The involvement of central histamine receptors in stress-induced responses of serum corticosterone and free fatty acids and in gastric ulcer development

Effect of psychogenic stress on gastrointestinal function

This review summarizes the studies published over the last twenty years on the effects of psychogenic stress on gastrointestinal function, using animal models. The effects of stress on gastric ulceration have received wide attention and the central and local mechanisms of mucosal damage have been, for the most part, clearly delineated. In comparison, relatively few studies have focused on the impact of stress on intestinal and colonic physiology, even though its influence on intestinal motility, mucosal permeability and inflammation has been established. More work is necessary in this field, especially considering the importance of irritable bowel syndrome in modern society.

Stress and brain histaminergic system: effects of weak electric foot-shock

A weak electric foot-shock stressful stimulus (0.5 mA x 1 s x 5 times) significantly increases plasma corticosterone (CS) levels and modifies [3H]-histamine ([3H]-HA) binding site constants related to H2 receptors in rat cortical membranes. Progressive and total recovery of basal binding characteristics occurs 90 min later. A double-foot-shock stress procedure delays [3H]-HA binding characteristic recovery instead of strengthening stress effects. This finding is further evidence of involvement of the brain's histamine receptors in the response to mild stress.

Evidence of correlations between mast-cell histamine and beta-endorphin (ir) from NIL-pituitary in the homeostasis

This study was designed to characterize physiological events related to a single or repeated experimental anaphylactoid reactions (by Compound 48/80) in non-stressed or cold-restrained rats. Acute treatment with Compound 48/80 (1 mg/kg, i.p.) increases Beta-endorphin(ir) content in the neurointermediate lobe (NIL) of rat pituitary. Moreover, repeated treatment with Compound 48/80 showed tolerance effects. These animals, exposed to stressful conditions, exhibited a fully evident paw oedema following carrageenin oedema-test, whereas saline-pretreated rats, under the same experimental conditions, showed reduced local inflammation. Since Compound 48/80 produces characteristic, systemic, anaphylactoid reaction in the rat, with a very high degree of selectivity in its action, our results suggest that mast-cell histamine and Beta-endorphin from NIL pituitary are involved in the body's reactivity to stressful stimuli.

Brain histamine response to stress in 12 month old rats

The regional brain histamine regulation in response to stress was investigated in 12 month old Sprague-Dawley male rats. Air blast exposure (15 min) induced significant (26.5%) elevation in hypothalamic HA level; midbrain and cortical HA concentrations were not affected. Histamine methyltransferase activity was not altered by stress in any of the brain regions investigated. Plasma corticosterone levels of stressed rats were significantly elevated (6.5 fold). Hence, the response of hypothalamic HA to stress is still evident in 12 month old rats.

Interference of clonidine and alpha-methyl-p-tyrosine with stress and central histaminergic stimulation of the corticosterone response in rats

In conscious rats clonidine given intracerebroventricularly 1 h prior to a mild stress of immobilization intensified the stress-induced increase of pituitary-adrenocortical response, measured indirectly through corticosterone concentration in blood serum. The corticosterone response to clonidine was abolished by i.c.v. pretreatment of rats with yohimbine, an alpha 2-adrenergic antagonist, and was antagonized by pretreatment with phenoxybenzamine, an alpha 1-adrenergic antagonist. Clonidine intensified also the corticosterone response induced in stressed rats by i.c.v. injected histamine, 2-pyridylethylamine (PEA), a H1-receptor agonist, and dimaprit, a H2-receptor agonist. The depletion of brain catecholamines by alpha-methyl-p-tyrosine (alpha-MT) considerably increased the corticosterone response to stress but did not substantially change the response to histamine, PEA and dimaprit in stressed rats. These results suggest that clonidine increases the corticosterone secretion induced by a mild stress and histamine and histamine H1 and H2 agonists mainly through the activation of central alpha 2-adrenoceptors. The increase by alpha-MT of the stress-induced corticosterone response may indicate the inhibitory role of central catecholamines in the pituitary-adrenocortical response to stress in rats.

Central histaminergic stimulation of pituitary--adrenocortical response in the rat

In conscious rats histamine, the H1-receptor agonist 2-pyridylethylamine (PEA), and the H2-receptor agonists dimaprit and impromidine given intracerebroventriculary (i.c.v.) increased the hypophyseal-adrenocortical response, evaluated indirectly through the corticosterone concentration in the blood serum. On a molar basis histamine was the most potent drug whereas its agonists were less potent in inducing an increased corticosterone response. Impromidine however, was far more active than dimaprit and PEA. The effect of histamine was significantly yet not totally antagonized by either mepyramine, a H1-receptor antagonist, or cimetidine, a H2-receptor blocker. The combination of mepyramine and cimetidine caused a considerably stronger inhibition than that induced by either antagonist given separately. Mepyramine impaired the corticosterone response to PEA, and the responses to impromidine and dimaprit were significantly diminished by cimetidine. The results suggest that i.c.v. histamine increases the pituitary-adrenocortical activity via both H1- and H2-receptors, and there seems to be no significant prevalence of either of these receptors in mediating this action of histamine.

Histamine and the hypothalamus

The chemical tools that could be used to examine the function of histamine in the brain are considered together with the evidence linking histamine specifically with the hypothalamus. The distribution of histamine and the enzymes responsible for its synthesis and metabolism is consistent with there being both mast cells and histaminergic nerve terminals within the hypothalamus. Iontophoresis, mepyramine binding and histamine-stimulated adenylate cyclase studies suggest that both histamine H1- and H2- receptors are present in the hypothalamus. In addition, intracerebroventricularly injected histamine receptor agonists and antagonists affect many functions associated with the hypothalamus such as cardiovascular control, food intake, body temperature control, and pituitary hormones whose release is mediated via the hypothalamus, such as corticotropin, growth hormone, thyroid stimulating hormone, prolactin, gonadotropins and vasopressin. However, only in the case of thyroliberin release, prolactin release, body fluid control and blood pressure control is there evidence yet that such effects are mediated via histamine receptors actually in the hypothalamus. The effects of enzyme inhibitors suggest endogenous histamine may be involved in the physiological control of thyroid stimulating hormone, growth hormone and blood pressure, and the effects of receptor antagonists support a role for endogenous histamine in prolactin control. Otherwise, there is little evidence for a physiological role for endogenous, as against exogenous, histamine whether it be from histaminergic terminals or mast cells. In addition, few studies have tried to distinguish possible effects on presynaptic receptors, postsynaptic receptors, hypothalamic blood vessels or the hypophyseal portal blood vessels. It is concluded that although there is good evidence now linking histamine and the hypothalamus more specific studies are required, for instance using microinjection or in vitro techniques and the more specific chemical tools now available, to enable a clearer understanding of the physiological role of histamine in the hypothalamus.