The purpose of this study was to investigate the effects of electroacupuncture (EA) on aqueous humor dynamics in rabbits. EA stimulation was performed through two acupuncture needles placed in close proximity to the sciatic nerve. The sites of needle entry were anesthetized. After 1 hr of EA stimulation, intraocular pressure (IOP) decreased and was accompanied by reductions of blood pressure and aqueous humor flow rate. The maximum reduction of IOP was 9 mmHg at 3 hr and decreases in norepinephrine and dopamine levels in aqueous humor occurred simultaneously. In addition, EA stimulation induced an 8-fold increase of endorphin levels in aqueous humor. Ocular hypotension induced by EA lasted for more than 9 hrs and was antagonized by naloxone pretreatment. Furthermore, the EA-induced ocular hypotension was reduced markedly in sympathetically denervated eyes compared with the response of intact, normal eyes. Antagonism of EA-induced ocular hypotension by naloxone, suppression of aqueous humor flow and catecholamine levels by EA and elevation of endorphin levels in aqueous humor by EA indicate that opioids/opiate receptors are involved in modulating ocular hydrodynamics in response to EA.

In rabbit's aqueous humor, norepinephrine, epinephrine, dopamine and serotonin were detected simultaneously by a high performance liquid chromatography with electrochemical detection. Furthermore, the changes in catecholamine levels in aqueous humor were evaluated after topical application of moxonidine, an imidazoline1/alpha 2 receptor agonist, in the presence and absence of efaroxan. The level of norepinephrine in aqueous humor was reduced by moxonidine treatment. However, under the same set of conditions, there were no significant changes in the levels of dopamine, epinephrine or serotonin. Pretreatment with efaroxan antagonized moxonidine-induced suppression of norepinephrine levels. In other in vivo experiments, moxonidine caused a decrease in intraocular pressure which was antagonized by pretreatment with efaroxan. In the superior cervical ganglion preparation, norepinephrine release was increased 5-fold by the presence of a high K+ medium. The K(+)-evoked norepinephrine secretion was reduced by 55% by moxonidine. Pretreatment with efaroxan blocked the moxonidine-induced inhibition of norepinephrine release. It is concluded that inhibition of norepinephrine release from the superior cervical ganglion and suppression of aqueous norepinephrine levels contribute to the moxonidine-induced lowering of intraocular pressure. Moreover, the antagonism of moxonidine's in vivo and in vitro effects by efaroxan suggests the involvement of imidazoline1 receptors, but does not preclude activity on alpha 2 adrenoceptors.

No abstract

The purpose of this study was to determine the efficacy of a newly prepared formulation containing biodegradable calcium phosphate nanoparticles (CAP) and 7-hydroxy-2-dipropyl-aminotetralin (7-OH-DPAT) in pigmented and non-pigmented rabbits using the surrogate end points of intraocular pressure (IOP) and aqueous flow rate. IOP (mmHg) was measured by utilizing a manometrically calibrated Mentor pneumatonometer. Rates of aqueous humor flow were measured with a Fluorotron Master by estimating the dilution rate of fluorescein. In non-pigmented rabbits, the ocular hypotension induced by topical administration of 7-OH-DPAT (75 microg) with CAP (115 microg) was more pronounced and sustained than that of 7-OH-DPAT without CAP. Furthermore, IOP-lowering effects of topically administered 7-OH-DPAT (125 microg) alone were markedly diminished in pigmented rabbits compared to non-pigmented rabbits. However, topical application of 7-OH-DPAT formulated with CAP produced significant dose-related (37.5, 75, 125 microg) reductions of IOP accompanied by suppression of aqueous humor flow rates in pigmented rabbits. It is postulated that 7-OH-DPAT in vehicle without CAP binds to pigments in the anterior segment of the pigmented rabbit's eyes, and this binding limits the 7-OH-DPAT's action. Pretreatment with raclopride, a dopamine D2/D3 receptor antagonist, reduced the ocular hypotensive effect induced by 7-OH-DPAT in vehicle containing CAP thereby supporting the role for dopamine D2/D3 receptors in modulating IOP. It is concluded that CAP, as a delivery system, enhances activity by 7-OH-DPAT in pigmented rabbit eyes suggesting that CAP is potentially useful for achieving controlled and targeted drug delivery for treatment of ocular diseases.

No abstract

The purpose of this study was to investigate mechanisms of suppression of norepinephrine release by 7-OH-DPAT, a dopamine D₂/D₃ receptor agonist, in PC12 cells pretreated with nerve growth factor (NGF). 7-OH-DPAT caused inhibition of basal and K⁺-evoked norepinephrine release, which could be blocked by pretreatment with raclopride, a D₂/D₃ receptor antagonist. Moreover, dopamine D₂ and D₃ receptors were identified by immunocytochemistry. Expression of D₂, D₃, and D₄ mRNAs and their proteins were detected using RT-PCR and immunoblotting. Furthermore, 7-OH-DPAT produced no change in cGMP levels; however, 7-OH-DPAT inhibited forskolin-stimulated cAMP accumulation that was antagonized by pretreatment with raclopride. In addition, 7-OH-DPAT inhibited carbachol-induced Ca²⁺ transient, conversely, 7-OH-DPAT had no effect on 4-aminopyridine-induced Ca²⁺ transient. Taken together, suppression of cAMP accumulation and calcium mobilization by 7-OH-DPAT is involved in the inhibition of norepinephrine release through activation of dopamine D₂/D₃ receptors.

Oxymetazoline, an α₂ agonist, was active in lowering intraocular pressure in normal and sympathetically denervated rabbit eyes. Ocular hypotension was accompanied by decreased aqueous humor inflow. Topical pretreatment with rauwolscine, an α₂ antagonist, reduced the oxymetazoline-induced hypotensive effect more in contralateral than in ipsilateral eyes indicating the possible involvement of central α₂ adrenoceptors. Efaroxan, a relatively selective imidazoline antagonist, and diclofenac, a cyclooxygenase inhibitor, failed to inhibit the oxymetazoline-induced ocular hypotensive response. Oxymetazoline induced mydriasis in treated eyes at all doses. In in vitro studies, oxymetazoline inhibited isoproterenol-stimulated cAMP production in rabbit iris-ciliary bodies and cultured rabbit nonpigmented ciliary epithelial cells. The inhibition of cAMP accumulation induced by oxymetazoline was antagonized by rauwolscine or by BRL-44408, a relatively selective α_2A-adrenoceptor antagonist. These data indicate that oxymetazoline lowered intraocular pressure by activating α_2A receptors (ciliary epithelium) and that the ocular hypotensive effect was not totally dependent on intact sympathetic nerves. Results suggest that mechanisms involving centrally mediated effects of oxymetazoline are probable and this possibility is currently under investigation.

Norepinephrine, 10(-6) M, reduced Cl- transport by 26% in 75% of isolated frog corneal epithelia. This inhibition was not previously reported. Since beta-adrenergic agonists are known to only stimulate Cl- transport, the action of specific alpha 1- and alpha 2-agonists on Cl- transport and electrical parameters was investigated. Phenylephrine, an alpha 1-agonist always stimulated the Cl(-)-dependent short-circuit current (Isc), but less than the beta-agonists. UK-14,304-18 (UK), a selective alpha 2-agonist, reduced both the Isc (by 31% at 10(-5) M) and the stroma-to-tear unidirectional Cl- flux. UK hyperpolarized the apical membrane potential difference and increased the transepithelial resistance and apical-to-basolateral resistance ratio. UK reduced forskolin-stimulated adenylate cyclase activity by 36%. The electrophysiological effects of UK are consistent with a reduction of the Cl- permeability at the apical membrane. Pretreatment with UK sensitized the tissue for a greater effect by forskolin. Results show that the frog corneal epithelium also possesses alpha 1- and alpha 2-receptors, the latter negatively coupled to the adenylate cyclase system. Cl- transport is thus regulated by an interaction between the positive effects of beta- and alpha 1-stimulation and the negative influence of alpha 2-stimulation.