The role of brain angiotensin in thirst and AVP release induced by hemorrhage.
This study investigated the role of brain angiotensin (Ang II) in thirst induced by hemorrhage. Hemorrhage by blood withdrawal from the femoral artery to 33% and 44% blood volume loss produces a dose response increase in plasma Ang II. In the brainstem there was no Ang II response to hemorrhage. In the hypothalamus, Brain Ang II was maximally elevated to 33% hemorrhage. Thus, plasma Ang II and brain Ang II had an independent response to hemorrhage. To further test the role of central versus peripheral Ang II, we tested the effect of central (50 mg) and peripheral (50 mg/kg) administration of captopril or central injection of 1 mg losartan or 3 mg CGP 42112A prior to a 33% hemorrhage in unanesthetized male Sprague-Dawley rats (250 g). Drinking was measured and AVP blood samples were taken before and after hemorrhage. The results show that central (i.v.t.) administration of captopril and losartan inhibited drinking compared to controls (0.33 +/- 0.3 ml vs. 2.3 +/- 0.8 ml: P < 0.05 and 0.20 +/- 0.09 ml vs.3.05 +/- 0.81 ml; P < 0.01, respectively) while peripheral (i.p.) captopril alone increased drinking in response to hemorrhage (5.81 +/- 0.81 ml vs. 2.3 +/- 0.8 ml; P < 0.05). AVP levels were elevated at 5 and 15 min, but neither injections of losartan or CGP 42112A i.v.t. affected this response to hemorrhage. We conclude that increased hypothalamic brain Ang II after hypovolemic hemorrhage stimulates thirst and blood pressure restoration and acts through AT1 receptors. The release of AVP in hemorrhage, however, does not rely exclusively on the angiotensinergic pathway in the brain.
Department of Physiology, College of Medicine, University of Florida, Gainesville 32610, USA. mip@phys.med.ufl.edu
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Phillips
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Heininger
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Toffolo
D000804:Angiotensin II / Q000097:blood / Q000378:metabolism / Q000502:physiology*; D057911:Angiotensin Receptor Antagonists; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001713:Biphenyl Compounds / Q000008:administration & dosage / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001810:Blood Volume / Q000502:physiology; D002216:Captopril / Q000008:administration & dosage / Q000494:pharmacology; D015331:Cohort Studies; D003115:Colony-Stimulating Factors / Q000008:administration & dosage / Q000494:pharmacology; D004326:Drinking / Q000187:drug effects / Q000502:physiology*; D006470:Hemorrhage / Q000097:blood* / Q000503:physiopathology; D007031:Hypothalamus / Q000098:blood supply / Q000737:chemistry / Q000378:metabolism; D007093:Imidazoles / Q000008:administration & dosage / Q000494:pharmacology; D007274:Injections, Intraperitoneal; D007276:Injections, Intraventricular; D019808:Losartan; D008297:Male; D009842:Oligopeptides / Q000008:administration & dosage / Q000494:pharmacology; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011945:Receptors, Angiotensin / Q000032:analysis / Q000378:metabolism; D011994:Recombinant Proteins; D013777:Tetrazoles / Q000008:administration & dosage / Q000494:pharmacology; D013894:Thirst / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D014667:Vasopressins / Q000097:blood* / Q000187:drug effects / Q000378:metabolism
D057911:Angiotensin Receptor Antagonists; D000806:Angiotensin-Converting Enzyme Inhibitors; D001713:Biphenyl Compounds; D003115:Colony-Stimulating Factors; D007093:Imidazoles; D009842:Oligopeptides; D011945:Receptors, Angiotensin; D011994:Recombinant Proteins; D013777:Tetrazoles; D014667:Vasopressins; D000804:Angiotensin II; C060894:CGP 42112A; D002216:Captopril; D019808:Losartan