Bronchospasm is a well recognized adverse reaction to radiographic
contrast media (RCM) and may occur more frequently in asthmatics and atopics. This study was designed to identify RCM which are most likely to cause
bronchospasm and to investigate underlying mechanisms mediating this response. Guinea pigs (mean
body weight 550 g, n = 46) were anaesthetized with
Hypnorm (5 ml kg-1) and Hypnovel (2 ml kg-1) and tracheal, jugular and pleural
cannulae introduced. Total airways resistance (Raw) was calculated from the slope of the pressure/flow relationship. The effects of RCM (
diatrizoate 370 mgI ml-1,
ioxaglate 320 mgI ml-1,
iotrolan 300 mgI ml-1 and
iopromide 300 mgI ml-1) at a dose of 4 ml kg-1
body weight or control solutions matched for volume, pH and osmolarity administered via the jugular vein on Raw were studied. The effects of pre-treatment (30 min before the administration of RCM) with
antihistamine (
Mepyramine (30 mg kg-1 i.p.)) or non-selective
endothelin receptor antagonist (SB209670 (1 mg kg-1 i.v.)) were investigated. The effectiveness of
corticosteroids prophylaxis (
prednisolone (20 mg kg-1 i.p.)) administered 18-24 h and 1 h pre-RCM was also assessed. Control animals received
normal saline pre-treatment before RCM administration. Lungs were taken for histological examination 30-40 min post-administration of RCM. Only
ioxaglate caused a significant (p < 0.05) increase in Raw (5.19 +/- 0.58 to 13.95 +/- 3.53 mmHg ml-1 min-1). Neither
mannitol nor saline control solutions had any effect on Raw. Pre-treatment with
Mepyramine, SB209670 or
prednisolone caused no significant change in the
ioxaglate induced increase in Raw. Histological examination of lung tissue from
ioxaglate treated animals showed no important abnormalities. In summary, only the ionic dimer
ioxaglate caused an increase in Raw. This effect was independent of osmolarity and could be the result of the chemical composition of the
contrast agent. It was not an inflammatory response and could not be prevented by prophylactic treatment with
antihistamine,
endothelin antagonist or
corticosteroids. The mechanisms responsible for the increase in Raw remain uncertain.