Dolores Prieto

EFFECTS OF TYROSINE KINASE INHIBITORS ON THE CONTRACTILITY OF RAT MESENTERIC RESISTANCE ARTERIES

1 A pharmacological characterization of tyrosine kinase inhibitors (TKI) belonging to two distinct groups (competitors at the ATP‐binding site and the substrate‐binding site, respectively) was performed, based on their effects on the contractility of rat mesenteric arteries.

Role of the endothelium in acetylcholine-induced relaxation and spontaneous tone of bovine isolated retinal small arteries

Acetylcholine induced a variable concentration-dependent relaxation of bovine isolated retinal small arteries contracted with PGF2 alpha. The acetylcholine-mediated relaxation was linearly related to the sodium nitroprusside-induced relaxation, suggesting that the endothelium is well preserved in the vessels and that the variable effect of acetylcholine is due to variations in the soluble guanylate-cyclase enzyme activity in the smooth muscle. The vessels became desensitized to acetylcholine by repeated exposures. L-arginine and indomethacin did not abolish the desensitization. The vessels also became desensitized to the direct smooth muscle relaxing effect of sodium nitroprusside, indicating that desensitization to the endothelium-dependent relaxation by acetylcholine is related primarily to the vascular smooth muscle cells. Atropine, methylene blue and removal of endothelium abolished the acetylcholine-induced relaxation completely, whereas indomethacin had no inhibitory action on the acetylcholine-induced relaxation, suggesting that acetylcholine mediates release of EDRF (nitric oxide: NO) through stimulation of muscarinic receptors. Methylene blue contracted endothelium intact retinal arteries but a spontaneous tone was not present in endothelial denuded arteries. This may indicate a basal release of both a contractile factor, e.g. endothelin, and a relaxing factor. NO, form the retinal endothelium. The results demonstrate that endothelial-derived factors may participate in normal as well as pathophysiological regulation of retinal vascular smooth muscle tone.

Heterogeneous involvement of endothelium in calcitonin gene-related peptide-induced relaxation in coronary arteries from rat

1 The effects of rat‐ and human‐CGRP and capsaicin were studied in isolated rings of rat proximal epicardial (PC) and distal intramyocardial (DC) coronary arteries. 2 The relaxing effect of rat‐CGRP was dependent on the level of vessel tone induced by prostaglandin F2α (PGF2α) in PC but not in DC arteries. Submaximally contracted DC and PC arteries were more sensitive to rat‐ than human‐CGRP. There was no difference in sensitivity to rat‐ and human‐CGRP between PC and DC arteries. 3 Substance P elicited a small relaxation only in 4 of the 6 PC arteries tested. PC and DC arteries were concentration‐dependently relaxed by capsaicin. The relaxation was partly inhibited by ruthenium red, thus suggesting that capsaicin causes specific release of CGRP from sensory nerve endings in rat coronary arteries. 4 The relaxant effect of rat‐CGRP was antagonized by endothelium removal and indomethacin but not methylene blue in endothelium‐intact PC arteries. The relaxation in DC arteries was not affected by any of these treatments, indicating a heterogeneous involvement of the endothelium in CGRP‐mediated coronary vasodilatation and the release of a cyclo‐oxygenase product in PC arteries in rats. 5 Glibenclamide had no inhibitory effect on the CGRP‐induced relaxation of PC and DC arteries, thus excluding the involvement of glibenclamide‐sensitive K+‐channels in the mechanism of action of CGRP in rat coronary arteries.

Regional heterogeneity in the contractile and potentiating effects of neuropeptide Y in rat isolated coronary arteries: modulatory action of the endothelium

1 Neuropeptide Y (NPY) induced a concentration‐dependent contraction of isolated rings of proximal epicardial (PC) and distal intramural (DC) coronary arteries of the rat, with an EC50 of ca. 1 × 10−7 m. The NPY‐induced contraction at 3 × 10−7 m was significantly smaller in PC than DC arteries: 34% vs. 55% of the 125 mm K+‐induced response, respectively. 2 NPY (2 × 10−8 m) increased the sensitivity to noradrenaline (NA) and 5‐hydroxytryptamine (5‐HT) more in PC (4.2 and 2.8 fold, respectively) than in DC arteries (2.2 and 1.4 fold, respectively). The maximal contractile response to NA and 5‐HT was increased more in DC (43% and 29%, respectively) than in PC arteries (20% and 12%, respectively). 3 Removal of the endothelium increased the sensitivity and maximal response to NPY as well as the spontaneous myogenic tone in PC but not in DC arteries. NPY had no relaxing effect on PC and DC arteries submaximally contracted with 10−6 m prostaglandin F2α, suggesting that spontaneous rather than stimulated release of endothelium‐derived relaxing factor (EDRF) depresses the contractile action of NPY in PC arteries. 4 The results indicate a heterogeneity in the contractile and potentiating action of NPY in rat coronary arteries depending on size or location in the coronary circulation.

Calcitonin gene-related peptide is a potent vasodilator of bovine retinal arteries in vitro.

Calcitonin gene-related peptide (CGRP) invariably induced a slow acting but potent relaxation of bovine retinal small arteries contracted with PGF2 alpha. Maximal relaxation obtained was 93% and 96% with a pD2-value of 8.97 and 8.86 for rat and human CGRP, respectively; thus the bovine retinal arteries cannot discriminate between CGRP from these two species. The CGRP-induced relaxation was reversible. Substance P was without effect on retinal arteries contracted with PGF2 alpha. Bradykinin relaxed 4 of 18 vessels tested in the concentration range of 11(-11)-10(-8) M whereas the vessels were contracted again at 3 x 10(-8) M. Bradykinin was without effect in the remaining 14 vessels. None of the peptides had a contractile effect on retinal arteries kept relaxed in normal buffer solution. Capsaicin 3 x 10(-5) M induced a relaxation comparable to that obtained by 10(-9) M of CGRP. The capsaicin-induced relaxation was reproducible and it was concentration dependently inhibited by ruthenium red which suggests that capsaicin releases CGRP in the arterial wall. The results indicate that CGRP has a powerful relaxing effect on the retinal vasculature indicating a role for CGRP in ocular blood flow regulation.

Effect of induced hypercholesterolemia in rabbits on functional responses of isolated large proximal and small distal coronary arteries.

We studied the effects of hypercholesterolemia on the vascular responses of proximal and distal parts of the rabbit coronary circulation in two consecutive studies. For 12 weeks, New Zealand White rabbits were fed a control diet or a diet with 1% cholesterol dissolved in either 3% coconut oil (study A) or ether (study B). Isolated proximal epicardial and distal intramyocardial coronary arteries from control and hypercholesterolemic rabbits were mounted for isometric tension recording in a double myograph. In study A for hypercholesterolemic rabbits (n = 12), the maximal relaxation and sensitivity to acetylcholine (ACh) were significantly decreased in proximal coronary segments contracted with 30 mmol/l potassium solution compared with segments from control rabbits (n = 13). The only change observed in distal coronary segments was a slight decrease in relaxation in response to low ACh concentrations (10(-8) and 3 x 10(-8) mol/l). However, in study B for proximal coronary and distal coronary segments from hypercholesterolemic rabbits (n = 13), the area under the ACh relaxation curve was increased compared with that of control rabbits (n = 12). Other parameters that were similarly affected in studies A and B include the following: 1) proximal coronary segments from hypercholesterolemic rabbits were more sensitive to sodium nitroprusside (SNP) than were those from control rabbits, but this was not true for distal coronary segments; 2) endothelial removal from arterial segments of control rabbits induced a significant increase in sensitivity and maximal relaxation to SNP of proximal coronary and distal coronary arteries; 3) in segments from hypercholesterolemic rabbits, the absence of endothelium did not alter the response of proximal coronary segments to SNP but did augment the relaxation of distal coronary segments to SNP; 4) the maximal response to 5-hydroxytryptamine in proximal coronary arteries from hypercholesterolemic rabbits was increased compared with those from control rabbits, whereas such changes were not observed in distal coronary arteries; and 5) histological examination showed the presence of atheromatous plaques in proximal coronary but not in distal coronary segments from treated animals. In conclusion, the present investigation demonstrates that induced hypercholesterolemia alters both the structure and function of proximal parts of the coronary circulation. In distal coronary arteries of hypercholesterolemic rabbits, the only change observed was an impaired endothelium-dependent cholinergic relaxation, but even this change appeared to be dependent on the manner in which cholesterol was added to the diet, although parallel studies are required to confirm this.

(+)-S-12967 and (–)-S-12968: 1,4-dihydropyridine stereoisomers with calcium channel agonistic and antagonistic properties in rat resistance arteries

1 The actions of (+)‐S‐12967 and (–)‐S‐12968 two isomers of a new 1,4‐dihydropyridine (DHP) derivative, were studied on 125 mm K+‐, Ca2+‐ and noradrenaline‐induced contractions in rat isolated mesenteric resistance arteries and compared to those of nifedipine. 2 The action of (+)‐S‐12967 and (–)‐S‐12968 was slow in onset in contrast to nifedipine. Both isomers had a dual contractile and relaxant action in arteries contracted with 125 mm K+; however, the (–)‐isomer was about 300 times more potent than the (+)‐isomer. The response to 125 mm K+, being depressed by 70%, recovered within 20 to 30 min for all DHP derivatives. All vessels were treated with 1 × 10−6 m phenoxybenzamine thus excluding the possibility that the contraction is mediated by activation of amine‐receptors. 3 Both (+)‐S‐12967 and (–)‐S‐12968 at low concentrations potentiated responses induced by Ca2+ in arteries activated by 125 mm K+ and inhibited the responses at higher concentrations. (+)‐S‐12967 and (–)‐S‐12968 had no contractile action in arteries kept in normal buffer. Nifedipine had only an inhibitory action on vessel responses to 125 mm K+ and Ca2+. 4 Both isomers and nifedipine depressed the maximal vessel response to noradrenaline by about 20% and 44%, respectively. 5 The results confirm that DHP calcium antagonists selectively inhibit vascular smooth muscle responses induced by high potassium and that the potency of 1,4‐DHP isomers may vary considerably. Furthermore, since the agonistic/antagonistic properties on the calcium channel were shared by both stereoisomers of the 1,4‐DHP molecule and apparently dependent on their concentration and the vascular smooth muscle membrane potential, it suggests that the agonistic action of 1,4‐DHPs may be ascribed to functional characteristics of their binding site regulating the Ca2+‐channel.

Effects of doxazosin on functional alterations of isolated coronary arteries from cholesterol-fed rabbits

Anti‐hypertensive treatment is much less successful at reducing coronary artery disease than at reducing mortality from stroke and congestive heart failure. The effects of the α‐adrenergic antagonist doxazosin on progression of atheromatous lesions and functional responses of isolated coronary arteries from cholesterol‐fed rabbits have been investigated.

Effects of (+)-S-12967 and (-)-S-12968, two enantiomers of a new slow-acting 1,4-dihydropyridine, on rat coronary resistance arteries

The action of (+)-S-12967 and (-)-S-12968, two isomers of a new 1,4-dihydropyridine molecule (2-(-7-amino-2,5-dioxaheptyl)-3-ethoxycarbonyl-4-(2,3-dichlorop hen yl)-5-methoxycarbonyl-6-methyl 1,4-dihydropyridine), was studied on responses of rat isolated coronary resistance arteries (i.d. about 230 microns) to K+, Ca2+, and 5-hydroxytryptamine (5-HT). Both isomers slowly relaxed coronary arteries contracted with 125 mM K+, reaching a maximal effect in about 2 h. In contrast, the maximal relaxing effect of nifedipine was obtained within 20 min. The response to 125 mM K+ did not recover within the 2-h washout period in vessels exposed to the isomers but returned to pre-drug levels within 40 min in vessels exposed to nifedipine. Nifedipine was 4 times more potent than the (-)-isomer which again was about 200 times more potent that the (+)-isomer. The IC50[M] values were approximately 1 nM, 4 nM and 0.8 microM, respectively. The relaxing effect of the isomers, which has a pKa of 8.6, was dependent on the extracellular pH being greater at high than low pH. Both isomers antagonized the vessel responses to K+ and Ca2+ and 5-HT. Higher concentrations of the isomers were required to antagonize responses to K+ and 5-HT than to Ca2+, probably due to the more depolarized state of the vascular smooth muscle in the latter experiments. In conclusion, the results demonstrate extracellular pH dependence as well as stereoselectivity regarding potency of (+)-S-12967 and (-)-S-12968 in rat coronary arteries.(ABSTRACT TRUNCATED AT 250 WORDS)