11. With respect to vascular smooth muscle, there are both vasoconstrictor and vasodilator autacoids. 12. Conversely, thromboxanes ( produced by platelet cells ) are vasoconstrictors and facilitate platelet aggregation. 13. Substances called vasoconstrictors can reduce the size of blood vessels, thereby increasing blood pressure. 14. Medications causing vasoconstriction, also known as vasoconstrictors , are one type of pupil dilation. 15. In this way he established the existence of vasomotor nerves, both vasodilator and vasoconstrictor . 16. It possesses structural similarity to several neurotransmitters, and has biological activity as a vasoconstrictor . 17. Ergotamine tartrate and caffeine are both vasoconstrictors , substances which act to constrict blood vessels. 18. It is also a potent vasoconstrictor . 19. When used as a vasoconstrictor used to decongest nasal mucosa, it is administered by inhalation. 20. Phenylephrine hydrochloride at 0.25 % is used as a vasoconstrictor in some suppository formulations.