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Stress activates the hypothalamic-pituitary-adrenal axis through release of corticotropin releasing hormone (CRH), leading to production of glucocorticoids that down-regulate immune responses. Acute stress, however, also has proinflammatory effects that seem to be mediated through the activation of mast cells. Stress and mast cells have been implicated in the pathophysiology of various inflammatory conditions, including some in the central nervous system, such as multiple sclerosis in which disruption of the blood-brain barrier (BBB) precedes clinical symptoms. We previously showed that acute restraint stress increases rat BBB permeability to intravenous 99 Tc gluceptate and that administration of the "mast cell stabilizer" disodium cromoglycate (cromolyn) inhibits this effect. In this study, we show that the CRH-receptor antagonist Antalarmin blocks stress-induced 99 Tc extravasation, whereas site-specific injection of CRH in the paraventricular nucleus (PVN) of the hypothalamus mimics acute stress. This latter effect is blocked by pretreatment of the PVN with cromolyn; moreover, restraint stress cannot disrupt the BBB in the diencephalon and cerebellum of W/W v mast cell-deficient mice. These results demonstrate that CRH and mast cells are involved in regulating BBB permeability and, possibly, brain inflammatory disorders exacerbated by acute stress.

Background: Mast cells play an important role in allergic inflammation by releasing vasoactive molecules, proteases and cytokines. Corticotropin-releasing hormone (CRH) and its structural analogue urocortin (Ucn) were shown to trigger skin mast cell activation and vascular permeability. We investigated the effect of acute stress on rat skin vascular permeability and CRH secretion, as well as the effect of intradermal CRH, and that of two histamine-1 receptor antagonists, azelastine and olopatadine, on vascular permeability. Methods: Rats were stressed by restraint and vascular permeability was assessed by extravasation of ⁹⁹Tc-gluceptate, while mast cell activation was determined by skin rat mast cell protease-1 (RMCP-1) content. Skin CRH content was evaluated by ELISA. The effect of intradermal injection of CRH and Ucn, as well as that of two histamine-1 receptor antagonists, azelastine and olopatadine, was assessed by Evan’s blue extravasation. Purified rat peritoneal mast cells (RPMCs) were also pretreated with azelastine (24 µM) or olopatadine (133 µM) for 5 min before challenge with compound 48/80 (0.5 µg/ml) for 30 min. Histamine secretion was measured fluorometrically. Intracellular Ca²⁺ ions were evaluated in RPMCs loaded with calcium crimson and stimulated with compound 48/80. Results: Acute stress increased skin vascular permeability and CRH content, while it decreased RMCP-1. Intradermal injection of CRH or Ucn induced substantial Evan’s blue extravasation that was inhibited by pretreatment with azelastine (24 µM) and olopatadine (133 µM). Both antihistamines also inhibited histamine release and intracellular increase of Ca²⁺ ions from RPMCs stimulated by compound 48/80. Conclusions: These results indicate that acute stress increases skin CRH that can trigger mast cell-dependent vascular permeability, effects inhibited by certain histamine-1 receptor antagonists, possibly acting to reduce intracellular Ca²⁺ ion levels.

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