Abstract
Tetrahymena populations were treated with 10^−15^ g ml^−1^ or 10^−6^ g ml^−1^ concanavalin‐A (Con‐A) in tryptone‐yeast medium for 1 h. Rat peritoneal immune cells (mast cells, lymphocytes, monocyte‐granulocyte group) were also treated with 10^−6^ g ml^−1^ Con‐A, for 1 h. The cells' hormone (ACTH, histamine, serotonin, endorphin, triiodothyronine (T~3~)) content was measured by using immunocytochemistry and flow cytometry. The extremely low dose of Con‐A universally and significantly elevated the hormone contents, while the result of higher dose was uncertain. In the immune cells, Con‐A significantly decreased the ACTH level in each cell type and histamine level in mast cells. The results demonstrate the very high sensitivity of Tetrahymena receptors for a non‐hormone (lectin) molecule, which can bind to the insulin receptors and mimics the effect of insulin. The results also show that Tetrahymena receptors are more sensitive to lower concentrations of molecules than to higher ones. The universal hormone‐production stimulating effect of Con‐A—which is observed in Tetrahymena—is specified in rat. Copyright © 2008 John Wiley & Sons, Ltd.