Effect of cyclic 
guanosine‐monophosphate on porcine retinal vasomotion

Abstract

ABSTRACT.Purpose: 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. Conclusion: Cyclic GMP lowers the frequency without affecting the amplitude of vasomotion in isolated porcine retinal arterioles.

Heterogeneity and weak coupling may explain the synchronization characteristics of cells in the arterial wall

“…The same is the case for procedures aimed at manipulating the concentration of cGMP within the vascular wall. Inhibition of endothelial NO synthase or guanylate cyclase (the latter of which produces cGMP in response to NO) may either inhibit vasomotion Hessellund et al 2006) or leave it more or less unaffected (Mauban & Wier 2004). Whereas in the present mesenteric vessel preparation we consistently find that the addition of 8Br-cGMP promotes synchronization Peng et al 2001;Rahman et al 2005), Haddock et al (2006) did not find this effect on adding dibutyryl-cGMP to endothelium-denuded rat cerebral arteries.…”

<i>L</i>-Arginine and <i>L</i>-Nitroarginine Methylester Effects on Vasomotion in Isolated Rabbit Eyes

“…Vasomotion refers to periodic oscillations in vascular tone that ensure the intermittent supply of blood to adjacent microvascular units [19,20] . Blood flow (Q) through the vessel is determined by the pressure difference between the two ends L-NAME 10 mg/ml L-NAME 20 mg/ml L-NAME 30 mg/ml L-Arg 100 mg/ml of the vessel (P1 -P2) and the vascular resistance (R) according to Ohm's law: P1 -P2 = Q !…”

“…Vasomotion refers to periodic oscillations in vascular tone that allow fine control of the capillary blood and facilitate exchange of metabolites, being a phenomenon described in practically all vascular beds. It has been assumed that in vitro techniques can serve as models for studying the mechanisms underlying vasomotion in vivo , and previous studies have already characterized vasomotion in isolated porcine retinal arterioles [19,20] .…”

Myogenic Oscillations in Rabbit Ocular Vasculature Are Very Low Frequency

“…Vasomotion refers to periodic oscillations in vascular tone that ensure the intermittent supply of blood to adjacent microvascular units. Several studies in anesthetized cats [16,17], isolated bovine [18,19] or porcine [20,21,22,23,24] retinal arteries studied in a myograph suggest that there are basal oscillations in vascular tone. Another study revealed myogenic tone and reactivity of the isolated rat external ophthalmic artery [25].…”