R. Mizuno et T. Ohhashi, 5-HYDROXYTRYPTAMINE-INDUCED NO-DEPENDENT RELAXATION IN ISOLATED STRIPS OF MONKEY POPLITEAL LYMPH-NODES, American journal of physiology. Heart and circulatory physiology, 37(6), 1995, pp. 2246-2251
5-Hydroxytryptamine (5-HT, 0.01-100 mu M) and 5-carboxamidotryptamine
(5-CT, 0.001-10 mu M) produced dose-related relaxations in strips cut
from monkey popliteal lymph nodes precontracted with a perfusion of Kr
ebs bicarbonate solution containing 80 mM KC1. These 5-HT agonists cau
sed no significant effect on the basal tone of the lymph node strips.
The 5-HT-induced relaxation is competitively antagonized by pretreatme
nt with a selective 5-HT1-like receptor antagonist, methiothepin (0.01
-0.1 mu M). Schild plot analysis showed that the pA(2) value and slope
of methiothepin against 5-HT were 8.80 +/- 0.11 and 0.99 +/- 0.07 (n
= 6), respectively. Pretreatment with methysergide (0.01-0.1 mu M) sig
nificantly attenuated the 5-HT-induced relaxation of the strips. On th
e other hand, treatment with ketanserin (0.01-0.1 mu M) and ICS-205-93
0 (0.01-0.1 mu M) caused no significant effect on the 5-HT-or the 5-CT
-induced relaxation. The 5-HT-induced relaxation was significantly red
uced by 10 mu M N-G-monomethyl-L-arginine, which was reversed by 1 mM
L-arginine. The relaxation in the lymph node strips was also significa
ntly reduced by treatment with 10 mu M methylene blue but not with 30
mu M aspirin. These results suggest that 5-HT1-like receptors exist in
the monkey popliteal lymph nodes. Stimulation of these receptors prod
uces an endogenous nitric oxide (NO)-dependent relaxation in lymph nod
e smooth muscle through an activation of cytosolic guanylate cyclase i
n the cells.