Shinde UA, Desai KM, Yu C, Gopalakrishnan V. Nitric oxide synthase inhibition exaggerates the hypotensive response to ghrelin: role of calcium-activated potassium channels.
J Hypertens 2005;
23:779-84. [PMID:
15775782 DOI:
10.1097/01.hjh.0000163146.20330.bc]
[Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE
To investigate the mechanism underlying the observation that infusion of the growth hormone secretagogue peptide, ghrelin, produces a decrease in mean arterial pressure (MAP) with no change in heart rate.
METHOD
The effect of a single bolus infusion of ghrelin (12 nmol/kg intravenously) on the changes in MAP and heart rate was determined in 12-week-old male anaesthetized Sprague-Dawley rats subjected to pretreatment with either the nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (L-NAME; 0.7 mg/ml by mouth for 5 days), or vehicle (control).
RESULTS
Ghrelin produced a significant decrease in MAP at 20 min (P < 0.05) after infusion in the control group, without any change in heart rate. The MAP recovered partially over 1 h. The ghrelin-evoked decrease in MAP was much greater (P < 0.01) and was sustained for 1 h in rats subjected to NOS inhibition. Pretreatment with the cyclo-oxygenase inhibitor, indomethacin, failed to affect the responses in either group. Intravenous infusion of 50 mug/kg each of apamin and charybdotoxin (ChTX), a combination that is known to block Ca-activated K channels or the endothelium-derived hyperpolarization process, attenuated the decrease in MAP evoked by ghrelin in both control and NOS-inhibited rats. A sodium nitroprusside-induced decrease in MAP was unaffected in the presence of apamin-ChTX, but acetylcholine-evoked hypotension was significantly reduced in both groups.
CONCLUSION
These data suggest that the Ca-activated, K-channel-mediated, ghrelin-evoked decrease in MAP may be significant in states of endothelial dysfunction associated with reduced nitric oxide availability.
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