Aporphine derivatives affect ocular function in diverse ways

The sympathetic nervous system has been implicated in the ocular effects of several classes of dopamine receptor agonists. Two agonists of the aporphine class, (-) N-propylnorapomorphine -)NPA) and norapomorphine (NA), were evaluated for effects on intraocular pressure (IOP) and pupil diameter (PD) in cats and normal (NL) and sympathectomized (SX) rabbits and on contractions of the cat nictitating membrane (CNM). Topically administered (-)NPA produced a monophasic IOP drop in the ipsilateral eye and a biphasic (increase, decrease) IOP response in the contralateral eye of normal rabbits. Pupil diameter increased bilaterally. In NL cats, the ipsilateral IOP and PD response to (-)NPA was biphasic (increase, decrease) and the contralateral IOP response was monophasic (increase). (-)NPA produced an increase in spontaneous motor activity (SMA) in rabbits and cats. NA lowered IOP unilaterally in NL rabbits. In SX rabbit eyes, (-)NPA lowered IOP as much as in NL eyes but with less mydriasis. NA did not lower IOP in SX rabbit eyes. Both (-)NPA and NA inhibited contractions of the CNM elicited by electrical stimulation of the pre- and post-superior cervical ganglionic nerves. (-)NPA, but not NA, inhibited contractions elicited by exogenous norepinephrine. These results suggest that aporphine derivatives produced two diametrically opposed effects on ocular function; 1) a centrally mediated effect that enhanced noradrenergic activity to elicit mydriasis, SMA and ocular hypertension, and 2) a peripherally mediated effect to produce miosis and ocular hypotension.