Quantitative studies of the ocular response to norepinephrine

The responses of the iris and intraocular pressure of conscious rabbits to norepinephrine (NE) given either topically or intravitreally have been determined. The dose-response curves for pupil dilatation and for decreased intraocular pressure occurring within 6 hr of the intravitreal administration of NE were similar and could be antagonized by prior intravenous injections of the α-adrenergic antagonists phenoxybenzamine or phentolamine. There were, however, marked differences in the time of onset and in the duration of the pupillary and pressure responses. A prolonged decrease in intraocular pressure, lasting more than 5 days, followed the intravitreal injection of NE. This prolonged pressure response could not be reversed by either phenoxybenzamine or phentolamine.