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Carotid baroreceptor function, the compliance of the carotid sinus wall, and the structure of the carotid artery were examined in dogs with elevated plasma norepinephrine (2,000-4,000 pg/ml) for 28 days. The dogs with high norepinephrine were normotensive (100 +/- 4.0 versus 98 +/- 4.0 mm Hg; p greater than 0.05) with bradycardia (65 +/- 4.0 versus 87 +/- 16 beats/min; p less than 0.05) compared with normal dogs in the conscious state. However, after pentobarbital anesthesia blood pressure was significantly higher in dogs with chronic norepinephrine infusion (165 +/- 6 mm Hg) compared with normal dogs (132 +/- 6 mm Hg). To assess baroreceptor sensitivity, multiunit carotid baroreceptor activity was recorded from the right carotid sinus nerve, and the carotid sinus wall compliance (sonomicrometers) was measured during nitroglycerin and phenylephrine injections. The threshold and saturation pressures increased from 96 +/- 3.9 to 117 +/- 4.2 mm Hg and from 145 +/- 4.3 to 171 +/- 5.7 mm Hg, respectively, in the normal dogs compared with the high norepinephrine dogs. The most striking differences were the marked increases in sensitivity of carotid baroreceptors (0.47 +/- 0.05 versus 1.99 +/- 0.45 spikes.sec-1.mm Hg-1; p less than 0.01) and maximum firing frequency of the baroreceptors (24 +/- 3.1 versus 48 +/- 4.4 spikes/sec; p less than 0.01), whereas the carotid sinus wall compliance was unchanged (0.014 +/- 0.003 versus 0.012 +/- 0.002 mm/mm Hg; p greater than 0.05). Similar alterations were observed using single fiber recordings, that is, an increase in threshold and saturation pressures and slope of baroreceptor units in dogs with elevated norepinephrine. The wall thickness and area of the carotid artery were determined. Both increased significantly (0.77 +/- 0.06 versus 1.30 +/- 0.12 mm and 9.0 +/- 0.8 versus 11.9 +/- 0.9 mm2; p less than 0.05) in dogs chronically infused with norepinephrine while the dry weight-to-wet weight ratio of left carotid artery tissue also increased from 26.0 +/- 0.73% to 29.0 +/- 0.57%. These studies indicate that 1) one of the possible mechanisms responsible for bradycardia in the conscious dogs with high norepinephrine is enhanced sensitivity of carotid baroreceptors; 2) the enhanced sensitivity of carotid baroreceptors is not due to a change in compliance of the carotid sinus wall; and 3) chronic elevation of norepinephrine causes hypertrophy or hyperplasia of the wall of the common carotid artery.
J Wang, and
M Ochoa, and
M B Patel, and
I H Zucker, and
A V Loud, and
G A Zeballos, and
T H Hintze
February 1981,
Circulation research,
J Wang, and
M Ochoa, and
M B Patel, and
I H Zucker, and
A V Loud, and
G A Zeballos, and
T H Hintze
May 1991,
Circulation research,
J Wang, and
M Ochoa, and
M B Patel, and
I H Zucker, and
A V Loud, and
G A Zeballos, and
T H Hintze
January 1984,
Hypertension (Dallas, Tex. : 1979),
J Wang, and
M Ochoa, and
M B Patel, and
I H Zucker, and
A V Loud, and
G A Zeballos, and
T H Hintze
October 1977,
Scandinavian journal of clinical and laboratory investigation,
J Wang, and
M Ochoa, and
M B Patel, and
I H Zucker, and
A V Loud, and
G A Zeballos, and
T H Hintze
April 1985,
The American journal of physiology,
J Wang, and
M Ochoa, and
M B Patel, and
I H Zucker, and
A V Loud, and
G A Zeballos, and
T H Hintze
May 1977,
Circulation research,
J Wang, and
M Ochoa, and
M B Patel, and
I H Zucker, and
A V Loud, and
G A Zeballos, and
T H Hintze
January 1978,
Acta biologica et medica Germanica,
J Wang, and
M Ochoa, and
M B Patel, and
I H Zucker, and
A V Loud, and
G A Zeballos, and
T H Hintze
December 1991,
The American journal of physiology,
J Wang, and
M Ochoa, and
M B Patel, and
I H Zucker, and
A V Loud, and
G A Zeballos, and
T H Hintze
June 1969,
The American journal of physiology,
J Wang, and
M Ochoa, and
M B Patel, and
I H Zucker, and
A V Loud, and
G A Zeballos, and
T H Hintze
January 1982,
Hypertension (Dallas, Tex. : 1979),
