Effect of cyclic guanosine-monophosphate on porcine retinal vasomotion.
OBJECTIVE
Vasomotion refers to periodic oscillations in vascular tone that ensure the intermittent supply of blood to adjacent microvascular units. Previous evidence from vessels outside the eye suggests that cyclic guanosine-monophosphate (cGMP) is involved in the regulation of vasomotion, but it is unknown whether this compound has an effect on vasomotion in retinal vessels.


METHODS
Retinal arterioles from porcine eyes were studied in a wire myograph. After initiation of vasomotion, the vessels were stimulated with increasing concentrations of the cGMP agonist 8-Br-cGMP (n = 6), the phosphodiesterase inhibitor zaprinast (n = 6) and the cGMP synthesis inhibitor L-NAME (n = 6). High concentrations of L-NAME blocked vasomotion, and control experiments (n = 20) using 8-Br-cGMP, S-nitroso-N-acetylpenicillamine (SNAP), adenosine and pinacidil were carried out to elucidate whether this effect was related to changes in the general tone of the vessel. Additionally, the relationship between oscillations in vascular tone and intracellular calcium concentration was studied.


RESULTS
Induction of cGMP agonistic activity with either 8-Br-cGMP or zaprinast lowered the vasomotion frequency significantly, whereas L-NAME-induced inhibition of cGMP increased this frequency. Neither of the agents affected the amplitude of the oscillations. The control experiments indicated that the effect of cGMP on vasomotion frequency was independent of the accompanying increase in tone. The oscillations in tone during vasomotion were accompanied by similar oscillations in intracellular calcium concentration.


CONCLUSIONS
Cyclic GMP lowers the frequency without affecting the amplitude of vasomotion in isolated porcine retinal arterioles.
Hessellund
Anders
A
Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark. ahe@akhphd.au.dk
Aalkjaer
Christian
C
Bek
Toke
T
D000818:Animals; D001160:Arterioles / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009213:Myography; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011688:Purinones / Q000494:pharmacology; D012161:Retinal Artery / Q000187:drug effects / Q000502:physiology*; D013552:Swine; D014664:Vasodilation / Q000187:drug effects; D014666:Vasomotor System / Q000502:physiology*
D004791:Enzyme Inhibitors; D010726:Phosphodiesterase Inhibitors; D011688:Purinones; C016276:8-bromocyclic GMP; D009569:Nitric Oxide; C011145:zaprinast; D006152:Cyclic GMP; D002118:Calcium; D019331:NG-Nitroarginine Methyl Ester