Experimental diabetes induces hyperreactivity of rabbit renal artery to 5-hydroxytryptamine

The influence of diabetes on the response of isolated rabbit renal arteries to 5-hydroxytryptamine (5-HT) was examined. 5-HT induced a concentration-related contraction that was higher in arteries from diabetic rabbits than in arteries from control rabbits. Endothelium removal did not significantly modify 5-HT contractions in arteries from control rabbits but enhanced the response to 5-HT in arteries from diabetic rabbits. Incubation with N(G)-nitro-L-arginine (L-NA) enhanced contractions to 5-HT in arteries from control and diabetic rabbits. In arteries with endothelium, this L-NA enhancement was lower in diabetic rabbits than in control rabbits. In arteries without endothelium, incubation with L-NA enhanced the maximal contractions to 5-HT in control rabbits but did not in diabetic rabbits. Indomethacin inhibited 5-HT-induced contraction of arteries from control rabbits and enhanced the maximal contraction to 5-HT of arteries from diabetic rabbits. In summary, diabetes enhances contractile response of rabbit renal artery to 5-HT. In control animals, this response is regulated by both endothelial and non-endothelial (neuronal) nitric oxide (NO) and by a vasoconstrictor prostanoid. Diabetes impairs the release of non-endothelial NO and the vasoconstrictor prostanoid.     

Mechanisms underlying diabetes enhancement of endothelin-1-induced contraction in rabbit basilar artery

The influence of alloxan-induced diabetes on the reactivity of rabbit basilar artery to endothelin-1 was examined. Endothelin-1 induced concentration-dependent contraction of basilar arteries that was higher in diabetic than in control rabbits. Endothelium removal produced a higher enhancement of the endothelin-1-induced contraction in control than in diabetic rabbits. N(G)-nitro-L-arginine (L-NOArg) enhanced the maximal contraction induced by endothelin-1 in control rabbits and potentiated this response in diabetic rabbits. Endothelin ETA receptor antagonist, cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ-123), inhibited endothelin-1-induced contraction in both rabbit groups. Endothelin ETB receptor antagonist, 2,6-Dimethylpiperidinecarbonyl-gamma-Methyl-Leu-Nin-(Methoxycarbonyl)-D-Trp-D-Nle (BQ-788), enhanced endothelin-1-induced contraction in control rabbits and decreased the potency of endothelin-1 in diabetic rabbits. Sodium nitroprusside-induced relaxation of basilar arteries was lower in diabetic than in control rabbits. These results suggest that mechanisms underlying rabbit basilar artery hyperreactivity to endothelin-1 include decreased endothelial modulation of endothelin-1-induced contraction, with impaired endothelial endothelin ETB receptor activity; decreased sensitivity to nitric oxide (NO) in vascular smooth muscle; and enhanced participation of muscular endothelin ETA and ETB receptors.     

Contribution of endothelin receptors and cyclooxygenase-derivatives to the altered response of the rabbit renal artery to endothelin-1 in diabetes

The influence of diabetes on regulatory mechanisms and specific receptors implicated in the response of isolated rabbit renal artery to endothelin-1 was examined. Endothelin-1 induced a concentration-dependent contraction that was less potent in arteries from diabetic rabbits than in arteries from control rabbits. Endothelium removal or N(G)-nitro-L-arginine (L-NOARG) enhanced contractions to endothelin-1 either in control and diabetic arteries. Indomethacin inhibited endothelin-1-induced response in control arteries, but enhanced it in diabetic arteries. In contrast to that observed in rubbed and in L-NOARG treated arteries, in the presence of indomethacin the contractile action of endothelin-1 was higher in diabetic arteries than in control arteries. Nimesulide enhanced endothelin-1 contractions both in control and diabetic arteries. Cyclo-(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ-123, endothelin ET(A) receptor antagonist), attenuated endothelin-1 vasoconstriction in control rabbits, while vasoconstriction resulted increased in diabetic rabbits. 2,6-Dimethylpiperidinecarbonyl-gamma-Methyl-Leu-N(in)-(Methoxycarbonyl)-D-Trp-D-Nle (BQ-788, endothelin ET(B) receptor antagonist), enhanced the contractile response in control rabbit arteries without modifying this response in diabetic rabbits. In summary, diabetes decreases the sensitivity of the rabbit renal artery to endothelin-1 by decreasing the ratio between vasoconstrictor and vasodilator prostanoids released after activation of endothelin ET(A) receptors.     

Different role of endothelin ETA and ETB receptors and endothelial modulators in diabetes-induced hyperreactivity of the rabbit carotid artery to endothelin-1

The influence of diabetes on regulatory mechanisms and specific receptors implicated in the contractile response of isolated rabbit carotid arteries to endothelin-1 was examined. Endothelin-1 induced a concentration-dependent contraction that was greater in arteries from diabetic rabbits than in arteries from control rabbits. Endothelium removal or N(G)-nitro-L-arginine enhanced contractions in response to endothelin-1 only in control arteries, without modifying the endothelin-1 response in diabetic arteries. Indomethacin, furegrelate (thromboxane A(2) inhibitor), or cyclo-(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ-123; endothelin ET(A) receptor antagonist) inhibited the contractions in response to endothelin-1, the inhibition being greater in diabetic arteries than in control arteries. 2,6-Dimethylpiperidinecarbonyl-gamma-methyl-Leu-N(in)-(methoxycarbonyl)-D-Trp-D-Nle (BQ-788; endothelin ET(B) receptor antagonist) enhanced the contraction elicited by endothelin-1 in control arteries and displaced to the right the contractile curve for endothelin-1 in diabetic arteries. In summary, diabetes induces hyperreactivity of the rabbit carotid artery to endothelin-1 by a mechanism that at least includes: (1) enhanced activity of muscular endothelin ET(A) receptors; (2) impairment of endothelin ET(B) receptor-mediated nitric oxide (NO) release; and (3) enhancement of the production of thromboxane A(2).     

Critical role of endothelial nitric oxide synthase and cyclooxygenase in response of rabbit basilar artery to serotonin

The modes of action of serotonin (5-HT) on the tone of the rabbit basilar artery were investigated in vitro with the aim of determining the exact role of the endothelium. After sacrificing the animal under pentobarbital anesthesia, 3-mm segments of the artery were removed and mounted in a 5-ml myograph for isometric tension recording. Vessels precontracted by histamine were relaxed by acetylcholine. Mean maximum relaxation at 10(-4) M was reduced from 79% to 22% (P < 0.001) by 10(-5) M N-nitro-L-arginine (L-NA), and from 73% to 63% (NS) by 3.12(-6) M indomethacin. Intact non-precontracted vessels were contracted by 5-HT (10(-9) M to 10(-5) M): 10(-5) M L-NA significantly increased the contractile force (approximately twofold), whereas 3.10(-6) M indomethacin significantly decreased it (to approximately 35%). In histamine-precontracted vessels, 5-HT induced at low concentrations (3.10(-9) M to 3.10(-8) M) a reduction in tone and induced an increase in tone at higher concentrations. At 10(-5) M, L-NA abolished the relaxant phase of the response, whereas 3.10(-6) M indomethacin potentiated it. In uridine triphosphate-precontracted segments, there was not a net reduction in tone under 5-HT at 3.10(-9) to 3.10(-8) M, but further contraction appeared at higher concentrations. The presence of 10(-5) M L-NA significantly increased the contraction to 5-HT, but 3.10(-6) M indomethacin did not significantly reduce it. Endothelial lesion reduced by about 50% the contractile response of L-NA-treated arteries to 5-HT; and conversely, endothelial lesion increased approximately twofold the contraction of indomethacin-treated arteries to 5-HT. We conclude that 5-HT causes the release from the endothelium of two vasoactive factors, one of which is probably the vasodilator nitric oxide, but the size of the relaxation may depend on the prevailing level of nitric oxide synthase activation. The second factor is a cyclooxygenase-dependent contractile agent. However, the contraction to 5-HT was not modified by the presence of the thromboxane synthase inhibitor CGS 13080 (10(-4) M), suggesting that thromboxane A2 is not the main contractile agent released.     

Diabetes potentiates acetylcholine-induced relaxation in rabbit renal arteries

The response of rabbit renal arteries to acetylcholine and its endothelial modulation in diabetes were investigated. Acetylcholine induced concentration-related endothelium-dependent relaxation of renal arteries that was significantly more potent in diabetic rabbits than in control rabbits. Pretreatment with N(G)-nitro-L-arginine (L-NOArg), indomethacin, or L-NOArg plus indomethacin induced partial inhibition of acetylcholine-induced relaxation. Inhibition induced by L-NOArg plus indomethacin was significantly higher in arteries from diabetic rabbits than in arteries from control rabbits. In renal arteries depolarised with KCl 30 mM and incubated with L-NOArg plus indomethacin, acetylcholine-induced relaxation was almost abolished in both groups of rabbits and this response was not different from that obtained in arteries without endothelium. Sodium nitroprusside induced concentration-dependent relaxation of renal arteries from control and diabetic rabbits without significant differences between the two groups of animals. These results suggest that diabetes potentiates the acetylcholine-induced relaxation in rabbit renal arteries. Increased release of nitric oxide and prostacyclin could be responsible for the enhanced relaxant potency of acetylcholine in diabetes.     

Mechanisms underlying the diabetes-induced hyporeactivity of the rabbit carotid artery to atrial natriuretic peptide

Atrial natriuretic peptide (ANP) plays an important role in the pathophysiology of the vascular complications in diabetes. The working hypothesis was that diabetes might modify the vascular actions of ANP in isolated rabbit carotid arteries and the mechanisms involved in these actions. ANP (10^?12–10^?7 M) induced a relaxation of precontracted carotid arteries, which was lower in diabetic than in control rabbits. In arteries from both groups of animals, endothelium removal increased the ANP-induced relaxation. Isatin inhibited the relaxation to ANP both in arteries with and without endothelium. Carotid arteries from diabetic rabbits showed a decreased natriuretic peptide receptor (NPR)-A expression and an enhanced NPR-C expression. Inhibition of NO-synthesis did not modify ANP-induced relaxation in control rabbits but inhibited it in diabetic rabbits. In arteries with endothelium indomethacin enhanced the relaxation to ANP in control rabbits but did not modify it in diabetic rabbits. In endothelium-denuded arteries indomethacin inhibited the relaxation to ANP in both groups of animals. In KCl-depolarised arteries, relaxation to ANP was almost abolished both in control and diabetic rabbits. Tetraethylammonium inhibited the relaxation to ANP, and this inhibition was higher in diabetic than in control rabbits. These results suggest that diabetes produces hyporeactivity of the rabbit carotid artery to ANP by a mechanism that at least includes a reduced expression of NPR-A, an enhanced expression of NPR-C and a reduced participation of K⁺-channels. Furthermore, diabetes enhances endothelial NO release and diminishes the ratio thromboxane A₂/prostacyclin. This increase of vasodilators could result from compensatory mechanisms counteracting the arterial hyporeactivity to ANP.     

L-硝基精氨酸对神经刺激所致大鼠肠系膜动脉反应的影响

目的观察大鼠肠系膜动脉对神经刺激引起的反应及其与NO的关系。方法：采用离体去除内皮血管实验方法，测定肠系膜动脉条的等容张力变化。结果：电刺激和化学（烟碱）刺激明显引起大鼠肠系膜动脉收缩，L－硝基精氨酸（L－NA，NO合成抑制剂）明显增强上述收缩反应，此增强作用可被L一精氨酸（NO供体）取消。L－NA对刺激交感神经末梢去甲肾上腺素的释放及对去甲肾上腺素的血管收缩作用均无明显影响。动脉条用哌唑嗪处理并用PGF(2a)部分收缩后，电刺激和烟碱均可引起血管舒张，此舒张效应可被L－NA抑制，该抑制作用又可为L-精氨酸逆转。结论：电刺激和化学（烟碱）刺激引起的动脉舒张效应为NO所致，并提示在大鼠肠系股动脉可能有与NO有关的血管扩张神经存在。     

Analysis of the depressant effect of the endothelium on contractions of rabbit isolated basilar artery to 5-hydroxytryptamine.

1. The effects of endothelium removal and of a number of pharmacological agents known to modify endothelial cell function on the contractile response of rabbit isolated basilar arteries to 5-hydroxytryptamine (5-HT) and other vasoconstrictors were studied. 2. Endothelium removal slightly reduced the contractile response to potassium chloride (40 mM) but markedly augmented and potentiated contractions to 5-HT (1 nM-10 microM). 3. L-NG-nitro-arginine (L-NOARG, 1-30 microM), an inhibitor of nitric oxide formation in vascular endothelial cells, evoked endothelium-dependent contraction, and augmented and potentiated contractions to 5-HT in endothelium-intact but not endothelium-denuded tissues. Prior incubation with L-arginine (1 mM), but not D-arginine (1 mM), abolished these effects of L-NOARG (1 microM). L-NOARG (30 microM) also augmented contractions of endothelium-intact tissues to noradrenaline, prostaglandin F2 alpha, and to a lesser degree endothelin-1. 4. Neither glibenclamide (3 microM) nor N-ethylmaleimide (1 microM), putative inhibitors of the effects of endothelium-derived hyperpolarizing factor (EDHF) and of agonist-stimulated endothelium-derived relaxing factor (EDRF) release respectively, had any effect on either resting tension or the contractile response to 5-HT. In some tissues indomethacin (3 microM), a cyclo-oxygenase inhibitor, produced a small contraction and augmented the contractile response to 5-HT, but in most cases indomethacin was without effect. 5. In endothelium-intact tissues precontracted with uridine 5'-triphosphate (UTP; 100 microM), 5-HT did not evoke relaxation but rather caused further contraction. Under the same conditions acetylcholine (0.01-10 microM) evoked endothelium-dependent relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)     

A contrasting effect of the diabetic state upon the contractile responses of aortic preparations from the rat and rabbit.

Diabetes was induced in rats by a single intraperitoneal injection of streptozotocin (65 mg kg-1). Rabbits were rendered diabetic by injecting alloxan (100 mg kg-1) into the lateral ear vein. Diabetes was confirmed by a significant elevation of serum glucose in both species 8 weeks after injection. The maximum contraction to noradrenaline (NA), 5-hydroxytryptamine (5-HT) and KCl was markedly diminished in thoracic aortic rings (AR) from diabetic rats with no change in the EC50 of the agonists. There were no differences in the contractile properties of AR from diabetic rabbits to NA, 5-HT or KCl. Diabetes did not alter the responsiveness of AR from the rat to angiotensin II (AII). However, AR from diabetic rabbits displayed a decreased maximal contraction and an increased EC50 to AII. The magnitude of the acetylcholine-induced relaxation to precontracted AR was not different between diabetic and control rats and rabbits. The contractile responses of AR to NA, 5-HT and KCl were depressed in diabetic rats, regardless of the control tissue to which they were compared. The decrease in maximal contraction to NA, 5-HT and KCl seen in diabetic animals was prevented by insulin replacement. The results demonstrated that while both rats and rabbits exhibited a similar degree of hyperglycemia after treatment with a diabetogenic agent, aortic preparations from the rabbit are not affected in the same way as the aorta from the diabetic rat when exposed to NA, 5-HT and KCl. This feature may be related to the marked differences between the extent of sympathetic innervation of the aorta in the rabbit and rat. Furthermore, the decrease in maximal contraction in rat aorta was non-specific with respect to agonists since it could also be demonstrated with KCl. Therefore, it follows that the diabetic state may affect processes responsible for contraction beyond the level of receptor activation.     

Endothelium-dependent relaxation in isolated renal arteries of diabetic rabbits

1 In this study, we have investigated the vasodilator response to acetylcholine under diabetes conditions in isolated renal arteries of rabbits. We have also examined the contribution of endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) to the endothelium-dependent relaxation caused by acetylcholine in the renal arteries of alloxan-induced diabetic rabbits. 2 Acetylcholine (10(-10) - 10(-4) M) produced cumulative concentration-response curve in the renal arteries of both control and diabetic rabbits. The EC50 values and maximal responses to acetylcholine were not significantly different relative to diabetic conditions. In order to isolate the EDHF component of acetylcholine-induced vasodilator response, L-nitro-methyl arginine ester (L-NAME, 10(-4) M) and indomethacin (10(-6) M) were added to the Krebs' solution throughout the experiment. Under these conditions, acetylcholine induced vasodilatation in the isolated renal arteries from both control and diabetic rabbits. The vasodilator response to acetylcholine was not affected under diabetic conditions. 3 Sodium nitroprusside (SNP)-induced relaxation was increased in the diabetic rabbits compared with the control animals. 4 Tetrabutyl ammonium (TBA, 0.5 mM) produced a significant reduction in acetylcholine-induced vasodilatation in both preparations from control and diabetic animals, consistent with involvement of K+ channels in mediating this response. Glibenclamide (1 microM) attenuated acetylcholine-induced vasodilatation in preparations from control animals only, while iberiotoxin (0.05 microM) significantly reduced the vasodilator response to acetylcholine in preparations from both control and diabetic animals. 5 The role of EDNO in mediating acetylcholine-induced vasodilatation was examined. The vascular preparations were incubated with 20 mM K(+)-Krebs' solution to inhibit the EDHF contribution to acetylcholine-induced vasodilatation. Under this condition, acetylcholine induced a vasodilator response in both preparations from control and diabetic rats. Pretreatment with L-NAME (10(-4) M) attenuated acetylcholine-induced vasodilatation in both preparations, indicating an nitric oxide-mediated vasodilator response. 6 Our results indicated that acetylcholine-induced vasodilatation in the isolated renal arteries of alloxan-induced diabetic rabbits was not affected under diabetic conditions. Acetylcholine-induced vasodilatation is mediated by two vasodilator components; namely, EDHF and EDNO. The contribution of EDHF and EDNO to acetylcholine-induced vasodilatation was not affected under diabetic conditions and there was no indication of endothelial dysfunction associated with diabetes. EDHF component was found to act mainly through high conductance Ca(2+)-activated K+ channels under normal and diabetic conditions, while the adenosine triphosphate-dependent K+ channels were involved in mediating acetylcholine vasodilator response in the control preparations only.     

Role of endothelium in the response to prostaglandin H2 in isolated dog arteries

Prostaglandin (PG) H2 produced a transient contraction followed by a relaxation in helical strips of dog coronary, mesenteric and renal arteries contracted with PGF2 alpha. The contraction was in the order of mesenteric greater than renal greater than coronary artery. Removal of endothelium abolished the contraction in these arteries and significantly potentiated the relaxation only in mesenteric arteries. The relaxation was greater in mesenteric arteries than in renal and coronary arteries, denuded of endothelium. PGI2-induced relaxations were not influenced by endothelium denudation. In the arteries contracted with K+, PGH2-induced relaxations were attenuated, compared to those contracted with PGF2 alpha. Treatment with ONO3708, an antagonist of vasoconstrictor PGs, abolished the PGH2-induced contraction and potentiated the relaxation in the K+-contracted arteries. The relaxant response was suppressed by diphloretin phosphate, a PG receptor antagonist, as was the response to PGI2. PGH2-induced contractions in dog coronary, mesenteric and renal arteries would be due to vasoconstrictor PGs produced preferentially in the endothelium. However, production of PGI2 from PGH2 in endothelial and subendothelial tissues do not appear to differ.     

Pharmacological characterization of postjunctional alpha-adrenoceptors in cerebral arteries from the sheep.

1. The responsiveness to noradrenaline was characterized in cerebral arteries from the sheep, since this species was large enough to permit a comparison of arteries from different parts of the cerebral vasculature. 2. Noradrenaline caused contraction of the basilar artery, middle cerebral artery and small pial arteries by stimulation of alpha 1-adrenoceptors. 3. The maximum contraction to noradrenaline was small in the basilar artery (28% of the 5-hydroxytryptamine (5-HT) maximum) but larger in the middle cerebral artery (78% of the 5-HT maximum) and pial artery (92% of the 5-HT maximum) of the sheep. 4. Cocaine (10 microM) potentiated noradrenaline-induced contractions in the sheep middle cerebral artery but not in the sheep basilar artery. 5. The noradrenaline contraction, relative to the 5-HT contraction, was not affected by removal of the endothelium in either the sheep basilar or middle cerebral artery. 6. The results showed a variation within the sheep cerebral vasculature in the response to noradrenaline which cannot be explained by regional differences in alpha-adrenoceptor subtypes, noradrenaline uptake mechanisms or endothelial function.     

Role of NO-synthases and cyclooxygenases in the hyperreactivity of male rabbit carotid artery to testosterone under experimental diabetes

Cardiovascular disease is the major cause of morbidity and mortality in diabetic patients, which in turn is also associated with low levels of serum testosterone. The working hypothesis was that diabetes might modify the mechanisms involved in the vascular actions of testosterone in isolated rabbit carotid arteries. Testosterone (10^?8–3 × 10^?4 M) induced a concentration-dependent relaxation of precontracted carotid arteries, which was higher in diabetic than in control rabbits. In control rabbits neither endothelium removal nor the nitric oxide synthase (NOS) inhibitor N^G-nitro-l-arginine (l-NOArg, 10^?5 M) modified the relaxant action of testosterone, and the cyclooxygenase (COX) inhibitor indomethacin (10^?5 M) enhanced this relaxation. In contrast, in diabetic rabbits endothelium removal, l-NOArg (10^?5 M) or indomethacin (10^?5 M) inhibited the testosterone induced relaxation. In arteries from diabetic rabbits, eNOS, iNOS and COX-2 expression and testosterone induced release of prostacyclin resulted enhanced in comparison with arteries from control rabbits. Testosterone (10^?4 M) strongly inhibited CaCl₂ (10^?5–3 × 10^?2 M) concentration-related contractions of the carotid artery both in control and diabetic rabbits. These results suggest that testosterone relaxes the rabbit carotid artery by blocking the extracellular calcium entry. Diabetes enhances the vasodilator response of the rabbit carotid artery to testosterone by a mechanism that at least includes an increased modulatory activity of the endothelial nitric oxide and an augmented release of COX-2 vasodilator, prostacyclin rather than the absence of COX-1 vasoconstrictor, thromboxane A₂. The hypotestosteronemia observed in diabetic rabbits could be a consequence of the increased expression of iNOS and could contribute to the hyperreactivity of the rabbit carotid artery to testosterone.     

The existence of a local 5-hydroxytryptaminergic system in peripheral arteries

BACKGROUND AND PURPOSE: 5-HT is a vasoconstrictor exhibiting enhanced effects in systemic arteries from subjects with cardiovascular disease. The effect of endogenous 5-HT on arteries is controversial, because the concentration of free circulating 5-HT is low and a 5-hydroxytryptaminergic system has not been identified in peripheral arteries. We hypothesized that a local 5-hydroxytryptaminergic system (including 5-HT synthesis, metabolism, uptake and release) with physiological function exists in peripheral arteries. EXPERIMENTAL APPROACH: The presence of key components of a 5-hydroxytryptaminergic system in rat aorta and superior mesenteric artery was examined using western blot analyses, immunohistochemistry and immunocytochemistry. The function of the rate-limiting enzyme in 5-HT biosynthesis, tryptophan hydroxylase (TPH), and 5-HT transporter was tested by measuring enzyme activity and 5-HT uptake, respectively. Isometric contraction of arterial strips was used to demonstrate the function of released endogenous 5-HT in arterial tissues. KEY RESULTS: mRNA for TPH-1 was present in arteries, with low levels of TPH protein and TPH activity. Expression and function of MAO A (5-HT metabolizing enzyme) was supported by immunohistochemistry, western analyses and the elevation of concentrations of 5-hydroxyindoleacetic acid (5-HT metabolite) after exposure to exogenous 5-HT. The 5-HT transporter was localized to the plasma membrane of freshly isolated aortic smooth muscle cells. Peripheral arteries actively took up 5-HT in a time-dependent and 5-HT transporter-dependent manner. The 5-HT transporter substrate, (+)-fenfluramine, released endogenous 5-HT from peripheral arteries, which potentiated noradrenaline-induced arterial contraction. CONCLUSIONS AND IMPLICATIONS: This study revealed the existence of a local 5-hydroxytryptaminergic system in peripheral arteries.     

Effects of soman on vascular contractility of rabbit arteries

The effects of soman (pinacolyl methylphosphonofluoridate), an organophosphorus cholinesterase inhibitor, on vascular contractility were examined on helically cut central ear arteries (CEA) or superior mesenteric arteries (M) from New Zealand White rabbits. Concentrations of soman up to 20 microM added cumulatively to arterial strips did not alter their resting tension. Concentrations of soman up to 10 microM also did not alter the tension responses to cumulatively added norepinephrine (NE), histamine, potassium (KCl), or serotonin (5-HT). Concentration-response curves obtained to each agonist initially, or 2 h later, did not differ in artery strips from control rabbits and those from rabbits given soman at 5 micrograms/kg sc daily for 7 d. Changes in responses to NE between the two time periods did differ in arteries from soman-treated and control rabbits in both the CEA and M, and to histamine in the M. Soman at 10 microM potentiated contractions to single concentrations of agonists in most cases. Soman at 10 microM also further increased the tension of strips already contracted by the agonists. Thus, although soman did not alter the concentration-response curves of the agonists at contracting rabbit arteries, it potentiated contractions to single concentrations of agonists both when added before the agonist and when added at the peak of the agonist-induced contraction. It also altered the rate of change with time of both M and CEA in responses to NE of artery strips from rabbits given soman at 5 micrograms/kg daily for 7 d.     

Mechanisms involved in the relaxant action of testosterone in the renal artery from male normoglycemic and diabetic rabbits

Kidney disease is a frequent complication in diabetes, and significant differences have been reported between male and female patients. Our working hypothesis was that diabetes might modify the vascular actions of testosterone in isolated rabbit renal arteries and the mechanisms involved in these actions. Testosterone (10^?8 to 10^?4 M) induced relaxation of precontracted arteries, without significant differences between control and diabetic rabbits. Both in control and diabetic rabbits endothelium removal inhibited testosterone relaxant action. In arteries with endothelium, incubation with indomethacin (10^?5 M), N^G-nitro-l-arginine (10^?5 M) or tetraethylammonium (10^?5 M) did not modify relaxations to testosterone neither in control nor in diabetic rabbits. In endothelium-denuded arteries indomethacin enhanced the relaxant action of testosterone, both in control and diabetic rabbits. In arteries from diabetic rabbits, eNOS, iNOS and COX-1 expression and testosterone-induced release of thromboxane A₂ and prostacyclin were not significantly different from those observed in control rabbits. However, COX-2 expression was significantly lower in diabetic rabbits that in control rabbits. In nominally Ca²⁺-free medium, cumulative addition of CaCl₂ (10^?5 to 3 × 10^?2 M) contracted previously depolarized arteries. Testosterone (10^?4 M) inhibited CaCl₂ contractions of the renal artery both in control and diabetic rabbits. These results show that testosterone relaxes the renal artery both in control and diabetic rabbits. This relaxation is modulated by muscular thromboxane A₂, it is partially mediated by endothelial prostacyclin, and it involves the blocking of extracellular Ca²⁺ entry. Diabetes does not modify the mechanisms involved in the relaxant action of testosterone in the rabbit renal artery.     

Comparison of endothelium-dependent relaxation in carotid arteries from Japanese white and Watanabe heritable hyperlipidemic rabbits

Modifications by atherosclerosis of endothelium-dependent and -independent relaxations were evaluated in carotid arteries isolated from Watanabe heritable hyperlipidemic (WHHL; age 20-29 months) and age-matched Japanese white (JW) rabbits. Marked, patchy atherosclerotic lesions were observed in all WHHL rabbit arteries. Endothelium-dependent relaxations induced by acetylcholine, partly depressed by N(G)-nitro-L-arginine (L-NA), were significantly inhibited in the WHHL rabbit arteries with atherosclerosis, compared with those in the arteries without atherosclerotic lesions from JW and WHHL rabbits. No difference was observed in the relaxation caused by superoxide dismutase in these arteries. Conversely, endothelium-dependent relaxations by substance P were greater in the arteries with and without atherosclerosis from WHHL rabbits than in the arteries from JW rabbits. Endothelium-independent relaxations elicited by sodium nitroprusside and 2,2-(hydroxynitrosohydrazino)bis-ethanamine (NOC18) did not differ in the arteries from JW and WHHL rabbits. The responses to acetylcholine and substance P of JW rabbit arteries with the endothelium were not attenuated by treatment with pertussis toxin. L-NA-resistant, endothelium-dependent relaxations by substance P were almost abolished by charybdotoxin, and atherosclerosis did not alter the response. It is concluded that endothelial functions, evaluated by substance P, in rabbit carotid arteries are not impaired by atherosclerosis and by long exposure to hyperlipidemia in vivo. Dysfunction of muscarinic receptors may be involved in the depressed response to acetylcholine. As far as the arteries used in the present study are concerned, responses mediated possibly by endothelium-derived hyperpolarizing factor (EDHF) are unlikely to be modulated by atherosclerosis.     

Eicosapentaenoic acid alters vascular reactivity and platelet adhesion in Watanabe heritable hyperlipidemic rabbits

Feeding a diet rich in eicosapentaenoic acid (EPA) to Watanabe heritable hyperlipidemic (WHHL) rabbits resulted in an attenuated aortic contractile response to the vasoconstrictor agent serotonin when compared to responses from WHHL rabbits fed normal rabbit chow. In contrast, only the maximal contractile response to norepinephrine was reduced in EPA-fed rabbit aortas. Additionally, methacholine-induced relaxations were potentiated in aortas obtained from the EPA-fed rabbits. When platelets obtained from EPA-fed rabbits were incubated with arachidonic acid, there was a reduced ability of the platelets to adhere to albumin-coated discs in comparison to control rabbit platelets. These data indicate a potentially beneficial effect of EPA in atherosclerotic WHHL rabbits.     

BLOCKADE BY PHENTOLAMINE OF THE POTENTIATION OF HISTAMINE-INDUCED VASOCONSTRICTION CAUSED BY SEROTONIN AND METHYSERGIDE IN THE RABBIT EAR ARTERY

1. In subconstrictor doses, both serotonin and methysergide potentiated the vasoconstrictor responses to histamine in the isolated artery of the rabbit ear. 2. In the presence of phentolamine (5 μg/ml) the potentiating actions of serotonin and methysergide were significantly reduced. 3. This blocking action of phentolamine could be overcome by increasing the concentration of serotonin or by washing the preparation. 4. In arteries taken from rabbits pretreated with reserpine, serotonin still potentiated the response to histamine and phentolamine still blocked this potentiation. 5. The concentration of phentolamine required to block potentiation also blocked the direct constrictor response to serotonin. It did, however, produce a significantly greater blockade of the vasoconstrictor response to noradrenaline. 6. The results indicate that the action of phentolamine in blocking the vascular potentiation produced by serotonin and methysergide is not due to a blockade of α-receptors.