Parathyroid hormone stimulates the endothelial nitric oxide synthase through protein kinase A and C pathways.
BACKGROUND
Parathyroid hormone (PTH), the major systemic calcium regulating hormone has been implicated in the development of hypertension and the occurrence of uraemic vascular changes. As nitric oxide synthase (NOS) is involved in the production of nitric oxide, and acute PTH effect is characterized by vasodilation, the effect of PTH on the endothelial NOS (eNOS) system was measured in cultured human umbilical cord vein endothelial cells (HUVEC) and the pathways possibly involved were studied.


METHODS
The presence of the PTH receptor-1 (PTHR1) on the HUVEC membrane was examined by RT-PCR, immunocytochemistry and western blot. HUVEC were stimulated with 10(-12) to 10(-10) mol/l PTH. The eNOS mRNA expression was established by RT-PCR and the eNOS protein levels were determined by western blot. The eNOS activity was measured by the conversion of [(14)C]arginine to [(14)C]citrulline.


RESULTS
PTHR1 has been found to be expressed in HUVEC and its expression is depressed by increasing concentrations of PTH. PTH induced a significant increase in eNOS mRNA (10(-11) mol/l: 1.87 +/- 0.16, P = 0.012; 10(-10) mol/l: 1.96 +/- 0.28, P = 0.007, fold of control), and protein expression. The eNOS activity was also significantly stimulated (10(-11) mol/l: 1139 +/- 203; 10(-10) mol/l: 1323 +/- 216 vs control: 621 +/- 154 cpm/150 mug protein, P < 0.01). The addition of calphostin C (PKC inhibitor) or Rp-cAMP (PKA inhibitor) reduced the eNOS mRNA, protein expression and activity of PTH-stimulated HUVEC. The combined treatment of calphostin C and Rp-cAMP abolished the eNOS protein expression and activity.


CONCLUSIONS
PTH induces an increased activity of the eNOS system; probably both PKA and PKC pathways are involved in this activation. Such data may explain the vasodilation observed after acute treatment with PTH.
Rashid
Gloria
G
Department of Nephrology and Hypertension, Meir Medical Center, Tchernichovsky 59, Kfar-Saba 44281, Israel. gloriar@clalit.org.il
Bernheim
Jacques
J
Green
Janice
J
Benchetrit
Sydney
S
D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D003720:Densitometry / Q000379:methods; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D008954:Models, Biological; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*
D004791:Enzyme Inhibitors; D010281:Parathyroid Hormone; D000242:Cyclic AMP; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C