Guanethidine (Ismelin*) is a substance which reduces the activity of the sympathetic nervous system (Maxwell et al.1). By virtue of this property, guanethidine has been used successfully as a hypotensive agent in essential hypertension over the last few years (Leishman et al.,2 Mertz,4 Sturzenegger et al.,5 Dollery et al.,6 Jaquerod and Spühler,3 and others).Unlike hexamethonium and pentolinium, guanethidine has no ganglion-blocking action. It also has no peripheral sympathicolytic effect, since the sensitivity of the receptors to sympathicomimetic substances is not decreased but is, on the contrary, increased. Guanethidine inhibits the release of levarterenol somewhere between the ganglion and the receptor (Fig. 1). It has a long-lasting effect: after one therapeutically active dose, the inhibition lasts for several days. In experiments on animals it could be shown to be still present after 3 weeks. Following oral administration to patients, the maximum effect is
OOSTERHUIS JA. Guanethidine (Ismelin) in Ophthalmology: I. Observations in Rabbits. Arch Ophthalmol. 1962;67(5):592–599. doi:10.1001/archopht.1962.00960020592013
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