Growth related changes in the content of heparin and 5-hydroxytryptamine of mast cells.

Heparin and 5-hydroxytryptamine (5-HT) were quantitated cytofluorometrically in individual mast cells from rats of various ages and body weights. Mast cells were studied in animals 35-200 days of age (150-575 g) representing a period of major body growth and about a quarter of the life span of the rat. Mast cell numbers as well as the content of both heparin and 5-HT in the mast cells was found to be strongly related to body weight and age of the animals. The number of mast cells increased about 3.5 times, the content of heparin in mast cells was doubled and the content of 5-HT increased at least three times during the growth period studied. There were great variations in the content of heparin and 5-HT within the cell populations of both young and old animals. The heparin content in the mast cell populations appeared to be either approximately normally distributed or slightly positively skewed. The skewness was not as marked as in a log-normal distribution. The 5-HT distribution profiles, on the other hand, were more strongly positively skewed. Except in the youngest age group, the 5-HT content appeared to be log-normally distributed within the mast cell population. A strong positive correlation was found between the median values of 5-HT and heparin content in the mast cell populations of growing rats.