Urokinase plasminogen activator regulates pulmonary arterial contractility and vascular permeability in mice.

The concentration of urokinase plasminogen activator (uPA) is elevated in pathological settings such as acute lung injury, where pulmonary arterial contractility and permeability are disrupted. uPA limits the accretion of fibrin after injury. Here we investigated whether uPA also regulates pulmonary arterial contractility and permeability. Contractility was measured using isolated pulmonary arterial rings. Pulmonary blood flow was measured in vivo by Doppler and pulmonary vascular permeability, according to the extravasation of Evans blue. Our data show that uPA regulates the in vitro pulmonary arterial contractility induced by phenylephrine in a dose-dependent manner through two receptor-dependent pathways, and regulates vascular contractility and permeability in vivo. Physiological concentrations of uPA (≤1 nM) stimulate the contractility of pulmonary arterial rings induced by phenylephrine through the low-density lipoprotein receptor-related protein receptor. The procontractile effect of uPA is independent of its catalytic activity. At pathophysiological concentrations, uPA (20 nM) inhibits contractility and increases vascular permeability. The inhibition of vascular contractility and increase of vascular permeability is mediated through a two-step process that involves docking to N-methyl-d-aspartate receptor-1 (NMDA-R1) on pulmonary vascular smooth muscle cells, and requires catalytic activity. Peptides that specifically inhibit the docking of uPA to NMDA-R, or the uPA variant with a mutated receptor docking site, abolished both the effects of uPA on vascular contractility and permeability, without affecting its catalytic activity. These data show that uPA, at concentrations found under pathological conditions, reduces pulmonary arterial contractility and increases permeability though the activation of NMDA-R1. The selective inhibition of NMDAR-1 activation by uPA can be accomplished without a loss of fibrinolytic activity.

Neuroprotection by glucagon: role of gluconeogenesis.

OBJECT: The severity of neurological impairment following traumatic brain injury (TBI) is exacerbated by several endogenous processes, including hyperglycemia, hypotension, and the generation of glutamate. However, in addition to controlling hyperglycemia, insulin has pleiotropic effects on tissue metabolism, which include reducing the concentration of the neurotoxic amino acid glutamate, making it unclear whether insulin's beneficial effects are attributable to the establishment of euglycemia per se. In the present study, the authors asked if reducing glutamate via approaches that do not lower glucose levels would improve neurological outcome following TBI. METHODS: Glucagon activates gluconeogenesis by increasing the hepatic uptake of amino acids such as glutamate and facilitating their conversion to glucose. Glucagon was administered as a single intraperitoneal injection before or after closed head injury (CHI). Neurological function, brain histological features, blood glutamate and glucose levels, and CSF glutamate concentrations were measured. RESULTS: A single intraperitoneal injection of glucagon (25 µg) into mice 10 minutes before or after CHI reduced lesion size by about 60% (p < 0.0001) and accelerated neurological recovery. The neuroprotective effect of glucagon was related to gluconeogenesis by decreasing the concentration of the neuroexcitatory amino acid glutamate in the circulation from 207 ± 32.1 µmol/L in untreated mice to 101.11 ± 21.6 µmol/L in treated mice (p < 0.001); a similar effect occurred in the CSF. The neuroprotective effect of glucagon was seen notwithstanding the attendant increase in blood glucose, the final substrate of gluconeogenesis. CONCLUSIONS: Glucagon exerts a marked neuroprotective effect post-TBI by decreasing CNS glutamate. Glucagon was beneficial despite increasing blood glucose. Favorable effects also occurred when glucagon was given prior to TBI, suggesting its involvement in the preconditioning process. Thus, glucagon may be of value in providing neuroprotection when administered after TBI or prior to certain neurosurgical or cardiac interventions in which the incidence of perioperative ischemia is high.