CHARACTERISTICS OF THE RESPONSES OF ISOLATED AND PERFUSED CANINE SPLENIC ARTERIES TO VASOACTIVE SUBSTANCES AND TO PERIARTERIALLY ELECTRICAL-STIMULATION

Pharmacological characteristics of the canine isolated splenic artery were investigated by the cannula insertion method for observing vascul ar responses to vasoactive agents and periarterial nerve stimulation. Four a-adrenoceptor agonists and tyramine induced vasoconstrictions in a dose-dependent manner, and the order of potency was noradrenaline ( NA) > phenylephrine > clonidine > methoxamine > tyramine. Xylazine (a selective alpha(2)-adrenoceptor agonist) did not elicit any vasoconstr iction. Several autacoids and KCl also constricted the splenic artery dose-dependently, and the order of potency was 5-hydroxytryptamine (5- HT) much greater than ATP = histamine much greater than KCl. The dose- response curves for clonidine and NA were shifted to the right by buna zosin (a selective al-adrenoceptor antagonist), but were not affected by midaglizole (a selective az-adrenoceptor antagonist). The parameter s of electrical stimulation to elicit a clear and constant vasoconstri ction were 0.2 msec of pulse duration, 6 V and 0.1 Hz. The vasoconstri ctive responses to electrical stimulation at 6-12 V, 0.1-10 Hz and 0.2 -1 msec of pulse duration were completely inhibited by tetrodotoxin (T TX) and strongly inhibited by guanethidine. The results in this study suggest that: 1) in contrast with other regional arteries, the canine splenic artery has an alpha(1)-adrenoceptor-related and clonidine-sens itive vasoconstrictive response, 2) this artery has no functional post synaptic alpha(2)-adrenoceptors, 3) it may be easier to observe the va scular responses to vasoactive agents in the isolated and perfused art erial segments, and 4) the isolated and perfused canine splenic artery is useful as a preparation to study the sympathetic nerve transmissio n.