Effect of octopamine on intraocular pressure of rabbits

vagoto~nized animals. This was characterized o3, ~ initial hypotensive reaction lasting for 8 seconds and then a follow-up hypertensive reaction. We found that centrally applied 2-amino-7-phosphono-heptaneoate (AP-7), a specific antagonist of NMDA receptor, did not ir.fiuence the initial response. This implied that the depressor response was not mediated through NMDA receptor. On the other hand, the hypertensive reaction induced by common carotid arteries clamping was attenuated by either AF7 or phencyclidine (PCP)+ Furthermore, using pressure microejection and single unit recording (Wang and Lee, 1989), we found that neurons in the rostral ventrolateral medulla (RVLM) were excited by locally applied NMDA and antagonized by AF7. This may suggest that RVLM neurons contain NMDA binding sites. Interestingly, carotid clamping also resulted in excitation of RVLM neurons. However, only was the cardiovascular neuronal (Brown and Guyenet, 1985) excitation antagonized by AP7. It is possible that clamping activates two endogeneous excitatory pathways to the RVLM neurons. Whereas only the cardiovascular neurons retain the NMDA-related inputs. It has been reported that glycine interacted with the allosteric site of NMDA receptor and the strychnine-sensitive glycine receptor in the CNS. Glycine enh~.-~.~,~,N M D A - r ~ a t e d reactions in the forebrain of hippocampus. These suggested that NMDA-mediated reactions were closely associated with glycine. However, we found injection of glycine (0.3-30 mole) into the lateral ventrical did not potentiate NMDA or carotid clamping-induced hypertension. Whether the glycine receptors in the RVLM are strychnine-sensitive requires further investigation. I~ conclusion, the present data demonstrated that NMDA was involved in the hypertensive reaction during carotid clamping in the rostral ventrolateral medulla.

References Brown, D.L., P.G. Guyenet., 1985, Circ. Res. 56, 359. Wang, Y., H.IC Lee., 1989, Neuropharmacology 28, 343.

P.tu.368 i

Effect of octopamine on intraocu]ar pressure of rabbits Tsai, J.T. and Tsai *, L.H. Department of Ophthalmo!oo~m,,Na~cnal Cheng Kung University Hospital, Tainan City, Taiwan 70101 and * Department of Physiology, Taipei .~*edic~s College, Taipei City, Taiwan 10105, Republic of China The effect of octopamine on the intraocular pressure of rabbits was investigated by topical administration. Changes of intraocular pressure were determined by comparison with the contralateral eye. Topically administered octopamine induced changes of intraocular pressure only at higher concentrations. The effect of octopamine was also studied by intravenous infusion and changes of intraocnlar pressure and arterial blood pressure were recorded. Pretreatment with several antagonists of adrenoceptors and dopamine receptor sites indicated that octopamine possesses the ability to affect dopamine receptor sites, especially DA-1 sites. This was further supported by the study of receptor binding with radiolabelled SCH23390 in the membrane fractions of isolated iris-ciliary body of rabbits. The effect of octopamine on the activity of adenylate cyclase which is linked to dopamine DA-1 receptors provided a supportive finding. The formation of cyclic AMP from a substrate of ATP stimulated by a dopamine DA-1 agonist in the iris-ciliary body of rabbits was affected by octopamine. The results suggest that ~topamine has selective effect on dopamine receptor sites, especially the DA-1 subtype, to cau,~,e a change in the intraocular pressure of rabbits.