3.6 In vivo effects of the BK-(1-9) fragments
Vasodilation is often translated in vivo to hypotension as a result of reduced peripheral vascular resistance. Thus, we aimed at assessing whether BK-(1-7) and BK-(1-5) were also able to reduce the arterial blood pressure. When administered intravenously (i.v ) in conscious male rats, BK-(1-9) induced a transient dose-dependent hypotension followed by a transient increase in heart rate (tachycardia) due to baroreflex activation. BK-(1-7) and BK-(1-5) induced a significant hypotension followed by tachycardia but, unlike BK-(1-9), this effect was dose-independent (Figures 7A and B, traces in Supplementary Figure S5). The dose-independent relationship observed for BK-(1-9) fragments could be due to extensive hydrolysis of these peptides in the circulation, mainly in the pulmonary vascular bed. To further explore this, we investigated whether the administration of BK-(1-9) and its fragments on a different vascular bed, thereby bypassing the pulmonary circulation upon their administration, could change the observed responses. Intra-arterial (i.a. ) administration of the BK-(1-9) led to an increased hypotension when compared to i.v. administration (Figures 7C and D, traces on Supplementary Figure S6), since BK-(1-9) is subjected to extensive hydrolysis in the pulmonary circulation (Ferreira et al. , 1967; Ryan et al. , 1968; Ryan et al. , 1994) when it is giveni.v. On the other hand, we could not detect any significant difference when BK-(1-7) or BK-(1-5) were i.a. or i.v.administered (Figures 7C and D), suggesting that the BK-(1-9) fragments are somehow more resistant to proteolysis in the pulmonary circulation. As ACE is the main peptidase involved in BK-(1-9) cleavage in vivo and this enzyme is particularly active in the pulmonary circulation (Orfanoset al. , 1999), we tested the effects of ACE inhibition in vivo with captopril (ACEi) on the cardiovascular effects led by BK-(1-9) fragments. As expected, treatment with captopril potentiated the hypotensive response to BK-(1-9) (Figures 7E and F, traces on Supplementary Figure S7). On the other hand, the cardiovascular effects of the BK-(1-9) fragments were not affected by ACEi (Figures 7E and F, traces on the Supplementary Figure S7). Taken together, our results suggest that the BK-(1-9) fragments induce a discreate hypotension in vivo, although significant when compared with saline administration, which were not affected by the activity of ACE.
Apart from its cardiovascular effects, BK-(1-9) is a potent pro-inflammatory agent (Cayla et al. , 2012). Thus, we evaluated whether the BK-(1-9) fragments could induce nociceptive reflexes and vascular permeability, which are known BK-(1-9) responses. We evaluated nociceptive reflexes in adult male mice following intradermal hind paw injection of BK peptides. Although BK-(1-7) and BK-(1-5) evoked nociceptive responses, the response to BK-(1-9) was significantly greater (Figure 8A). Increased microvascular permeability was assessed by extravasation of Evans’ Blue dye, following administration of the BK peptides into the footpad of mice. As expected, BK-(1-9) increased vascular permeability in the footpad, but equivalent molar doses of BK-(1-7) or BK-(1-5) had no significant effect (Figure 8B).