AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 6 1074-R1080, Copyright © 1986 by American Physiological Society
Mechanical effects of vasoactive drugs on carotid sinus
L. B. Bell, J. L. Seagard, E. J. Zuperku and J. P. Kampine
Carotid sinus diameter (CSD) is influenced by changes in sympathetic tone
and vasoactive agents. This study was designed to determine which
mechanical properties of the carotid sinus region were influenced by
infusing vasoconstrictors (epinephrine, 4.56 X 10(-6) M, and phenylephrine,
9.85 X 10(-5) M) and a vasodilator (nitroprusside, 1.68 X 10(-4) M). CSD,
carotid sinus length (CSL), pressure (CSP), and compliance (CSC), and
arterial pressure were all recorded simultaneously from the isolated
constant-flow-perfused carotid sinus region of 11 anesthetized dogs (35
mg/kg pentobarbital sodium) before and after drug perfusion. CSC was
measured by a method previously described in which 13 microliters of
perfusate is injected into the segment in a step-like manner and the
resultant step change in pressure recorded. The compliance of the vessel
segment is read on-line after a calibration procedure. CSD and CSL were
measured using sonomicrometer length gauges positioned across and along the
length of the carotid sinus segment. At a CSP of 99.9 +/- 0.6 (SE) mmHg,
CSD, CSL, and CSC were 8.50 +/- 0.44 mm, 9.44 +/- 0.84 mm, and 0.46 +/-
0.05 microliter/mmHg, respectively. Decreasing CSP to 50 mmHg significantly
reduced CSD and CSL and increased CSC. Increasing CSP to 150 mmHg produced
opposite results. Vasoconstrictor drug infusion significantly decreased and
vasodilator drug infusion significantly increased both CSD and CSL,
producing parallel shifts in the CSP-CSD and -CSL curves toward and away
from the pressure axis. The shift to new pressure-volume curves resulted in
no change in CSC in response to the vasoactive agents.
