Topical decongestants are vasoconstrictors, and work by constricting the blood vessels within the nasal cavity. Using triptans and other vasoconstrictors as abortive treatments for migraine with brainstem aura is contraindicated. Treatments include iced saline, and topical vasoconstrictors such as adrenalin or vasopressin. It is regulated by vasoconstrictors (agents that cause vasoconstriction). The chemicals involved may be irritants, hallucinogens, convulsants, nerve poisons or vasoconstrictors. They are potent direct vasoconstrictors, constricting arteries and veins and increasing blood pressure. Conversely, thromboxanes (produced by platelet cells) are vasoconstrictors and facilitate platelet aggregation. Mepivicaine is the least vasodilatory anesthetic as it has no vasoconstrictors and no preservatives added. Terlipressin and related analogues are used as vasoconstrictors in certain conditions. Substances called vasoconstrictors reduce the caliber of blood vessels, thereby increasing blood pressure. Substances called vasoconstrictors can reduce the size of blood vessels, thereby increasing blood pressure. Endothelins are the most potent vasoconstrictors known. Vasoconstrictors and volume expanders are the mainstay of treatment. Vasoconstrictors are also used clinically to increase blood pressure or to reduce local blood flow.