AJP - Heart and Circulatory Physiology, Vol 240, Issue 2 274-H285, Copyright © 1981 by American Physiological Society
Adrenergic mechanisms in canine intralobar pulmonary arteries and veins
S. Greenberg, P. J. Kadowitz, A. Hyman and F. A. Curron
The responses of canine intralobar pulmonary arteries (IPA) and veins (IPV)
to transmural nerve stimulation (TNS), and exogenously administered
norepinephrine (NE) were studied to evaluate the alpha-adrenergic
neuroeffector system in the canine pulmonary vasculature. IPA and IPV
elicited contractions in response to both NE (10(-10) to 10(-5) M) and TNS
(0.5-32 Hz, 2 ms duration and delay). The equilibrium (steady state)
contractile responses of IPA and IPV to TNS were abolished with the
adrenergic neuronal blocking agents guanethidine and bretylium and the
depolarization blocking agent tetrodotoxin in concentrations which did not
affect the responses to NE or KCl. The contractile responses of IPA and IPV
to TNS and NE were reduced in a concentration-dependent way, by the
alpha-adrenergic receptor-blocking agents phentolamine, tolazoline and
clonidine. The contractile responses of IPA and IPV to TNS and NE were
enhanced after inhibition of neuronal reuptake of NE (uptake1) with
cocaine, as well as after blockade of extraneuronal reuptake of NE
(uptake2) with hydrocortisone. Analysis of the equilibrium responses of the
IPA and IPV to TNS and NE with an Arunlakshana-Schild plot to define the
concentration of alpha 1-receptor antagonists necessary to double the ED50
for TNS and NE (defined as the pA2), demonstrated that the postsynaptic
alpha-receptors of IPV differed from that of IPA. These data support the
conclusions that IPA and IPV 1) contain a functional adrenergic innervation
and neuroeffector system, 2) contract in response to both TNS and NE, 3)
demonstrate the presence of mechanisms for both uptake1 and uptake2 of NE,
and 4) IPV contain postsynaptic alpha-receptors that may differ from each
other.
