Cholestyramine in uraemic pruritus.

In a patient with longstanding severe uraemic pruritus who was undergoing chronic haemodialysis cholestyramine caused the pruritus to disappear completely within a few days. A four-week randomised controlled double-blind study was therefore performed in 10 other patients with uraemic pruritus who were on chronic haemodialysis. The pruritus improved considerably in four of the five treated patients, whereas only one of those treated with placebo experienced relief. The patient who had no relief while on cholestyramine showed a considerable improvement when the dose subsequently doubled. One of the five patients receiving cholestyramine experienced mild and easily reversible constipation, and another suffered nausea. Neither of these complications prevented the patients from continuing treatment. Cholestyramine seems to be useful in treating uraemic pruritus, although it is not known how it acts.     

Radioimmunologic tests in children with pruritus and with a combination of pruritus and allergic respiratory disease

Radioimmunological tests were carried out in 180 children with pruritus and 167 children with pruritus and allergic respiratory diseases. Difference between these groups was statistically insignificant in case of food allergy. Results of RAST were more often positive in case of respiratory allergy in the patients with pruritus and coexisting allergic respiratory diseases than in patients with skin involvement only. Reaction was more intense and allergy polyvalence measured with RAST was higher. All differences were statistically significant (p less than 0.001 or 0.01). Mean IgE levels was higher in children of all age groups in case of pruritus coexisting with allergic respiratory diseases.     

Effect of aspirin on pruritus.

The effect of 900 mg aspirin on persistent itch from chronic dermatoses other than urticaria (eight patients) and other causes (five patients) was measured subjectively using a 10 cm line and objectively as nocturnal scratch using limb meters. There was no change in itch or scratch and it is concluded that aspirin neither affects itch centrally by a pain related mechanism nor affects itch physiologically by cyclo-oxygenase inhibition in the skin.     

Endothelin-1 causes pruritus in mice

Endothelin (ET)-1 evokes a burning pruritus sensation when injected intradermally in humans and nocifensive behavior when injected into the hind paw of rodents. Because pain and pruritus are clearly distinct nociceptive sensory modalities in humans, the current study evaluates the potential of ET-1 to elicit scratching behavior in mice. Mice received an intradermal injection of 1-30 pmol ET-1; 10 microg of the mast cell degranulator compound, 48/80; 100 nmol histamine; or vehicle into the scruff, and the number of scratching bouts displayed during the first 40 mins was recorded. ET-1 caused dose-dependent scratching bouts, which, like the responses to histamine and compound 48/80, occurred mainly during the first 5 to 10 mins of injection, but fewer episodes were also seen up to 35 mins. The effect of ET-1 was maximal at 10 pmol (total 40 +/- 7 bouts), a value similar to that caused by histamine (52 +/- 5 bouts) and compound 48/80 (53 +/- 6 bouts). The selective ET(B) receptor agonist, IRL-1620 (10 pmol), was not pruritic per se, and actually inhibited responses to histamine and ET-1. Pruritus induced by ET-1 was inhibited by the ET(A) receptor antagonists, 10 nmol BQ-123 (co-injected; net inhibition, 87%) and 10 mg/kg atrasentan (intraperitoneal administration; net inhibition, 83%), or the ET(B) receptor antagonist, 20 mg/kg A-192621 (intraperitoneal administration; net inhibition, 64%), but the response was augmented by co-injection of the ET(B) receptor antagonist, 3 nmol BQ-788 (net potentiation, 234%). Responses to compound 48/80 or responsiveness of vehicle-treated mice were unaffected by these antagonists. Thus, ET-1 displays potent pruritic actions in the mouse mediated to a substantial extent via local ET(A) receptors. The findings with IRL-1620 and BQ-788 suggest that local ET(B) receptors exert an antipruritic role, but, for reasons still unknown, the results obtained using systemic A-192621 injection are at variance with this view.     

Enhancement of experimental pruritus and mechanically evoked dysesthesiae with local anesthesia

Pain reduces itch-a commonly known effect of scratching the skin. Experimentally produced itch from histamine is sometimes accompanied by secondary sensations of pain. The present study investigated the effects of eliminating this pain, by means of a local anesthetic, on the itch and the enhanced mechanically evoked itch and pain that occur after an intradermal injection of histamine. In ten human subjects, the volar forearm was injected with either 20 microl of 2% chloroprocaine (experimental arm), or 20 microl of saline (control arm). Histamine 10 microl was injected into each bleb, and the resulting magnitude of itch estimated. The borders of three cutaneous areas were mapped within which mechanical stimulation of the skin surrounding the bleb elicited abnormal sensations (dysesthesiae): alloknesis, defined as itch evoked by innocuous stroking, and hyperalgesia and hyperknesis, characterized, respectively, by enhanced pain and enhanced itch evoked by pricking the skin with a fine tipped filament. The magnitude and duration of itch were significantly greater and the areas of dysesthesia significantly larger for the experimental than for the control arm. It is hypothesized that there exist two classes of histamine-sensitive primary afferent neurons. One class is "pruritic", and mediates itch whereas the other is "antipruritic", and evokes a centrally mediated reduction in histamine-evoked itch and dysesthesiae. It is further suggested that the anesthetic blocked the discharges of the antipruritic afferents, preventing the central inhibition from occurring and thereby unmasking the effects of the pruritic afferents.