BACKGROUND
bradykinin  is a vasoactive peptide released from its high molecular weight precursors, the kininogens, through the action of serine proteases, the kallikreins, playing a crucial role in pathologic processes like inflammation, infectious diseases, and cancer  <cit> .
the brain and spinal cord contain all of the components necessary for kinin formation and action.
in addition, central nervous system traumas lead to kinin formation  <cit> .
bk type- <dig>  receptors are mostly expressed in pathological or stressful situations related to tissue damage  <cit>  including tumors  <cit> .
the bk type- <dig>  receptor is defined as a constitutive one, being normally encountered in many tissues, including the brain  <cit> .
it is well known that the blood-brain barrier  in brain tumor regions  shows different plasma protein extravasation  characteristics when compared with the bbb of normal brain tissue and this effect is particularly related to the increase of b <dig> receptors  <cit> .
in animal models, b <dig> receptor agonists like cereport®  have been used by the intracarotid route to enhance the delivery of chemotherapeutic agents to the brain tumor area  <cit> .
b <dig> receptor agonists with low metabolic resistance  have already been unsuccessfully tested on ppe extravasation through the btb in brain tumors  <cit> .
the b <dig> receptor agonist, sar-des-arg9bk , shows some resistance to enzymatic degradation that is due to the addition of amino acids to the amino-terminal portion of the molecule  <cit> .
thus, it is possible that sar could be successful in promoting ppe through the btb, having potential uses in enhancing the delivery of chemotherapeutic agents to brain tumors.
in order to test this hypothesis, we investigated the effect of sar on ppe using the rat c <dig> glioma model  <cit> .
RESULTS
eighty percent of c6-inoculated animals developed brain tumors after a period of  <dig> days .
we determined ppe in experimental groups of animals treated with bradykinin , the bk receptor b <dig> agonist  or the bk receptor b <dig> antagonist  .
ppe in the tumor area of c6-inoculated animals was  <dig>  ±  <dig>  μg eb/g dry tissue, a value that did not differ from those observed in tumor-free animals inoculated with vehicle only , or inoculated with cell vehicle plus sar .
injection of bk into c6-inoculated animals also did not change the tumor ppe .
it is important to note that in all groups the left  hemispheres presented ppe values similar to those of the right  hemisphere in the control animals.
however, sar significantly increased ppe in the tumor area of c6-inoculated animals  .
this effect was abolished, with a return to basal levels, by pre-treatment of the animals with the bk receptor b <dig> antagonist leu .
the effect of sar in increasing ppe in c6-inoculated right hemispheres  was also observed  when compared to the contralateral non-tumoral hemisphere  .
discussion
we demonstrate here that the selective b <dig> receptor agonist sar  <cit>  enhances ppe in c <dig> glioma without affecting the normal brain parenchyma.
it has been previously shown that sar at  <dig> nmol/kg also does not alter the systemic blood pressure of rats  <cit> .
the effect of sar was blocked by pre-treatment with the selective b <dig> receptor antagonist leu, suggesting that ppe can be modulated by b <dig> receptors in the glioma model of c6-inoculated rats.
it was recently described that gliomas may express both b <dig> and b <dig> bk receptors, with b <dig> being located closer to the periphery of the tumor cells while b <dig> was observed throughout the cell  <cit> .
in view of their effects on vascular dilatation and blood flow, bradykinin receptor agonists have been tested in the chemotherapy of brain tumors  <cit> , whereas bradykinin itself was less used for this purpose  <cit>  due to its lower efficacy and shorter blood half-life.
in contrast to other authors  <cit>  we did not observe an effect of bk by itself in enhancing bbb or btb permeability.
fast bk degradation could account for this difference since we used a femoral vein, whereas other authors used more proximal accesses like the carotid artery  <cit> .
the b <dig> receptor agonist rmp- <dig>  has been successfully employed to enhance btb permeability to chemotherapeutic agents  <cit> , but in the animal models already tested only local or regional routes like the carotid artery were used  <cit> .
in general, b <dig> receptors are non-constitutive  <cit>  and restricted to pathologic processes including tumors or degeneration  <cit> .
systemically administered metabolically resistant b <dig> receptor agonists may be useful to increase chemotherapy levels at the target site, with higher specificity and lower toxicity than b <dig> receptor agonists.
thus, we believe that sar injected together with chemotherapeutic agents may be useful to increase drug delivery specifically to the brain tumor with less toxicity to non-affected areas.
additionally, because eb circulates bound to albumin, it is reasonable to think that sar could increase the delivery of several chemotherapeutic agents of molecular weight similar to, or lower than that of albumin  <cit> .
although the evans blue method is less sensitive than other labeling methods like quantitative autoradiography, for example, we used it because it was the only method available to us at the time of this experiment.
however, the evans-blue method is of low cost, can be easily reproduced by other laboratories, and was sensitive enough to detect differences provoked by sar in these experiments.
bk or bk agonists have been previously used to increase btb permeability but, due to their faster enzymatic degradation  <cit> , they were injected into the carotid artery.
however, our findings suggest, that sar administered intravenously remains stable and thus could be an attractive agent for the treatment of brain or even other tumors  <cit>  that express bk b <dig> receptors.
CONCLUSIONS
our data suggest that the b <dig> receptor modulates ppe in the blood tumor barrier of c <dig> glioma.
a possible role for the systemic use of sar in the chemotherapy of gliomas or other cns neoplasms deserves further study.

 bradykinin is a vasoactive peptide released from its high molecular weight precursors, the kininogens, through the action of serine proteases, the kallikreins, playing a crucial role in pathologic processes like inflammation, infectious diseases, and cancer. the brain and spinal cord contain all of the components necessary for kinin formation and action. in addition, central nervous system traumas lead to kinin formation. bk type- receptors are mostly expressed in pathological or stressful situations related to tissue damage including tumors. the bk type- receptor is defined as a constitutive one, being normally encountered in many tissues, including the brain. it is well known that the blood-brain barrier in brain tumor regions shows different plasma protein extravasation characteristics when compared with the bbb of normal brain tissue and this effect is particularly related to the increase of b receptors. in animal models, b receptor agonists like cereport® have been used by the intracarotid route to enhance the delivery of chemotherapeutic agents to the brain tumor area. b receptor agonists with low metabolic resistance have already been unsuccessfully tested on ppe extravasation through the btb in brain tumors. the b receptor agonist, sar-des-arg9bk, shows some resistance to enzymatic degradation that is due to the addition of amino acids to the amino-terminal portion of the molecule. thus, it is possible that sar could be successful in promoting ppe through the btb, having potential uses in enhancing the delivery of chemotherapeutic agents to brain tumors. in order to test this hypothesis, we investigated the effect of sar on ppe using the rat c glioma model.  eighty percent of c6-inoculated animals developed brain tumors after a period of days. we determined ppe in experimental groups of animals treated with bradykinin, the bk receptor b agonist or the bk receptor b antagonist. ppe in the tumor area of c6-inoculated animals was ± μg eb/g dry tissue, a value that did not differ from those observed in tumor-free animals inoculated with vehicle only, or inoculated with cell vehicle plus sar. injection of bk into c6-inoculated animals also did not change the tumor ppe. it is important to note that in all groups the left hemispheres presented ppe values similar to those of the right hemisphere in the control animals. however, sar significantly increased ppe in the tumor area of c6-inoculated animals. this effect was abolished, with a return to basal levels, by pre-treatment of the animals with the bk receptor b antagonist leu. the effect of sar in increasing ppe in c6-inoculated right hemispheres was also observed when compared to the contralateral non-tumoral hemisphere. discussion we demonstrate here that the selective b receptor agonist sar enhances ppe in c glioma without affecting the normal brain parenchyma. it has been previously shown that sar at nmol/kg also does not alter the systemic blood pressure of rats. the effect of sar was blocked by pre-treatment with the selective b receptor antagonist leu, suggesting that ppe can be modulated by b receptors in the glioma model of c6-inoculated rats. it was recently described that gliomas may express both b and b bk receptors, with b being located closer to the periphery of the tumor cells while b was observed throughout the cell. in view of their effects on vascular dilatation and blood flow, bradykinin receptor agonists have been tested in the chemotherapy of brain tumors, whereas bradykinin itself was less used for this purpose due to its lower efficacy and shorter blood half-life. in contrast to other authors we did not observe an effect of bk by itself in enhancing bbb or btb permeability. fast bk degradation could account for this difference since we used a femoral vein, whereas other authors used more proximal accesses like the carotid artery. the b receptor agonist rmp- has been successfully employed to enhance btb permeability to chemotherapeutic agents, but in the animal models already tested only local or regional routes like the carotid artery were used. in general, b receptors are non-constitutive and restricted to pathologic processes including tumors or degeneration. systemically administered metabolically resistant b receptor agonists may be useful to increase chemotherapy levels at the target site, with higher specificity and lower toxicity than b receptor agonists. thus, we believe that sar injected together with chemotherapeutic agents may be useful to increase drug delivery specifically to the brain tumor with less toxicity to non-affected areas. additionally, because eb circulates bound to albumin, it is reasonable to think that sar could increase the delivery of several chemotherapeutic agents of molecular weight similar to, or lower than that of albumin. although the evans blue method is less sensitive than other labeling methods like quantitative autoradiography, for example, we used it because it was the only method available to us at the time of this experiment. however, the evans-blue method is of low cost, can be easily reproduced by other laboratories, and was sensitive enough to detect differences provoked by sar in these experiments. bk or bk agonists have been previously used to increase btb permeability but, due to their faster enzymatic degradation, they were injected into the carotid artery. however, our findings suggest, that sar administered intravenously remains stable and thus could be an attractive agent for the treatment of brain or even other tumors that express bk b receptors.  our data suggest that the b receptor modulates ppe in the blood tumor barrier of c glioma. a possible role for the systemic use of sar in the chemotherapy of gliomas or other cns neoplasms deserves further study. 
a possible role for the use of sar in the chemotherapy of gliomas deserves further study. our data suggest that the b receptor modulates ppe in the blood tumor barrier of c glioma. pre-administration of the bradykinin b antagonist -des-arg blocked the sar-induced ppe in the tumor area. while it is well known that bradykinin b agonists increase plasma protein extravasation in brain tumors, the bradykinin b agonists tested thus far are unable to produce this effect. here we examine the effect of the selective b agonist bradykinin sar-des-arg9bk, a compound resistant to enzymatic degradation with prolonged activity on ppe in the blood circulation in the c rat glioma model.
 while it is well known that bradykinin b agonists increase plasma protein extravasation in brain tumors, the bradykinin b agonists tested thus far are unable to produce this effect. here we examine the effect of the selective b agonist bradykinin sar-des-arg9bk, a compound resistant to enzymatic degradation with prolonged activity on ppe in the blood circulation in the c rat glioma model.  sar administration significantly enhanced ppe in c rat brain glioma compared to saline or bk. pre-administration of the bradykinin b antagonist -des-arg blocked the sar-induced ppe in the tumor area.  our data suggest that the b receptor modulates ppe in the blood tumor barrier of c glioma. a possible role for the use of sar in the chemotherapy of gliomas deserves further study. 