Parasympathetic impairment of baroreflex control of heart rate in Dahl S rats.
To test the hypothesis that impaired baroreflex control of heart rate in Dahl salt-sensitive (S) rats is due to an impairment of the parasympathetic limb of the bradycardic response, baroreflex sensitivity was evaluated in conscious, chronically instrumented Dahl S and salt-resistant (R) animals. Sensitivity was impaired in Dahl S rats when bolus doses of phenylephrine were administered (0.863 +/- 0.042 vs. 1.43 +/- 0.055 ms/mmHg), but it was not different than in R rats when tested with sodium nitroprusside. When the sensitivities before and after blocking the parasympathetic nervous system with atropine were compared, it was revealed that 82% of the reflex bradycardia resulting from bolus doses of phenylephrine was due to the parasympathetic nervous system, whereas the majority (73%) of the bradycardia induced by 5-min infusions of phenylephrine was due to withdrawal of sympathetic tone. Neither baroreflex sensitivity to infusions of phenylephrine (73% sympathetic) or to infusions after atropine (100% sympathetic) were significantly different between S and R rats. Therefore, the impairment of the heart rate reflex in Dahl S rats is due to an impairment of the parasympathetic limb of the response. In addition, a high-salt diet before the development of hypertension did not alter baroreflex sensitivity in either Dahl S or R rats.
Whitescarver
S A
SA
Department of Physiology and Biophysics, University of Kentucky Medical Center, Lexington 40536.
Ott
C E
CE
Kotchen
T A
TA
D000818:Animals; D001286:Atropine Derivatives / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006973:Hypertension / Q000139:chemically induced; D007267:Injections; D008297:Male; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D010276:Parasympatholytics / Q000494:pharmacology; D051381:Rats; D012965:Sodium Chloride / Q000008:administration & dosage; D012982:Sodium, Dietary / Q000009:adverse effects; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology
D001286:Atropine Derivatives; D010276:Parasympatholytics; D012982:Sodium, Dietary; D012965:Sodium Chloride; C006649:methylatropine