Adrenomedullin-induced endothelium-dependent relaxation in porcine ciliary arteries.
OBJECTIVE
To investigate adrenomedullin-induced relaxation in isolated porcine ciliary arteries.


METHODS
In a myograph system (isometric force measurement), precontracted vessels ( approximately 0.1 micro M U46619; thromboxane A(2) analogue or approximately 10 nM endothelin-1) were exposed, in a cumulative manner, to increasing concentrations of adrenomedullin (1 nM to 1 micro M) in the presence or absence of different drugs. Some experiments were conducted in vessels with nonfunctional (intentionally mechanically damaged) endothelium.


RESULTS
Adrenomedullin evoked marked relaxation [maximum relaxation (Rel(max)): 85.5 +/- 3.0%; negative log M concentration inducing 50% of Rel(max) (pD(2)): 7.4 +/- 0.1] in comparison to time-controls (Rel(max): 19.2 +/-4.8%; P < 0.001). Relaxation was inhibited by 3 micro M CGRP[8-37] (CGRP(1) receptor antagonist; Rel(max): 27.2% +/- 5.3%; P < 0.001) but not by 3 micro M adrenomedullin[22-52] (presumed adrenomedullin receptor antagonist; P = 0.75). Adrenomedullin-induced relaxation was less pronounced in nonfunctional endothelium vessels (Rel(max): 67.6% +/- 3.1%; pD(2): 6.9 +/- 0.1; P < 0.01). In vessels with functional endothelium, relaxation was not significantly influenced by 0.1 mM N(G)-nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthesis inhibitor), 10 micro M indomethacin (a cyclooxygenase inhibitor), or 10 micro M 17-octadecynoic acid (a cytochrome P(450) inhibitor). In contrast, relaxation was significantly inhibited by either 10 mM tetraethylammonium (nonselective potassium channel inhibitor; P < 0.01) or 50 nM apamin (small conductance potassium channel inhibitor), together with 50 nM charybdotoxin (large and intermediate potassium channel inhibitor; P < 0.01). In the presence of these potassium channel inhibitors, the amount of relaxation was not significantly different (P > 0.50) from that observed in vessels with nonfunctional endothelium.


CONCLUSIONS
In isolated porcine ciliary arteries, adrenomedullin induces relaxation that involves CGRP(1) receptors and is in part endothelium dependent. Endothelium-dependent relaxation was blocked by some potassium channel inhibitors, suggesting the possible release of an endothelium-derived hyperpolarizing factor (EDHF).
Dettmann
Eike S
ES
Laboratory of Ocular Pharmacology and Physiology, University Eye Clinic Basel, Basel, Switzerland.
Vysniauskiene
Ineta
I
Wu
Renyi
R
Flammer
Josef
J
Haefliger
Ivan O
IO
D053607:Adrenomedullin; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D000077221:Calcitonin Gene-Related Peptide Receptor Antagonists; D019842:Ciliary Arteries / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology; D010446:Peptide Fragments / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism; D018015:Receptors, Calcitonin Gene-Related Peptide / Q000502:physiology; D013552:Swine; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology*
D000077221:Calcitonin Gene-Related Peptide Receptor Antagonists; D004791:Enzyme Inhibitors; D010446:Peptide Fragments; D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D018015:Receptors, Calcitonin Gene-Related Peptide; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; C058636:calcitonin gene-related peptide (8-37); D053607:Adrenomedullin; D009569:Nitric Oxide; D015740:Calcitonin Gene-Related Peptide; D019331:NG-Nitroarginine Methyl Ester