Histamine and the skin

The role of histamine in urticaria is reviewed with particular reference to experiments on cold contact urticaria. In this model, histamine release clearly has a central role, but the failure of drugs which suppress histamine release to alleviate symptoms, other than itching, suggests that other pharmacological agents must be involved. Evidence is presented that prostaglandin E may play a role in some of these patients. The discovery that human blood vessels possess H2 receptors as well as H1 receptors is discussed with particular reference to the role of combined H1 and H2 pharmacological blockade.

Increased concentrations of arachidonic acid, prostaglandins E2, D2, and 6-oxo-F1 alpha, and histamine in human skin following UVA irradiation

The buttock skin of clinically normal human subjects was subjected to approximately 2.5 minimal erythema doses of ultraviolet A irradiation. Deep red erythema developed during irradiation, faded slightly within the next few hours, increased to maximum intensity between 9-15 h, and decreased gradually thereafter although still persisting strongly at 48 h. Suction blister exudates were obtained at 0, 5, 9, 15, 24, and 48 h after irradiation as well as suction blister exudates from a contralateral control site and assayed for arachidonic acid, prostaglandins D2 and E2, and the prostacyclin breakdown product 6-oxo-prostaglandin F1 alpha by gas chromatography-mass spectrometry, and for histamine by radioenzyme assay. Increased concentrations of arachidonic acid and prostaglandins D2, E2, and 6-oxo-prostaglandin F1 alpha were found maximally between 5-9 h after irradiation, preceding the phase of maximal erythema. Elevations of histamine concentration occurred 9-15 h after irradiation, preceding and coinciding with the phase of maximal erythema. At 24 h, still at the height of the erythemal response, all values had returned to near control levels. Hence increased concentrations of arachidonic acid and its products from the cyclooxygenase pathway, and of histamine, accompany the early stages up to 24 h. A causal role in production of the erythema seems likely for these substances although other mediators are almost certainly involved.

Levels of prostaglandins and arachidonic acid in UV-B irradiated human skin before and after topical application of benzyl-2,5-diacetoxybenzoate, a salicylic acid derivative

Benzyl-2,5-diacetoxybenzoate (BDAB) was tested for anti-inflammatory activity on experimentally inflamed skin. Human abdominal skin was irradiated with three minimal erythema doses of UV-B (290-320nm) radiation to give a maximum erythema at 24 hours with an associated rise in PGE2 and PGF2 alpha levels measured by gas chromatography-mass spectrometry. Topical application of a 1% w/w preparation of BDAB neither decreased the evoked erythema nor diminished the rise in PGE2 and PGF2 alpha concentrations. BDAB, applied topically, was judged to be ineffectual as an anti-inflammatory agent in UV-B erythema.

Increased levels of 6-oxo-PGF1 alpha in human skin following ultraviolet B irradiation

1 Clinically normal human abdominal skin in 11 subjects, was irradiated with three times the minimal-erythema dose of ultraviolet B (u.v. B) irradiation. 2 Erythema was assessed visually, and exudate was recovered by a suction bulla technique from normal skin, and from skin at 6, 24 and 48 h after irradiation. 3 Erythema was moderate at 6 h, but increased to a maximum at 24 h, which was maintained at 48 h. 4 6-oxo-PGF1 alpha was markedly raised at 6 h, moderately raised at 24 h, but had returned to control levels at 48 h, when the erythema was still maximal. 5 Prostaglandin I2, the precursor of 6-oxo-PGF1 alpha and 6-oxo-PGF1 alpha may, therefore, play a part in the early inflammatory process after u.v. B irradiation, but is unlikely to be responsible for the erythema still present at 48 h.

Dissociation of histamine release and clinical improvement following treatment of acquired cold urticaria by prednisone

1 Corticosteroids are known to suppress evoked histamine release from human skin in vitro. Therefore the effect of prednisone, on cold evoked histamine release and clinical response was studied in six patients with acquired cold urticaria. 2 Following cold challenge all six patients developed an immediate urticarial response of the forearm and elevation of histamine levels, measured by superfusion cascade bioassay of the venous blood draining the forearm. 3 After treatment with prednisone, in an oral dose of 20-25 mg for 1 to 5 days, a suppression of evoked histamine release occurred in all but one patient. However, there was no corresponding decrease of erythema or oedema, though pruritus was improved in most patients. 4 The lack of clinical improvement in erythema and oedema, despite reduction in histamine levels, suggests that histamine may not be the principal mediator of the vascular response to cold challenge in acquired cold urticaria.

Aquagenic urticaria: evidence of cholinergic and histaminergic basis

Two patients with urticaria evoked at the site of contact of skin with water have been studied. Protection of the skin from contact with water by prior application of petrolatum ointment prevented wealing, but removal of the stratum corneum enhanced wealing. Organic solvents did not themselves evoke wealing, but they enhanced the reaction to subsequent challenge by water. That the release of acetylcholine is an essential step in the pharmacogenesis of wealing in aquagenic urticaria is indicated by the suppressive effect of locally-applied scopolamine on water-evoked wealing. Aquagenic urticaria is also associated with elevated blood histamine levels and degranulation of mast cells in the water-challenged skin. The relationship of acetylcholine and histamine to each other and to contact of water with the skin remains uncertain.

Aquagenic pruritus

Three patients were studied in whom brief contact of the skin with water at any temperature evoked intense itching without visible changes in the skin. The patients were otherwise apparently healthy, and this chronic and disabling disorder tended to attract a "psychogenic" label. Pharmacological studies showed that the condition was associated with local release of acetyl choline in the skin, mast-cell degranulation, and raised blood histamine concentrations. It responded well to antihistamines in two of the three patients. Aquagenic pruritus is probably common, but it is generally unrecognised and may be misdiagnosed. Antihistamines may induce a good therapeutic response.

Nevus oligemicus. A variant of nevus anemicus

A man had a long history of a persistent, fixed area of livid erythema on the trunk. The distribution of hair, sweat, and sensation were normal as were the histologic findings in the affected skin. The involved area had a decreased total skin blood flow and a lower surface temperature compared with surrounding uninvolved skin, but showed normal responses to vasoconstrictor and vasodilator stimuli. Incomplete sympathetic blockade partially abolished the erythema. We suggest that the appearance of the nevus is caused by increased vasoconstrictor tone in the thermoregulatory vessels of the involved skin, leading to relative stasis in the superficial "nutritional" vasculature. This would seem to be a new example of a "pharmacological nevus" showing similarities to and differences from nevus anemicus.

The anti-inflammatory and pharmacological effects of topically applied flurbiprofen on human skin 24 hours after ultraviolet B irradiation

Human abdominal skin was irradiated, with three minimal erythema doses of ultraviolet B (290-320 nm) radiation, producing maximal erythema at 24h, with an associated rise in PGE2 and PGF2 alpha, measured by gas chromatograph-mass spectrometry. Topical applications of 5% flurbiprofen, a prostaglandin synthetase inhibiting drug applied immediately after irradiation, partially suppressed the u.v.B. evoked erythema at 24h but totally prevented elevation of PGE2 and PGF2 alpha, without any associated significant rise in arachidonic acid. These findings support the view that erythema due to u.v.B. is only partly mediated by products of cyclo-oxygenase pathway, and should prompt a search for other mediators, including non-prostaglandin metabolites of arachidonic acid.

Time course changes in levels of arachidonic acid and prostaglandins D2, E2, F2 alpha in human skin following ultraviolet B irradiation

1 Clinically normal human abdominal skin was irradiated with three minimal-erythema doses of ultraviolet B irradiation, (u.v.B). 2 Erythema was assessed visually, and exudate recovered by a suction bulla technique from normal skin, and at 10 min, 2, 6, 18, 24 and 48 h after irradiation. 3 Erythema was barely visible at 2 h, but increased to maximum at 24 h, which was maintained at 48 h. 4 Increased arachidonic acid and prostaglandin E2, F2 alpha and D2 concentrations in the exudate, measured by gas chromatography-mass spectrometry, accompanied the developing erythema, with the maximal rise of arachidonic acid, prostaglandin E2 and D2 occurring at the height of the erythema at 24 h. 5 At 48 h, still at the height of the erythemal response, arachidonic acid and PGE2 levels had returned to near normal. 6 Concentrations of arachidonic acid and of its products from the cyclo-oxygenase pathway, parallel the development of i.u.B. erythema in the first 24 h.

The effects of indomethacin on arachidonic acid and prostaglandins e2 and f2alpha levels in human skin 24 h after u.v.B and u.v.C irradiation

1 Clinically normal human abdominal skin was irradiated with either three times its minimal erythema dose (MED) of ultraviolet B (u.v.B) or six MEDs of ultraviolet C (u.v.C) radiation. In both instances erythema was maximal at 24 h. 2 Exudate was recovered by a suction bulla technique from normal and irradiated skin at 24 h after irradiation. 3 Arachidonic acid, prostaglandins E2 and FSalpha, as measured by GC--MS, were significantly elevated at 24 h. Radioimmunoassay also showed increased PGF2alpha-like concentrations. 4 Oral indomethacin only partially reduced the erythema resulting from both types of radiation but totally suppressed the elevation of PGE 2 and F2alpha concentrations. 5 Topical indomethacin also suppressed u.v.B-induced increases in prostaglandins E2 and F2alpha. Unexpectedly, the vehicle alone produced a similar suppressive effect on prostaglandins although erythema appeared unaltered. 6 Most of the arachidonic acid metabolized by indomethacin-sensitive pathways is not converted to prostaglandins E2 and F2alpha in human skin.

Increased prostaglandins E2 and F2alpha in human skin at 6 and 24 h after ultraviolet B irradiation (290- 320 nm)

1 Abdominal skin of 25 human subjects was irradiated with three times its minimal erythema dose of ultraviolet (u.v.) B radiation. Erythema appeared after 2 h, was of moderate degree at 6 h, and maximal at 24 and 48 h.

2 Exudate was recovered by a suction bulla technique from the subject's normal and erythematous skin either at 6, 24 or 48 h after irradiation.

3 Superfusion cascade bioassay of exudate showed increased prostaglandin (PG)-like activity, measured in PGE₂ equivalents, at 6 and 24 h after irradiation. The maximum rise was at 24 h, coinciding with the peak of the erythema. However, prostaglandin concentrations were not significantly above that of controls at 48 h when the erythema was still maximal.

4 Radioimmunoassay for PGF_2α yielded values in close agreement with the bioassay results.

5 Gel partition chromatography, after conversion of extracted residues from the exudate to ¹⁴C methyl esters, showed increased incorporation of radioactivity at 6 h, maximal at 24 h. At 48 h there was no significant difference from control levels. The major increased activity, maximal at 24 h, co-chromatographed with arachidonic acid and PGE₂ and PGF_2α. The materials provisionally identified as the latter three compounds also co-chromatographed with their corresponding methyl esters on t.l.c., although the arachidonic acid-like material contained at least two peaks. No evidence was obtained for the 1 or 3 series of PGs. On g.l.c. the material obtained from the PGF_2α zone co-chromatographed with authentic PGF_2α as the methyl ester trimethylsilyl ether. The PGE₂ zone converted to methyl ester n-butyloxime trimethylsilyl ether also co-chromatographed with authentic PGE₂, but with some distinct shouldering.

6 The evidence presented provides support for the presence of increased amounts of arachidonic acid, PGE₂ and PGF_2α-like compounds during the first 24 h of u.v.B erythema, with concordance of the erythema and prostaglandin levels. At 48 h this relationship could not be demonstrated.

Inflammation in human skin induced by ultraviolet irradiation

Pharmacologically active mediators of inflammation were obtained from suction bullae raised on normal and ultraviolet B (290-320 nm) inflamed human abdominal skin. The exudates obtained from the bullae were examined by superfusion cascade bioassay, by radioimmunoassay for PGF2alpha and by column, thin-layer and gas-liquid chromatography. Ultraviolet B (u.v.-B) irradiation of human skin produced an erythema which appeared after 2 hr, increased in severity up to 24 hr and persisted for more than 48 hr. Bioassayable and radioimmunoassayable prostaglandin activity was elevated at 6 hr, was maximal at 24 hr and had returned to normal 48 hr. Topical application of indomethacin suppressed both the erythema and the increased concentration of PGF2alpha as measured by radioimmunoassay. Chromatographic studies confirmed increased prostaglandin activity at 6 and 24 hr and in addition demonstrated an increase in arachidonic acid-like activity. The results suggest that prostaglandins may play an important role between 6 and 24 hr of u.v.-B-induced erythema. Whether the reduction of erythema by indomethacin can be partially or wholly attributable to inhibition of prostaglandin biosynthesis is uncertain.

Prostaglandin activity in sustained inflammation of human skin before and after aspirin

1. Pharmacologically active mediators of inflammation were obtained from suction bullae raised on normal and inflamed human abdominal skin. These contained a clear inflammatory exudate, which was analysed for known mediators of inflammation.

2. The exudates were examined for smooth muscle-contracting activity by a superfusion cascade bioassay, for prostaglandin F2α by radioimmunoassay and by Lipidex 5000 gel-partition chromatography for other prostaglandins and related compounds.

3. Tetrahydrofurfuryl nicotinate (Trafuril) was applied topically before and after systemic administration of aspirin. Trafuril alone caused a sustained inflammatory response within minutes of application, which was reduced by prior administration of aspirin (a known prostaglandin synthetase inhibitor).

4. Exudate from inflamed skin showed increased prostaglandin activity compared with exudate from contralateral non-inflamed skin. However, aspirin prevented this increase in prostaglandin activity. Analysis by thin-layer and gas—liquid chromatography further suggested that Trafuril-induced inflammation was mediated by certain prostaglandins and related compounds.

5. No evidence was obtained to suggest any change in histamine or bradykinin after Trafuril. We suggest that the response caused by Trafuril is mediated by increased synthesis of prostaglandins. Aspirin, by blocking prostaglandin synthesis, prevents or reduces the erythema.

Induced tolerance in cold urticaria caused by cold-evoked histamine release

The interrelations between cold sensitivity and release of histamine and other mediators in five patients with cold urticaria undergoing cold tolerance treatment were studied. Tolerance to cold was produced in all patients by repeated cold exposure. In four patients tolerance was maintained by once daily exposures. In the fifth patient 4-hourly exposures were necessary. Cold sensitivity was associated with histamine release in venous blood draining urticated skin. No prostaglandin activity was detected, and low concentrations of kinin activity were found in blood draining the normal and exposed skin of healthy subjects as well as in patients with cold urticaria. After induction of tolerance, no histamine release occurred on challenge by cold. Relapse of sensitivity was associated with reappearance of histamine release on challenge. The conclusion that tolerance is due to depletion of histamine stores in skin after repeated cold exposure was supported by diminished wealing in response to injection of a histamine liberator (compound 48/80) in cold-tolerant skin.