Search

Previous work in our laboratory has shown that Cannabis sativa (marijuana) contains water-soluble, high molecular weight components that have extremely potent intraocular pressure (IOP) lowering activity. Aqueous extraction of other plants has now shown that a number of them also contain components with potent IOP lowering activity in rabbits. These include tobacco, cabbage, lettuce, several greens, Senecio anonymus, Erigeron philadelphicus, and several others. Not all plants tested were active, however, indicating that while more ubiquitous than originally thought, these materials are not apparently extractable from all plants. The chemical composition of the active fraction from tobacco was found to be different from that derived from Cannabis sativa.

Further studies have been made with water soluble marihuana-derived material (MDM). Neither adrenergic, cholinergic, aldosterone, dopamine or serotonin antagonism affected the fall in intraocular pressure induced by MDM. Partial blockade was obtained with galactose, glucose, or mannose, but not arabinose, when the latter were given at intravenous concentrations of 1 gm/animal and MDM was given at 25 micrograms animal, suggesting that these sugars may be involved at the active site of the MDM glycoproteins. Dexamethasone was without effect on either intravenous or intravitreal MDM indicating that the MDM effect is not a non-specific response to a protein. A similar plant glycoprotein, larch arabinogalactan, at 200 micrograms/animal was without effect on intraocular pressure. Aqueous humor flow rate was increased 3 hours after MDM administration, a period corresponding to the intraocular pressure increase caused by MDM, and fell to 20% of control values when the fall in intraocular pressure occurred. Blood flow through the iris was increased at both one and six hours after intravenous MDM injection indicating a vasodilation which could contribute to the initial increase in intraocular pressure. Intravitreal injection of MDM in rabbit and rhesus monkey caused a fall in intraocular pressure only after a 24 hour delay: the unilateral response indicated that systemic metabolism was not required for activity and the delay was likely caused by the diffusion time to the ciliary processes from the mid-vitreal injection site. The changes in beta-receptors, adenylate cyclase and carbonic anhydrase in the ciliary processes are minimal indicating a possible vascular mechanism of action of MDM.

Both anticoagulants (heparin and streptokinase) and non-steroidal anti-inflammatory compounds (aspirin and indomethacin) were used against a water-soluble derivative of marihuana, MDM. While the anticoagulants had no effect on the ocular effects of MDM, both aspirin and indomethacin altered the time course and effected the MDM-induced reduction of intraocular pressure. The usual initial hypertensive effect of intravenous MDM was eliminated and the later intraocular pressure fall occurred earlier as well as being inhibited by about 35 to 50%. Assay for prostaglandins revealed that intravenous MDM (3.86 micrograms) caused a marked rise in PGE2 concentration of the aqueous humor and iris-ciliary body during the first hour or two after administration of MDM, but normal values occurred at 4, 6, and 8 hours when the intraocular pressure is reduced by up to 60%. Following intravitreal MDM (0.002 microgram), however, the PGE2 levels remained unchanged over 24 hours, despite the induction of a fall in intraocular pressure between 14 and 18 hours which lasts for many hours. Prostaglandin appears to be involved in the hypertensive phase of intraocular pressure change after intravenous MDM injection; and, while the fall in intraocular pressure may contain a component partially mediated by prostaglandins, there is no evidence that intravitreal MDM induces any effect on prostaglandin levels. The involvement of prostaglandins, therefore, in the mediation of MDM-induced ocular hypotensive effects is apparently small.

Some biochemical factors of the iris-ciliary body of the rabbit have been examined for effects induced by water-soluble marihuana-derived material (MDM). Adenylate cyclase activity and sensitivity to beta-adrenergic agonists were unchanged, as measured 4 hours after MDM administration in vivo. Magnesium-dependent and anion-sensitive, but not sodium-potassium, ATPase activities were inhibited 6 hours after MDM administration in vivo, although they were unaffected by in vitro incubation. Topical administration of a potent substance P antagonist had no effect on the time course or magnitude of intravenous MDM-induced ocular effects in rabbit. Intravenously administered sugars antagonized the effects of MDM on intraocular pressure. A variety of drugs which display a range of biochemical effects varying from beta-adrenergic receptor agonism, to alteration of glycoprotein residues were employed. None of the agents employed, ranging from cAMP modifiers to protein synthesis blockers, had any effect on the MDM-induced response. It is apparent that the mechanism underlying the ocular hypotensive effect of MDM does not reside in mediation through adenylate cyclase, ATPase or substance P, but rather through a mechanism mediated by terminal sugar moieties on the molecule. The data suggest that modification of the surface membrane glycoprotein residues on the ciliary epithelium can induce marked alterations in aqueous humor flow rate.

A water soluble material, isolated from Cannabis sativa, has been tested in albino and pigmented rabbits and rhesus monkeys for both ocular and systemic effects. Intravenous administration produced a dose-related fall in intraocular pressure in both albino and pigmented rabbits with concentrations as low as 0.005 mg/animal being effective, but no response was found in monkeys. High concentrations (0.2 to 1 mg/animal) induced a hypertensive phase in intraocular pressure prior to the ocular hypotension; higher concentrations (2 or 5 mg/animal) also induced antidiuresis and general relaxation. Tachyphylaxis was found to repeated daily injections. Alpha and beta-adrenergic antagonists caused some reduction of the hypertensive phase but had no effect on the hypotensive phase. Superior cervical ganglionectomy did not influence the time course of the intraocular pressure response. Indomethacin inhibited the hypertensive intraocular pressure phase but was ineffective against the hypotensive phase. Systemic blood pressure was unchanged following intravenous administration of 0.2 mg material/animal. Aqueous tumor protein concentration was increased at both 1 and 6 hours after intravenous administration, becoming greater at the later time. Aqueous humor turnover rate was substantially reduced reaching a minimum 8.75 hours after administration. Topical administration was ineffective in eyes when the epithelium was removed in rabbits with and without pretreatment with aspirin. Neither gastric nor suppository administration of large quantities (10 mg or greater) of material had any influence on intraocular pressure.

Studies have been made in an attempt to elucidate the mode of action of water-soluble marihuana-derived material (MDM). MDM lowers intraocular pressure (IOP) at systemic dose levels greater than 5 micrograms/rabbit by reducing aqueous humor inflow. Blood pressure, body temperature, and PO2 remain constant despite the wide variation in IOP caused by high dose levels of MDM, viz. an initial hypertensive phase followed by a hypotensive phase. Blood PCO2 and pH, however, both decrease with 1 mg MDM/rabbit indicating an acidosis which may partially explain some of the fall in IOP caused by MDM at this high dose level. Low doses of MDM (50 micrograms/animal), however, induce no such changes in systemic chemistry, illustrating the absence of an MDM effect which can explain the greater than 50% fall in IOP. Repeated injections of MDM on a weekly basis indicate a sequentially reduced effect on IOP. MDM, when incubated in vitro for 6 hours with saline, aqueous or vitreous, always induced a fall in IOP; incubation in these media for 24 hours, however, reduced the capacity to induce an IOP decrease. When aqueous or vitreous was removed from animals which had received intravitreal injections of MDM 24 hours previously (thus, at a time when the IOP in these animals was low) and was reinjected intravitreally into fresh recipient rabbits, the IOP fell in the recipients with aqueous, but not vitreous. Only when high doses of MDM (greater than or equal to 2 mg) were given systemically to a donor rabbit was any evidence obtained of a fall in IOP in recipient rabbits at short times after the donor injection (less than 10 min); at greater times after the donor injections whole blood or serum from donor rabbits failed to elicit a fall in IOP in recipient animals. These data indicate that, in vivo, MDM is bound or metabolized rapidly in rabbits when MDM is given systemically.