Hoagland KM, Maddox DA, Martin DS. Bradykinin B2-receptors mediate the pressor and renal hemodynamic effects of intravenous bradykinin in conscious rats.
JOURNAL OF THE AUTONOMIC NERVOUS SYSTEM 1999;
75:7-15. [PMID:
9935264 DOI:
10.1016/s0165-1838(98)00166-0]
[Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Bradykinin (BK) is a peptide which evokes remarkably different changes in cardiovascular function. Systemic bolus injection of BK results in a rapid drop in blood pressure via an endothelium-dependent mechanism. On the other hand, local administration of BK can activate a powerful pressor reflex by stimulating afferent nerves located in the abdominal viscera, the heart, and the kidney. In the present study, the cardiovascular and renal hemodynamic effects during sustained (intravenous infusion) and transient (intravenous bolus injection) elevations in circulating BK were characterized and the receptor mechanism eliciting these effects was investigated. Mean arterial pressure (MAP), heart rate (HR), and renal blood flow (RBF) were recorded from conscious unrestrained rats while five-point cumulative dose-response curves were constructed during infusion or bolus injection of BK (5-80 microg kg(-1)). Infusion of BK produced dose-dependent increases in MAP (maximum response = 27 +/- 3 mmHg) accompanied by a significant tachycardia (maximum response = 159 +/- 20 bpm), a 28 +/- 6% increase in RBF, and no changes in renal vascular resistance (RVR). The BK-induced increases in MAP, HR, and RBF were abolished after treatment with a ganglion blocker (maximum responses: MAP = 2 +/- 3 mmHg, HR = 13 +/- 4 bpm, RBF = 4 +/- 2%) or with an agent which blocks B2-receptors (maximum responses: MAP = 1 +/- 1 mmHg, HR = 6 +/- 5 bpm, RBF = 6 +/- 2%). In marked contrast, bolus administration of BK resulted in hypotensive responses (maximum decline in MAP = -37 +/- 4 mmHg), reflex tachycardia (maximum increase in HR = 45 +/- 9 bpm), increases in RBF (maximum response = 13 +/- 4%), and significant reductions in RVR (maximum response = 38 +/- 5%). These responses were also prevented when B2-receptors were blocked (maximum responses: MAP = 3 +/- 2 mmHg, HR = 17 +/- 6 bpm, RBF = 3 +/- 3%, RVR = 9 +/- 4%). In summary, BK infusions activated a cardiopressor reflex while BK injections caused hypotension. These opposite effects were both mediated via B2-receptors. These findings suggest that BK can have complex effects on the cardiovascular system that may be dependent on the sites, magnitude, and duration of elevated BK concentrations.
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