Inhibitory effects of nordihydroguaiaretic acid on ET_A‐receptor‐mediated contractions to endothelin‐1 in rat trachea

Abstract

1 It has been shown previously that nordihydroguaiaretic acid (NDGA) inhibits endothelin-1 (ET-1)-induced contractions in rat isolated tracheal smooth muscle. To investigate the underlying mechanisms, this study examined the effects of NDGA on various aspects of the ETA and ETB receptor-effector systems which mediate ET-l-induced contractions in this preparation. 2 NDGA inhibited contractions induced by each of the isoforms of ET (ET-1, ET-2 and ET-3) but not those induced by the ETB receptor-selective agonist, sarafotoxin S6c, the cholinoceptor agonist, carbachol or the depolarizing spasmogen, KCl. T-type Ca2+-channels, Na+-channels or protein kinase C.8 In summary, NDGA selectively inhibited ET-1-induced contractions in rat tracheal smooth muscle via a lipoxygenase-independent mechanism involving inhibition of the ETA but not the ETB, receptoreffector system. NDGA did not appear to inhibit the initial events in the ETA signal transduction pathway, such as receptor binding and protein kinase C activation. However, NDGA inhibited the intracellular Ca2+-dependent component of ET-1-induced contraction, possibly by inhibiting mobilisation of intracellular Ca2+. As an apparent direct consequence of inhibiting the ETA receptor-effector system, NDGA markedly changed the time course of ET-1-induced contractions; from a slowly developing and sustained contraction into a transient contraction resembling that induced by sarafotoxin S6c.

Ca2+ signalling by endothelin receptors in rat and human cultured airway smooth muscle cells

“…Rat tracheal airway smooth muscle cells grown to con¯uence in serum-containing medium contained a clear predominance of ET B receptors, which is in marked contrast with previous ®ndings of approximately equal proportions of ET A and ET B receptors in intact rat tracheal smooth muscle (Henry, 1994). Nevertheless, the inclusion of a 2-day period of serum deprivation caused a reduction in the density of ET B receptors from over 20,000 sites cell 71 to around 5000 sites cell 71 , without any noticeable change in ET A receptor density which remained constant at approximately 5000 sites cell 71 .…”

“…Nevertheless, the inclusion of a 2-day period of serum deprivation caused a reduction in the density of ET B receptors from over 20,000 sites cell 71 to around 5000 sites cell 71 , without any noticeable change in ET A receptor density which remained constant at approximately 5000 sites cell 71 . Thus, maintenance of rat tracheal airway smooth muscle cells in a serum-free medium, which may well mimic the in vivo environment more closely than serum-containing medium, resulted in cultured cells which contained equal proportions of ET A and ET B receptors and which were similar to the proportions previously observed in intact rat tracheal smooth muscle (Henry, 1994). The selective alteration of ET B receptor numbers during cell culture in serum-containing medium is consistent with recent ®ndings in lamb airway smooth muscle cells (Maxwell et al, 1998) and with functional reports of enhanced ET B -mediated responses when subjected to short term cell culture conditions (Woodcock & Land, 1992;Adner et al, 1995).…”

“…The potency of endothelin-1 in increasing peak [Ca 2+ ] i in rat airway smooth muscle cells corresponded closely to the potency of endothelin-1 in contracting rat isolated tracheal segments (Henry, 1993(Henry, , 1994 ] i in only about 30% of cells. There appeared to be three distinct sub-populations of rat airway smooth muscle cells in this culture, de®ned as possessing either (a) ET A , (b) ET B or (c) both ET A and ET B receptors, based upon the ability of single cells to respond to ET A stimulation following prior exposure to the ET B agonist sarafotoxin S6c.…”

“…In both mouse and rat trachea, the airway smooth muscle band contained ET A and ET B receptors in approximately equal proportions (Henry, 1994;Carr et al, 1996) and each receptor subtype was linked to smooth muscle contraction. Consequently, endothelin-1-induced contractions were inhibited in the combined presence of the ET A receptor-selective antagonist, BQ-123 and the ET B receptor-selective antagonist BQ-788, but not by either antagonist alone.…”

Endothelins‐induce cyclicAMP formation in the guinea‐pig trachea through an ETA receptor‐ and cyclooxygenase‐dependent mechanism

“…These findings are substantiated by the reported ability of ET-1 to release prostaglandin E2 (PGE2) and prostaglandin D2 in guinea-pig trachea (Hay et al, 1993) and by the fact that lipoxygenase metabolites are more apt to constrict the airways rather than to induce cyclicAMP formation (Saotome et al, 1991;Dahl'en et al, 1993;Henry, 1994).…”