title: V1 receptor activation induced by hemorrhage and sympathoinhibition in the mesentery and hindquarters of spontaneously hypertensive rats.
abstract: The aim of this study was to determine the effects of vasopressin V1 receptor antagonism on regional hemodynamics in spontaneously hypertensive rats (SHR/Izm). Changes in blood flow in the superior mesenteric artery or terminal aorta were measured in rats with a chronically implanted electromagnetic flowmeter. The combination of a non-hypotensive hemorrhage (0.3 ml/100 g weight) and ganglionic blockade with hexamethonium bromide (C6; 25 mg/kg weight) had no effect on mesenteric resistance. On the other hand, subsequent intravenous administration of a peptide vasopressin V1 receptor antagonist (V1A; 10 microg/kg:[d(CH2)5(1)-O Methyl-Tyr(2)-Arg8]-vasopressin) significantly reduced mesenteric resistance in SHR/Izm but had no effect on hindquarter resistance. Furthermore, the infusion of C6 (after pretreatment with hemorrhage plus V1A) induced a marked reduction of blood pressure and a significant decrease in superior mesenteric resistance only in SHR/Izm. Thus, we showed an altered reactivity to V1A in the superior mesenteric and/or hindquarter vascular regions of SHR/Izm, suggesting that maintenance of elevated resistance in the mesenteric vascular bed mainly relates to a potential vasopressin-mediated vasoconstriction and that a new sympathetic vasoconstrictor tone is generated within the superior mesenteric vascular bed to compensate for hypotensive intervention (minor hemorrhage plus V1A) in conscious SHR/Izm.
authors.affiliation: Department of Neurophysiology, Graduate School of Biomedical Sciences, Hiroshima University, Minami-ku, Hiroshima 734-8551, Japan.
authors.forename: Chi Hong
authors.initials: CH
authors.lastname: Xing
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Teranishi
mesh_terms: D000818:Animals; D065092:Antidiuretic Hormone Receptor Antagonists; D001794:Blood Pressure; D006470:Hemorrhage / Q000378:metabolism* / Q000473:pathology*; D008297:Male; D051381:Rats; D011918:Rats, Inbred SHR; D017208:Rats, Wistar; D017483:Receptors, Vasopressin / Q000378:metabolism*; D013565:Sympatholytics / Q000494:pharmacology*
chemical_list: D065092:Antidiuretic Hormone Receptor Antagonists; D017483:Receptors, Vasopressin; D013565:Sympatholytics