Tracheal smooth muscle responses to substance P and neurokinin A in the piglet.
The tachykinins substance P (SP) and neurokinin A (NKA) have been shown to induce airway smooth muscle contraction in mature animals, and the enzyme neutral endopeptidase (NEP) modulates this effect. We evaluated maturation of SP- and NKA-induced tracheal smooth muscle contraction and modulation of their effects by NEP in anesthetized, paralyzed, and artificially ventilated piglets less than 4 days, 2-3 wk, and 10 wk of age. Tracheal smooth muscle tension was measured in vivo from an open tracheal segment by use of a force transducer. Intravenous SP caused a dose-dependent increase in tracheal tension in all three age groups; however, the response in less than 4-day-old piglets was significantly weaker than in 2- to 3- and 10-wk-old piglets. NKA caused a dose-dependent increase in tracheal tension only in 2- to 3- and 10-wk-old piglets. The response of tracheal tension to NKA was weaker than the response to SP in all age groups. Atropine (2 mg/kg) significantly diminished the responses of tracheal tension to SP and NKA, indicating a cholinergic contribution to these responses at all ages. Intravenous thiorphan, a known NEP inhibitor, potentiated the effects of SP only in 2- to 3- and 10-wk-old piglets and did not affect the response of tracheal tension to NKA at any age. Biochemical analyses demonstrated a significant increase in tracheal NEP activity in comparably aged piglets over the first 10 wk of life.(ABSTRACT TRUNCATED AT 250 WORDS)
Haxhiu-Poskurica
B
B
Department of Pediatrics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
Haxhiu
M A
MA
Kumar
G K
GK
Miller
M J
MJ
Martin
R J
RJ
D000818:Animals; D000831:Animals, Newborn; D001794:Blood Pressure / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D024510:Muscle Development; D009130:Muscle, Smooth / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D015260:Neprilysin / Q000378:metabolism; D015288:Neurokinin A / Q000494:pharmacology*; D013373:Substance P / Q000494:pharmacology*; D013552:Swine; D014132:Trachea / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology
D013373:Substance P; D015288:Neurokinin A; D015260:Neprilysin