Adenosine enhances the relaxing influence of rat and bovine retinal tissue

Retinal tissue from different species continuously releases a factor lowering tone of isolated arteries. This was demonstrated by placing retinal tissue in close proximity to an isolated artery. This factor is called the "retinal relaxing factor" (RRF) (Delaey & Van de Voorde, Circ Res 1998, 83:714-720). The potential influence of adenosine on this relaxing influence was investigated using isometric tension recording of isolated arteries. The presence of bovine retinal tissue enhanced the vasorelaxing effect of adenosine on isolated bovine retinal artery. The presence of a non-selective adenosine receptor antagonist (8-(p-sulfophenyl)theophylline, 0.1 mM) showed a significant blocking effect of adenosine. When the retinal arteries were contracted with 120 mM K+, adenosine no longer induced relaxation of the preparation with bovine retinal tissue. This is in line with the concept that adenosine enhances the influence of RRF. Neither a NO-synthase inhibitor (nitro-L-arginine, 0.1 mM), a cyclooxygenase inhibitor (indomethacin, 10 mM) or an epoxyeicosatrienoic acid inhibitor (miconazole, 10 mM) influenced the enhanced vasodilating effect of adenosine on retinal arteries in the presence of bovine retinal tissue. In rat carotid artery adenosine elicited no relaxation in the absence of rat or porcine retinal tissue. However, a small relaxation is observed in the presence of rat retinal tissue, but not in the presence of porcine retina. In conclusion, our findings indicate that adenosine potentiates the relaxing influence of bovine retinal tissue on bovine retinal artery. Neither NO, cyclooxygenase metabolites of epoxyeicosatrienoic acids seem to be involved in this enhanced vasorelaxing response. Our results suggest the involvement of RRF released from bovine retina. The fact that rat retinal tissue, but not porcine retinal tissue, enhances the relaxing effect of adenosine on rat carotid artery, indicates species differences

Influence of Strain on the Kinetics of Phase Transitions in Solids

We consider a sharp interface kinetic model of phase transitions accompanied by elastic strain, together with its phase-field realization. Quantitative results for the steady-state growth of a new phase in a strip geometry are obtained and different pattern formation processes in this system are investigated

Clozapine directly relaxes bovine retinal arteries

Purpose: It was suggested that clozapine might be helpful in the development of new antiglaucoma agents, as it combines lowering the intraocular pressure after topical instillation with vasodilation. This study aimed to evaluate and characterize the vasodilatory effect of clozapine in isolated bovine retinal arteries ( BRAs). Methods: Retinal arteries were isolated from bovine eyes and mounted in the organ bath of a small vessel myograph. Results: Cumulative addition of clozapine ( 1 nM to 10 mu M) caused a concentration- dependent relaxation of the BRAs. Removal of the endothelium, inhibition of nitric oxide synthase and of soluble guanylyl cyclase reduced the clozapine response, whereas cyclooxygenase inhibition had no influence. A Ca2+ channel activator, a 5- hydroxytryptamine receptor antagonist, and an adenosine receptor antagonist failed in affecting the clozapine- induced relaxations. Conclusions: Clozapine relaxes bovine retinal arteries. Endothelium- derived NO seems to be involved, whereas prostanoids, calcium entry blockade, 5- HT7 receptor stimulation, and adenosine receptor stimulation do not

Evaluation of vacuum bonded GaAs/Si spin-valve transistors

In this article a new type of spin-valve transistor, a hybrid GaAs/Si device, is presented. In this device the Si emitter is replaced by a GaAs emitter launcher structure. The integration of the GaAs with the Si was done by means of a room temperature vacuum bonding technique. By using a soft NiFe/Au/Co spin-valve structure as metal base, a 63% change in collector current is obtained at room temperature for a saturation field of 30 Oe. The corresponding in-plane magnetoresistance is only 1%

Intrinsic vasomotricity and adrenergic effects in a model of isolated rabbit eye

Título da Revista: Acta Ophthalmologica ScandinavicaPurpose: We aimed to investigate the responsiveness of the ocular arteries to adrenergic drugs in a model of perfused isolated rabbit eye. Methods: Rabbit external ophthalmic arteries (n = 15) in a head-mounted preparation were cannulated and the retinal and uveal vasculature perfused at a constant flow with warmed tyrode. The three-way polypropylene catheter was further connected to a pressure transducer and intraluminal pressure was taken as a measure of vascular resistance. Effects of intra-arterial injections of phenylephrine (group A, n = 5), prazosin (group B, n = 5) and phentolamine (group C, n = 5) on the recorded pressure were obtained. Student’s paired-t test and one-way analysis of variance were used for statistical analysis (p < 0.05). Results: Intrinsic vasomotricity was observed in all preparations prior to any drug administration. Phenylephrine produced an increase in total vascular resistance. Intrinsic vasomotricity became more evident, showing a lower frequency but higher amplitude of oscillations. Evoked vasomotor responses with phenylephrine (250 lg ⁄ ml) were inhibited by intra-arterial administration of the selective a1-adrenergic antagonist, prazosin (0.5 mg⁄ ml), as well as the non-selective a-adrenergic antagonist phentolamine (6 mg⁄ ml). Conclusions: Rabbit external ophthalmic arteries showed spontaneous contractions under constant perfusion. Phenylephrine elicited a vasoconstrictor response that was inhibited by adrenergic antagonists. In addition, the intrinsic vasomotricity was enhanced by phenylephrine and blocked by adrenergic antagonists. These results show that under in vitro perfusion the territory presents similar responses to adrenergic drugs to those observed in in vivo models and also provides evidence of myogenic autoregulatory properties in the rabbit ophthalmic artery and ⁄ or choroidCIISA (Centro de Investigação Interdisciplinar em Sanidade Animal