Norepinephrine Sensitivity Research Articles

Effects of diabetes on reactivity of sciatic vasa nervorum in rats

The aim was to investigate the effects of 2 months of streptozotocin-induced diabetes mellitus in rats on the responses of sciatic vasa nervorum to vasoactive drugs. Changes in perineurial blood flow were monitored by laser-Doppler flowmetry during drug superfusion in vivo. Laser-Doppler flux was reduced by 53.3% after 2 months of diabetes. A 38-fold increase in norepinephrine sensitivity was found in diabetic compared to nondiabetic rats. Co-superfusion of norepinephrine and a high dose (100 μM) of the nitric oxide synthase inhibitor, N G-nitro-L-arginine, resulted in 116-fold and 3.6-fold increases in norepinephrine sensitivity in nondiabetic and diabetic rats, respectively, such that dose-response curves for changes in vascular conductance were superimposed. This suggests that the increased norepinephrine sensitivity in diabetes was caused by defective endothelial nitric oxide production or action. After norepinephrine preconstriction, acetylcholine caused dose-dependent increases in vascular conductance, sensitivity being 8.1-fold greater in nondiabetic than diabetic rats. In contrast, endothelium-independent responses to the nitrovasodilator, glyceryl trinitrate, were relatively unaffected by diabetes. Thus, diabetes causes a deficit in nitric oxide mediated endothelium-dependent relaxation of vasa nervorum, resulting in increased vasoconstrictor sensitivity which is likely to impair perfusion and contribute to the pathogenesis of neuropathy.

The influence of total porto-systemic shunting on the noradrenaline response and on the contractile effects of various vasoactive agents in small rat portal veins and hepatic arteries.

Contractile responses were studied in isolated tubal segments of branches of the rat portal vein (diameter 300 microns) and hepatic artery (diameter 200 microns) 1, 3 and 6 weeks after total porto-systemic shunt operation (PCS). 5-Hydroxytryptamine contracted hepatic arteries concentration-dependently, whereas it produced only weak and inconsistent contractions in portal veins. Vasopressin effectively contracted hepatic arteries, but had no effect on portal veins. Both vessel types responded to prostaglandin F2 alpha with contractions, although the drug potency was relatively low. The responses to these agents were not changed significantly in hepatic arteries or portal veins of PCS rats compared with controls at any of the postoperative time intervals. In both portal veins and hepatic arteries noradrenaline produced contraction-dependent contractions, portal veins being 3 times more sensitive to noradrenaline than hepatic arteries. PCS did not change the nor-adrenaline sensitivity in hepatic arteries, whereas it increased the noradrenaline sensitivity in portal veins after 1, but not after 3 or 6 weeks. This effect was enhanced by cocaine, suggesting a partial sympathetic denervation of branches of the portal vein as well as a complete reinnervation within 3 weeks. Furthermore, the results of this study indicate no influence in any vessel type on the response to several vasoactive agents after depriving the liver of splanchnic venous blood.

Chronic renal neuroadrenergic hypertension is associated with increased renal norepinephrine sensitivity and volume contraction.

Individuals with essential hypertension have been characterized by increased renal sympathetic vascular tone with decreased plasma volume and normal cardiac output compared with normotensive individuals. We used a servo-controlled intrarenal infusion system to evaluate the hemodynamic, renal excretory, and plasma hormonal responses to 28-day, low-level elevations in the intrarenal adrenergic neurotransmitter norepinephrine. In uninephrectomized dogs (n = 6), servo-controlled norepinephrine infusion increased mean arterial pressure from 95.6 +/- 3.1 to 115.7 +/- 4.9 mm Hg on day 1 without concomitant reductions in renal blood flow. Arterial hypertension was sustained and renal vascular resistance increased during the 28 days of servo-controlled norepinephrine infusion despite significant decreases in the daily dose of intrarenal norepinephrine (1.49 +/- 0.23 to 0.47 +/- 0.25 mg/d) necessary to maintain renal blood flow constant. Arterial pressure returned to control values with the cessation of servo-controlled norepinephrine, whereas renal blood flow and renal vascular resistance remained slightly decreased and increased, respectively. Cumulative sodium balance exhibited a net 177 +/- 37 mmol sodium loss over the 28 days of norepinephrine infusion, indicating that the hypertension did not result from sodium retention or expansion of extracellular fluid volume. Intrarenal norepinephrine did not change plasma epinephrine, norepinephrine, or vasopressin concentrations. Atrial natriuretic factor, however, increased at 7 and 14 days of servo-controlled norepinephrine, and plasma renin activity increased on day 14 of norepinephrine infusion. We conclude that low-level elevation of intrarenal adrenergic neurotransmitter produces sustained arterial hypertension that is independent of expansion in extracellular fluid volume, increases in circulating catecholamines or plasma renin activity, or reductions in renal blood flow. This hypertension may be associated with increased renal vascular sensitivity to norepinephrine and/or other renal vasoactive factors.

Effects of hypertension on hypercholesterolemia-induced changes in contraction of rabbit aorta and carotid artery

Reactivity of aortic and carotid strips from control; hypertensive; hypercholesterolemic; and hypertensive/hypercholesterolemic rabbits was studied. Maximal stress was less in strips from hypertensive/hypercholesterolemic animals. Norepinephrine sensitivity was increased in the carotid artery from hypertensive/hypercholesterolemic animals (EC 50: 0.11 μM; 0.35 μM control). CaCl 2 sensitivity during norepinephrine-induced contractions was enhanced by hypertension and hypercholesterolemia (carotid EC 50: 0.10 mM; 0.38 mM control; aorta EC 50: 0.12 mM; 0.82 mM control) Similar results were obtained during membrane depolarization. 5-hydroxytryptamine sensitivity (EC 50: 0.15μM carotid; 0.18 μM aorta) was decreased during hypertension (EC 50: 0.51 μM carotid; 1.13 μM aorta) and by hypercholesterolemia (EC 50: 1.76 μM carotid; 1.53 μM aorta). Our results support the hypothesis that hypertension and hypercholesterolemia increase vascular sensitivity by increasing Ca 2+ permeability. Our results also suggest that hypertension and hypercholesterolemia selectively decrease 5-hydroxytryptamine-induced contractions.

Comparison of guinea‐pig, bovine and rat α1‐adrenoceptor subtypes

1. To elucidate a possible role of species differences in the classification of alpha 1-adrenoceptor subtypes, we have characterized the alpha 1-adrenoceptors in guinea-pig spleen, kidney and cerebral cortex and in bovine cerebral cortex using concentration-dependent alkylation by chloroethylclonidine and competitive binding with 5-methlurapidil, methoxamine, (+)-niguldipine, noradrenaline, oxymetazoline, phentolamine, SDZ NVI-085, tamsulosin and (+)-tamsulosin. Rat liver alpha 1B-adrenoceptors were studied for comparison. Chloroethylclonidine-sensitivity and (+)-niguldipine affinity were also compared at cloned rat and bovine alpha 1a-adrenoceptors. 2. Chloroethylclonidine concentration-dependently inactivated alpha 1-adrenoceptors in all five tissues. While chloroethylclonidine inactivated almost all alpha 1-adrenoceptors in rat liver and guinea-pig kidney and brain, 20-30% of alpha 1-adrenoceptors in guinea-pig spleen and bovine brain were resistant to alkylation by 10 microM chloroethylclonidine. With regard to concentration-dependency guinea-pig kidney and brain were approximately 10 fold less sensitive than guinea-pig spleen or rat liver. 3. In rat liver, all drugs tested competed for [3H]-prazosin binding with steep and monophasic curves. Drug affinities were relatively low and resembled most closely those of cloned rat alpha 1b-adrenoceptors. 4. In guinea-pig spleen, all drugs tested competed for [3H]-prazosin binding with steep and monophasic curves. Drug affinities were relatively low and resembled most closely those of cloned rat alpha 1b-adrenoceptors. 5. In guinea-pig kidney most drugs tested competed for [3H]-prazosin binding with steep and monophasic curves and had relatively low drug affinities close to those of cloned rat alpha 1b- and alpha 1d-adrenoceptors. However, noradrenaline and tamsulosin had consistently biphasic competition curves recognizing 36-39% high and 61-64% low affinity sites. 6. In guinea-pig cerebral cortex, all drugs tested competed for [3H]-prazosin binding with shallow and biphasic curves. While most drugs recognized approximately 25% high affinity sites, tamsulosin and noradrenaline recognized approximately 50% high affinity sites. Drug affinities at the high and low affinity sites except those for tamsulosin and noradrenaline resembled those at cloned alpha 1a- and alpha 1b-adrenoceptors, respectively. 7. In bovine cerebral cortex all drugs tested except for noradrenaline competed for [3H]-prazosin binding with shallow and biphasic curves. All drugs recognized approximately 70% high affinity sites. Drug affinities at the high and low affinity sites resembled those at cloned alpha 1a- and alpha 1b-adrenoceptors, respectively. Noradrenaline competition curves in bovine cerebral cortex were steep and monophasic. 8. When cloned rat and bovine alpha 1a-adrenoceptors transiently expressed in COS cells were studied in a direct side-by-side comparison, both species homologues had similar chloroethylclonidine-sensitivity and (+)-niguldipine affinity. 9. We conclude that properties of bovine alpha 1A- and alpha 1B-adrenoceptors are very similar to those of other species such as rat. alpha 1-Adrenoceptor subtypes in guinea-pigs resemble alpha 1A- and alpha 1B-adrenoceptors in other species but chloroethylclonidine sensitivity and competition binding profiles of noradrenaline and tamsulosin are not compatible with previously established alpha 1-adrenoceptor subtype classification.

Systolic blood pressure is related to catecholamine sensitivity in subcutaneous abdominal fat cells.

A relationship between abdominal obesity and hypertension is well established. In search for an early-onset defect in adipocyte function linking these two conditions, we compared catecholamine sensitivity in subcutaneous abdominal fat cells with 24-hour systolic, mean arterial and diastolic blood pressure in 16 healthy, normotensive subjects. Clear inter-individual variations in the adipocyte lipolytic adrenoceptor sensitivity (pD2) for noradrenaline were observed in dose-response experiments (i.e., about 4 log units). An inverse and independent correlation was found between the 24-hour systolic blood pressure and pD2 for noradrenaline (r = -0.67, p < 0.01). The mean arterial blood pressure was also negatively correlated to peripheral noradrenaline sensitivity (r = -0.58, p < 0.05). However, no significant relationship between the 24-hour diastolic blood pressure and pD2 for noradrenaline was demonstrated. In conclusion we suggest that catecholamine resistance in subcutaneous fat cells may be associated with autonomic dysfunction and impaired blood pressure regulation. This finding is supported by the fact that both noradrenaline sensitivity and 24-hour systolic blood pressure also are correlated to the individual orthostatic heart rate responses, reflecting the sympathetic nervous system tone (r = 0.61, p = 0.01 and r = -0.53, p = 0.03, respectively). The relationship between noradrenaline sensitivity and systolic blood pressure may be of importance in the early development of hypertension in man.

Effect of age on noradrenaline responses in rat tail artery and aorta: role of endothelium.

1. We have analysed the impact of ageing on the contractile responses induced by noradrenaline on endothelium intact and denuded aorta and tail artery rings from Sprague-Dawley rats. In addition, the influence of age on noradrenaline stimulation of phosphoinositide hydrolysis was investigated. 2. The sensitivity and the phosphatidylinositol hydrolysis to noradrenaline in aorta and tail artery were not modified by age. Intact tail artery rings showed a greater maximal contraction (Emax) to noradrenaline in old as compared to young animals. However, no Emax modification by age was observed in aorta (intact or denuded) and in denuded tail artery rings. 3. Removal of endothelial cells resulted in an increase of noradrenaline sensitivity but not the Emax in aorta from each age group. 4. In contrast, the absence of endothelium did not modify (young rats) or diminish (aged rats) the alpha 1-adrenoceptor-mediated responses in tail artery. 5. These results seem to indicate that: (1) there is no influence of age on noradrenaline responses in presence of endothelium; and (2) responses in denuded preparations seem to indicate a differential role of endothelium on noradrenaline responses obtained in different vascular beds.

Capillary zone electrophoresis with laser-induced fluorescence detection for the determination of nanomolar concentrations of noradrenaline and dopamine: application to brain microdialysate analysis.

Determination of catecholamines by capillary zone electrophoresis with laser-induced fluorescence detection was performed on low-concentration samples, which were derivatized with naphthalene-2,3-dicarboxaldehyde to give highly fluorescent compounds. When the borate concentration in the derivatization medium was decreased from 130 to 13 mM, sensitivity for noradrenaline (NA) and dopamine (DA) was greatly enhanced while resolution between these two compounds decreased. A 50 mM borate concentration in derivatization medium was chosen since it provided maximal resolution between NA and DA, together with a high separation efficiency (3.1 million theoretical plates per meter for DA). The injection of 2.4 nL of a NA and DA solution derivatized at 10(-9) M produced peaks with signal-to-noise ratio of 8:1 and 3:1, respectively, corresponding to 1.8 amol of each catecholamine. The calibration curves were linear when NA and DA solutions were derivatized at concentrations ranging from 10(-6) to 10(-9) M. This method was used to determine NA in brain extracellular fluid: a peak corresponding to a basal level of 5 x 10(-9) M endogeneous NA was observed in microdialysates from the medial frontal cortex of the rat, and its nature was confirmed by both electrophoretic and pharmacological validations.

Effects of cold adaptation and noradrenaline on thermosensitivity of rat hypothalamic neurons studiedin vitro

The experiments performed on rat brain slices have shown that cold adaptation of an animal influences the thermosensitivity of hypothalamic medial preoptical neurons. The adaptation is followed by an increase in the proportion of 38–41°C-thermoresponsive neurons and by a decrease in the proportion of 35–38°C-thermoresponsive units. In control animals, noradrenaline (NA) increased the responses of hypothalamic neurons to the action of 35–38°C temperature and decreased them to the action of 38–41°C temperature. Cold adaptation prevented the effects of NA on neuronal thermosensitivity, which suggests that their NA sensitivity is modified by cold adaptation.

The effect of hyperglycaemia on function of rat isolated mesenteric resistance artery.

1. Noradrenaline sensitivity and acetylcholine-induced relaxation were investigated in mesenteric resistance arteries from female Wistar rats (220-250 g) following exposure to isotonic supraphysiological glucose solutions (20 and 45 mM, in physiological buffer, 2 h incubation). 2. Arteries incubated in 20 mM glucose demonstrated enhanced noradrenaline sensitivity compared with those in physiological buffer. 3. Profoundly impaired endothelium-dependent relaxation to acetylcholine was observed in arteries incubated in 20 and 45 mM glucose. 4. Indomethacin (10 microM) normalized noradrenaline sensitivity in 20 mM glucose, but unmasked an enhanced maximum response in 20 and 45 mM glucose relative to controls. 5. Addition of L-arginine (0.1 mM) prevented the abnormality of acetylcholine-induced relaxation in the 20 mM glucose medium and significantly improved relaxation in 45 mM glucose. 6. The aldose reductase inhibitor, ponalrestat (10(-5) M, ZENECA Pharmaceuticals), prevented impaired acetylcholine-mediated relaxation in 20 mM glucose and significantly improved relaxation in 45 mM glucose. 7. Indomethacin (10 microM) improved maximum relaxation but did not alter impaired sensitivity to acetylcholine in the high glucose media (20 and 45 mM). 8. Superoxide dismutase (SOD, 150 u ml-1) also prevented impaired acetylcholine-induced relaxation in 20 mM glucose but not in 45 mM glucose. 9. Endothelium-independent relaxation to sodium nitroprusside (SNP, 10(-9)-10(-5) mM) was normal in 20 mM glucose but was slightly, although significantly impaired by 45 mM glucose. 10. Enhanced responsiveness of rat isolated mesenteric resistance arteries to noradrenaline caused by elevated glucose would appear to be mediated through abnormal cyclo-oxygenase activity and the reduced tonic release of nitric oxide. 11. Hyperglycaemia may lead to abnormal endothelium-dependent relaxation in these arteries through several mechanisms which include a role for increased free radical production, polyol pathway activation and altered L-arginine metabolism.

Effects of maturation on alpha-adrenergic receptor affinity and occupancy in small cerebral arteries

The present experiments examine the hypothesis that changes in receptor affinity and occupation mediate maturational changes in norepinephrine sensitivity in small cerebral arteries. In second-order (2B) and fourth-order (4B) branch middle cerebral artery segments from newborn and adult sheep, we first found that a stretch ratio based on artery diameter better estimated optimal prestretch than did passive tension. Next, we determined norepinephrine dose-response relations before and after prazosin, yohimbine, and benextramine. Prazosin competitively blocked contractions to norepinephrine, but yohimbine had no effect, indicating that alpha 1-adrenoceptors mediated contraction. Norepinephrine sensitivity [determined from the -log of the half-maximal effective dose (pD2)], maximal response, and binding affinity all decreased with age in 4B but not 2B segments. Receptor occupancy at the pD2 increased with age only in 2B segments. In conclusion, maturation of ovine middle cerebral arteries involves branch-specific changes in affinity and receptor occupation of the alpha 1-adrenoceptors that mediate contractile responses to norepinephrine. Age-related changes in receptor density and/or intrinsic efficacy probably are involved also.

Effects of neuropeptide Y and vasoactive intestinal peptide on human venous smooth muscle in vivo.

The direct and noradrenaline-modulating effects of neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP) on venous smooth muscle were studied in healthy volunteers employing the dorsal hand vein compliance technique. Local infusions of NPY had no measurable effect on venous tone, but coinfusion of a constant high dose of NPY (242 pmol/min) with noradrenaline caused a 2.9-fold increase in the mean ED50 for noradrenaline. The dilating effect of VIP on preconstricted hand veins was weak, maximal venodilation could not be achieved, because systemic side effects occurred at submaximally venodilating doses. Coinfusion of noradrenaline with a weakly venodilating, constant dose of VIP (93.2 pmol/min) caused a 0.5-fold decrease in the sensitivity for noradrenaline. Although functional interactions between NPY or VIP and noradrenaline could be demonstrated, the dosages of the peptides required were high. Thus our results indicate that neither NPY nor VIP exert a major direct or noradrenaline-modulating effect on human veins.

Vascular mechanisms of cyclosporin-induced hypertension in the rat.

Numerous studies have explored the pathogenesis of cyclosporin A (CysA)-induced hypertension; however, none has assessed the impact of CysA treatment on resistance arteries in the setting of elevated blood pressure. Therefore, we studied the chronic effect of CysA on rat mesenteric artery resistance vessels (ex vivo). CysA (25 mg/kg per d for 7 d), but not vehicle, significantly raised systolic blood pressure (13.4 +/- 2.2 mmHg, P < 0.003, n = 9 per group). The resistance vessels from CysA-treated rats showed a small but significant decrease in norepinephrine sensitivity (P < 0.03) and a pronounced decrease in endothelium-dependent and -independent relaxation (P < 0.001) compared to controls. Endothelin-1 sensitivity tended to be diminished (P = 0.07). The direct (in vitro) effect of CysA was subsequently evaluated in resistance vessels from nontreated animals (n = 8) and exposed to CysA (2 micrograms/ml) for 24 h. As observed in vivo, CysA significantly decreased endothelium-dependent and -independent relaxations (P < 0.05) and attenuated norepinephrine sensitivity (P = 0.06). Methylene blue, a nitric oxide quencher, significantly inhibited the acetylcholine-induced relaxation in control, but not in CysA vessels, suggesting a selective action of CysA on the nitric oxide pathway. We conclude that CysA-induced hypertension is the consequence of a primary effect on resistance vessel relaxation, not increased vasoconstriction, as previously suggested.

Catecholamine resistance in fat cells of women with upper-body obesity due to decreased expression of beta 2-adrenoceptors.

Upper-body obesity is an important risk factor for developing non-insulin dependent diabetes. To investigate the possibility that a lipolysis defect is present in this form of obesity, we examined the adrenergic regulation of lipolysis in abdominal subcutaneous fat cells from 25 women with upper-body obesity and 24 non-obese women. Lipolytic noradrenaline sensitivity (but not the maximum rate of lipolysis) was reduced by 10-fold in obese women (p < 0.01). The noradrenaline resistance could be ascribed to a 10-fold decrease in lipolytic beta 2-adrenoceptor sensitivity (p < 0.01). The lipolytic sensitivity of beta 1- and alpha 2-adrenergic receptors was normal in the obese women. A 70% reduction in the cell surface density of beta 2-adrenoceptors was observed compared to the control subjects (p < 0.01). However, beta 1-receptor density as well as steady-state mRNA levels for beta 1- and beta 2-receptors were normal in obese women. Lipolytic noradrenaline sensitivity correlated inversely with BMI (adjusted r2 = 0.76 together with fat cell volume in stepwise regression analysis). The fasting plasma level of free cortisol was 30% lower in obese compared to non-obese women (p < 0.05) but obesity did not influence resting plasma catecholamine levels. Thus, lipolytic catecholamine resistance is present in abdominal obesity, due to low density of beta 2-adrenoceptors, which in its turn may be caused by a post-transcriptional defect in beta 2-receptor expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelial function in the isolated perfused mesentery and aortae of rats with streptozotocin-induced diabetes: effect of treatment with the aldose reductase inhibitor, ponalrestat.

1. Noradrenaline sensitivity and relaxation to acetylcholine were investigated in the isolated perfused mesentery and in aortic rings of control and streptozotocin (STZ)-induced (50 mg kg-1) diabetic Charles River rats. 2. In addition, noradrenaline sensitivity and acetylcholine relaxation were similarly assessed in streptozotocin-induced diabetic rats treated from the time of onset of diabetes with the aldose reductase inhibitor, ponalrestat (100 mg kg-1 day-1). 3. The untreated diabetic rats (2-10 weeks after injection of STZ) demonstrated enhanced vascular sensitivity to noradrenaline in the perfused mesenteric arterial tree, compared with age matched controls (pEC50 [-log concentration (M)]: diabetic 5.62 +/- 0.09, n = 18, versus control 5.23 +/- 0.07, n = 16, P < 0.01). 4. Acetylcholine-induced relaxation was significantly impaired in the perfused mesentery of the diabetic animals compared to controls (pED50 [-log dose (mol)]: diabetic 9.87 +/- 0.10, n = 20, versus controls, 10.29 +/- 0.09, n = 20, P < 0.05). 5. In contrast, the aortic ring preparations demonstrated no significant functional differences between the diabetic and control groups in response to either noradrenaline (pEC50: diabetic 7.66 +/- 0.08, n = 15, versus controls 7.55 +/- 0.06, n = 15, NS), or acetylcholine (pEC50: diabetics 7.30 +/- 0.06, n = 15, versus controls 7.40 +/- 0.09, n = 15, NS). 6. Treatment with the aldose reductase inhibitor, ponalrestat, did not affect the increased vascular reactivity to noradrenaline, or impaired relaxation to acetylcholine in the perfused mesentery.

Prevention by insulin treatment of endothelial dysfunction but not enhanced noradrenaline‐induced contractility in mesenteric resistance arteries from streptozotocin‐induced diabetic rats

1. Streptozotocin-induced diabetic rats (Wistar) were implanted with sustained release insulin pellets (release rate = 4 u day-1) or with placebo pellets (palmitic acid) from the onset of glycosuria. 2. Noradrenaline sensitivity, endothelium-dependent relaxation to acetylcholine and endothelium-independent relaxation to sodium nitroprusside were assessed in mesenteric resistance arteries from the insulin-treated (IT) diabetic animals and compared to placebo-implanted (PI) diabetics and age-matched controls. 3. Arteries from PI-diabetic rats (8-10 weeks) demonstrated an enhanced maximal response to noradrenaline compared to controls, which was not prevented by insulin treatment (control 2.65 +/- 0.17 mN mm-1, n = 18 arteries versus PI-diabetic 3.73 +/- 0.40 mM mm-1, n = 5, P < 0.05; control versus IT-diabetic 4.02 +/- 0.19 mN mm-1, n = 22, P < 0.001). Sensitivity to noradrenaline was similar between the three groups. 4. In the presence of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), IT and PI arteries were more sensitive to noradrenaline than control arteries (pEC50: control 5.75 +/- 0.08, n = 17, versus PI-diabetic 6.14 +/- 0.09, n = 8, P < 0.05; control versus IT-diabetic 6.38 +/- 0.08, n = 20, P < 0.001). 5. The maximum contractile response to depolarizing 125 mM K+ was significantly enhanced in IT-diabetic arteries but not PI-diabetic when compared to control arteries (maximum response: control 3.74 +/- 0.15 mN mm-1, n = 18, versus PI-diabetic 3.61 +/- 0.19 mN mm-1, n = 11, NS; control versus IT-diabetic 4.66 +/- 0.18 mN mm-1, n = 22, P < 0.001). 6. Endothelium-dependent relaxation to acetylcholine was profoundly impaired in the PI-diabetic arteries, but in the IT-diabetic arteries was not significantly different from controls (pEC50: control 7.64 +/- 0.19, n = 17, versus PI-diabetic 6.07 +/- 0.12, n = 8, P < 0.001; control versus IT-diabetic 7.36 +/- 0.09, n = 22, NS). 7. Endothelium-independent relaxation to sodium nitroprusside was slightly but significantly impaired in the PI-diabetic arteries, but was not significantly different in the IT-diabetic arteries compared to controls (pEC50: control 7.78 +/- 0.10, n = 13, versus PI-diabetic 7.31 +/- 0.13, n = 13, P <0.05; control,versus IT-diabetic 7.64 +/- 0.09, n = 16, NS).

Exercise training alters endothelium-dependent vasoreactivity of rat abdominal aorta.

We tested the hypothesis that adaptations in peripheral arterial vasoreactivity are induced by exercise training. Male rats were trained to run on a treadmill at 30 m/min (15 degrees incline) for 1 h/day 5 days/wk for 10-12 wk. Efficacy was indicated by a 51% increase (P < 0.05) in citrate synthase activity in soleus muscle of exercise-trained (ET) rats compared with that of sedentary (SED) control rats. Responses to vasoactive compounds were examined in vitro using rings of abdominal aorta. Maximal isometric contractile tension evoked by KCl, norepinephrine (NE), and phenylephrine were not different between groups; sensitivity to phenylephrine was also not different between groups. However, sensitivity was lower for both KCl and NE in vessels from ET animals. Endothelium removal did not influence KCl sensitivity but did abolish the difference in NE sensitivity of vessel segments between ET and SED animals. Maximal vasodilator responses induced by acetylcholine (ACh; NE or prostaglandin F2 alpha preconstriction) were greater in vessel rings from ET rats. However, dilatory responses by sodium nitroprusside (NE or prostaglandin F2 alpha preconstriction) and forskolin (NE preconstriction) were not different between groups, indicating that the augmented ACh-induced dilatory response resulted from an adaptation of the endothelium. Blockade of nitric oxide synthase activity diminished ACh-induced vasodilation by 79 and 100% in SED and ET rats, respectively. These results indicate that training alters vasomotor function in rat abdominal aortas through adaptations of both endothelium and smooth muscle.

Rhythmic contractions of isolated small arteries from rat: influence of the endothelium

Small arteries of the mesenteric arcade from Wistar rats display rhythmic oscillations superimposed on the tonic contractile response when exposed to submaximal doses of noradrenaline. We have previously shown that mechanical removal of the endothelium abolishes these oscillations. In the present study different methods to eliminate or modify the influence of the endothelium were used in order to further characterize the mechanisms behind rhythmic contractions in these vessels. Endothelium was removed either mechanically or chemically by perfusing the vessels with 0.3% CHAPS. The absence of functional endothelium enhanced noradrenaline sensitivity and simultaneously abolished oscillations in tension and membrane potential, but did not affect resting membrane potential. The rhythmic activity was also reduced or abolished by exposure to haemoglobin, methylene blue, LY83583 or L-NNA. Indomethacin and propranolol were without effect. Sodium nitroprusside or the permeant analogue of cyclic GMP, 8-bromo cyclic GMP, restored rhythmic activity in precontracted endothelium-denuded vessels. The data suggest that release of nitric oxide from the endothelium, and subsequent generation of cyclic GMP in the smooth muscle, activates oscillations in membrane potential and tension; the oscillator itself appears to be located within the smooth muscle cells.

Optical biosensors based on fish pigment cells

Melanophores (black pigment cells) in isolated fish scales have the ability to either aggregate their intracellular pigment granules to the centre or disperse them throughout the cell. Noradrenaline stimulates aggregation within these cells. The sensitivity of noradrenaline is considerably increased after approximately one week of isolation of the scales in a tissue culture medium. In order to measure simultaneously pigment aggregation in several isolated scales, a multichannel fibre-optic system has been developed. The system enables the scales to be constantly perfused with tissue culture medium, which in turn allows measurements to be made over long periods of time. After nine days of isolation there is an approximately 12 000-fold increase in noradrenaline sensitivity. The fibre-optic system, combined with cultured melanophores and molecular biology techniques, should provide a number of interesting biosensing possibilities.

Difference between aortic and renal vascular reactivity in cyclosporin A treated rats and the effect of cicletanine.

4 Groups of 2 month-old male Wistar rats were treated with a) cyclosporin A (CyA) 30 mg/kg/day alone, b) CyA plus cicletanine (Cic) 60 mg/kg/day, c) vehicle (vegetable oil) 1 ml/100 g rat/day and d) no treatment for 8 weeks. The reactivity of isolated papillary muscle to isoprenaline and Ca2+ was not altered in any of the treated groups. Endothelium-dependent relaxation induced by acetylcholine was inhibited in aorta ring segments from CyA-treated rats as compared to that of control and CyA + Cic-treated rats. The relaxation induced by acetylcholine in rat aortas was similar in all groups in the presence of 10 microM indomethacin. Noradrenaline sensitivity of aortic segments was not affected by any treatments applied. The Ca(2+)-concentration response curves of aorta segments from CyA-treated and CyA + Cic-treated rats were shifted to the right as compared to control rats. In interlobar renal arteries the endothelium-dependent relaxation induced by acetylcholine was not affected by any form of treatment. In renal arteries 10 microM indomethacin increased the maximal relaxation induced by acetylcholine about 50%. In these vessels noradrenaline sensitivity in CyA and CyA + Cic treated rats was higher than in controls. Cocaine, 3 microM, shifted the noradrenaline concentration response curve to the left about 0.4 log units in all renal vessel groups, thus renal vascular smooth muscle sensitivity to noradrenaline was significantly greater in vessels from rats receiving CyA than in vessels from control rats. Administration of CyA induced only slight renal morphological changes. Cic was without effect on CyA induced morphological abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)