RESUMO
The effects of pertussis toxin on the intraocular pressure (IOP) lowering effect of clonidine and isoproterenol as well as on the inhibitory effects of clonidine and neuropeptide Y on adenylate cyclase activity of ciliary processes were studied in albino rabbits. I.v. administered pertussis toxin elicited transient changes in IOP which, however, returned to control values during 2-3 days. In the following days the IOP lowering effect of the alpha 2-adrenergic agonist clonidine was abolished and that of the nonselective beta-adrenergic agonist isoproterenol was attenuated. At the same time, the inhibitory effects of clonidine and neuropeptide Y on basal as well as stimulated adenylate cyclase activities in homogenates of ciliary processes were grossly diminished. The effects of pertussis toxin on the IOP lowering action of adrenergic agonists and on the inhibitory action of clonidine and neuropeptide Y on adenylate cyclase activity were ascribed to an impairment of the function of a G protein in ciliary processes, probably G(i) protein. It is suggested that the decrease of IOP induced by clonidine is due to inhibition of adenylate cyclase.