|MadSci Network: Biochemistry|
I could not find any studies that directly answered your question. However, based upon evidence obtained from studies on other tissues and after conferring with Dr. Paul McGuire (Department of Cell Biology and Physiology, University of New Mexico), I believe that the answer is that marijuana (specifically, cannabinoids) produce vasodilation (increased caliber of blood vessels). The paper written by C. Hillard (reference 1) listed below reviews evidence that marijuana produces vasodilation. In many cases, there is evidence that this effect may be mediated by what are termed CB1 receptors. Although this paper does not discuss effects of cannabinoids on vasuclature in the eye, Porcella et al. (see reference 2) demonstrate that there are significant numbers of CB1 receptors in the eye. So, it is possible that marijuana dilates the blood vessels in the eye by binding to CB1 receptors. Your question may also be related to the interest of a number of scientists / pharmaceutical companies in developing and using synthetic cannabinoids for the treatment of glaucoma. The antiglaucoma properties of marijuana is the result of its ability to lower intraocular pressure (which may, in part, be due to its ability to produce vasodilation). The Porcella paper lists several references related to this topic. REFERENCES 1 Hillard, C.J. (2000) J. Pharmacol. Exp. Ther. 294, 27-32. 2 Porcella, A., Maxia, C., Gessa, G.L., and Pani, L. (2000) Eur. J. Neurosci. 12, 1123-1127.
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