Modulation of adenosine-induced responses in the guinea-pig trachea during long-term caffeine treatment: possible role of epithelium.
The responses to adenosine were studied on isolated, methacholine-precontracted tracheal strips of guinea pigs in the course of long-term caffeine or solvent treatment. Guinea pigs were fed caffeine for 10 weeks (average serum caffeine concentration: 39.1 +/- 3.9 microM). In epithelium-intact tracheal preparations (EITPs), sensititization to adenosine-induced relaxation (AIR) developed. It attained a maximum in week 1 of caffeine treatment, and then its level diminished and disappeared completely by weeks 4 - 6. In epithelium-denuded tracheal preparations (EDTPs), an increase in the sensitivity to adenosine was observed from week 1 to week 10 (a 4 - 6-fold reduction in EC50). Use of a coaxial bioassay system confirmed the role of epithelium in this process. The enhancement of the AIR of the EITPs was not modified by inhibitors of cyclooxygenase and lipoxygenase. Following depletion of the neuropeptides by acute capsaicin pretreatment, the AIR of the EITPs was strongly enhanced after caffeine treatment for 6 weeks. In chronically caffeine-treated EITPs, the inhibition of neutral endopeptidase led to dramatic reduction of the AIR. On the basis of the results by inhibiting nitric oxide synthase, it can be supposed that nitric oxide released from EITPs of long-lasting caffeine-treated animals operated as a constrictor agent. Our results show that chronic caffeine treatment gives rise to an initial sensitization to adenosine of the EITPs, this being followed by the development of a specific adaptive process in the epithelial cells, which counterbalances the increased tracheal sensitivity to adenosine.
Brugós
László
L
Department of Pulmonology, University of Debrecen, Medical and Health Science Center, PO Box 12, Debrecen H-4012, Hungary.
Gesztelyi
Rudolf
R
Zsuga
Judit
J
Cseppento
Agnes
A
Benko
Ilona
I
Galajda
Zoltán
Z
Deák
György
G
Sipka
Sándor
S
Roszer
Tamás
T
Kovács
Péter
P
Szilasi
Mária
M
Edes
István
I
Szentmiklósi
András József
AJ
D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002110:Caffeine / Q000097:blood / Q000494:pharmacology*; D002211:Capsaicin / Q000494:pharmacology; D004205:Cromolyn Sodium / Q000494:pharmacology; D004848:Epithelium / Q000502:physiology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009569:Nitric Oxide / Q000502:physiology; D019335:Nitroarginine / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects* / Q000502:physiology
D019335:Nitroarginine; D009569:Nitric Oxide; D002110:Caffeine; D000241:Adenosine; D004205:Cromolyn Sodium; D002211:Capsaicin