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 neurotra nsmitters, substance P (SP). This study was designed to determine whet her the decreased reactivity was due to decreased responsiveness to an other neurotransmitter, neurokinin A (NKA), decreased lung SP content, decreased affinity or number of NK1 receptors, and/or decreased numbe r of C-fibers. Duncan Hartley guinea pips were exposed to filtered air (FA) or to SS for 6 h/day, 5 days/week for 5 weeks starting at;week o f age. SS exposure did not change, (1) airway reactivity to NKA inject ed into the pulmonary artery of their isolated perfused lungs (rt = 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 nerv e profiles of the terminal bronchioles or small airways (ri = 6 each g roup). 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.