Pharmacological nature of nicotine-induced contraction in the rat basilar artery: involvement of arachidonic acid metabolites.

The pharmacological nature of nicotine-induced contraction in the rat basilar artery is poorly understood. The purpose of this study was to investigate the endothelium dependency and involvement of arachidonic acid metabolites in nicotine-induced contraction in the rat basilar artery. The rat basilar artery was removed from the brain and cut into a spiral preparation. Nicotine (3x10(-5) to 10(-2) M) induced the concentration-dependent contraction in the rat basilar artery, and the maximal contraction was obtained at 3x10(-3) M. The contraction induced by nicotine (3x10(-3) M) was significantly attenuated by the presence of saponin (0.05 mg/ml, 15 min). Phospholipase C (PLC) inhibitors (NCDC and U-73122), calcium-independent phospholipase A(2) (iPLA(2)) inhibitor (BEL), cyclooxygenase-2 (COX-2) inhibitors (nimesulide, L-745,337 and celecoxib), and a 5-lipoxygenase (5-LOX) inhibitor (ZM-230487) concentration-dependently attenuated the nicotine-induced contraction. A cytosolic phospholipase A(2) (cPLA(2)) inhibitor (AACOCF3), secretory phospholipase A(2) (sPLA(2)) inhibitor (indoxam), and cyclooxygenase-1 (COX-1) inhibitors (flurbiprofen and ketoprofen) did not affect the nicotine-induced contraction. From these results, it was suggested that nicotine-induced contraction in the rat basilar artery is endothelium-dependent and is due to arachidonic acid metabolites.

Hypersensitivity to hydroxyl radicals in rat basilar artery after subarachnoid hemorrhage.

Vasospasm after subarachnoid hemorrhage (SAH) is a serious complication and we have been investigating the relationship between vasoconstrictors and vasospasm after SAH. The present study was designed to investigate the vasocontractile responses to reactive oxygen species in isolated rat basilar arteries from the control and experimental SAH rats. Contractile responses to hydroxyl radicals in basilar arteries from SAH rats were 3-6-fold higher than those in control rats. The present results clearly indicate that hypersensitivity to hydroxyl radicals may contribute to the vasospasm after SAH.

Involvement of endothelial cyclo-oxygenase metabolites in noradrenaline-induced contraction of rat coronary artery.

1. Noradrenaline (NA; 0.3 micromol/L) caused a contraction of the rat coronary artery that markedly increased in the presence of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME; 100 micromol/L) and arachidonic acid (1 micromol/L; P < 0.05). 2. The present experiments attempted to elucidate the endothelium dependency of the contraction and to pharmacologically characterize the factors involved in the contraction induced by NA (0.3 micromol/L) in the presence of L-NAME and arachidonic acid in ring preparations of the rat coronary artery. 3. The NA (0.3 micromol/L)-induced contraction was attenuated by a chemical remover of the endothelium (saponin at concentrations of 0.1 and 0.4 mg/mL) in a concentration-dependent manner (P < 0.05). 4. The cyclo-oxygenase (COX)-1 inhibitor flurbiprofen (0.01-1 micromol/L) and the COX-2 inhibitor nimesulide (0.01-1 micromol/L) attenuated the NA-induced contraction in a concentration-dependent manner and the inhibitory effect of flurbiprofen was significantly more potent than that of nimesulide (P < 0.05). The 5-lipoxigenase inhibitor ZM-230487 (1 micromol/L) did not affect the NA-induced contraction. 5. The thromboxane A2 (TXA2) synthetase inhibitor OKY-046 (30 micromol/L) and the TXA2 antagonist S-1452 (0.1-10 micromol/L) did not attenuate the NA-induced contraction. 6. These results indicate that the contraction induced by NA in the rat coronary artery in the presence of L-NAME and arachidonic acid is endothelium dependent and is due to endothelial COX metabolites of arachidonic acid.

Enhanced reactivity to vasopressin in rat basilar arteries during vasospasm after subarachnoid hemorrhage.

Subarachnoid hemorrhage increases the plasma level of vasopressin, a well-known vasoconstrictor. We examined the sensitivity to vasopressin in rat basilar artery after subarachnoid hemorrhage using a rat subarachnoid hemorrhage model. Vasospasm was observed 1-2 days after subarachnoid hemorrhage induction, and the contractile response to vasopressin in rat basilar arteries was assessed. The concentration-response curve for vasopressin in subarachnoid hemorrhage (1 day) rats shifted leftward compared with that of control rats. The concentration-response curve for vasopressin V(1) receptor agonist also shifted leftward and upward compared with that of control rats. The concentration-response curve for vasopressin was inhibited not by vasopressin V(2) receptor antagonist but by vasopressin V(1) receptor antagonist. Thus, it was demonstrated that the vasoconstricting effect of vasopressin was significantly enhanced in the vasospasm phase after subarachnoid hemorrhage.

Cysteinyl leukotrienes and leukotriene B mediate vasoconstriction to arginine vasopressin in rat basilar artery.

Arginine vasopressin (AVP) has been reported to be involved in the development of cerebral vasospasm after haemorrhage and cerebral oedema following ischaemia. Endogenously produced 5-lipoxygenase metabolites are able to contract isolated endothelium-preserved arterial strips and modulate vascular permeability. The present study addresses the role of 5-lipoxygenase and its products, namely cysteinyl leukotrienes (CysLTs) and leukotriene (LT) B4, in the contraction induced by AVP in rat basilar artery. Contractile responses to LTD4, LTC4, LTB4 or AVP were assessed in spiral preparations of rat endothelium-intact basilar artery. Contractions to AVP were determined in the absence or presence of 5-lipoxygenase inhibitors or CysLT1 or BLT receptor antagonists. Contractile responses to leukotrienes and AVP are expressed as a percentage of the contraction induced by 80 mmol/L KCl. Leukotriene D4, LTC4 and LTB4 acted as vasoconstrictor agents in rat basilar artery, causing contractions (all at concentrations of 1 micromol/L) of 42 +/- 13, 54 +/- 15 and 25 +/- 6% of the response to 80 mmol/L KCl, respectively. A concentration-response curve was constructed for AVP over the range 1 pmol/L to 10 nmol/L and an EC50 value of 0.19 +/- 0.02 nmol/L (n = 30) was determined. The presence of the 5-lipoxygenase inhibitors ZM 230487 (10 nmol/L and 0.1 and 1 micromol/L) and AA 861 (1, 3, 10, and 30 micromol/L), the CysLT1 receptor antagonist MK 571 (3, 10 and 30 micromol/L) or the BLT receptor antagonists CP 105696 and LY 255283 (3, 10 and 30 micromol/L for both) in the organ bath significantly attenuated the contractions induced by AVP in rat basilar artery (P < 0.05). The experimental results of the present study provide the first evidence for the involvement of CysLTs and LTB4 in the in vitro constriction induced by AVP in rat basilar artery. In the context of previously reported involvement of AVP in the development of cerebral vasospasm and oedema, the present study draws attention to the potential role played by the 5-lipoxygenase pathway in these pathological processes.

Participation of vasopressin in the development of cerebral vasospasm in a rat model of subarachnoid haemorrhage.

1. Previous studies have suggested the involvement of arginine vasopressin (AVP) and inflammation in the development of cerebral vasospasm after subarachnoid haemorrhage (SAH). The aim of the present study was to clarify the role of AVP in the arterial narrowing following cerebral haemorrhage by examining the effect of SR 49059 (a V(1) receptor antagonist) on the diameter of rat basilar artery exposed to SAH. The effect of the 5-lipoxygenase inhibitor ZM 230487 on AVP-induced contraction of rat basilar arteries was also investigated. 2. After 1 h and 2 days from SAH induction, brains were removed and pictures of the basilar arteries were taken. The external diameter of the basilar artery was measured in the presence and absence of SR 49059 (1 mg/kg, i.v.). For in vitro experiments, the basilar arteries isolated from control and SAH rats (at 1 h and at 2 days from SAH induction) were cut into spiral preparations and the AVP (0.3 nmol/L)-induced contraction in the presence of ZM 230487 was investigated. Each group analysed (i.e. control, SAH 1 h and SAH 2 days) consisted of eight rats. 3. The diameter of rat basilar arteries decreased by 43 and 25% at 1 h and 2 days from SAH induction, respectively, compared with control. The administration of SR 49059 significantly reduced cerebral vasospasm. After SAH induction, the diameter of the basilar artery in SR 49059-treated groups decreased by only 22% (at 1 h) and by 3% (at 2 days) compared with the control group (P < 0.01). In basilar arterial strips, ZM 230487 attenuated the vasopressin-induced contraction in both control and SAH groups. However, SAH groups showed a significant resistance of the AVP-induced contraction in the presence of ZM 230487 compared with control (P < 0.05). 4. The results suggest that the cerebral vasospasm in SAH rats is due, at least in part, to endogenous AVP and may involve an increase in the activity of 5-lipoxygenase. SR 49059 may represent a potential therapeutic strategy for the treatment of cerebral vasospasm.

Diversity of endothelium-derived vasocontracting factors--arachidonic acid metabolites.

Vascular endothelium releases vasocontracting and/or vasorelaxing substances. Here, we report the diversity of endothelium-derived vasocontracting factors (EDCFs), arachidonic acid metabolites, and discuss the pathophysiological significance. In the canine basilar artery and the rabbit intrapulmonary artery, acetylcholine-induced contractions (ACh-induced EDC) are due to endothelial thromboxane A2 (TXA2) (TXA2-type). The ACh-induced EDC in the rabbit coronary artery is due to endothelial leukotrienes (LTs) (LTs-type). In addition, in the rat coronary artery, nicotine and noradrenaline (NAd)-induced EDCs are due to endothelial COX-metabolites (COX metabolite-type). These arachidonic acid metabolites derived from endothelium (activation by vasoactive substances including ACh, NAd and nicotine) cause a contraction of vascular smooth muscle cells and may disturb the local circulation. These EDCFs (TXA2, LTs and COX-metabolites) may be involved in the pathophysiology of cardiovascular immuno-inflammatory diseases.

Noradrenaline-induced contraction mediated by endothelial COX-1 metabolites in the rat coronary artery.

Noradrenaline-induced contraction of the rat coronary arteries was significantly augmented by the presence of NG-nitro-L-arginine methyl ester (L-NAME) and arachidonic acid. The experiments in the study presented here were undertaken to characterize pharmacologically the augmented noradrenaline-induced contraction in ring preparations of rat coronary arteries. The contraction was stopped by a chemical remover of endothelium (saponin). Oxygen radical scavengers, superoxide dismutase and catalase, significantly attenuated the contraction. Cyclooxygenase-1 inhibitors (flurbiprofen, 10(-7) M) attenuated the noradrenaline-induced contraction and cyclooxygenase-2 (nimesulide, 10(-7) M) slightly attenuated the contraction. A thromboxane A2 (TXA2) synthetase inhibitor (OKY-046) and a TXA2 receptor antagonist (S-1452) did not affect the contraction. Based on these results, it was suggested that the contraction induced by noradrenaline in the rat coronary artery in the presence of L-NAME and arachidonic acid is endothelium-dependent, and that it involves reactive oxygen species and endothelial cyclooxygenase-1 metabolites of arachidonic acid.