Exogenous nitric oxide donation causes desensitization of arteriolar relaxing activity in vivo: an intravital analysis in mice.
BACKGROUND
The NO/cGMP pathway plays a crucial role in regulation of tissue perfusion. However, a NO-induced desensitization of cGMP-mediated relaxation has been reported in isolated tissue. To examine whether a similar phenomenon can be detected in vivo, we analyzed relaxations of microvessels in response to repeated applications of NO.


METHODS
The investigations were performed by means of dynamic intravital fluorescence microscopy in the dorsal skinfold chamber of female balb/mice. First, the microvasculature was maximally preconstricted by the application of the vasoconstrictor 5-hydroxytryptamine. Subsequently, relaxation was induced by applying an NO-donator, the S-nitrosoglutathione, to the contracted vessels. Following buffer exchange, constriction and relaxation were repeated. Drugs were given topically into the chamber, directly onto the skin muscle. The response of arterioles to topical administration of vasoactive drugs was determined as the change of the diameter, and quantified using standard software.


RESULTS
The relaxation of arterioles was reduced after repetitive application. The short pretreatment with NO-donor entailed a reduced relaxation of arterioles in response to following application. The absolute change in vessel diameter induced by S-nitrosoglutathione was significantly reduced from 21 μm to 16 μm after the first and the second application, respectively. However, the data also revealed a noticeable reduction of the constricting activity of 5-hydroxytryptamine during the second application, indicating a possible desensitization of the 5-hydroxytryptamine response or a humoral and/or neuronal compensatory mechanisms.


CONCLUSIONS
The NO-induced cGMP-mediated relaxation of microvessels was quantified, and the phenomenon of desensitization visualized in vivo by means of dynamic fluorescence microscopy.
Ring
Andrej
A
Department of Surgery, Trauma Center, University Hospital Bergmannsheil, Bochum, Germany. andrej.ring@ruhr-uni-bochum.de
Mullershausen
Florian
F
Goertz
Ole
O
Koesling
Doris
D
Muhr
Gert
G
Steinau
Hans-Ulrich
HU
Steinstraesser
Lars
L
Langer
Stefan
S
D000818:Animals; D001160:Arterioles / Q000187:drug effects* / Q000502:physiology; D062109:Dermatologic Surgical Procedures; D005260:Female; D006162:Guanylate Cyclase / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008856:Microscopy, Fluorescence / Q000379:methods; D009569:Nitric Oxide / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D026422:S-Nitrosoglutathione / Q000494:pharmacology*; D012701:Serotonin / Q000494:pharmacology; D018490:Serotonin Agents / Q000494:pharmacology; D012867:Skin / Q000098:blood supply; D013524:Surgical Flaps / Q000098:blood supply*; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology
D020030:Nitric Oxide Donors; D018490:Serotonin Agents; D009569:Nitric Oxide; D012701:Serotonin; D026422:S-Nitrosoglutathione; D006162:Guanylate Cyclase