A sensitive and specific double-antibody enzyme-linked immunoassay (EIA) for detecting a motilin-like immunoreactive substance (M-IS) in human plasma has been developed. In competitive reactions, the motilin antibody was incubated with a plasma sample (or motilin standard) and beta-D-galactosidase-linked synthetic motilin. Free and antibody-bound enzymes were separated using an anti-rabbit IgG-coated immunoplate. Enzyme activity on the plate was determined by fluorophotometric analysis. This immunoassay allows the detection of 20 to 200 fmol/ml (54 to 540 pg/ml) of motilin. The mean level of M-IS detected in human plasma was 53.9 +/- 25.6 pg/ml.

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The effect of terfenadine on the plasma concentrations of substance P and vasoactive intestinal polypeptide (VIP) was studied in 7 healthy subjects and 8 subjects with the common cold. Before terfenadine administration, the mean plasma substance P concentration of the subjects with the common cold was significantly higher than that of the healthy subjects. The increased mean plasma substance P concentration of the subjects with the common cold was decreased after terfenadine administration. In the healthy subjects, the mean plasma substance P concentration was unchanged by terfenadine administration. The mean plasma VIP concentration of the subjects with common cold was slightly higher than that of the healthy subjects before and after terfenadine administration, with no significant difference.

Before terfenadine treatment, the mean substance P and vasoactive intestinal polypeptide (VIP) concentrations in nasal secretions from nasal allergy patients tended to be higher than the values of healthy subjects. During terfenadine treatment, the mean substance P concentrations in nasal secretions from patients allergic to house dust or pollen were significantly decreased to 62 and 39% of the initial values, respectively. The mean VIP concentrations in nasal secretions from the house dust allergy patients and the pollen allergy patients were significantly decreased to 52 and 18% of the initial values, respectively. Plasma substance P and VIP concentrations were not affected by nasal allergic symptom and terfenadine treatment.

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