Guanethidine (GTD)

Guanethidine is an antihypertensive drug that reduces the release of catecholamines, such as norepinephrine. Guanethidine is transported across the sympathetic nerve membrane by the same mechanism that transports norepinephrine itself (NET, uptake 1), and uptake is essential for the drug's action. Once guanethidine has entered the nerve, it is concentrated in transmitter vesicles, where it replaces norepinephrine.It may also inhibit the release of granules by decreasing norepinephrine. Guanethidine is transported by uptake 1 into the presynaptic terminal transported by Norepinephrine transporter (NET). (In this it competes with norepinephrine so can potentiate exogenously applied norepinephrine). It becomes concentrated in norepinephrine transmitter vesicles, replacing norepinephrine in these vesicles. This leads to a gradual depletion of norepinephrine stores in the nerve endings.