Potential Sites of Action of TNPA: A Dopamine-2 Receptor Agonist

Roles of Dopaminergic D1and D2Receptors in Catecholamine Release from the Rat Adrenal Medulla

“…Secondly, in support of this idea showing the inhibitory effect of R-(-)TNPA on the CA release, it has been shown that the levels of NE in aqueous humor of the rabbit were reduced by 38% and 79% at 1 and 2 hr, respectively, following topical application of R-(-)TNPA (Chu et al, 1999). Following pretreatment with raclopride, a D2 receptor antagonist, and a subsequent challenge with R-(-)TNPA, the depression of intraocular pressure and levels of NE induced by R-(-)TNPA (2 hr) were antagonized.…”

“…Following pretreatment with raclopride, a D2 receptor antagonist, and a subsequent challenge with R-(-)TNPA, the depression of intraocular pressure and levels of NE induced by R-(-)TNPA (2 hr) were antagonized. Thus, it is concluded that immunohistochemical identification of D2 receptors in the ciliary body of the rabbit associated with the suppression of aqueous NE levels by topical application of the D2 receptor agonist, R-(-)TNPA, provide strong evidence of prejunctional (neuronal) site of action of R-(-)TNPA (Chu et al, 1999). Antagonism of R-(-)TNPA-induced ocular hypotension by raclopride coupled with the immunohistochemical and NE data suggest that D2 dopamine receptors are located on postganglionic sympathetic neurons in the ciliary body.…”

The effect of topical natural ergot alkaloids on the intraocular pressure and aqueous humor dynamics in rabbits with α-chymotrypsin-induced ocular hypertension

“…Moreover, both D 1 and D 2 dopamine receptors appear to play a role in the regulation of intraocular pressure [15]. Whereas activation of D 1 dopamine receptors has been generally shown to increase intraocular pressure, most likely by increasing aqueous humor production [10,37], D 2 agonists have been found to lower intraocular pressure by reducing aqueous humor inflow [5]. Ergoline derivatives mainly acting at dopamine receptors, such as bromocriptine, cianergoline, lergotrile and pergolide, have been shown to lower intraocular pressure in rabbits [24], monkeys [33] and humans [17].…”

Ocular Hypotension Induced by Electroacupuncture

“…Removal of aqueous humor samples from rabbits by paracentesis has been described previously (10). Prior to the paracentesis procedure, groups of rabbits were subjected to 1 hr-EA and then sacrificed rapidly with an overdose of sodium pentobarbital at the appropriate times.…”