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Comparison Of Rat And Human Eyes For The Presence And Distribution

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Purpose:Cannabinoids have been reported to reduce intraocular pressure (IOP) primarily by activating the CB1 receptors. Although CB2 receptors have also been implicated, their role and distribution are unclear. In this study, the location of the CB1 and CB2 receptors was compared in the rat and human cornea, iris and retina.

Methods:Cornea, iris and retina were dissected from freshly enucleated rat and human eyes (n=3 per group). Death to preservation time for human corneas was approximately 4 hours. Rat brain samples served as a positive control for CB1 and rat liver for CB2 receptors. After dissection, tissues were homogenized and RNA isolated using an Invitrogen kit. Only samples with absorbance 260/280nm ratio of 1.9 were considered for further study. A total of 5µg RNA was reverse transcribed to cDNA, which was used as a template for PCR reaction. CB1 and CB2 primers from rat were used to identify genes of interest in rat tissue; similarly human primers were used to identify genes in human tissue. The PCR products were verified for both band presence and intensity after a run on a 2% agarose gel. First-strand cDNA was added to the appropriate forward and reverse primers for real-time PCR amplification (39 cycles). A semi-quantitative delta-delta Ct method was used to analyze and interpret the results.

Results:In rat tissues, CB1 receptors in the brain were 3 fold more abundant than CB2; in the liver there were 9 fold more CB2 receptors than CB1 receptors. CB1 and CB2 receptors were present in equal amounts in the rat cornea with 4 fold more CB1 receptors than CB2 in the rat iris and 2 fold more CB2 than CB1 receptors in the rat retina. CB1 and CB2 receptor distribution in human tissues was similar to rat tissues except for the retina. Human corneas had twice as many CB1 than CB2 receptors, 5 fold more CB1 than CB2 receptors in the human iris while the human retina had 2 fold more CB1 receptors than CB2.

Conclusions:The preponderance of CB2 receptors in the rat retina compared to the humans was unexpected. The vastly greater presence of CB1 receptors in the rat and human iris' indicates that CB1 receptors may have a significant role in IOP regulation. These differences should be considered when translating studies conducted in the rat to humans. Further quantitations of results are underway.

Source: Comparison Of Rat And Human Eyes For The Presence And Distribution Of Cb1 And Cb2 Receptors -- Rosen et al. 52 (6): 4588 -- ARVO Meeting Abstracts
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