRs cosegregates with a hypertensive rather than a hyperactive phenotype. Moreover, altered receptor-mediated regulation (α-adrenergic, peptidergic, and purinergic) of VSMC NGF production may contribute to elevated vascular tissue NGF, suggesting a mechanism leading to the high levels of NGF associated with hypertension in SHRs and WKHTs.