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).