Excitatory and inhibitory effects of 5-hydroxytryptamine in mesenteric arteries of spontaneously hypertensive rats

Mechanisms Involved in Serotonin-Induced Vasodilatation

“…Serotonin inhibits the electrically evoked release of [3H]-noradrenaline from several vascular preparations, such as the dog saphe nous vein [3,[32][33][34][35], the rat mesenteric ar tery [36], the rat renal vasculature [37], the rat vena cava [38,39], and the human saphe nous vein [40], In the dog saphenous vein, contractile responses to electrical stimula tion were also inhibited by serotonin, but responses to exogenous noradrenaline were unaffected or enhanced [3,32,33,41,42]; these experiments provide indirect evidence for prejunctional sympathetic inhibition, as do similar observations in the rabbit basilar artery [43], despite the complicating factors of the direct contractile effects of serotonin and its amplifying effect on responses to other vasoconstrictors. Evidence from some of these indirect studies has also excluded the apparent involvement of muscarinic cholinergic receptors, histamine H| and H2 receptors, dopamine receptors, and eicosanoid mediators, in the prejunctional inhibi tory effect of serotonin.…”

Ketanserin

“…Conflicting data have been reported which suggest that contractions of canine basilar and coronary arteries and of saphenous vein in response to serotonin may be due to activation of a mixed population of S2-serotonergic receptors and other not yet identified receptors (3 1,120,183, 203,205,265,274). Low concentrations of ketanserin inhibit vasoconstriction induced by serotonin in the perfused vascular bed, e.g., from guinea pig stomach and intestine, and in the perfused kidney from normotensive or hypertensive rats (169,234,265). Because of their partial agonistic properties, some serotonergic antagonists (e.g., methysergide) mimic at certain dose levels the vasoconstrictor effect of serotonin itself.…”

“…This antagonism is of the competitive type (pA2 values from 8.4 to 9.1) in most blood vessels, e.g., rat caudal and mesenteric arteries and portal and external jugular veins, rabbit femoral, pulmonary, and tibia1 arteries and aorta, canine gastrosplenic, internal carotid, and middle cerebral arteries and gastrosplenic veins, bovine coronary and pulmonary arteries, and human hand and basilar arteries and saphenous veins (5,92,139,147,159,163,234,239,265,267,269,274,275). However, the antagonism is of a noncompetitive type or of a dual competitive/ noncompetitive type in a relatively small number of other blood vessels, e.g., canine saphenous veins, basilar and coronary arteries, cat middle cerebral arteries, rabbit basilar arteries, and human hand veins (5,6,22,31,93,183,203,244,265,274).…”

“…Subthreshold or threshold concentrations of serotonin potentiate (amplify) contractions of blood vessels induced by other vasoconstrictor agonists, including angiotensin 11, histamine, norepinephrine (whether exogenously added or released from sympathetic nerves), degradation products of fibrin and fibrinogen, prostaglandin FZu, thromboxane A2, and the thromboxane A2 mimetic U 44069 (46,64,89,142,164,172,182,234,265,266,(268)(269)(270). This amplifying effect of serotonin on responsiveness to other vasoactive agents also occurs in vivo in sheep and man (184,226).…”

Differential Responses of Rat Aorta and Mesenteric Artery to Norepinephrine and Serotonin in vitro

“…serotonin is known to stimulate the release of norepinephrine in blood vessels [7][8][9] as well as to potentiate the effect of the pressor response to norepinephrine and angiotensin II [10].…”