Human vascular endothelial cells express oxytocin receptors

Pharmacological studies in humans and animals suggest the existence of vasc ular endothelial vasopressin (AVP)/oxytocin (OT) receptors that mediate a v asodilatory effect. However, the nature of the receptor subtype(s) involved in this vasodilatory response remains controversial, and its coupled intra cellular pathways are unknown. Thus, we set out to determine the type and s ignaling pathways of the AVP/OT receptor(s) expressed in human vascular end othelial cells (ECs). Saturation binding experiments with purified membranes of primary cultures of ECs from human umbilical vein (HUVEC), aorta (HAEC), and pulmonary arter y (HPAEC) and [H-3]AVP or [H-3]OT revealed the existence of specific bindin g sites with a greater affinity for OT than AVP (K-d = 1.75 vs. 16.58 nM). Competition binding experiments in intact HUVECs (ECV304 cell line) with th e AVP antagonist [I-125]4-hydroxyphenacetyl-D-Tyr(Me)-Phe-Gln-Asn-Arg-Pro-A rg-NH2 or the OT antagonist [I-125]D(CH2)(5)[O-Me-Tyr-Thr-Orn-Tyr-NH2]vasot ocin, and various AVP/OT analogs confirmed the existence of a single class of surface receptors of the classical OT subtype. RT-PCR experiments with total RNA extracted from HUVEC, HAEC, and HPAEC and specific primers for the human V1 vascular, V2 renal, V3 pituitary, and OT receptors amplified the OT receptor sequence only. No new receptor subtype could be amplified when using degenerate primers. DNA sequencing of the co ding region of the human EC OT receptor revealed a nucleotide sequence 100% homologous to that of the uterine OT receptor reported previously. Stimulation of ECs by OT produced mobilization of intracellular calcium and the release of nitric oxide that was prevented by chelation of extra- and intracellular calcium. No stimulation of cAMP or PG production was noted. F inally, OT stimulation of ECs led to a calcium- and protein kinase C-depend ent cellular proliferation response. Thus, human vascular ECs express OT receptors that are structurally identic al to the uterine and mammary OT receptors. These endothelial OT receptors produce a calcium-dependent vasodilatory response via stimulation of the ni tric oxide pathway and have a trophic action.