Effects of topical natural ergot alkaloids on intraocular pressure and aqueous humor dynamics in ocular normotensive rabbits.

Although it has been suggested that ergot derivatives may play a role in antiglaucoma therapy, little attention has been paid to the ocular hypotensive action of these drugs. Having previously reported in our laboratory that topical dihydroergocristine decreases intraocular pressure both in ocular normotensive and alpha-chymotrypsin-induced ocular hypertensive rabbits, the aim of the present work was to assess the effect of natural ergot alkaloids, ergocristine, alpha-ergocryptine and ergocornine, on the intraocular pressure and aqueous humor dynamics in ocular normotensive rabbits in order to further explore the ocular actions of these compounds. Intraocular pressure was measured with a pneumatonometer manometrically calibrated for the rabbit eye. Changes in tonographic facility of aqueous humor outflow and rate of aqueous humor inflow were evaluated in anesthetized rabbits. Natural ergot alkaloids were found to reduce intraocular pressure in ocular normotensive eyes in a dose-related fashion. These compounds decreased both tonographic outflow facility and, to a greater extent, aqueous humor inflow, which explains their final hypotensive effect.     

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

BACKGROUND: We previously reported that topical natural ergot alkaloids ergocristine, alpha-ergocryptine and ergocornine dose-dependently reduce intraocular pressure in ocular normotensive rabbits, most likely by decreasing aqueous humor inflow. In the present study, the effects of these compounds on intraocular pressure and aqueous humor dynamics in a rabbit model for ocular hypertension were assessed. METHODS: Experiments were conducted in albino rabbits made ocular hypertensive by intracameral injection of alpha-chymotrypsin. Intraocular pressure responses to drug vehicle and seven different doses of topical natural ergot alkaloids were examined in order to obtain dose-response relationships for comparing the intraocular pressure-lowering effect and potency of these drugs. Tonographies were also performed to ascertain the actions of natural ergot alkaloids on aqueous humor dynamics in alpha-chymotrypsin-induced ocular hypertensive rabbits. RESULTS: Topical application of the natural ergot alkaloids ergocristine, alpha-ergocryptine and ergocornine lowered intraocular pressure in alpha-chymotrypsin-induced ocular hypertensive rabbits in a dose-related fashion, with ergocristine displaying the greatest intraocular pressure-lowering effect. Tonographic studies revealed a decrease in the tonographic outflow facility following topical application of natural ergot alkaloids, although only the effects of both ergocristine and alpha-ergocryptine reached statistical significance. All natural ergot alkaloids tested significantly reduced the calculated aqueous humor inflow. CONCLUSION: This study suggests that the natural ergot alkaloids ergocristine, alpha-ergocryptine and ergocornine effectively decrease intraocular pressure in the alpha-chymotrypsin-induced model of ocular hypertension. Since these compounds reduce the tonographic aqueous humor outflow facility, their final ocular antihypertensive effect appears to result from a remarkable reduction of the aqueous humor inflow.     

Aqueous humor dynamics in alpha-chymotrypsin-induced ocular hypertensive rabbits.

Aqueous humor dynamics were studied in alpha-chymotrypsin-induced ocular hypertensive rabbits either by tonographic or two-level constant pressure perfusion techniques. A significant correlation was obtained between the values of outflow facility in alpha-chymotrypsin-induced ocular hypertensive rabbits as determined by tonography and constant pressure perfusion. The mean value of tonographic outflow facility in ocular hypertensive rabbits was not statistically different from that found in ocular normotensive rabbits. On the contrary, the estimated rate of aqueous inflow in ocular hypertensive rabbits was about 1.5-fold higher than that of ocular normotensive ones. While topical timolol lowered intraocular pressure and aqueous humor inflow in ocular hypertensive rabbits, pilocarpine did not produce any significant effect. Aqueous humor protein was significantly increased in ocular hypertensive eyes. The results of this study show that accurate measurements of outflow facility can be obtained in alpha-chymotrypsin-induced ocular hypertensive rabbits by tonographic technique. Our data suggest that the long-term ocular hypertension induced by alpha-chymotrypsin in albino rabbits may be secondary to an increase in the rate of aqueous humor inflow, likely produced by a breakdown of the blood-aqueous barrier. This finding strongly conflicts with the hypothesis of trabecular blockage as the cause of alpha-chymotrypsin-induced ocular hypertension in this species.     

The effect of topical CS-088, an angiotensin AT1 receptor antagonist, on intraocular pressure and aqueous humor dynamics in rabbits

PURPOSE: To evaluate the ocular hypotensive effect of topical CS-088, an angiotensin AT1 receptor antagonist, and the effect of CS-088 on aqueous humor dynamics. METHODS: The effects of CS-088 on intraocular pressure (IOP) were studied in 2 models of rabbit ocular hypertension. Experimental ocular hypertension was induced in albino rabbits by injecting alpha-chymotrypsin into the anterior chamber (alpha-chymotrypsin rabbit). The effects of the single application of CS-088 were examined. Additionally, CS-088 was repeatedly administered over a period of 3 weeks to hereditary ocular hypertensive rabbits (buphthalmic rabbits, JWHR bu/bu) and the IOPs were monitored throughout the experiment. The effects of CS-088 on aqueous humor dynamics were also examined in normal rabbits. In this study, the methods of IOP recovery rate, two-level constant pressure perfusion and fluorescein-dextran perfusion were used respectively to determine the aqueous inflow, outflow facility and uveoscleral outflow (USF). RESULTS: CS-088 at 1% and 2% significantly lowered the IOP in the alpha-chymotrypsin rabbits with a maximum IOP reduction of 10.1 mmHg. The maximum effect obtained with 2% CS-088 was no greater than that with 1% CS-088. In the buphthalmic rabbits, 2% CS-088 also lowered IOP significantly. Timolol was effective in both models. In the study on aqueous humor dynamics, a slight increase in USF (17%) was seen after a topical application of CS-088 whereas changes in aqueous inflow or outflow facility were not observed. CONCLUSIONS: Topical CS-088 can decrease IOP in rabbits. Despite the USF change, the ocular hypotensive mechanism by CS-088 was not fully determined.     

Topical vanadate lowers intraocular pressure in rabbits

In unanesthetized rabbits the topical application of vanadate lowered intraocular pressure. Tonographic outflow facility and episcleral venous pressure were unaltered by topical vanadate. As estimated from the tonographic data, aqueous humor flow was reduced by approximately 30%. Posterior chamber aqueous humor ascorbate increased in the eye receiving topical vanadate, and this was compatible with a decreased rate of aqueous humor flow. Topical vanadate did not alter anterior chamber aqueous humor protein or cyclic AMP. In five monkeys intraocular pressure was also significantly reduced by topical vanadate.     

A comparative study of topical natural ergot alkaloids on the intraocular pressure and aqueous humor dynamics in oclular normotensive and α-chymotrypsin-induced ocular hypertensive rabbits

Background Although it has been suggested that ergot derivatives may play a role in antiglaucoma therapy, little attention has been paid to the ocular hypotensive action of these drugs. Having previously reported that topical natural ergot alkaloids ergocristine α-ergocryptine and ergocornine dose-dependently reduce intraocular pressure in ocular normotensive and α-chymotrypsin-induced ocular hypertensive rabbits, the aim of the present work was to compare the effect of ergocristine, α-ergocryptine and ergocornine on the intraocular pressure and aqueous humor dynamics in ocular normotensive and α-chymotrypsin-induced ocular hypertensive rabbits, in order to further explore the ocular actions of these compounds. Methods Experiments were conducted in albino ocular normotensive and hypertensive rabbits by intracameral injection of α-chymotrypsin. Intraocular pressure responses to drug vehicle and seven different doses of topical natural ergot alkaloids were examined, in order to obtain dose–response relationships for comparing the intraocular pressure-lowering effect and potency of these drugs. Tonographies were also performed to ascertain the actions of natural ergot alkaloids on aqueous humor dynamics. Results All natural ergot alkaloids tested reduced intraocular pressure in a dose-related fashion. The ocular hypotensive effect was greater in α-chymotrypsin-induced ocular hypertensive rabbits for the three compounds tested. All natural ergot alkaloids tested decreased both tonographic outflow facility and, to a greater extent, aqueous humor inflow in ocular normotensive and in α-chymotrypsin-induced ocular hypertensive rabbits. Conclusion Taken together, our data suggest that these compounds decrease both tonographic outflow facility and, to a greater extent, aqueous humor inflow, which explains their final effect in ocular normotensive and in α-chymotrypsin-induced ocular hypertensive rabbits. Reductions in aqueous humor inflow observed after topical application of natural ergot alkaloids in α-chymotrypsin-induced ocular hypertensive rabbits can only be explained by a marked inhibition of active secretion of aqueous humor, since processes involved in aqueous humor formation may probably be altered after α-chymotrypsin injection.     

Correlation of aqueous humor ascorbate with intraocular pressure and outflow facility in hereditary buphthalmic rabbits

The hypotensive effect of ascorbate on intraocular pressure has been reported following topical application, oral administration, or anterior chamber infusion in animals. The present report describes the correlation of aqueous humor ascorbate concentration with intraocular pressure as well as outflow facility in vivo. Low aqueous ascorbate level was seen in buphthalmic eyes with high intraocular pressure and low outflow facility. The opposite correlation was observed in normal eyes. Ascorbate concentration in the anterior chamber of the rabbit eye is apparently related to the alteration of outflow facility and the movement of fluid in the anterior chamber.     

Effects of brinzolamide on aqueous humor dynamics in monkeys and rabbits.

This study examines the mechanisms by which brinzolamide reduces intraocular pressure (IOP) in healthy rabbits and in monkeys with unilateral ocular hypertension. Intraocular pressures were measured by pneumatonometry and aqueous flow was determined by fluorophotometry before and after three twice-daily drops of 1% brinzolamide to both eyes per monkey and after similar treatment to one eye per rabbit. In monkeys, outflow facility was determined by fluorophotometry and uveoscleral outflow was calculated. In rabbits, outflow facility was determined by two-level constant pressure infusion and uveoscleral outflow was measured by an intracameral tracer technique. Compared with contralateral vehicle-treated rabbit eyes, IOP was reduced in brinzolamide-treated eyes by 2.5 +/- 1.9 mmHg (mean +/- standard deviation; p =.006) at four hours after the second dose. Aqueous flow was reduced by 0.50 +/- 0.65 microl/min (p =.02). This effect was found in rabbits previously treated with brinzolamide but not in naive rabbits. Treated hypertensive eyes of monkeys had a reduction in IOP of 7.3 +/- 8.8 mmHg (p = 0.01) and aqueous flow of 0.69 +/- 1.10 microL/min (p = 0.05) when compared with baseline. Brinzolamide did not affect outflow facility or uveoscleral outflow in either rabbits or monkeys. It is concluded that, in normotensive eyes of rabbits and hypertensive eyes of monkeys, brinzolamide reduces IOP by reducing aqueous flow and not by affecting aqueous humor drainage.     

Studies of aqueous humor dynamics in man. IV. Effects of pilocarpine upon measurements in young normal volunteers.

The acute effects of topical pilocarpine 4 per cent, administered to one eye, have been studied in replicate experiments in young volunteers. One hour after medication administration the intraocular pressure was significantly lower. The magnitude of the reduction exceeded that predicated from the significant increase of true facility of outflow. This is explained by the observation of a significant reduction of calculated aqueous humor flow. Pilocarpine caused a significant increase of pseudofacility, a clinically useful drug effect not previously reported. One hour after medication administration, measured episcleral venous pressure was not different from the pretreatment level.     

Angiotensin (1-7) reduces intraocular pressure in the normotensive rabbit eye

PURPOSE: In the present study the effects of exogenous angiotensin II and its breakdown metabolite angiotensin (1-7) on the intraocular pressure (IOP) and on aqueous humor dynamics in normotensive rabbit eye were evaluated. METHODS: Male New Zealand White rabbits with normal IOP were used for intravitreous and topical administration of the test compounds. IOP was measured in conscious rabbits by pneumatonometer after topical anesthesia. Outflow measurements were made with a two-level constant pressure method in anesthetized animals. RESULTS: Angiotensin (1-7) administered intravitreously reduced IOP within 1 to 5 hours (P < 0.05). This effect was abolished by the selective angiotensin (1-7) antagonist A-779, and partially by the selective angiotensin II type 2 receptor antagonist PD123319. When olmesartan, an angiotensin II type 1 receptor blocker, was administered simultaneously with angiotensin (1-7), no antagonism was seen. Intravitreous administration of CGP42112 A, an angiotensin II type 2 receptor agonist, and angiotensin II did not significantly influence IOP, nor did topical administration of these compounds alter IOP. Angiotensin II significantly reduced outflow facility (P < 0.01) dose dependently, whereas angiotensin (1-7) had no effect. CONCLUSIONS: Angiotensin (1-7) is a biologically active vasodilatory and antiproliferative heptapeptide, and its vascular effects counteract those of angiotensin II. It reduces intraocular pressure possibly by a selective Mas receptor, without changing aqueous humor outflow facility in the normotensive rabbit eye.     

Effect of various drugs on pseudofacility and aqueous humor formation in the rabbit eye.

Norepinephrine and epinephrine reduce aqueous humor formation by an amount less than sufficient to reduce the intraocular pressure. Both drugs increase pseudofacility and true outflow facility which both contribute to reduce the pressure. Neither drug changes the value of x_c, the pressure index of the capillaries, which indicates that large hemodynamic changes do not occur. Phenylephrine has no effect on pseudofacility, since, although x_c is reduced, the fluid permeability is increased in a compensatory manner: an increase in true outflow facility is responsible for the small pressure fall.Pilocarpine causes a minor increase in aqueous humor formation, has no effect on pseudofacility yet lowers the intraocular pressure, albeit by only 2 mmHg. In order to lower intraocular pressure, therefore, pilocarpine must increase true outflow facility.Prostaglandin E₁ increases intraocular pressure, aqueous humor formation, x_c and pseudofacility. PGE₁ is known to induce venous congestion and this correlates with the increase in x_c since a secondary rise in capillary pressure would follow. The increase in aqueous humor formation accounts for the increase in intraocular pressure. The increase in pseudofacility accounts for about half of the increase in total outflow facility found with PG's, at least at times up to 2 hr after topical PG application.     

地塞米松对兔眼房水中一氧化氮及钙离子含量的影响

目的　观测兔眼球结膜下注射地塞米松后其眼压 (P)、房水流畅系数 (C)及房水中一氧化氮 (NO)浓度和Ca2 含量的变化 ,探讨NO、Ca2 在皮质类固醇性青光眼 (GIG)发病中的可能作用。方法　隔日定时给新西兰幼龄白兔双眼球结膜下注射地塞米松 0 5mg ,共 15次 ,3 0d ,隔日定时测定双眼眼压及C值 ,实验结束时抽取房水测定房水中NO及Ca2 浓度。结果　地塞米松使兔眼眼压升高 (P <0 0 5 )、C值及房水中NO浓度下降 (P <0 0 5 ) ;但对兔眼房水中Ca2 的含量无明显影响。结论　眼局部长期应用地塞米松可诱导高眼压 ,引起房水中NO含量显著降低 ,提示NO参与了GIG的发病     

Adenosine 3',5'-monophosphate increases the outflow of aqueous humor from the rabbit eye.

Direct administration of cyclic-AMP into the anterior chamber increases the outflow facility of the eye for aqueous humor. This is consistent with the hypothesis that catecholamines lower the intraocular pressure of the rabbit eye, at least in part, by a cyclic-AMP-mediated mechanism. This mechanism is active in the outflow channels and increases the rate at which aqueous humor leaves the anterior chamber.     

Increased intraocular pressure following topical azide or nitroprusside.

In rabbits the topical administration of sodium azide (NaNs) or sodium nitroprusside (SNP) increased intraocular pressure in a dose-response manner. These agents, which activate guanylate cyclase, elevated cyclic GMP in the aqueous humor. Systemic blood pressure and pulse were not altered. Tonographic outflow facility was unchanged, suggesting an increase in aqueous humor flow as the mechanism for the elevation of intraocular pressure. Posterior chamber aqueous humor ascorbate concentration was decreased in the eye receiving the NaN3 or SNP. Systemic pretreatment with phenoxybenzamine, an alpha-adrenergic blocking agent, prevented the elevation of intraocular pressure observed following NaN3 and SNP. Pretreatment with systemic indomethacin, propranolol, or acetazolamide or the topical application of atropine or epinephrine failed to alter the elevation of intraocular pressure by either NaN3 or SNP.     

Aqueous flow in human eyes is reduced by forskolin, a potent adenylate cyclase activator

Forskolin, which lowers intraocular pressure in rabbits, monkeys, and human subjects, was tested for its effect on the rate of aqueous humor flow and on outflow facility. Topical sodium fluorescein was used to measure the rate of aqueous humor flow in forskolin or placebo treated eyes. Tonography was used to determine outflow facility before forskolin administration and at 3 hr after administration of the drug. In eight human subjects who showed reduction of intraocular pressure in response to a single drop of forskolin, flow was reduced by an average of 34%, compared to the contralateral eye during the same period of time. No significant change in outflow facility occurred. The action of forskolin in reducing intraocular pressure was the direct result of a reduction in net aqueous flow.     

Effects of vasoactive intestinal polypeptide (VIP) on intraocular pressure, facility of outflow and formation of aqueous humor in the monkey

Stimulation of the facial nerve causes a non-cholinergic vasodilation in the uvea and a rise in the intraocular pressure in rabbits, cats and monkeys. Vasoactive intestinal polypeptide (VIP) has been suggested as the neurotransmitter mediating these effects. In the present investigation, the effects of VIP on aqueous humor dynamics were studied in cynomolgus monkeys. After intracameral injection of 1 microgram VIP, the outflow facility was higher in the experimental eye than in the control; 0.42 +/- 0.46 compared with 0.33 +/- 0.03 microliter cm H20-1 min-1, difference 0.09 +/- 0.04 microliter cm H2O-1 min-1. Intravenous infusion of VIP, 160 ng min-1, increased aqueous humor flow from 1.12 +/- 0.07 to 1.65 +/- 0.09 microliter min-1. Almost the same effect, a 50% increase in aqueous humor flow, was found after intracameral administration of 90 micrograms VIP. This dose of VIP caused a significant increase in intraocular pressure (IOP) in the experimental eye. The maximal difference in IOP between the experimental eye and the control eye was 7.5 +/- 0.4 cm H2O. A lower dose of VIP, 30 micrograms intracamerally, increased aqueous humor flow by about 20%, but had no consistent effect on IOP. The effect of VIP on aqueous humor flow was not affected by pretreatment with indomethacin. The results suggest that most of the rise in IOP caused by intracameral VIP administration is due to a rise in the pressure in the veins into which the aqueous humor is drained. Enhanced formation of aqueous humor plays a smaller role. The effects of VIP on aqueous humor formation and outflow facility suggest that the facial nerve may be involved in nervous control of aqueous humor dynamics, as VIP is most probably released in the eye by stimulation of the facial nerve.     

Effects of multiple dosing of epinephrine on aqueous humor dynamics in human eyes.

Numerous studies have provided conflicting evidence to explain the ocular hypotensive mechanism of action of epinephrine. Although epinephrine has been shown consistently to increase outflow facility, its effects on aqueous flow and uveoscleral outflow are not as clear. The purpose of this study was to clarify the effects of multiple doses of topical epinephrine on aqueous humor dynamics in human eyes. This was done by evaluating the four main parameters that determine steady state intraocular pressure. These parameters were assessed at baseline and after a week of twice-daily treatment of epinephrine hydrochloride 2% to one eye. Twenty-six human volunteers were enrolled in the study. Intraocular pressure was measured by pneumatonometry, aqueous flow and trabecular outflow facility by fluorophotometry, episcleral venous pressure by venomanometry and uveoscleral outflow by mathematical calculation. In epinephrine-treated eyes compared to baseline, intraocular pressure and aqueous flow were reduced from 21.2 +/- 0.3 to 17.1 +/- 0.2 mmHg (19%, p = .01) and 3.3 +/- 0.2 to 2.9 +/- 0.2 microl/min (12%, p = .03), respectively. Trabecular outflow facility obtained by fluorophotometry was increased from 0.18 +/- 0.02 to 0.26 +/- 0.03 microl/min/mmHg (44%, p = .02). Topical epinephrine did not significantly affect uveoscleral outflow or episcleral venous pressure. In conclusion, multiple topical doses of epinephrine lowered intraocular pressure in human volunteers by reducing aqueous humor formation and increasing trabecular outflow facility. The increase in uveoscleral outflow suggested by other studies was not observed.     

Different Effects of Topical Prazosin and Pilocarpine on Uveoscleral Outflow in Rabbit Eyes

Purpose:To investigate the effects of topical prazosin and pilocarpine on uveoscleral outflow(Fu) in rabbits.Methods:Sixteen rabbits were randomly divided into the control group (5 rabbits, only topical application of normal saline in the fight eye of each rabbit), Prazosin (PZ) treated group (6 rabbits, only 0.1％ Prazosin eyedrop 0.1％ in the right eye of each one) and Pilocarpine (PC) treated group (5 rabbits, 1％ Pilocarpine eye drop in each fight eye). Intraocular pressure (IOP) of bilateral eyes of each rabbit was measured before and 1h after topical application of the eye drop. And the bilateral eyes were perfused with Fluorescein-isothiocyanate bovine serum albumin (FITC-BSA) as the tracer into the anterior chamber of each rabbit for 30 min at 90 min after topical treatment. Then the rabbits were killed for Fu measurement.Results:IOP of PZ-treated eyes decreased [(0.71±0.07)kPa] in 1 hour after PZ application. IOP of PC-treated eyes decreased [(0.70±0.08)kPa] in 1 hour after PC application. Th     

The effect of topical PGF2 alpha on uveoscleral outflow and outflow facility in the rabbit eye.

Prostaglandin F2 alpha (PGF2 alpha) is a powerful ocular hypotensive agent in rabbit, cat, dog, monkey and human. In cynomolgus monkeys, the intraocular pressure (IOP) lowering is due to increased uveoscleral outflow (Fu). Because the anatomy of the rabbit outflow apparatus differs significantly from that of the primate, we sought to determine whether the mechanism of the PGF2 alpha-induced IOP fall was the same. PGF2 alpha tromethamine salt (PGF2 alpha-TS) (50 micrograms) applied to one eye of 14 conscious rabbits produced a significant IOP fall of 7.4 +/- 0.9 mmHg (P less than 0.001). In untreated control eyes, Fu determined from the quantity of intracamerally perfused [125I]albumin found in the ocular and periocular tissues accounted for 5-8% of total aqueous outflow. In 15 unilaterally PGF2 alpha-treated rabbits, after 4-6 hr dosing Fu was 49 +/- 14% higher in the treated than in the contralateral control eyes. Total outflow facility of outflow from the anterior chamber to the general circulation were measured concurrently in 11 rabbits using a two-level constant pressure perfusion and isotope accumulation technique. Both facilities tended to be higher in the treated eyes than in the controls, with a strong correlation between drug-induced changes in total facility and changes in facility of flow to blood (r = 0.85, P less than 0.001). In eight rabbits treated unilaterally with 50 micrograms PGF2 alpha-TS, the fluorophotometrically determined aqueous formation rate was probably not decreased relative to control eyes. Protein levels in the aqueous humor were approximately eight-fold higher in PG-treated vs. control eyes, suggesting a drug-induced compromise of the blood-aqueous barrier.(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies on the mechanism of action of timolol and on the effects of suppression and redirection of aqueous flow on outflow facility

Long-term use of drugs that suppress aqueous humor formation, such as timolol and dorzolamide, or that redirect aqueous humor outflow from the trabecular meshwork, such as prostaglandin F2alpha analogues, could cause underperfusion of the trabecular meshwork and a secondary decrease in outflow facility. We investigated the mechanism of suppression of aqueous humor formation by timolol in monkey eyes by measuring aqueous humor ascorbate levels. We also determined whether suppression of aqueous humor formation with and without redirection of aqueous humor away from the trabecular meshwork could lead to a subsequent reduction in outflow facility, and whether this reduction was correlated with increased fibronectin levels in anterior chamber aqueous humor. In cynomolgus monkeys, unilateral dose/aqueous humor formation response curves were generated for timolol, dorzolamide, and a combination of timolol + dorzolamide. Aqueous humor formation and/or outflow facility were measured in both eyes after approximately four days, four weeks and seven weeks of twice daily treatment with 3.5 microg timolol + 1.0 mg dorzolamide to one eye and 30% DMSO to the other. In some monkeys, 5 microg prostaglandin F2alpha-isopropyl ester (PG) was added to timolol + dorzolamide for 4-week treatments. Intraocular pressure and corneal endothelial transfer coefficients (k(a)) were also measured at four weeks. Aqueous humor fibronectin levels were determined in four monkeys after approximately 9.5 weeks of timolol + dorzolamide treatment. Aqueous humor formation, intraocular pressure, and aqueous humor ascorbate levels were also determined in rhesus monkeys at baseline and after a single unilateral topical administration of 25 microg timolol. Compared to baseline for the same eye, aqueous humor formation was significantly decreased in treated eyes at all doses of timolol and at 1.8 and 4 mg dorzolamide. Compared to the opposite control eye, aqueous humor formation was lower in treated eyes after 3.5 and 5 microg timolol and after all doses of dorzolamide. Aqueous humor formation after treatment with 3.5 microg timolol + 1.0 mg dorzolamide was decreased in treated vs. control eyes, after four days and was suppressed in both treated and control eyes after four weeks of treatment, but not when PG was added. There was no difference in k(a) values with or without the addition of PG. Intraocular pressure was significantly lower in both treated and control eyes vs. baseline after approximately 6.5 weeks treatment with timolol + dorzolamide when taken 2 hr after the last dose and after approximately 3.5 weeks treatment with timolol + dorzolamide + PG when measured 6 hr after the last dose. Outflow facility after treatment with timolol + dorzolamide was unchanged after four days, tended to be lower in the treated vs. control eyes after four and seven weeks, and was significantly lower in treated vs. control eyes after four weeks treatment with timolol + dorzolamide + PG (0.352 +/- 0.052 vs. 0.515 +/- 0.096 microl min(-1) mmHg(-1), p < or = 0.02). Both treated vs. control eye aqueous humor fibronectin levels were below the level of detection for our assay (0.01 microg ml(-1)). The 25 microg timolol dose decreased ipsilateral, but not contralateral intraocular pressure (12.6 +/- 1.7 vs. 15.2 +/- 0.9; p < 0.05) and aqueous humor formation (1.40 +/- 0.08 vs. 2.03 +/- 0.09 microg ml(-1), p < or = 0.01). There was no difference in anterior chamber ascorbate levels in treated vs. control eyes or compared to their respective baselines. Our findings indicate that timolol affects neither ciliary epithelial transport of ascorbate nor aqueous fibronectin levels. Our data also indicate that decreasing aqueous humor formation over a period of time can lead to reduction in outflow facility, particularly when combined with therapy that redirects aqueous from the trabecular meshwork. Future intraocular pressure-lowering therapies for glaucoma may better be directed at enhancing flow through the trabecular pathway as opposed to decreasing aqueous humor formation or rerouting aqueous humor away from the trabecular meshwork.