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R. D. Glickman, N. Kumar, D. W. Marshak, Y.-B. Shui, D. C. Beebe, N. Holekamp; Histamine Content of Human Vitreous Humor as a Function of Time of Day. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5903.
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Previous studies have reported a diurnal variation in the histamine content of retina and choroid of rodents and primates, presumably reflecting changes in the activity of retinopetal histaminergic axons. This study was conducted to determine if histamine content in human vitreous humor exhibited a similar diurnal variation.
Samples of vitreous humor from 19 human patients undergoing therapeutic vitrectomies were obtained and analyzed for histamine content by ELISA (Oxford Biomedical Research Kit EA31). The time of the vitrectomy of each patient was converted to Zeitgeber Time (ZT) and compared to the measured histamine content of the patient’s vitreous sample.
Histamine was found in the vitreous samples of all 19 eyes, with an average value of (mean ± s.d) 9.92 ± 3.49 ng/ml (median = 10.59 ng/ml, or 95.3 pmol/ml). This overall value was comparable to previous reports of histamine content in human tissues, e.g. 39.2 pmol/ml in plasma and 388.1 pmol/ml in CSF (Khandelwal et al., 1982). No correlation, however, was found between the histamine content and ZT: Pearson correlation coefficient = 0.032, and a t-test comparing the values for procedures performed at ZT < 5 h and ZT ≥ 5 h was not significant (P > 0.05). There did appear to be a relation between histamine content and underlying pathology: eyes with macular pucker had the lowest (5.90 ± 3.65 ng/ml, n = 5) and eyes with more advanced epiretinal membranes and diabetic retinopathy had the highest (11.51 ± 2.12 ng/ml, n = 8) histamine content, a significant difference (p = 0.02, t-test).
Because samples were obtained from patients with retinal diseases, it is possible that nonspecific histamine from underlying inflammatory processes masked a diurnal variation in histamine released from the retina. A test for this hypothesis would be to assay the samples for methylhistamine, a histamine metabolite produced by histamine methyltransferase (HMT), which may more accurately reflect histamine release from the retina, because there is little or no HMT activity in the vitreous body.
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