Effects of cilnidipine on nitric oxide and endothelin-1 expression and extracellular signal-regulated kinase in hypertensive rats.

We evaluated the effects of cilnidipine, a long-acting Ca(2+) channel antagonist, on endothelial nitric oxide synthase (eNOS), preproendothelin-1 and endothelin ETA receptor expression in the left ventricle, and evaluated the relations between these effects and coronary microvascular remodeling and extracellular signal-regulated kinases belonging to one subfamily of mitogen-activated protein kinases in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Cilnidipine (DOCA-cilnidipine, 1 mg/kg/day, subdepressor dose) or vehicle (DOCA-vehicle) was given after induction of DOCA-salt hypertension for 5 weeks. The eNOS mRNA and protein expression in the left ventricle was significantly lower in DOCA-vehicle than in control rats and significantly higher in DOCA-cilnidipine than in DOCA-vehicle rats. Preproendothelin-1 and endothelin ETA receptor expression levels and phospho-p42/p44 extracellular signal-regulated kinase activities were significantly increased in DOCA-vehicle compared with control rats and significantly suppressed in DOCA-cilnidipine compared with DOCA-vehicle rats. DOCA-vehicle rats showed a significant increase in the wall-to-lumen ratio, perivascular fibrosis and myocardial fibrosis, with all these parameters being significantly improved by cilnidipine. These results led us to conclude that phospho-p42/p44 extracellular signal-regulated kinase activities may contribute to the coronary microvascular remodeling of DOCA rats and that protective effects of cilnidipine on cardiovascular remodeling may be at least in part mediated by an increased eNOS expression and a decreased endothelin-1 and endothelin ETA receptor expression in the left ventricle.     

Antihypertensive effect of an endothelin receptor antagonist in DOCA-salt spontaneously hypertensive rats.

1. Endothelin-1 gene expression is enhanced in aorta and mesenteric arteries, and possibly other vessels, of deoxycorticosterone acetate (DOCA)-salt hypertensive rats but is normal or reduced in spontaneously hypertensive rats (SHR). Bosentan, a mixed ETA/ETB endothelin receptor antagonist, blunts the development of elevated blood pressure of DOCA-salt hypertensive rats but not in SHR. In this study we investigated whether treatment of DOCA-salt SHR with bosentan would result in blunted rise in blood pressure. 2. SHR, aged 13 weeks, were implanted with silastic containing DOCA and offered 1% saline to drink. Systolic blood pressure was measured by the tail-cuff method. Endothelin-1 mRNA abundance in aorta and mesenteric arteries was measured by Northern blot analysis. Content of immunoreactive endothelin in blood vessels was measured by radioimmunoassay. 3. Systolic blood pressure rose less in bosentan-treated DOCA-salt SHR (to 223 +/- 2 mmHg) in comparison to the untreated rats (241 +/- 1), a small but significant difference (P < 0.001). However, blood pressure of bosentan-treated DOCA-salt SHR was still higher than in age-matched SHR. Endothelin-1 mRNA abundance and content of immunoreactive endothelin were increased in the aorta and the mesenteric arterial bed of DOCA-salt SHR, and were unaffected by treatment with bosentan. 4. These data support the hypothesis of a role of endothelin-1 in blood pressure elevation in this hypertensive model with malignant hypertension. They also support the hypothesis that an antihypertensive effect of the mixed ETA/ETB endothelin receptor antagonist, bosentan, is found when experimental hypertensive animals exhibit enhanced endothelin-1 gene expression in blood vessels.     

Affinity of central adenosine A1 receptors is decreased in spontaneously hypertensive rats

Functional defects in purinergic neurotransmission have been related to the development of arterial hypertension in spontaneously hypertensive rats. In order to elucidate the molecular basis of this perturbation, we have directly characterized adenosine A₁ receptors using radioligand binding to rat brain membranes of Wistar Kyoto (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). Saturation studies with [³H]1,3-dipropylcyclopentylxanthine ([³H]DPCPX) showed a lower affinity in both 5- and 48-week-old SHRSP in comparison with age-matched WKY. Similarly, competition experiments with [³H]DPCPX showed lower affinity of R-N⁶-phenylisopropyladenosine for the low-affinity binding site in 5- and 48-week-old SHRSP in comparison with WKY. In both studies, the difference in K_D values was abolished by guanosine-5′-triphosphate in 5-week-old rats and mitigated in 48-week-old animals. No differences in B_max values were observed in 5-week-old rats, whereas in 48-week-old SHRSP the number of receptors was significantly higher in comparison with age-matched WKY. Saturation experiments with the A₁-selective agonist [³H]2-chloro-N⁶-cyclopentyladenosine ([³H]CCPA) demonstrated a higher affinity in 5-week-old SHRSP, whereas in 48-week-old hypertensive animals it was lower than in control WKY rats. No difference in receptor number was detected in comparison with age-matched WKY. In conclusion, our data demonstrated a diminished affinity of central adenosine A₁ receptors for antagonists and for the low affinity state of the agonist binding site in genetically hypertensive rats. This might be due to structural changes of the receptor protein, to an altered G protein or defective receptor-G-protein coupling in arterial hypertension.     

Role of endothelin ETB receptor in the pathogenesis of monocrotaline-induced pulmonary hypertension in rats

We investigated the role of endothelin ETB receptor in the development of monocrotaline-induced pulmonary hypertension, by using the spotting-lethal (sl) rat, which carries a naturally occurring deletion in the endothelin ETB receptor gene. Three weeks after injection of saline or monocrotaline (60 mg/kg, s.c.), hemodynamics, cardiac hypertrophy and endothelin-1 levels in right ventricle were determined. Monocrotaline produced a marked pulmonary hypertension associated with increases in right ventricular pressure and hypertrophy, pulmonary arterial medial thickening and the endothelin-1 levels. The monocrotaline-induced alterations tended to be enhanced in ETB-deficient homozygous rats, compared with cases in wild-type rats. The treatment with selective ETA receptor antagonist ABT-627 [2R-(4-methoxyphenyl)-4S-(1,3-benzodioxol-5-yl)-1-(N,N-di(n-butyl)aminocarbonyl-methyl)-pyrrolidine-3R-carboxylic acid] for 3 weeks (10 mg/kg/day, twice daily) almost completely suppressed the monocrotaline-induced pulmonary hypertension and related organ damage both in ETB-deficient and wild-type animals to the same levels. Thus, we suggest that the antagonism of the ETA receptor is essential for the protection from monocrotaline-induced pulmonary hypertension, irrespective of the presence of the ETB receptors, although a protective role of ETB receptor-mediated action in the pathogenesis of this disease model cannot be ruled out.     

The effect of the endothelin ET(A) receptor antagonist CI-1020 on hypoxic pulmonary vasoconstriction.

The mechanism of Hypoxic Pulmonary Vasoconstriction is unknown. The role of endothelin-1 in hypoxic pulmonary vasoconstriction was studied in precontracted small and large pulmonary arteries using the endothelin ETA receptor antagonist sodium-2-benzol [1,3]dioxol-5-yl-4-(4-methoxyphenyl)-4-oxo-3-(3,4,5-trimethoxy-ben zyl)-but-2-enoate (CI-1020). Small rat pulmonary arteries exhibit a mixed endothelin ETA receptor and endothelin ETB2 receptor population whereas large rat pulmonary arteries contain only endothelin ETA receptors. CI-1020 inhibited endothelin-1 in small vessels via endothelin ETA receptor blockade (1 and 10 microM) and at high concentrations via endothelin ETA receptor and endothelin ETB2 receptor blockade (100 microM). CI-1020 (0.01, 0.1 and 1 microM) inhibited endothelin-1 in large vessels via endothelin ETA receptor blockade alone. CI-1020 (1, 10 and 100 microM) significantly reduced hypoxic pulmonary vasoconstriction in small vessels, by -9.8+/-1.4, -9.2+/-2.3 and -8.0+/-1.7% 80 mM K+, respectively, compared to +2.5+/-4.2% with vehicle (P < 0.05). CI-1020 (0.01, 0.1 and 1 microM) had no significant effect upon hypoxic pulmonary vasoconstriction in large vessels. In small, but not large, pulmonary arteries hypoxic pulmonary vasoconstriction is due in part to the action of endothelin-1 at the endothelin ETA receptor.     

Down-regulated VEGF expression in the diabetic heart is normalized by an endothelin ETA receptor antagonist

Recently, down-regulation of vascular endothelial growth factor (VEGF) in the heart was suggested as a potential molecular explanation for the increased risk of cardiovascular morbidity and mortality in patients with diabetes. Increased endothelin-1 production is reported in diabetes. Here, we report that down-regulated VEGF expression in the diabetic rat heart is normalized by an endothelin ETA receptor antagonist, suggesting that endothelin antagonism may be a novel therapeutic strategy for diabetic heart.     

Superiority of YM598 over atrasentan as a selective endothelin ETA receptor antagonist

The binding affinities of (E)-N-[6-methoxy-5-(2-methoxyphenoxy)[2,2'-bipyrimidin]-4-yl]-2-phenylethenesulfonamide monopotassium salt (YM598) for native human endothelin ETA and ETB receptors expressed in human coronary artery smooth muscle cells (CASMC) and a human melanoma cell line, SK-Mel-28, respectively, were examined, and the results compared with those for the endothelin receptor antagonists atrasentan and bosentan. The in vivo endothelin ETA receptor inhibitory activities of YM598 and atrasentan were also compared through the suppression of the big endothelin-1-induced pressor response in pithed rats. Ki values of YM598, atrasentan, and bosentan for native human endothelin ETA receptors were 0.772, 0.0551, and 4.75 nM, while those for native human endothelin ETB receptors were 143, 4.80, and 40.9 nM, respectively. The calculated selectivity ratios of YM598, atrasentan, and bosentan for endothelin ETA versus ETB receptors were 185, 87 and 8.6, respectively. In pithed rats, YM598 and atrasentan inhibited the big endothelin-1 (1 nmol/kg)-induced pressor response in a dose-dependent manner on both intravenous and oral administration. The inhibitory effect of YM598 was less potent than that of atrasentan when these agents were intravenously administered, but closely similar on oral administration. These results suggest that YM598 has high selectivity for native human ETA against ETB receptors, and that YM598 is superior to atrasentan as an ETA receptor antagonist with regard to pharmacological bioavailability in rats.     

Characterization of 5-hydroxytryptamine receptors mediating contractions in basilar arteries from stroke-prone spontaneously hypertensive rats.

1. The 5-hydroxytryptamine (5-HT) induced-contraction in ring preparations of basilar arteries from Wistar-Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) was pharmacologically characterized in vitro. 2. Contractile responses to 5-HT (1 nM-100 nM) and their pD2 values in arteries from SHRSP at 6 months of age were significantly greater than those in age-matched WKY, although the maximum response did not differ between the two groups. 3. There were no significant differences in contractile responses to U-44619, endothelin-1, neuropeptide Y, and angiotensin II between WKY and SHRSP arteries. 4. Spiperone (1 nM-1 microM, a 5-HT2 receptor antagonist), produced biphasic displacement of the 5-HT curves in WKY and SHRSP arteries. The response to high concentrations of 5-HT was concentration-dependently antagonized by spiperone, while the response to low concentrations of 5-HT was resistant to blockade by spiperone, and the spiperone-resistant contractile responses induced by 5-HT were greater in SHRSP than in WKY. Ketanserin (1-100 nM, 5-HT2) also produced a biphasic shift of the 5-HT curves for both arteries. 5. Methiothepin (10 and 100 nM, 5-HT1 and 5-HT2) potently inhibited 5-HT-induced contractions in both groups. In addition, methiothepin (100 nM) produced a parallel shift to the right of the component of 5-HT-induced contractile responses that was resistant to blockade by spiperone in both groups. 6. The contractile effects of 5-HT in WKY and SHRSP arteries were not affected by MDL 72222 (1 microM, 5-HT3) and SDZ 205-557 (1 microM, 5-HT4). In addition, cocaine (10 microM), pargyline (50 microM), prazosin (10 microM), indomethacin (3 microM) and SQ 29,548 (1 microM) did not affect the contractile effects of 5-HT in either artery. 7. Contractile responses to 5-carboxamidotryptamine, CGS 12066B, pindolol and propranolol were greater in SHRSP arteries than in WKY arteries, whereas contractions in response to 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), alpha-methyl-5-HT and 2-methyl-5-HT did not differ between the two groups. Cisapride failed to contract basilar arteries in both groups. Furthermore, a correlation analysis showed a highly significant correlation between the pD2 values of 5-HT agonists in WKY and SHRSP arteries and their published binding affinities at the 5-HT1B subtype. 8. These findings suggest that 5-HT elicits vasoconstriction in rat basilar arteries by stimulation of a mixed receptor population of 5-HT2 and 5-HT1-like receptors (similar to the 5-HT1B receptor subtype), and that the contraction mediated by 5-HT1-like receptors is enhanced in the basilar artery from SHRSP.     

Decreased density of alpha 2-adrenoceptors in medulla oblongata of spontaneously hypertensive rats

To study the role of medullary alpha-adrenoceptors in hypertension, we compared specific binding of [3H]prazosin and [3H]clonidine in different brain regions of spontaneously hypertensive rats (SHR), stroke-prone SHR (SHRSP), and normotensive Wistar-Kyoto rats (WKY). As compared with age-matched WKY, Bmax values for specific [3H]clonidine binding in the medulla oblongata were significantly lower in SHR and SHRSP at 16-24 weeks of age. In the SHRSP medulla oblongata, the decrease was more prominent in dorsomedial and ventrolateral regions than in the ventromedial region. Density of alpha 2-adrenoceptor binding sites was also decreased in the medulla oblongata of young (4-5-week-old) SHRSP. In contrast, there was no difference in Kd and Bmax values for medullary [3H]prazosin binding between WKY and SHRSP. The dorsomedial and ventrolateral regions of the SHRSP medulla oblongata showed significantly lower levels of norepinephrine (NE). Thus, the present study demonstrates that there is a specific loss of alpha 2-adrenoceptors in the medulla oblongata of SHR and SHRSP that may be partly involved in the pathogenesis of spontaneous hypertension.     

Changes in autonomic activity and baroreflex sensitivity with the hypertension process and age in rats

1. Autonomic activity and baroreflex sensitivity (BRS) were compared in age-matched conscious groups of Wistar Kyoto (WKY) rats, spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SHRSP). 2. Male WKY rats, SHR and SHRSP aged 4-30 weeks were used. Autonomic activity and BRS were estimated by power spectral and cross-spectral analysis of systolic blood pressure (SBP) and SBP-SBP (SS) interval fluctuations, respectively. 3. The time-course of heart rate (HR), SBP, the amplitude of the low-frequency component of SBP fluctuation (SBP-LF; prazosin-sensitive index) and the amplitude of the high-frequency component of the SS interval fluctuation (SS-HF; atropine-sensitive index) consisted of two periods. In the first period (up to 10 or 15 weeks of age), BP, SBP-LF and SS-HF increased with age. The order of SBP-LF was SHRSP > SHR > WKY rats throughout this period. During the second period, BP was sustained at certain levels in all strains, but changes in SBP-LF and SS-HF with age were different among strains. In particular, in SHRSP, SBP-LF markedly decreased with age after 10 weeks. Baroreflex sensitivity in WKY rats increased gradually with age, whereas the BRS in SHR and SHRSP decreased before 6 weeks of age and remained lower than that in WKY rats. 4. In conclusion, the present study shows that both prazosin-sensitive and atropine-sensitive indices are associated with the elevation of BP in all strains studied. However, hypertension after 15 weeks of age in SHRSP is sustained despite a paradoxical reduction in sympathetic activity with an abnormal control of BRS. Therefore, the contribution of autonomic activity to hypertension may be discussed separately as a developmental period and a sustained period.     

Upregulation of vascular ET(B) receptor gene expression after chronic ET(A) receptor blockade in prediabetic NOD mice

In the aorta of prediabetic non-obese diabetic mice, a model of human type 1 diabetes, we investigated gene expression of the endothelin receptors and contractility to big endothelin-1 and endothelin-1 at the ages of 10 and 16 weeks. A subgroup of 10- week-old animals was treated with the endothelin ETA receptor antagonist LU461314 (30 mg/kg per day for 6 weeks). Blood glucose levels were normal in all animals. Real-time polymerase chain reaction analysis revealed that vascular ETB receptor expression was higher in 10-week-old non-obese diabetic (NOD) mice compared with controls. In 16-week-old NOD mice, but not in control mice, ETB receptor mRNA was twofold lower (P < 0.05 vs 10-week-old NOD mice). In all groups ETA receptor expression was unaffected by age or treatment. Contractions to big endothelin-1 and endothelin-1 were lower in 10-week-old NOD mice compared with controls. Treatment with LU461314 increased ETB receptor expression in 16-week-old NOD mice, but had no effect on vascular contractility. These data indicate that dysregulation of ETB receptor expression and a decreased contractile response to big endothelin-1 and endothelin-1 are present in the prediabetic state of a model of human type 1 diabetes. These alterations occur independent of glucose levels. Furthermore, ETA receptor blockade is effective in increasing ETB receptor gene expression, suggesting a potential role for endothelin ETA antagonists in the treatment of type 1 diabetes.     

Differences in regional vascular sensitivity to endothelin-1 between spontaneously hypertensive and normotensive Wistar-Kyoto rats.

1. The systemic and regional haemodynamic effects of porcine endothelin-1 (endothelin) have been measured in anaesthetized spontaneously hypertensive (SH) rats rendered areflexic by ganglion blockade; comparisons were made with age-matched Wistar-Kyoto (WKY) control animals. 2. In both SH and WKY rats endothelin (0.1-1 nmol kg-1 i.v.) elicited an initial, short-lived (less than 2 min), fall in blood pressure which was associated with substantial increases in hindquarter and carotid vascular conductances. Both the blood pressure falls and the peripheral vasodilator responses were greater in SH than in WKY rats. 3. The initial depressor effects of endothelin were followed by marked and sustained increases in blood pressure associated with constriction in carotid, hindquarter, renal and mesenteric vascular beds. Vasoconstrictor responses were quantitatively similar in the two rat strains. 4. Pretreatment with indomethacin (5 mg kg-1 i.p. or i.v.) did not alter the responses to endothelin, 1 nmol kg-1, in SH rats. 5. The regional haemodynamic effects of intravenously administered acetylcholine (0.01-1 microgram kg-1), nitroprusside (0.3-10 micrograms kg-1) and angiotensin II (0.01-0.1 microgram kg-1) were similar in SH and WKY rats. 6. Endothelin (10(-10)-3 x 10(-8) M) contracted aortic rings from both SH rats and WKY control animals. Removal of the endothelium enhanced significantly the sensitivity of tissues from both WKY and SH rats to endothelin; the increase in sensitivity was greater in tissues from SH than WKY rats. 7. The results demonstrate qualitative similarities in the complex haemodynamic effects of endothelin in SH rats and WKY control animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Basic and therapeutic relevance of endothelin-mediated regulation.

Three endothelin family peptides (endothelin-1, -2 and -3) exert an extremely potent and long-lasting vasoconstrictor action as well as other various actions through stimulating two subtypes of receptor (ETA and ETB). Vascular endothelial cells produce only endothelin-1. Although the pharmacological actions of exogenous endothelin-1 have been extensively analyzed, the physiological roles of endogenous endothelin-1 have long been obscure. Using potent and selective receptor antagonists, endothelin-1 has been demonstrated to contribute slightly to the maintenance of regional vascular tone. In gene-targeted mice, endothelin family peptides and their receptors have been shown to play an important role in the embryonic development of neural crest-derived tissues. In addition to its potent vasoconstrictor action, endothelin-1 has direct mitogenic actions on cardiovascular tissues, as well as co-mitogenic actions with a wide variety of growth factors and vasoactive substances. Endothelin-1 also promotes the synthesis and secretion of various substances including extracellular constituents. These effects of endogenous endothelin-1 would appear to be naturally concerned with the development and/or aggravation of chronic cardiovascular diseases, e.g. hypertension, pulmonary hypertension, vascular remodeling (restenosis, atherosclerosis), renal failure, and heart failure. A great many non-peptide and orally active endothelin receptor antagonists have been developed, and shown to exert excellent therapeutic effects in animal models as well as human patients with these diseases.     

Differential effects of BQ-123 against endothelin-1 and endothelin-3 on the rat vas deferens: evidence for an atypical endothelin receptor.

1. Endothelin-1 and endothelin-3 enhanced concentration-dependently the rat vas deferens twitch response to electrical stimulation, endothelin-1 being three times more potent. Sarafotoxin S6c was at least 200 times less active than endothelin-1. 2. The response to endothelin was antagonized in a competitive manner by the supposedly selective ETA receptor antagonist, BQ-123 (pA2:7.0 +/- 0.1). In contrast, the endothelin-1 concentration-response curve was only shifted two fold in the presence of 10 microM BQ-123, while no effect was observed at 1 microM. 3. This evidence suggests the rat vas deferens contains an endothelin receptor not conforming to the ETA/ETB receptor subtype classification so far proposed.     

The endothelin ETA receptor antagonist,BQ-123, normalizes the response of SHR aorta to Ca2+ channel activator

Hypertension is associated with a hypersensitive response to the Ca²⁺ channel activator, Bay K 8644. We investigated the effect of the endothelin ET_A receptor antagonist, BQ-123, on the contractions induced by Bay K 8644 in aorta from spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats. BQ-123 (1 μM) decreased the sensitivity to Bay K 8644 of aorta of SHR down to that of WKY. This observation is consistent with a role for endothelin in hypertension.     

Role of endothelin ET(B) receptors in the renal hemodynamic and excretory responses to big endothelin-1

We determined the role of endothelin ET(B) receptor in the renal hemodynamic and excretory responses to big endothelin-1, using A-192621, a selective endothelin ET(B) receptor antagonist and the spotting-lethal (sl) rat, which carries a naturally occurring deletion in the endothelin ET(B) receptor gene. An intravenous injection of big endothelin-1 produced a hypertensive effect, which is greater in wild-type (+/+) rats pretreated with A-192621 and in homozygous (sl/sl) rats. Big endothelin-1 markedly increased urine flow, urinary excretion of sodium and fractional excretion of sodium in wild-type rats treated with the vehicle. These excretory responses to big endothelin-1 were markedly reduced by pharmacological endothelin ET(B) receptor blockade. On the other hand, big endothelin-1 injection to the endothelin ET(B) receptor-deficient homozygous animals resulted in a small diuretic effect. When renal perfusion pressure was protected from big endothelin-1-induced hypertension by an aortic clamp, the excretory responses in vehicle-treated wild-type rats were markedly attenuated. In homozygous or A-192621-treated wild-type rats, there was a small but significant decreasing effect in urine flow. In addition, big endothelin-1 significantly elevated nitric oxide (NO) metabolite production in the kidney of wild-type rats but not in the homozygous rats. We suggest that the diuretic and natriuretic responses to big endothelin-1 consist of pressure-dependent and pressure-independent effects and that the increased NO production via the activation of endothelin ET(B) receptors in the kidney is closely related to the big endothelin-1-induced excretory responses.     

Impaired heart function and noradrenaline release after ischaemia in stroke-prone spontaneously hypertensive rats

1. Stroke-prone spontaneously hypertensive rats (SHRSP) are a strain of rat that exhibit severely high blood pressure and stroke attacks at an early age, but their heart function in vitro has seldom been studied in detail. Although the activity of the sympathetic nervous system is known to increase after myocardial ischaemia, there is little information about the cardiac release of noradrenaline (NA) associated with heart function after ischaemia in SHRSP. The aim of the present study was to examine heart function and cardiac NA release after ischaemia in SHRSP. 2. Isolated hearts of 4- and 8-month-old SHRSP and age-matched Wistar-Kyoto (WKY) rats were perfused in a working heart preparation and were subjected to 30 min ischaemia followed by 30 min reperfusion. Heart function and coronary flow were monitored throughout the experiment. Coronary effluent was collected for determination of NA using high-performance liquid chromatography coupled with electrochemical detection. 3. Under baseline conditions, cardiac output of 4-month-old SHRSP was slightly but significantly decreased compared with that of WKY rats (P < 0.05), although coronary flow was maintained normally at this age. Eight-month-old SHRSP showed a further impairment of systolic heart function, with lower coronary flow and higher coronary vascular resistance under baseline conditions. Elevated left ventricular end-diastolic pressure was evident in SHRSP at both ages before ischaemia. Heart function was severely damaged after 30 min global ischaemia in SHRSP from both age groups. Stroke-prone spontaneously hypertensive rats also showed lower coronary flow and higher coronary vascular resistance during reperfusion. 4. Coronary NA was not detectable in WKY rats or SHRSP at 4 months of age under baseline conditions. In 8-month-old SHRSP, pre-ischaemic NA release was significantly higher than that in age-matched WKY rat controls. The concentration of NA in the coronary effluent of SHRSP during reperfusion was also significantly higher than that of WKY rats at both ages. 5. These data demonstrate that SHRSP have early impairment of both systolic and diastolic heart function compared with WKY rats. Severe damage of heart function and coronary flow after ischaemia in SHRSP was accompanied with an increased release of NA, which may play a harmful role in heart function impairment in SHRSP after ischaemia.     

RELAXANT EFFECTS OF VASODILATOR PEPTIDES ON ISOLATED BASILAR ARTERIES FROM STROKE-PRONE SPONTANEOUSLY HYPERTENSIVE RATS

1. The relaxant effects of vasodilator peptides were examined in ring preparations of basilar arteries from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats. 2. Vasoactive intestinal peptide and peptide histidine iso-leucine produced similar endothelium-independent relaxations in basilar arteries from WKY rats and SHRSP. Calcitonin gene-related peptide (CGRP) elicited endothelium-independent relaxations in both groups and the CGRP-induced relaxation was greater in SHRSP than in WKY rats. Substance P and neurokinin A did not relax basilar arteries from either group. 3. Both WKY rat and SHRSP basilar arteries were relatively insensitive to atrial natriuretic peptide, brain natriuretic peptide and C-type natriuretic peptide. 4. Bradykinin (BK) potently relaxed basilar arteries with endothelium, but BK produced contractions in endotheliumrubbed arteries in both WKY rats and in SHRSP. There was no significant difference in the relaxant response to BK between WKY rat and SHRSP arteries. 5. Adrenomedullin (AM) produced endothelium-independent relaxations in both groups and the relaxant response to AM was significantly greater in SHRSP than in WKY rats. 6. Human CGRP(8–37; 1 μmol/L), a CGRP receptor antagonist, significantly inhibited both relaxant responses induced by CGRP and AM in WKY rats and in SHRSP arteries. 7. Among various peptides tested, the responses to CGRP and AM were higher in basilar arteries from SHRSP than in those from WKY rats. The relaxation produced by AM may be via CGRP receptors in WKY rat and SHRSP basilar arteries.     

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.     

Responses to endothelium-derived factors and their interaction in mesenteric arteries from Wistar-Kyoto and stroke-prone spontaneously hypertensive rats

1. Responses to endothelium-derived nitric oxide (EDNO), indomethacin-sensitive endothelium-derived contracting factor (EDCF) and hyperpolarization by endothelium-derived hyperpolarizing factor (EDHF) and the interaction among these factors in mesenteric arteries from 16-week-old Wistar Kyoto (WKY) rats and age-matched stroke-prone spontaneously hypertensive rats (SHRSP) were studied, observing the time-course of the response to 10-5 mol/L acetylcholine (ACh). 2. The effects of EDNO, EDCF and EDHF were blocked by Nomega-nitro-l-arginine (10-4 mol/L), indomethacin (10-5 mol/L) and a combination of apamin (5 x 10-6 mol/L) and charybdotoxin (10-7 mol/L), respectively. 3. The response to EDNO observed in the absence of EDCF and EDHF was not different between preparations from WKY rats and SHRSP. The response to EDCF observed in the absence of EDNO and EDHF was slightly greater in preparations from SHRSP. The response to EDHF in the absence of EDNO and EDCF was much greater in preparations from WKY rats. 4. Endothelium-derived contracting factor attenuated the relaxation in response to EDNO, the attenuation being greater in preparations from SHRSP. Relaxation in response to EDNO was blocked by EDHF in preparations from WKY rats, but not in preparations from SHRSP. 5. The response to EDCF was augmented by both EDNO and EDHF. The augmentation was greater in preparations from SHRSP. 6. The response to EDHF was attenuated by EDNO in preparations from WKY rats, but not in preparations from SHRSP. The response to EDHF was attenuated by EDCF in preparations from both WKY rats and SHRSP, the attenuation being greater in preparations from SHRSP. 7. These results suggest that there are interactions among these factors in terms of their release or the response to ACh in mesenteric arteries that differ between preparations from WKY rats and SHRSP. In addition, involvement of factors other than these three factors, which also differs between preparations from WKY rats and SHRSP, is suggested.