The purpose of this study was to investigate the nature of the
serotonin-induced coronary chemoreflex in the conscious monkey. Ten chronically prepared and four acute monkeys were used in this study. Five chronically prepared animals had
catheters in the left atrium, ascending aorta, descending aorta, and, bilaterally, in the common carotid arteries. In addition,
Silastic catheters were placed next to both vagi to permit vagal block with 2%
lidocaine.
Serotonin was injected (12-200 micrograms/kg) into the left atrium, ascending aorta, descending aorta, or, bilaterally, into the carotid arteries while blood pressure, heart rate, and respiratory movements were recorded.
Injections of
serotonin were associated with
hypertension and
bradycardia followed by
tachycardia, all of which were preceded by a
cough response.
Atropine blocked the
bradycardia, whereas
atropine and
phentolamine eliminated the cardiovascular components of the reflex. Vagal blockade eliminated the
bradycardia but otherwise did not alter the response to left atrial
serotonin. Three monkeys were prepared with aortic and left atrial
catheters. Subsequently, they were subjected to sinoaortic deafferentation.
Serotonin injected into these animals did not alter blood pressure or respiration. The results of this study show that
serotonin injected into the left atrium of the conscious monkey produces respiratory and cardiovascular alterations by its effect on aortic and carotid chemoreceptors, and that there is no coronary chemoreflex in the conscious monkey.