HISTAMINE H-1 RECEPTOR ACTIVATION MEDIATES THE PREFERENTIAL RELEASE OF ADRENALINE IN THE RAT ADRENAL-GLAND

Histamine elicited the release of catecholamines from ''in vitro'' perfused rat adrenals with an EC(50) of 3 mu M. This concentration was in the same range as those which caused a fall in the arterial blood pressure when infused intravenously in anaesthetized rats. Histamine stimulation was potently blocked by dexclorfeniramine (IC50) = 300 pM), but affected by ranitidine, suggesting the involvement of H-1 receptors. Histamine released preferentially adrenaline. Mast cells were not detected within adrenal medulla by histochemical techniques. Compound 48/80 did not trigger catecholamine release. Catecholamine secretion evoked by splanchnic nerves stimulation was not modified by a combination of H-1 and H-2 antagonists. In conclusion, the histamine that elicited adrenaline release for rat adrenals comes from blood circulation not from local mast cells or splanchnic nerves. These effects are mediated through the activation of H-1 receptors.