Serotonin (5-HT) and the rat's eye. Some pilot studies

Serotonin (5-hydroxytryptamine, 5-HT) is a biogenic amine which has a multitude of more or less clearly established effects on peripheral vessels. It influences blood viscosity, platelet aggregation, and vasoconstruction and -dilatation, it enhances capillary permeability, it is the precursor of melatonin (a hormone with diurnal production in the eye). Because of these actions a role for serotonin in the development of glaucoma and diabetic retinopathy might be suspected. In a series of pilot studies on rats the effects of serotonin on the anterior and posterior segments of the eye were studied. Serotonin had marked influence on the retinal and choroidal vasculature. The optic disk seemed to be very sensitive to serotonin. Possibly it had an influence on the blood-retinal barrier. It caused transient cataracts, probably by decreasing the production of aqueous. It blocked tropicamin-induced mydriasis. The techniques and provisional results of measurement of serotonin in human aqueous are also described.