Distribution of histamine in developing rat tissues.

An antiserum against conjugated histamine was used to reveal the location and time of the appearance of the amine in different organs during the development of fetal and early postnatal rats. Tissues were fixed in 4% 1-ethyl-3(3-dimethyl-aminopropyl) carbodiimide and standard indirect immunofluorescence technique was used. Histamine-immunoreactivity (HA-ir) was first detected in the rat fetus on the 10th embryonic day (day E10) in the embryonic liver. The liver remained immunoreactive during the second half of the fetal life. In addition to some small HA-ir cells in the stomach wall and in the kidneys on day E16, the papillary muscles of the fetal heart also exhibited patchy immunofluorescence at this stage. On day E18, HA-ir cells appeared in many other organs including lungs, gastric mucosa and smooth muscle cells of the stomach wall, heart muscle and subcutaneous tissue. The distribution of HA-ir in fetal tissues was most extensive on day E20 when the kidney tubules and the skin also exhibited bright fluorescence. These results suggest that histamine is widely distributed during fetal development in different cell types.