EXPERIMENTAL HISTAMINE PRURITUS .2. NATURE - PHYSICAL AND ENVIRONMENTAL FACTORS INFLUENCING DEVELOPMENT AND SEVERITY

[摘要] Pertinent literature on the nature of itching is summarized. When the histamine wheal is increased greatly in size, either by the subcut. injn. of mecholyl or by superimposed injns. of histamine, the intensity of itching is diminished. When the wheal of an objective histamine reaction is inhibited by applying tourniquet with a pressure of 50 mm. Hg, the flare remains unchanged, and itching persists. The flare is apparently an integral part of itching as produced by histamine. The wave-like character of histamine itching can be inhibited by appln. of a blood pressure cuff and elevation of pressure to 50 mm. Hg. The wave-like character of itching may be due to forceful arterial pulsations, the amplitude of which is diminished by pressure. Burning is considered to be a severe form of itching When an initial intradermal injn. of histamine produces itching, 2 additional injns. at the same site commonly result in burning. When histamine is used, burning is considered as y, and itching as x, y = 3x. Refractoriness to histamine can be produced by successive injns. in a single site, and after it develops, may persist unchanged for as long as 4 hrs. and be present residually for 24 hrs. Itching can be produced by a burning stimulus in an area of subsiding anesthesia. Introduction of a sub-painful stimulus (histamine plus infrared light) in an area of subsiding anesthesia results in the development of a large area of surrounding itchy skin. When the skin temp. is raised to 41[degree]C, followed by 3 consecutive injns. of histamine in a concn. which had resulted previously in itching are injd. into a single site, mild pain may be produced. The reaction for this development is p = y1 + y2, where p equals pain, y1-is burning produced by repeated injns. of histamine, and y2 is burning produced by infra-red light. The degree of tissue injury is greater in the site of 4 consecutive injns. than at that of a single injn. In a large group of patients, the itch threshold varied between 1:1000 and 1:10,000,000 with a majority of patients falling in the 1:100,000 range. Consecutive daily and weekly testing in 12 control subjects showed frequent minor variations in the itch threshold, and indicates the necessity for control testing immediately prior to any given expt. Itch threshold was found to vary considerably in tests performed on the wrist, upper forearm and lower aspect of the arm. Itch thresholds were uniform on identical areas of opposite forearms, but intensity of pruritus varied in 12 of 16 patients. Itch thresholds in individuals patients varied considerably in forearm, upper back and legs; in general, they were lower on the leg, intermediate on the forearm, and somewhat higher on the back. Itch threshold in 20 patients tended to be lower at night than during the day. Skin temp. detd. on the forearm, upper back, and leg in 20 patients varied between extremes of 29.7[degree]C and 34.9[degree]C in these 3 areas. Avg. temp. in the same areas varied between 32.6[degree]C and 33.3[degree]C. The narrow range of temp. variation did not appreciably affect the subjective reaction to histamine. Electrical skin resistance varied greatly from patient of patient, and more moderately in individual subjects; the procedure was of no value as a control observation on the emotional state of the individual. Itch thresholds detd. prior to and during the menses, and in the inter-menstrual period showed no significant differences in 18 patients. Studies in 20 patients on histamine reactions after elevation of temp. of the skin to 39[degree]C demonstrated that heat tended to lower the itch threshold. When the skin temp. was lowered to 25[degree]C, the itch threshold frequently was raised.