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Modulation of Baroreflex Sensitivity by Endogenous Angiotensins in Lamb Solitary Tract Nucleus
Author(s) -
Shaltout Hossam A.,
Rose James C.,
Chappell Mark C.,
Diz Debra I.
Publication year - 2010
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.24.1_supplement.624.7
Subject(s) - baroreflex , phenylephrine , baroreceptor , microinjection , endocrinology , medicine , solitary nucleus , solitary tract , chemistry , heart rate , reflex , antagonist , angiotensin ii receptor type 1 , angiotensin ii , blood pressure , endogeny , reflex bradycardia , receptor
We and others find that within the nucleus of the solitary tract (NTS) of the rat endogenous Ang II attenuates while Ang‐(1–7) facilitates the baroreflex sensitivity (BRS) in the control of heart rate. It is not known whether this same relationship exists in the sheep NTS. Therefore, we performed microinjection studies in 6 wk old sheep (n = 5) under chloralose‐urethane anesthesia (35/750 mg/kg) which maintains both increases and decreases in BRS for heart rate control. To assess the effects of blockade of either the AT1 or Ang‐(1–7) (AT7) receptors, we tested BRS before and after bilateral NTS injection of the AT1 antagonist candesartan (CV, 200 pmol/200 nl at 4 injection sites) and retested the reflex again after the AT7 antagonist D‐Ala7‐Ang‐(1–7) (D‐Ala, 10 pmol/200 nl at 4 injection sites). BRS was tested using various doses of phenylephrine to determine the slope of the relationship between changes in mean arterial pressure (MAP) and pulse interval as ms/mm Hg. Resting BRS was 0.3 ± 0.2 ms/mm Hg and MAP was 81 ± 7 mm Hg. NTS injection of CV increased BRS to a new baseline of 1.0 ± 0.2 ms/mm Hg, (p<0.05). From this elevated level D‐Ala significantly reduced BRS back to baseline. There was no effect of either agent on MAP. These data suggest that baseline baroreceptor reflex control of heart rate in lambs is regulated by Ang II and Ang‐(1–7) in the NTS in an opposite manner. Support: HD‐047584, HD‐017644, HL‐51952.