Abstract
It has been reported that the splenic smooth muscles of several species of animals can be contracted with noradrenaline (1-4), adrenaline (1, 3-9), isoproterenol (1, 3-5), acetylcholine (5-8), serotonin (7), histamine (1, 7), tyramine (7), angiotensin (10), or BaCl2. The existence of alpha-adrenergic receptors has been confirmed in the splenic smooth muscles in the cat, dog, kid, rabbit, and human (1, 5, 8, 11). The stimulation of the alpha-adrenergic receptors in the spleen produces contraction of the organ. It is of interest that isoproterenol, which stimulates the beta-adrenergic receptors, contracts the spleen in cats and mice, but the drug relaxes it in mice when the concentration was very low. The isoproterenol-induced contraction of the spleen in cats can be inhibited by dichloroisoproterenol or dibenamine (1), and the isoproterenol-induced relaxation of it in mice can be inhibited by MJ-1999 or propranolol (4). Two explanations are possible for these findings; one is that there are beta-adrenergic receptors in the spleen and the other is that isoproterenol stimulates the alpha-adrenergic receptors in the spleen to produce contraction. As to the mechanism of the contraction of the spleen produced by acetylcholine, Burn and Rand proposed hypothesis in 1960: acetylcholine releases noradrenaline and adrenaline in the spleen, and these catecholamines produce the contraction (12, 13).
The present experiments were undertaken to examine whether there were beta-adrenergic receptors in the spleen, and to confirm the hypothesis proposed by Burn and Rand.
