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Effects of Angiotensin II and Dietary Salt on Neurogenic Vasomotor Tone: Dose Dependancy
Author(s) -
McBryde Fiona Dianne,
Barrett Carolyn J,
Guild SarahJane,
Malpas Simon C
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a754-b
Subject(s) - vasomotor , angiotensin ii , blood pressure , medicine , blockade , endocrinology , mean arterial pressure , anesthesia , heart rate , receptor
In addition to its direct vasoconstrictive actions there is accumulating evidence that angiotensin II (Ang II) exerts its effect at least in part through increasing sympathetic nerve activity (SNA). We have examined the effect of different concentrations of Ang II on vasomotor SNA, and a possible interaction with dietary salt. New Zealand white rabbits were instrumented to continuously measure mean arterial pressure (MAP) during 3 weeks of Ang II infusion. The depressor response to the ganglionic blocker pentolinium tartrate (5mg/kg) was used to assess vasomotor SNA on days 0, 7 and 21 of the Ang II infusion. The first group of rabbits received 50ng/kg/min Ang II and showed a rapid increase in MAP of 23±3mmHg. The depressor response to ganglionic blockade was significantly reduced throughout the Ang II infusion suggesting a sustained suppression of vasomotor SNA. A second group of rabbits received 20ng/kg/min Ang II and showed a slow increase in pressure beginning Day 7 and peaking by Day 12 (ÄMAP=20±7mmHg). There was no change to the depressor response to blockade suggesting no change in vasomotor SNA levels. A third group also received 20ng/kg/min Ang II and increased dietary salt (0.9% NaCl via drinking water), and developed hypertension similar to the second group but the responses to ganglionic blockade were significantly smaller than baseline at Day 7 (2±0.5mmHg c.f. 27±1mmHg) and larger than baseline by Day 21 (33±1mmHg) suggesting initial suppression of SNA followed by increased vasomotor SNA by the end of the infusion. We conclude that there is a dose‐dependant effect of Ang II on both MAP and neurogenic vasomotor tone, and that this relationship may be further modulated by increased dietary salt.