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Age-dependent regulation of vasopressin V_1a receptors in preglomerular vessels from the spontaneously hypertensive rat

Renal Research Group, Institute of Medicine, University of Bergen, N-5021 Bergen, Norway

Submitted 10 November 2003 ; accepted in final form 10 December 2003

Experiments were performed to get insight into the role of AVP receptor V_1a regulation with age, i.e., during development and maintenance of high blood pressure. Previous studies showed an increased gene expression and renal vascular response to AVP in young spontaneously hypertensive rats (SHR). The age regulation of the V_1a receptor was examined in preglomerular vessels from 5-, 10-, 20-, and 70-wk-old SHR using normotensive Wistar-Kyoto rats (WKY) as controls. Real-time PCR and ligand binding were used for analysis of receptor expression, and the change in cytosolic calcium concentration during stimulation of isolated preglomerular vessels with AVP was studied. Studies showed an increase of the V_1a receptor protein and mRNA from 5-and 10-wk-old SHR compared with vessels from 20- and 70-wk-old SHR. In 5-wk-old SHR receptor density was 84 ± 13 fmol/mg protein, and 38 ± 11 fmol/mg protein in 70-wk-old SHR (P < 0.05). mRNA in the 5- and 70-wk-old SHR was 15,854 ± 629 and 3,181 ± 224 V_1a mRNA/108 18S ribosomal RNA, respectively (P < 0.001). Values from WKY at all ages were similar to 20- and 70-wk-old SHR. During stimulation with AVP, the change in cytosolic calcium in vessels from 5-wk-old SHR increased 234 ± 59 nM, whereas the increase was 89 ± 9 nM in 70-wk-old SHR (P = 0.03). These results indicate that the V_1a receptor is increased at protein and mRNA level during development of hypertension in SHR but is normalized when hypertension is established.

hypertension; calcium signaling; renal circulation

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