Effects of bradykinin on [3H]-norepinephrine release in rat hypothalamus

Endostatin inhibits bradykinin-induced cardiac contraction

.Endogenous fragments of extracellular matrix are known to possess various biological effects. Levels of endostatin, a fragment of collagen type XVIII, increase in certain cardiac diseases, such as cardiac hypertrophy and myocardial infarction. However, the influence of endostatin on cardiac contraction has not been clarified. In the present study, we investigated the effects of endostatin on bradykinin-induced atrial contraction. Isometric contractile force of mouse isolated left atria induced by electrical current pulse was measured. Voltage-dependent calcium current of guinea pig ventricular myocytes was measured by a whole-cell patch-clamp technique. Endostatin (100–1,000 ng/ml) alone treatment had no influence on left atrial contraction. On the other hand, pretreatment with endostatin (300 ng/ml) significantly inhibited bradykinin (1 µM)-induced contraction and voltage-dependent calcium current. These data suggest that endostatin may decrease bradykinin-induced cardiac contraction perhaps through the inhibition of voltage-dependent calcium channel.

Reversal of fructose-induced hypertension and insulin resistance by chronic losartan treatment is independent of AT2 receptor activation in rats

OBJECTIVES

To examine whether angiotensin II type 2 receptors (AT2R) are involved in the reversal of fructose-induced hypertension and insulin resistance after chronic angiotensin II type 1 receptor (AT1R) blockade.

METHODS

Sprague-Dawley rats on fructose-enriched or regular diets were pretreated with losartan, an AT1R antagonist, or vehicle for 2 weeks before two-step glucose and insulin clamp experiments with [3-3H]glucose infusion. The hepatic glucose production (HGP) and whole-body glucose uptake (WBGU) were calculated during basal, euglycemic and euglycemic hyperinsulinemic periods. Blood pressure was measured before and after acute losartan (10 mg/kg, i.v. bolus), alone or in combination of PD123319 (PD, 50 microg/kg per min), an AT2R antagonist, or CGP42112 (2 microg/kg per min), an AT2R agonist, during the clamp study.

RESULTS

In rats on a regular diet, acute infusion of losartan alone or in combination with PD, an AT2R blocker, did not alter blood pressure and glucose metabolism during experiments. Fructose feeding for 6 weeks significantly increased blood pressure and attenuated insulin-mediated suppression of HGP and stimulation of WBGU. Both acute and chronic administration of losartan suppressed fructose-induced hypertension. Concomitant treatment with PD and losartan blunted the acute but not chronic losartan-mediated depressor effect. Acute losartan treatment further reduced insulin-induced suppression of HGP, but simultaneously increased insulin-stimulated WBGU. These acute metabolic effects of losartan were eliminated when PD was co-administered with losartan. Conversely, chronic losartan pretreatment significantly enhanced suppression of HGP and increased stimulation of WBGU by insulin, which were not altered when PD or CGP 42112 was superimposed on losartan during the clamp experiments.

CONCLUSIONS

These results suggest that reversal of high fructose-induced hypertension and insulin resistance by chronic losartan treatment is not dependent on AT2R activation and that functional activation of AT1R plays a major role in the pathogenesis of high fructose-induced hypertension and insulin resistance.

Nitric oxide inhibits the bradykinin B2 receptor-mediated adrenomedullary catecholamine release but has no effect on adrenal blood flow response in vivo

The role of nitric oxide (NO) in bradykinin (BK)-induced adrenal catecholamine secretion still remains obscure. The present study was to investigate whether an inhibition of NO synthase with N(omega)-nitro-L-arginine methyl ester (L-NAME) would modulate BK-induced adrenal catecholamine secretion (ACS) and adrenal vasodilating response (AVR) in anesthetized dogs. Plasma catecholamine concentrations were determined with an HPLC coupled with an electrochemical detector. All drugs were locally administered to the left adrenal gland via intra-arterial infusion. BK dose-dependently increased both ACS and AVR. Hoe-140, a selective B(2) antagonist, significantly blocked the BK-induced increases in both ACS and AVR. In the presence of L-NAME, the BK-induced ACS was significantly enhanced, while the simultaneous AVR remained unaffected. These results suggest that the both BK-induced ACS and AVR are primarily mediated by B(2) receptors in the canine adrenal gland. Our results also suggest that the enhanced ACS in response to BK in the presence of L-NAME may have resulted from a specific inhibition of NO formation in the adrenal gland. It is concluded that the BK-induced NO may play an inhibitory role in the B(2)-receptor-mediated mechanisms regulating ACS, while it may not be implicated in the B(2)-receptor-mediated AVR under in vivo conditions.

Protein kinase C: a physiological mediator of enhanced transmitter output

Protein kinase C (PKC), activated by either diacylglycerol and/or arachidonic acid, through the activation of presynaptic receptors or nerve or nerve depolarization is involved is involved in the enhancement of transmitter release from many neural types. This facilities is most likely mediated by the phosphorylation of proteins involved in vesicle dynamics although a role for ion channels cannot be ruled out. PKC is not fundamental to the release process but rather has a modulatory role of PKC is to help maintain transmitter output during prolonged or elevated levels of activation and this seems to parallel suggestions that PKC is involved in the movement of reserve pools of vesicles into release-study sites. presynaptic facilitatory actions mediated by PKC are also involved in integrated modulatory functions such as long term potentiation, again where it elevates or maintains transmitter output. Although studies have tried to identify specific roles for various PKC isoforms, the actions of phorbol esters in elevators transmitter release do not fit with known potencies on individual isoforms and lit suggests that PKC may be located at an intraneuronal location which is difficult to access for lipophilic phorbol esters and further work is required in this area.

Modulatory effect of bradykinin on noradrenaline release in isolated atria from normal and B2 knockout transgenic mice

The modulatory effect of bradykinin on electrically-induced noradrenaline release was assessed in isolated atria from normal and B2 knockout transgenic mice preincubated with [3H]noradrenaline. Concentrations of 1, 3 and 10 nM of bradykinin did not significantly alter the outflow of radioactivity whereas higher concentrations of bradykinin (30 and 100 nM) enhanced it. The facilitatory effect of 30 nM bradykinin was inhibited by a selective bradykinin B2 receptor antagonist. Hoe 140 (D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]bradykinin, 30 nM), and by a protein kinase C inhibitor, bisindolylmaleimide (1 microM). The co-administration of bradykinin (1 to 100 nM) with either [Leu8]des-Arg9-bradykinin (100 nM), AcLys[DbetaNal7,Ile8]des-Arg9-bradykinin (30 nM) (bradykinin B1 receptor antagonists) or diclofenac (1 microM) (a cyclooxygenase inhibitor), shifted the facilitatory effect of bradykinin to lower concentrations. The facilitatory effect of bradykinin also was enhanced by enalaprilat (1 microM) and mergetpa (1 microM), inhibitors of angiotensin-converting enzyme (kininase II) and kininase I, respectively. In contrast, selective bradykinin B1 receptor agonists, des-Arg9-bradykinin (1 to 100 nM) and Sar[D-Phe8]des-Arg7-bradykinin (1 to 100 nM), did not significantly affect the stimulation-induced outflow of radioactivity. Neither bradykinin (100 nM) nor des-Arg9-bradykinin (100 nM) had any modulatory effect in B2 knockout transgenic mice. These findings suggest that the facilitatory effect of bradykinin on noradrenaline release in the mouse atria is mediated exclusively by presynaptic bradykinin B2 receptors which are linked to protein kinase C. The greater release of noradrenaline with bradykinin under inhibition of prostaglandins production and kininases I and II activity might be of importance in pharmacotherapies.

Interaction of the renin-angiotensin system, bradykinin and sympathetic nerves with cholinergic transmission in the rat isolated trachea

1. The present study was undertaken to investigate the interaction of the renin-angiotensin system (RAS), bradykinin and the sympathetic nervous system with cholinergic transmission in the rat airways. Experiments were performed on epithelium-intact and epithelium-denuded preparations of rat isolated trachea which had been incubated with [3H]-choline to incorporate [3H]-acetylcholine into the cholinergic transmitter stores. Tracheal preparations were subjected to electrical field stimulation (trains of 1 ms pulses, 5 Hz, 15 V) and the stimulation-induced (S-I) efflux taken as an index of transmitter acetylcholine release. 2. In both epithelium-intact and epithelium-denuded tracheal preparations, the alpha 2-adrenoceptor agonist UK14304 (0.1 and 1 microM) inhibited the S-I efflux, in a concentration-dependent manner. The inhibition of S-I efflux produced by UK14304 (1 microM) was antagonized by the selective alpha 2-adrenoceptor antagonist idazoxan (0.3 microM). Idazoxan (0.3 microM) alone had no effect on the S-I efflux. 3. Angiotensin II (0.1 and 1 microM) was without effect on the S-I efflux in either epithelium-intact or epithelium-denuded tracheal preparations. When angiotensin-converting enzyme was inhibited by perindoprilat (10 microM), angiotensin II (1 microM) was also without effect on the S-I efflux. Similarly, in the presence of idazoxan (0.3 microM), to block prejunctional alpha 2-adrenoceptors, angiotensin II (0.1 and 1 microM) did not alter the S-I efflux. When added alone, perindoprilat (10 microM) did not alter the S-I efflux. 4. In epithelium-denuded preparations, bradykinin (0.01-1 microM) inhibited the S-I efflux. In epithelium-intact preparations, there was also a tendency for bradykinin (0.1 and 1 microM) to inhibit the S-I efflux but this was not statistically significant. However, when angiotensin-converting enzyme and neutral endopeptidase were inhibited by perindoprilat (10 microM) and phosphoramidon (1 microM), respectively, bradykinin (1 microM) significantly inhibited the S-I efflux in epithelium-intact preparations as well as in epithelium-denuded preparations. The inhibition of the S-I efflux produced by bradykinin, in the combined presence of perindoprilat (10 microM) and phosphoramidon (1 microM), was unaffected by the additional presence of the cyclo-oxygenase inhibitor indomethacin (10 microM) and/or the nitric oxide synthase inhibitor NG-nitro-L-arginine (100 microM), in either epithelium-intact or epithelium-denuded preparations. 5. In conclusion, the findings of the present study suggest that airway parasympathetic nerves are endowed with alpha 2-adrenoceptors which subserve inhibition of transmitter acetylcholine release. Under the present conditions, however, transmitter acetylcholine release is not subject to transneuronal modulation by noradrenaline released from adjacent sympathetic nerves in the airways. Moreover, angiotensin II and perindoprilat do not appear to modulate acetylcholine release from parasympathetic nerves of the airways. In contrast, bradykinin inhibits acetylcholine release from airway parasympathetic nerves but this action of bradykinin is limited by the activity of epithelial angiotensin-converting enzyme and/or neutral endopeptidase. The inhibitory action of bradykinin on cholinergic transmission in the airways does not appear to involve the liberation of prostaglandins or nitric oxide.

Angiotensin converting enzyme inhibition unmasks the sympathofacilitatory effect of bradykinin in human right atrium

OBJECTIVE

To investigate the role of angiotensin converting enzyme (ACE) inhibition in bradykinin-mediated modulation of noradrenaline release in human and rat atrium.

METHODS

Human and rat atrial slices were incubated with [3H]-noradrenaline, superfused with Krebs-Henseleit solution and stimulated electrically at 5 Hz. The stimulation-induced outflow of radioactivity was taken as an index of endogenous noradrenaline release.

RESULTS

In the absence of ACE inhibition 0.01-1 micromol/l bradykinin failed to alter the release of noradrenaline in human atrium. In contrast, 0.001-0.1 micromol/l bradykinin enhanced the release of noradrenaline in rat atrium. In the presence of 3 micromol/l of the ACE inhibitor captopril, however, bradykinin significantly enhanced the release of noradrenaline in human atrium. The bradykinin B1-receptor agonist (Des-Arg9)-bradykinin (0.01-1 micromol/l) had no effect on the release of noradrenaline in human atrium both in the absence and in the presence of 3 micromol/l captopril. Captopril (3 micromol/l) potentiated the facilitatory effect of bradykinin in rat atrium. The selective bradykinin B2-receptor antagonist D-Arg[Hyp3,Thi5, D-Tic7,Oic8]-bradykinin (Hoe 140, 0.3 micromol/l) and the cyclo-oxygenase inhibitor indomethacin (10 micromol/l) reduced the facilitatory effect of bradykinin significantly in the presence of captopril in rat and human atrium. Prostaglandin F2alpha (0.1 micromol/l), prostaglandin E2 (0.3 micromol/l) and the thromboxane A2 receptor agonist U-46 619 (0.1 micromol/l) enhanced the release of noradrenaline in human atria, whereas 0.1 micromol/l prostaglandin I2 had no effect.

CONCLUSION

These data suggest that bradykinin facilitates the release of noradrenaline in human and rat atrium by activation of bradykinin receptors of the B2-subtype and subsequent release of facilitatory prostaglandins. The facilitatory effect of bradykinin in human atrium can only be demonstrated when its enzymatic degradation is prevented by ACE inhibition.

Modulatory effect of bradykinin on the release of noradrenaline from rat isolated atria

1. We investigated the modulation by bradykinin (BK) of electrically induced noradrenaline release in rat isolated atria preincubated with [3H]-noradrenaline. 2. BK (1-100 nM) enhanced significantly the stimulation-induced outflow of radioactivity in a concentration-dependent manner with a calculated EC50 of 0.58 nM. 3. Des-Arg9-BK (0.1-100 nM), a selective B1 receptor agonist, did not modify the stimulation-induced outflow of radioactivity. Hoe 140 (10 nM), a selective B2 receptor antagonist, but not [Leu8]-des-Arg9-BK (100 nM), a selective B1 receptor antagonist, blocked the facilitatory effect of BK. 4. The effect of BK was not affected by diclofenac (1 microM), a cyclo-oxygenase inhibitor. Bisindolylmaleimide (1 microM), a protein kinase C inhibitor, significantly reduced the facilitatory effect of BK (10 nM), angiotensin II (0.3 microM) and phorbol dibutyrate (0.1 and 1 microM) but not of fenoterol (1 microM). 5. The results suggest that BK enhances noradrenaline release via a prejunctional B2 kinin receptor in the rat atrium. The effect appears to involve protein kinase C as a second messenger.

Bradykinin modulation of alpha 2-adrenoceptors in the nucleus tractus solitarii of the rat. An in vitro autoradiographical study

The existence of an interaction between bradykinin (Bk) receptors and the alpha 2-adrenoceptors were evaluated by means of quantitative receptor autoradiography in the nucleus tractus solitarii (NTS) of the rat. In competition experiments using L-noradrenaline (0.1 nM to 10 microM) against [3H]p-aminoclonidine ([3H]PAC) (10 nM) it was observed that Bk produced an increase in the IC50 value of L-noradrenaline in a concentration response manner, which reached a maximum of about 100% with 10 nM of the peptide associated with a small decrease in the B0 value (15%). In saturation experiments Bk promoted a significant increase in the KD value of [3H]PAC (60%) and a decrease in the Bmax value (36%). The specific Bk B2 receptor antagonist HOE-140 fully counteracted the effect of Bk on the alpha 2-adrenoceptors as analyzed by the competition experiments. Furthermore, des-Arg9-Bk, a Bk analog which exhibits selective agonist activity to the Bk B1 receptor subtype did not produce any effect on the alpha 2-adrenoceptors, suggesting that the Bk B2 receptor subtype may be mediating the Bk action on the alpha 2-adrenoceptors in the NTS. The effect of Bk (10 nM) was analyzed together with GTP (0.1 nM) in competition experiments and no change in the ability of L-noradrenaline to compete for [3H]PAC binding sites was observed in the presence of GTP, suggesting that the receptor interaction between the Bk B2 receptors and the alpha 2-adrenoceptors may be a G-protein dependent mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)