Y. Kohno et al., HETEROGENEITY OF NEUROGENIC RESPONSES IN INTRAMENINGEAL AND EXTRAMENINGEAL ARTERIES OF DOGS, British Journal of Pharmacology, 116(6), 1995, pp. 2557-2562
1 Neurogenic responses to transmural electrical stimulation were exami
ned in endothelium-denuded extrameningeal (vertebral and carotid) and
intrameningeal (spinal, basilar and middle cerebral) arteries isolated
from dogs. 2 In the extrameningeal arteries, transmural electrical st
imulation produced a phasic contraction. This contraction was abolishe
d by tetrodotoxin, prazosin and guanethidine. However, alpha,beta-meth
ylene ATP and N-G-nitro-L-arginine (L-NOARG) had no significant effect
on the contractile responses. 3 In the intrameningeal arteries, the n
eurogenic responses to electrical stimulation were composed of a trans
ient contraction and relaxation. The transient contraction was selecti
vely inhibited by guanethidine or after desensitization of P-2X-purino
ceptors with alpha,beta-methylene ATP. L-NOARG abolished the relaxatio
n but not the contraction induced by electrical stimulation. Prazosin
had no effect on either neurogenic response. 4 Noradrenaline produced
a large contraction in the extrameningeal arteries which was selective
ly inhibited by prazosin. alpha,beta-Methylene ATP produced neither co
ntraction nor inhibition of the response to noradrenaline in the extra
meningeal arteries. 5 In the intrameningeal arteries, alpha,beta-methy
lene ATP produced a greater contraction than noradrenaline. The respon
se to alpha,beta-methylene ATP was selectively abolished by desensitiz
ation of P-2X-purinoceptors with alpha,beta-methylene ATP itself. The
contractile response to noradrenaline was inhibited by rauwolscine but
not by prazosin. 6 ATP produced endothelium-dependent relaxations in
the extrameningeal and intrameningeal arteries, which were attenuated
by endothelium removal. 7 NADPH diaphorase-positive fibres were dense
in the middle cerebral and basilar arteries but rare or absent in the
spinal artery. In the extrameningeal arteries diaphorase-positive trac
es were observed in the vasa vasorum. 8 The present findings indicate
that the neurogenic responses of intrameningeal arteries of dogs are c
omposed of NO-ergic and sympathetic purinergic components, while the e
xtrameningeal arteries tested produced only sympathetic adrenergic res
ponses, suggesting that regional heterogeneity may be associated with
a sudden transition in innervation and receptor expression at the meni
nx.