Platelet-derived growth factor does not constrict rat intracerebral arterioles in vitro

Platelet-derived growth factor-induced severe and chronic vasoconstriction of cerebral arteries: proposed growth factor explanation of cerebral vasospasm

OBJECTIVE

After subarachnoid hemorrhage (SAH), platelet-derived growth factor-BB (PDGF-BB) is secreted in and around the cerebral arteries. To clarify the role of PDGF-BB in the development of vasospasm after SAH, we determined whether PDGF-BB alone can cause long-lasting vasoconstriction of a severity similar to that of vasospasm. In addition, the anti-vasospastic effect of trapidil, an antagonist of PDGF-BB function, was investigated.

METHODS

We infused recombinant PDGF-BB (10 microg/mL saline as the vehicle) (n = 14) into the subarachnoid space of rabbits and analyzed alterations in the caliber of the basilar artery using repeated angiography. To study the role of PDGF-BB on the development of vasospasm, trapidil was administered continuously starting 1 hour after SAH, on day 0 (0.63-1.25 mg/kg /h or vehicle) for 47 hours (n = 24), or after the full development of cerebral vasospasm on day 2 (3.0 mg/kg/h or vehicle) for 0.5 hours (n = 17), and alterations in the caliber of the basilar artery were monitored.

RESULTS

PDGF-BB caused long-lasting vasoconstriction, with maximum constriction of 56% (P < .001) of the control value (= 100%) on day 2, resembling vasospasm seen after SAH. Prolonged administration of intravenous trapidil, starting soon after SAH, prevented the development of vasospasm in a dose-dependent manner (P < .05, .01, or .001). Intravenous or intra-arterial administration of trapidil significantly dilated vasospasm (P < .01) on day 2, at least transiently.

CONCLUSION

PDGF-BB, a growth factor synthesized in the subarachnoid space after SAH, can cause severe and long-lasting vasoconstriction. Significant prevention and resolution of vasospasm can be achieved by the PDGF-BB antagonist trapidil. We propose that excessive production of PDGF-BB, essentially aiming to repair injured arteries, causes cerebral vasospasm. Although the half-life of trapidil in serum may be shorter than that of PDGFG-BB-derived spasmogenic signaling, trapidil is a candidate drug for constructing a new therapeutic modality for preventing and resolving vasospasm.

Platelet-derived growth factor receptors expressed in response to injury of differentiated vascular smooth muscle in vitro: effects on Ca2+ and growth signals

Vascular smooth muscle cells (VSMCs) in the intact vascular wall are differentiated for contraction, whereas the response to vascular injury involves transition towards a synthetic phenotype, with increased tendency for proliferation. Platelet-derived growth factor (PDGF) is thought to be important for this process. We investigated expression and functional coupling of PDGF receptors (PDGFRs) alpha and beta in rat tail arterial rings kept in organ culture, in order to capture early events in the phenotypic transition. In freshly dissected rings no PDGFR immunoreactivity was found in medial VSMCs, whereas PDGFR alpha was detected in nerve fibres. After organ culture for 1-4 days PDGFR alpha and beta as well as phospholipase Cgamma2 (PLCgamma2), known to couple to PDGFR, were expressed in VSMCs within 100 microm of the cut ends. Calponin, a marker for the contractile phenotype, was decreased near the injured area, suggesting that cells were in transition towards synthetic phenotype. In these cells, which showed functional Ca2+-release from the sarcoplasmic reticulum, PDGF-AB (100 ng x mL(-1)) had no effect on [Ca2+]i, whereas cultured VSMCs obtained from explants of rat tail arterial rings responded to PDGF-AB with an increase in [Ca2+]i. However, PDGFR within the cultured rings coupled to growth signalling pathways, as PDGF-AB caused a tyrphostin AG1295-sensitive activation of extracellular signal-regulated kinases 1 and 2 and of [3H]-thymidine incorporation. Thus, early expression of PDGFR in VSMC adjacent to sites of vascular injury coincides with signs of dedifferentiation. These receptors couple to growth signalling, but do not activate intracellular Ca2+ release.

Broad-spectrum and selective serine protease inhibitors prevent expression of platelet-derived growth factor-BB and cerebral vasospasm after subarachnoid hemorrhage: vasospasm caused by cisternal injection of recombinant platelet-derived growth factor-BB

BACKGROUND AND PURPOSE

Plasma serine protease cascade, including the complement system and thrombin, is activated in the subarachnoid space during the acute phase after subarachnoid hemorrhage (SAH). To examine the effect of protease cascade-based inflammation and subsequent vascular repair in the development of cerebral vasospasm, we examined the effect of 2 synthetic serine protease inhibitors-FUT-175, an inhibitor of thrombin and the complement system, and argatroban, a selective inhibitor of thrombin-on the development of cerebral vasospasm in a rabbit SAH model.

METHODS

One hundred Japanese White male rabbits were used in the study. The SAH was simulated by a single injection of autologous arterial blood into the cisterna magna. To evaluate the development of cerebral vasospasm, the caliber of the basilar artery was measured on x-ray film before and at 2 days after SAH. Nine groups of rabbits (n=6 each) were treated with continuous intravenous injection of FUT-175 (2.5, 5, 10, or 20 mg/d), argatroban (1.25, 2.5, or 5 mg/d), or the same amount of saline (vehicle) for 48 hours, starting 40 minutes after SAH. Two days after SAH, the expression of homodimer of platelet-derived growth factor-BB (PDGF-BB) in the basilar artery was examined with immunohistochemical techniques. In 20 normal rabbits, 5 microg of recombinant PDGF-BB or vehicle was injected into the cisterna magna, and the basilar arteries were examined on angiograms for 48 hours.

RESULTS

Significant differences were observed in the caliber of the basilar arteries between the vehicle group and the groups with the 3 larger doses of FUT-175 (vehicle, 52+/-5.0%; 5 mg, 79+/-5.7%; 10 mg, 80+/-2.5%; 20 mg, 80+/-3.7%) and between the vehicle group and the groups with the 2 larger doses of argatroban (vehicle, 52+/-6.4%; 2.5 mg, 81+/-9.0%; 5 mg, 85+/-4.1%) (P<0.05). In the histological examination, administration of effective doses of FUT-175 or argatroban suppressed the expression of PDGF-BB in the endothelial and medial smooth muscle cell layers. Exogenous PDGF-BB caused delayed and prolonged vasoconstriction on normal basilar arteries.

CONCLUSIONS

Activation of the serine protease cascade and/or thrombin after SAH was demonstrated to play an essential role in the development of cerebral vasospasm. The expression of PDGF-BB-like protein in the arterial walls correlated with the development of cerebral vasospasm. Elevated PDGF-BB level in the subarachnoid space was found to induce delayed and chronic vasoconstriction.

Platelet-derived growth factor-induced vasodilatation in mesenteric resistance arteries by nitric oxide: blunted response in spontaneous hypertension

Platelet-derived growth factor (PDGF) is a potent mitogen for vascular smooth-muscle cells, but its effects on vasomotion remain controversial. Both vasoconstriction and vasodilatation of isolated rat aortic rings have been reported. The effects of PDGF on responses of perfused mesenteric resistance arteries from normotensive Wistar-Kyoto and spontaneously hypertensive rats were studied by using a video dimension analyzer. PDGF receptor messenger RNA (mRNA) expression in endothelial cells isolated from mesenteric arteries of both normotensive and hypertensive rats was studied by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. In both normotensive and hypertensive rats, PDGF-BB concentration-dependently induced vasodilatation (maximal response, 25 +/- 4% and 13 +/- 4% at 10(-8) M, respectively; p < 0.05, normotensive vs. hypertensive rats). Endothelium removal or preincubation with N(omega)-nitro-L-arginine methyl ester, but not indomethacin, inhibited these relaxations, indicating that these vasodilatations are endothelium dependent and mediated by nitric oxide. RT-PCR analysis showed that both PDGF-alpha and -beta receptor mRNAs were present in endothelial cells of the mesenteric arteries of normotensive as well as hypertensive rats. In addition, relaxations induced by both PDGF-AA and -AB were significantly less than those induced by PDGF-BB in both strains, suggesting that vasodilatation is mediated mainly by the PDGF-beta receptor subtype. No vasoconstriction was observed after application of PDGF-BB to both normotensive and hypertensive mesenteric arteries with or without endothelium. In rat mesenteric resistance arteries, PDGF induces endothelium-dependent vasodilatation mediated by nitric oxide. At sites where PDGF is released or locally produced, therefore, the growth factor may participate in regulating vascular tone, and this endothelium-dependent regulation is attenuated in spontaneous hypertension.

Role of tyrosine phosphorylation in excitation-contraction coupling in vascular smooth muscle

Increasingly it is recognized that tyrosine phosphorylation plays an important part in the regulation of function in differentiated contractile vascular smooth muscle. Tyrosine kinases and phosphatases are present in large amounts in vascular smooth muscle and have been reported to influence a number of processes crucial to contraction, including ion channel gating, calcium homeostasis and sensitization of the contractile process to [Ca2+]i. This review summarizes current understanding regarding the role of tyrosine phosphorylation in excitation-contraction coupling in blood vessels.

Increase in tone and intracellular Ca2+ in rabbit isolated ear artery by platelet-derived growth factor

1. The effect of platelet-derived growth factor (PDGF-AB) on tone and intracellular Ca2+ ([Ca2+]i) was examined in rabbit isolated ear arteries. Arteries were mounted in a myograph and loaded with the Ca(2+)-sensitive fluorescent indicator, fura-2, for concurrent measurements of isometric force and [Ca2+]i. 2. PDGF-AB contracted rabbit ear artery in a concentration-dependent manner. PDGF-AB induced tone was associated with a rise in [Ca2+]i. In the presence of noradrenaline, PDGF-AB induced a similar rise in [Ca2+]i but contraction in response to PDGF-AB in the presence of noradrenaline was increased compared with PDGF-AB alone. 3. PDGF-AB-induced rise in [Ca2+]i and tone were abolished by removal of extracellular Ca2+ (with addition of BAPTA, a Ca2+ chelator), and by preincubation with a dihydropyridine calcium channel blocker, (-)-202,791. Bistyrphostin, a selective inhibitor of tyrosine kinases, also inhibited PDGF-AB-induced tone, but had no effect on noradrenaline- or potassium-induced tone. 4. PDGF-AB contracts rabbit ear artery by increasing Ca2+ entry through voltage-operated calcium channels. This effect involves activation of a tyrosine kinase.

Acute and long-term effects of tissue culture on contractile reactivity in renal arteries of the rat

To evaluate long-term effects of contractile and mitogenic stimuli on the contractile reactivity of arterial smooth muscle, we measured the incorporation of the thymidine analogue 5-bromo-2'-deoxyuridine (BrdUrd) and mechanical responses in arterial segments that had been maintained in tissue culture. The experiments were performed on renal arteries that had been isolated from adult rats, chemically sympathectomized, mechanically denuded from endothelium and mounted under distension. Exposure of arterial segments for up to 3 weeks to culture medium supplemented with fetal calf serum resulted in the following consecutive changes: a strong acute contraction, selective pharmacological changes that included decreased contractile responses to phenylephrine and vasopressin and increased relaxing responses to isoproterenol, increased incorporation of BrdUrd, a progressive fall in contractile responses to all vasoconstrictor stimuli, and an increase in excitability. Serum-free medium resulted in a much smaller acute arterial contraction, induced less incorporation of BrdUrd, accelerated the occurrence of hyperexcitability, but did not affect early pharmacological changes or the subsequent fall in overall arterial contractility with tissue culture. Dialysis of the serum or addition of ketanserin abolished the contractile effect of serum but did not affect the incorporation of BrdUrd or the loss of contractility with tissue culture. Addition of serotonin to serum-free culture medium mimicked the contractile response to serum but not the stimulation of BrdUrd incorporation. These data indicate that tissue culture alters the properties of the arterial wall, that contraction does not underlie the proliferative response of arterial smooth muscle to serum-derived mitogens in vitro, and that stimulation of DNA synthesis does in itself not lead to selective changes in arterial contractility.