Am. J. Respir. Crit. Care Med., Vol 151, No. 5, May 1995, 1589-1596.
Distribution of functional adrenergic receptor subtypes in the microcirculation of rat trachea
MR Corboz, ST Ballard, ST Boyette and AE Taylor
College of Medicine, University of South Alabama, Mobile 36688, USA.
Although blood flow to the pulmonary airways is known to be largely under
sympathetic control, virtually nothing is known about adrenergic regulation
of vascular segments within the airway microcirculation. To evaluate the
distribution of functional adrenergic receptor subtypes in the microvessels
of the large airways, the change in diameter of adventitial vessels in rat
trachea was measured following suffusion with selective and nonselective
receptor agonists and antagonists. Microvessels were viewed with a video
microscope, and vessel diameters were measured using video calipers.
Arterioles (11.0 to 40.0 microns, n = 32), small postcapillary venules
(11.0 to 26.0 microns, n = 16), medium venules (28.0 to 59.5 microns, n =
40), and large collecting venules (61.0 to 99.0 microns, n = 42) were
distinguished. Similar sensitivities to norepinephrine (NE), a mixed alpha
1 and alpha 2 agonist, were observed in arterioles and medium venules with
EC50 (agonist concentration needed to produce 50% of the maximal response)
for contraction of 2.4 x 10(-7) and 3.3 x 10(-7) M, respectively. Large
venules (EC50 of 1.6 x 10(-6) M) were significantly (p < 0.05) less
sensitive than arterioles to NE. In the presence of propranolol, a beta
receptor antagonist, the EC50 values for NE were not different between the
three vessel groups, although the response to low doses of NE was
significantly increased in arterioles. When vessels were treated with
propranolol and phenylephrine, a selective alpha 1 agonist, arterioles
(EC50 of 4.1 x 10(-7) M) were significantly more sensitive than large
venules (EC50 of 4.9 x 10(-6) M).(ABSTRACT TRUNCATED AT 250 WORDS)
