Exp. Eye Res. (1977) Suppl., 411-414

Effect of Cytochalasin B on Conventional Drainage of Aqueous Humor in the Cynomolgus Monkey* PAUL L. KAUFMAN, ANDERS BILL AND ERNST H. B~R~NY

Department of Pl~ysiologyand Medical Biophysics and the Department of Medical Pharmacology, University of Uppsala, Uppsala, Su'eden, and the Department of Ophthalmology, University of Wisconsin Medical School, Madison, Wis. 53706, U.S.A. The effect of intracameral infusion of cytochalasin B (25/~g/ml) on gross outflow facility, true facility, uveoscleral flow, and aqueous humor formation was determined in cynomolgus monkeys. The results indicate that cytochalasin B causes a marked decrease in resistance to flow through the tissues between the anterior chamber and the canal of Schlemm. The effect was present in normal eyes and in an eye in which the ciliary muscle had been disinserted from the scleral spur.

1. Introduction Cytochalasin B reversibly increases gross outflow facility in cynomolgus monkeys (Kaufman and B£rAny, 1977). This effect is not mediated by ciliary muscle contraction, since it occurs in eyes in which the ciliary muscle has been disinserted from the seleral spur (Kaufnmn and BArAny, 1976). We demonstrate here that this effect in normal and "disinserted" eyes is due to a dramatic reduction in the outflow resistance of the conventional aqueous drainage pathways.

2. Materials and Methods Five eynomolgus monkeys (Macacafascicularis) were studied. In four monkeys, both eyes were previously untouched. The fifth monkey had previously undergone total irideetomy (Kaufman a i d Lfitjen-Drecoll, 1975) and 360 ° ciliary muscle disinsertion (Kaufman and BArAny, 1976) in the eye studied, and had subsequently shown no gross facility response to intravenous or intraeameral piloearpine in that eye. The monkeys were anesthetized with intramuscular sodium methohexital (Brietal, Lilly) and anesthesia was maintained with intravenous sodium pentobarbital.

Normal animals The eyes were connected to pressure transducers and continuously weighed reservoirs, and gross facilities (Cgl) were determined (Bill and BSrAny, 1966). Each eye was then connected to an infusion apparatus and an external mixing circuit (Bill, 1971). The fluid (BAr£ny, 1964) perfused through the anterior chamber on one side contained 0"1% unlabelled albumin, [laI]albumin in tracer amounts, and 2"5/zl dimethylsulfoxide (DMSO)/ml. On the other side, the fluid contained 0.1% unlabelled albumin, [125I]albumin in tracer amounts, 2"5 tzl DMSO/ml and 25 ~g cytocMlasin B/ml. The perfusion rate was 20 td/min. Perfusion was performed for 30-60 rain at an intraocular pressure (IOP) 2-4 mmHg above the spontaneous level, and then for another 30-60 min at an IOP 7-8 mmHg higher or (in the case of two animals with very high facility after eytochalasin B) at the spontaneous level. Gross outflow facility during infusion, Cg2, was calculated as (A flow into reservoir)/ AIOP. * Reprint requests to Dr Paul L. Kaufman, University of Wisconsin Hospitals, 1300 University Avenue, Madison, Wisconsin 53706, U.S.A. 411

412

P.L. KAUFMAN, A. BILL AND E. H. BARANY

Blood samples collected every 5-10 rain permitted calculation of the flow of anterior chamber fluid from each eye into the general circulation (Bill, 1966). True facility, Ctrue, was calculated as (Aflow to blood)/AIOP. In two monkeys, the anterior chambers were perfused with non-radioactive fluid at the end of the experiments and uveoseleral flow was calculated (Bill, 1966).

Disinserted eye The anterior chamber was cannulated, IOP measured, and the rate of aqueous humor formation determined (Bill, 1971). The perfused mock aqueous contained DMSO, [lalI]albumin, and carrier albumin as above. The rate of perfusate flow from the eye was determined continuously and IOP adjusted by means of a weighed reservoir. The rate of flow of anterior chamber fluid into the general circulation was calculated. After perfusion at two different IOPs, permitting calculation of Cg and Ctrue, the perfused fluid was changed to one containing cytochalasin B, 25/~g/ml. Perfusion was then continued at a low and then a high IOP, and Cg and Ctrue calculated again.

3. Results

Normal animals Table I shows the gross facility values Cg1 and Cg 2 calculated from the change in net inflow from the external system, and the true facility calculated from the flow of radioactive fluid into the general circulation. In all eyes treated with cytochalasin B, Cg 2 and Ctrue were much higher than in the control eyes although the values for Cg 1 were similar. Cg 2 and Ctrue were rather similar, indicating t h a t the increase in gross facility was due to a change in true facility. The differences that were observed between Cg 2 and Ctrue were due to two factors: (1) gross facility includes true facility TABLE I

Effect of intracameral cytochalasin B, 25 ixg/ml, in normal cynomolgus monkey eyes Experiment

Gross facility (tzl/min/mmHg) Cgt

Cg2

True facility (/zl/min/mmHg)

1

Cy C

0-26 0.23

0.49 0.15

0.71 0.22

2

Cy C

0.42 0.46

5.44 0.45

3.73 0.41

3

Cy C

0.19 0.30

1"51 0.30

1.25 0.31

4

Cy C

0.86 0.54

3'66 0"90

4.90 1-12

Uveoscleralflow (p,1/min)

1.21 0.89 Not determined 0"70 0"74 Not determined

Gross facility determined before (Cgl) and during (Cg~)perfusion of the anterior chamber with DMSO or DMSO plus cytochalasin B. True facility was determined simultaneously with Cg2. Cy, eye perfused with cytochalasin B; C, control eye.

CYTOCHALASIN

B AND FACILITY

413

plus pseudofacility and (2) in the calculations of Ctrue the albumin entering the general circulation was assumed to be distributed within 7-2% of the body weight. This assumption can introduce a considerable error because the distribution space varies between animals, and probably explains why true facility was sometimes found to be greater than gross facility. Cytochalasin B apparently had little effect on uveoscleral drainage (Table I).

Disinserted eye (Fig. 1) With DMS0 Cg and Ctruewere both 0-15/A/min/nlmHg. After the administration of cytochalasin B the flow from the external system into the eye increased markedly, as did the flow of anterior chamber fluid into the general circulation. Cg increased to 1.54/h/min/mmHg and Ctrue increased to 1.48/A/min/mmHg. E

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FIG. 1. Effect of intracameral eytochalasin B, 25/zg/ml, in an eye with a disinserted ciliary muscle. A rise in eye pressure was produced by increasing the net inflow from an external system (solid line) into the eye before and after the administration of cytochalasin B. The effect on eye pressure, rate of aqueous humor formation and flow of anterior chamber fluid into the general circulation (dashed line) are shown. The values for the rate of flow into the general circulation and aqueous formation are the steady state values observed.

Before cytochalasin B was given, the pressure elevation caused a moderate reduction in the rate of aqueous humor formation. After the administration of cytochalasin B the pressure rise seemed to stop all formation of aqueous humor. 4. Discussion

Our results confirm that in the cynomolgus monkey, normal eyes and eyes with disinserted ciliary muscles respond to intracameral administration of cytochalasin B with a large increase in gross facility of outflow (Kaufman and B£rAny, 1977). The

414

P. L. KAUFMAN, A. BILL AND E. IL B_A_R_A_NY

increase in gross facility is due mainly to a reduction of the resistance in the routes draining aqueous humor into the general circulation. The effect is not mediated by ciliary muscle contraction. Ab interno trabeculotomy of one quadrant in enucleated normal rhesus monkey eyes eliminates over 80% of the outflow resistance in the trabeculotomized quadrant, as determined by perfusion of the anterior chamber at pressures comparable to those used in our experiments (Ellingsen and Grant, 1971). In enucleated normal human eyes, the percentage of the resistance eliminated by one, two, or four quadrant ab inferno trabeculotomy is about 750/0 in the trabeculotomized segments (Grant, 1963; Ellingsen and Grant, 1972). Since cytochalasin B eliminates approximately the same proportion of the resistance, its main effect must be on the same structures. The observation that after administration of cytochalasin B a moderate rise in I O P m a y stop aqueous formation suggests that the drug also has effects on the ciliary epithelium. ACKNOWLEDGMENTS We are grateful for the expert technical assistance of Ing. Ulf UllstrSm. The study was supported by grants from the Swedish Medical Research Council (B7414x-147-10A) and the U.S.P.H.S. National Institutes of Health (5 RO1 EY 00475-09, EY 00231-10-11, Special Fellowship 1 F03 EY 55678-01-02, and 5 S01 RR-05435-14), Bethesda, Maryland. REFERENCES BArOny, E. H. (1964). Simultaneous measurement of changing intraocular pressure and outflow facility in the vervet monkey by constant pressure infusion. Invest. Ophthalmol. 3, 135-43. Bill, A. (1966). Conventional and uveo-scleral drainage of aqueous hmnor in the cynomolgus monkey (Macaca irus) at normal and high intraocular pressures. Exp. Eye Res. 5, 45-54. Bill, A. (1971). Effects of longstanding stepwise increments in eye pressure on the rate of aqueous humor formation in a primate (Cercopithecus ethiops). Exp. Eye Res. 12, 184-93. Bill, A. and BArOny, E. H. (1966). Gross facility, facility of conventional routes and pseudofacility of aqueous humor outflow in the cynomolgus monkey. Arch. Ophthalmol. 75, 665-73. Ellingsen, B. A. and Grant, W. M. (1971). Influence of intraocular pressure and trabeculotomy on aqueous outflow in enucleated monkey eyes. Invest. Ophthalmol. 10, 705-9. Ellingsen, B. A. and Grant, W. M. (1972). Trabeculotomy and sinusotomy in enucleated human eyes. Invest. Ophthalmol. 11, 21-8. Grant, W. M. (1963). Experimental aqueous perfusion in enucleated human eyes. Arch. Ophthal. tool. 69, 783-801. Kaufman, P. L. and B£r£ny, E. H. (1976). Loss of acute pilocarpine effect on outflow facility following surgical disinsertion and retrodisplaeement of the ciliary muscle from the scleral spur in the cynomolgus monkey. Invest. OphthalmoL 15, 793-807. Kaufman, P. L. and B£r£ny, E. H. (1977). Cytochalasin B reversibly increases outflow facility in the eye of the cynomolgus monkey. Invest. OpNhalmol. Visual Sci. 16, 47-53. Kaufman, P. L. and Liitjen-Dreeoll, E. (1975). Total iridectomy in the primate in vivo: surgical technique and postoperative anatomy. Invest. Ophthalmol. 14, 766-71.

Effect of cytochalasin B on conventional drainage of aqueous humor in the cynomolgus monkey.

Exp. Eye Res. (1977) Suppl., 411-414 Effect of Cytochalasin B on Conventional Drainage of Aqueous Humor in the Cynomolgus Monkey* PAUL L. KAUFMAN, AN...
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