Pharmacological evidence for a novel cysteinyl-leukotriene receptor subtype in human pulmonary artery smooth muscle

Abstract

1. To characterize the cysteinyl-leukotriene receptors (CysLT receptors) in isolated human pulmonary arteries, ring preparations were contracted with leukotriene C(4) (LTC(4)) and leukotriene D(4) (LTD(4)) in either the absence or presence of the selective CysLT(1) receptor antagonists, ICI 198615, MK 571 or the dual CysLT(1)/CysLT(2) receptor antagonist, BAY u9773. 2. Since the contractions induced by the cysteinyl-leukotrienes (cysLTs) in intact preparations failed to attain a plateau response over the concentration range studied, the endothelium was removed and the tissue treated continuously with indomethacin (Rubbed+INDO). In these latter preparations, the pEC(50) for LTC(4) and LTD(4) were not significantly different (7.61+/-0.07, n=20 and 7.96+/-0.09, n=22, respectively). However, the LTC(4) and LTD(4) contractions were markedly potentiated when compared with data from intact tissues. 3. Leukotriene E(4) (LTE(4)) did not contract human isolated pulmonary arterial preparations. In addition, treatment of preparations with LTE(4) (1 microM; 30 min) did not modify either the LTC(4) or LTD(4) contractions. 4. Treatment of preparations with the S-conjugated glutathione (S-hexyl-GSH; 100 microM, 30 min), an inhibitor of the metabolism of LTC(4) to LTD(4), did not modify LTC(4) contractions. 5. The pEC(50) values for LTC(4) were significantly reduced by treatment of the preparations with either ICI 198615, MK 571 or BAY u9773 and the pK(B) values were: 7.20, 7.02 and 6.26, respectively. In contrast, these antagonists did not modify the LTD(4) pEC(50) values. 6. These findings suggest the presence of two CysLT receptors on human pulmonary arterial vascular smooth muscle. A CysLT(1) receptor with a low affinity for CysLT(1) antagonists and a novel CysLT receptor subtype, both responsible for vasoconstriction. Activation of this latter receptor by LTC(4) and LTD(4) induced a contractile response which was resistant to the selective CysLT(1) antagonists (ICI 198615 and MK 571) as well as the non-selective (CysLT(1)/CysLT(2)) antagonist, BAY u9773.

Figure 1

Cysteinyl-leukotriene concentration-effect curves produced in human isolated pulmonary arterial preparations. The results are derived from intact tissues (endothelium present, solid circle) and tissues devoid of an endothelium and treated with indomethacin (Rubbed+INDO, empty circle). Contractions were expressed as per cent of norepinephrine (10 μM) contraction and values aremeans±s.e.means (see Table 1 for the number of lung samples for LTC₄ and LTD₄). LTE₄ data were derived from four different lung samples. *Indicates values significantly different from results in intact preparations when analysed for each concentration (Student's t-test; P<0.05).

Figure 2

The effects of S hexyl glutathione (S-hexyl-GSH) on LTC₄ concentration effect curves in human isolated pulmonary vascular preparations devoid of an endothelium and treated with indomethacin (Rubbed+INDO). Control and results obtained in tissues treated with S-hexyl-GSH (100 μM, 30 min) are presented. Values are means±s.e. means in paired preparations from three different lung samples. Contractions were expressed as per cent of norepinephrine (10 μM) contraction.

Figure 3

The effects of BAY u9773 on basal tone in intact human isolated pulmonary vascular preparations. Results of a representative experiment are shown (n=3 lung samples).

Figure 4

LTC₄ concentration-effect curves produced in human isolated pulmonary arterial preparations devoid of an endothelium and treated with indomethacin (Rubbed+INDO). Control and results obtained in tissues treated with (a) ICI 198615 (1 μM, 30 min), panel (b) MK 571 (1 μM, 30 min), and panel (c) BAY u9773 (3 μM, 30 min). Values are means±s.e.means (see Table 2 for significance and number of preparations used). Contractions were expressed as per cent of norepinephrine (10 μM) contraction.

Figure 5

LTD₄ concentration-effect curves produced in human isolated pulmonary arterial preparations devoid of an endothelium and treated with indomethacin (Rubbed+INDO). Control and results obtained in tissues treated with (a) ICI 198615 (1 μM, 30 min), (b) MK 571 (1 μM, 30 min), and (c) BAY u9773 (3 μM, 30 min). Values are means±s.e.means (see Table 2 for significance and number of preparations used). Contractions were expressed as per cent of norepinephrine (10 μM) contraction.

Figure 6

LTC₄ and LTD₄ concentration-effect curves produced in human isolated pulmonary arterial preparations devoid of an endothelium and treated with indomethacin (Rubbed+INDO). Control and results obtained in tissues treated with LTE₄ (1 μM, 30 min). Values are means±s.e.means in paired preparation from four lung samples. Contractions were expressed as per cent of norepinephrine (10 μM) contraction.

Figure 7

A schematic presentation of the CysLT receptors present in human pulmonary arterial vascular smooth muscle. LTC₄ activates two receptors in arterial preparations. One receptor has a low affinity for the selective CysLT₁ antagonists (ICI 198615 and MK 571) and is antagonized by the dual antagonist (BAY u9773). Another ‘novel CysLT receptor subtype' is activated only by LTC₄ and LTD₄ and the contractions are not blocked by any of these antagonists.