Histamine in the retina.

Retina and choroid were rapidly and gently extracted from chickens, guinea-pigs, rats, rabbits and cows. They were frozen, weighted and pooled in 3% trichloroacetic acid in a refrigerator. Using a radioenzymic assay, histamine was found to be present in the retina of guinea-pig (4.26 +/- 0.677 nmol g-1), rabbit (1.08 +/- 0.422 nmol g-1) and cow (0.189 +/- 0.036 nmol g-1), but not detected in chicken and rat. In the choroid, histamine was found in all species except rat (chicken: 4.92 +/- 0.542 nmol g-1; guinea-pig: 121.5 +/- 4.46 nmol g-1; rabbit: 18.7 +/- 3.93 nmol g-1; cow; 0.36 +/- 0.095 nmol g-1). The study verifies the presence of histamine in the retina of some species, and thereby supports previous fluorometry assays.