Effects of extended sidestream smoke exposure on components of the C-fiber axon reflex

We have previously shown that young guinea pigs repeatedly exposed to sidestream cigarette smoke (SS) develop decreased airway reactivity of the C-fiber system without changing reactivity to one of its neurotransmitters, substance P (SP). This study was designed to determine whether the decreased reactivity was due to decreased responsiveness to another neurotransmitter, neurokinin A (NKA), decreased lung SP content, decreased affinity or number of NK₁ receptors, and/or decreased number of C-fibers. Duncan Hartley guinea pigs were exposed to filtered air (FA) or to SS for 6 h/day, 5 days/week for 5 weeks starting at 1 week of age. SS exposure did not change, (1) airway reactivity to NKA injected into the pulmonary artery of their isolated perfused lungs (n = 6-7 each group), (2) lung SP content as measured by enzyme immunoassay (n = 12 each group), (3) NK₁ receptor number or affinity as measured by radioligand binding (n = 7 each group), or (4) SP-immunoreactive nerve profiles of the terminal bronchioles or small airways (n = 6 each group). Thus, SS exposure does not decrease C-fiber system by reducing NKA responsiveness, decreasing SP content, changing NK₁ receptors, or decreasing the number of C-fibers.