Rat jugular vein relaxes to norepinephrine, phenylephrine and histamine

Circular muscle of the rat external jugular vein contracted to serotonin, angiotensin and potassium chloride but not to norepinephrine, phenylephrine, histamine or carbamylcholine. In contrast, rabbit and guinea-pig jugular veins contracted to norepinephrine, phenylephrine and histamine, although contractions to norepinephrine were small in guinea-pig jugular veins. Norepinephrine, phenylephrine and histamine produced a concentration-dependent sustained relaxation of serotonin-induced contractions in the rat jugular vein, as did isoproterenol, nitroglycerin and papaverine. Propranolol blocked relaxation to norepinephrine, phenylephrine and isoproterenol whereas metiamide, a H2 receptor antagonist blocked relaxation to histamine. alpha adrenergic receptor blockade with phentolamine or prazosin resulted in greater relaxation to norepinephrine whereas cocaine did not enhance norepinephrine-induced vasodilation. This study supports the premise that norepinephrine may exert prominent beta adrenergic receptor stimulation in some blood vessels and that this effect may be more apparent in veins than arteries.