Mesenteric vasoconstrictor response to 5-hydroxytryptamine in the in situ blood autoperfused rat mesentery: involvement of 5-HT(2B) and/or 5-HT(2C) receptor activation

Renal Sympathetic Hyperactivity in Diabetes Is Modulated by 5-HT1D Receptor Activation via NO Pathway

Renal vasculature, which is highly innervated by sympathetic fibers, contributes to cardiovascular homeostasis. This renal sympathetic outflow is inhibited by 5-HT in normoglycaemic rats. Considering that diabetes induces cardiovascular complications, we aimed to determine whether diabetic state modifies noradrenergic input at renal level and its serotonergic modulation in rats. Alloxan diabetic rats were anaesthetized (pentobarbital; 60 mg/kg i.p.) and prepared for in situ autoperfusion of the left kidney to continuously measure systemic blood pressure (SBP), heart rate (HR), and renal perfusion pressure (RPP). Electrical stimulation of renal sympathetic outflow induces frequency-dependent increases (Δ) in RPP (23.9 ± 2.1, 59.5 ± 1.9, and 80.5 ± 3.5 mm Hg at 2, 4, and 6 Hz, respectively), which were higher than in normoglycaemic rats, without modifying HR or SBP. Intraarterial bolus of 5-HT and 5-CT (5-HT_1/5/7 agonist) reduced electrically induced ΔRPP. Only L-694,247 (5-HT_1D agonist) reproduced 5-CT inhibition on sympathetic-induced vasoconstrictions, whereas it did not modify exogenous noradrenaline-induced ΔRPP. 5-CT inhibition was exclusively abolished by i.v. bolus of LY310762 (5-HT_1D antagonist). An inhibitor of guanylyl cyclase, ODQ (i.v.), completely reversed the L-694,247 inhibitory effect. In conclusion, diabetes induces an enhancement in sympathetic-induced vasopressor responses at the renal level. Prejunctional 5-HT_1D receptors, via the nitric oxide pathway, inhibit noradrenergic-induced vasoconstrictions in diabetic rats.

Cardiovascular effects of antiobesity drugs: are the new medicines all the same?

Waiting for a definite answer from well-designed randomized prospective clinical trials, the impact of the new antiobesity drugs -liraglutide, bupropion/naltrexone, phentermine/topiramate and lorcaserin- on cardiovascular outcomes remains uncertain. What has been learned from previous experience with older medicines is that antiobesity drugs may influence cardiovascular health not only causing weight reduction but also through direct actions on the cardiovascular system. Therefore, in the present review, we examine what is known, mainly from preclinical investigations, about the cardiovascular pharmacology of the new antiobesity medicines with the aim of highlighting potential mechanistic differences. We will show that the two active substances of the bupropion/naltrexone combination both exert beneficial and unwanted cardiovascular effects. Indeed, bupropion exerts anti-inflammatory effects but at the same time it does increase heart rate and blood pressure by potentiating catecholaminergic neurotransmission, whereas naltrexone reduces TLR4-dependent inflammation and has potential protective effects in stroke but also impairs cardiac adaption to ischemia and the beneficial opioid protective effects mediated in the endothelium. On the contrary, with the only exception of a small increase in heat rate, liraglutide only exerts favorable cardiovascular effects by protecting myocardium and brain from ischemic damage, improving heart contractility, lowering blood pressure and reducing atherogenesis. As far as the phentermine/topiramate combination is concerned, no direct cardiovascular beneficial effect is expected for phentermine (as this drug is an amphetamine derivative), whereas topiramate may exert cardioprotective and neuroprotective effects in ischemia and anti-inflammatory and antiatherogenic actions. Finally, lorcaserin, a selective 5HT_2C receptor agonist, does not seem to exert significant direct effects on the cardiovascular system though at very high concentrations this drug may also interact with other serotonin receptor subtypes and exert unwanted cardiovascular effects. In conclusion, the final effect of the new antiobesity drugs on cardiovascular outcomes will be a balance between possible (but still unproved) beneficial effects of weight loss and "mixed" weight-independent drug-specific effects. Therefore comparative studies will be required to establish which one of the new medicines is more appropriate in patients with specific cardiovascular diseases.

Elucidation of the profound antagonism of contractile action of phenylephrine in rat aorta effected by an atypical sympathomimetic decongestant

Vasoconstrictive properties of sympathomimetic drugs are the basis of their widespread use as decongestants and possible source of adverse responses. Insufficiently substantiated practice of combining decongestants in some marketed preparations, such are those containing phenylephrine and lerimazoline, may affect the overall contractile activity, and thus their therapeutic utility. This study aimed to examine the interaction between lerimazoline and phenylephrine in isolated rat aortic rings, and also to assess the substrate of the obtained lerimazoline-induced attenuation of phenylephrine contraction. Namely, while lower concentrations of lerimazoline (10⁻⁶ M and especially 10⁻⁷ M) expectedly tended to potentiate the phenylephrine-induced contractions, lerimazoline in higher concentrations (10⁻⁴ M and above) unexpectedly and profoundly depleted the phenylephrine concentration-response curve. Suppression of NO with NO synthase (NOS) inhibitor N^w-nitro-L-arginine methyl ester (L-NAME; 10⁻⁴ M) or NO scavanger OHB₁₂ (10⁻³ M), as well as non-specific inhibition of K⁺-channels with tetraethylammonium (TEA; 10⁻³ M), have reversed lerimazoline-induced relaxation of phenylephrine contractions, while cyclooxygenase inhibitor indomethacin (10⁻⁵ M) did not affect the interaction between two vasoconstrictors. At the receptor level, non-selective 5-HT receptor antagonist methiothepin reversed the attenuating effect of lerimazoline on phenylephrine contraction when applied at 3×10⁻⁷ and 10⁻⁶ M, but not at the highest concentration (10⁻⁴ M). Neither the 5-HT_1D-receptor selective antagonist BRL 15572 (10⁻⁶ M) nor 5-HT₇ receptor selective antagonist SB 269970 (10⁻⁶ M) affected the lerimazoline-induced attenuation of phenylephrine activity. The mechanism of lerimazoline-induced suppression of phenylephrine contractions may involve potentiation of activity of NO and K⁺-channels and activation of some methiothepin-sensitive receptors, possibly of the 5-HT_2B subtype.

Zolmitriptan: a novel portal hypotensive agent which synergizes with propranolol in lowering portal pressure

OBJECTIVE

Only a limited proportion of patients needing pharmacological control of portal hypertension are hemodynamic responders to propranolol. Here we analyzed the effects of zolmitriptan on portal pressure and its potential interaction with propranolol.

METHODS

ZOLMITRIPTAN, PROPRANOLOL OR BOTH WERE TESTED IN TWO RAT MODELS OF PORTAL HYPERTENSION: common bile duct ligation (CBDL) and CCl4-induced cirrhosis. In these animals we measured different hemodynamic parameters including portal venous pressure, arterial renal flow, portal blood flow and cardiac output. We also studied the changes in superior mesenteric artery perfusion pressure and in arterial wall cAMP levels induced by zolmitriptan, propranolol or both. Moreover, we determined the effect of splanchnic sympathectomy on the response of PVP to zolmitriptan.

RESULTS

In both models of portal hypertension zolmitriptan induced a dose-dependent transient descent of portal pressure accompanied by reduction of portal flow with only slight decrease in renal flow. In cirrhotic rats, splanchnic sympathectomy intensified and prolonged zolmitriptan-induced portal pressure descent. Also, propranolol caused more intense and durable portal pressure fall when combined with zolmitriptan. Mesenteric artery perfusion pressure peaked for about 1 min upon zolmitriptan administration but showed no change with propranolol. However propranolol enhanced and prolonged the elevation in mesenteric artery perfusion pressure induced by zolmitriptan. In vitro studies showed that propranolol prevented the inhibitory effects of β2-agonists on zolmitriptan-induced vasoconstriction and the combination of propranolol and zolmitriptan significantly reduced the elevation of cAMP caused by β2-agonists.

CONCLUSION

Zolmitriptan reduces portal hypertension and non-selective beta-blockers can improve this effect. Combination therapy deserves consideration for patients with portal hypertension failing to respond to non-selective beta-blockers.

Characterization of contractile 5-hydroxytryptamine receptor subtypes in the in situ autoperfused kidney in the anaesthetized rat

Using several 5-hydroxytryptamine (5-HT) agonists and antagonists, we attempted to characterize the receptor subtypes involved in the contractile response to 5-HT in the in situ autoperfused rat kidney. An intra-arterial (i.a.) bolus injection of 5-HT (0.00000125 to 0.1 microg/kg) increased renal perfusion pressure in a dose-dependent way but did not affect the systemic blood pressure. The selective 5-HT2 receptor agonist alpha-methyl-5-HT (alpha-methyl-5-hydroxytryptamine) and the non-selective 5-HT2C receptor agonist (1-(3-chlorophenyl)piperazine), m-CPP, caused a local vasoconstrictor effect in the autoperfused rat kidney, whereas BW723C86, a selective 5-HT2B receptor agonist, the 5-HT1 receptor agonist 5-carboxamidotryptamine, 5-CT, and the selective 5-HT3 receptor agonist m-CPBG (1-(m-chlorophenyl)-biguanide) did not modify the renal perfusion pressure. The vasoconstrictor effect elicited by alpha-methyl-5-HT and m-CPP was significantly decreased by ritanserin (a 5-HT2 receptor antagonist), SB 206553 (3,5-Dihydro-5-methyl-N-3pyridinylbenzo[1,2.b:4,5-b']dipyrrole(1H)-carboxamide hydrochloride), a selective 5-HT2B/2C receptor antagonist and enalapril, but was not modified by pretreatment with spiperone (a 5-HT2A receptor antagonist). The results of protein expression analyses allow us to postulate that 5HT-SRC (a 5-HT2C receptor protein) is expressed in renal tissue and differentially expressed in renal artery. Our data suggest also that the serotonergic vasoconstrictor response induced in the in situ autoperfused rat kidney would be mediated by local 5-HT2C receptor activation.

Effects of Daidzein Sulfates on Blood Pressure and Artery of Rats

The aim of this study is to investigate the hypotensive and vasodilator effects of daidzein sulfates, a water-solubility derivative of daidzein. Tail cuff blood pressure of spontaneously hypertensive rat (SHR) was measured with non-invasive Electro-Sphygmomanometer. An isometric tension of rat mesenteric artery ring segments was recoded in vitro on a myograph. The results showed that daidzein sulfates (20 and 40 mg/kg) could decrease blood pressure of SHR in single dose and multi-doses. Daidzein sulfates (1-100 microM) inhibited the contraction of rat mesenteric arterial ring segments induced by norepinephrine (NA) and 5-hydroxytryptamine (5-HT). Daidzein sulfates (100-1000 microM) inhibited arterial segment's contraction induced by KCl and CaCl(2). The concentration- contractive curves were shifted toward right in a non-parallel manner with decreased E(max.) Daidzein sulfaltes inhibited the extracellular Ca(2+)-dependent contraction. Daidzein sulfates of 100 and 300 microM significantly inhibited the contraction induced by CaCl(2) in Ca(2+)-free solution, which is an extracellular Ca(2+)-dependent contraction; but daidzein sulfates did not inhibit the intracellular Ca(2+)-dependent NA-induced contraction, in Ca(2+)-free solution. The results suggest that daidzein sulfates possess significant hypotensive and vasodilator effects which mainly derive from artery smooth muscle cells by inhibiting the receptor-mediated Ca(2+)-influx.

Effect of 5-hydroxytryptamine on neurogenic vasoconstriction in the isolated, autoperfused hindquarters of the rat

1. In the present study, we analysed the effect of different doses of 5-hydroxytryptamine (5-HT; intravenous infusions of 0.001-40 microg/kg per min) in the autoperfused hindquarters of the rat subjected to electrical stimulation (frequencies of 0.5-20 Hz) of the lumbar chains, investigating the relationship between the adrenergic and serotonergic systems in this vascular bed. 2. Because we observed that 5-HT inhibited the increases in perfusion pressure induced by electrical stimulation of the lumbar chains, we used different agonists and antagonists to analyse the mechanism of action of 5-HT. 3. The effect of 5-HT was inhibited by methiothepin (a non-specific 5-HT receptor antagonist), but not by ritanserin (a selective 5-HT2 receptor antagonist). The effects of 5-HT were mimicked by 5-carboxamidotryptamine (a 5-HT1 receptor agonist) and L-694 247 (a selective 5-HT1D receptor agonist), but not by 8-hydroxy-2-dipropylaminotetralin (a 5-HT1A receptor agonist), CGS-12066B (a 5-HT1B receptor agonist), alpha-methyl-5-HT (a 5-HT2 receptor agonist), 1-(3-chlorophenyl) piperazine (a 5-HT2C receptor agonist) or 1-phenylbiguanide (a 5-HT3 receptor agonist). The selective 5-HT1D/1B receptor antagonist BRL 15572 inhibited the effect of the agonist L-694 247. 4. Our data suggest that 5-HT inhibits the increases in perfusion pressure induced by the electrical stimulation of the lumbar chains, acting on presynaptic 5-HT1D receptors and decreasing the release of noradrenaline from the sympathetic nerves in the hindquarter vascular bed of the rat.

Vasoconstrictor Responses to 5-Hydroxytryptamine in the Autoperfused Hindquarters of Spontaneously Hypertensive Rats

In this work we studied the responses and receptors involved in the effects of intra-arterial 5-hydroxytryptamine (5-HT) in the in situ autoperfused hindquarters of spontaneously hypertensive rats (SHR). Intra-arterial administration of the highest doses (50-1,000 ng/kg) produced a vasoconstrictor effect that was inhibited by ritanserin (a selective 5-HT2 receptor antagonist), SB 206553 (a selective 5-HT(2B/2C) receptor antagonist) and spiperone (a nonspecific 5-HT(1/2A) receptor antagonist), and was mimicked by alpha-methyl-5-HT (a selective 5-HT2 receptor agonist) and m-CPP (a selective 5-HT2C receptor agonist), but not by the intra-arterial administration of BW 723C86, a selective 5HT2B receptor agonist. SB 206553 and spiperone inhibited alpha-methyl-5HT-induced vasoconstriction in the hindquarters of SHR. Our data suggest that the vasoconstrictor response induced by 5-HT in the autoperfused hindquarters of SHR is mainly mediated by the activation of 5-HT2A and 5-HT2C receptors.

5-Hydroxytryptamine-induced vasodilator responses in the hindquarters of the anaesthetized rat, involve beta2-adrenoceptors

These studies were conducted to examine the role of the vasoactive mediators nitric oxide (NO) and adrenaline (epinephrine) in the serotonin (5-hydroxytryptamine; 5-HT)-induced vasodilator response in the hindquarter vascular bed of anaesthetized rats. Intra-arterial administration of doses of 5-HT in the range 0.12-25 ng kg(-1) produced a dose-independent vasodilator effect in the hindquarters. The selective 5-HT(1D/1B) receptor agonist, L-694,247 at intra-arterial doses of 0.0012-1000 ng kg(-1), as well as adrenaline (at doses of 0.05-50 ng kg(-1) i.a.), mimicked the dose-independent vasodilator effect induced by intra-arterial administration of 5-HT. Intravenous pre-treatment with the selective beta2-receptor antagonist ICI 118,551 (0.5 mg kg(-1)) blocked the vasodilator effect of 5-HT, adrenaline and L-694,247. Additionally, the inhibitor of NO synthase NG-nitro-L-arginine (L-NAME) (at a dose of 10 mg kg(-1) i.v.) blocked the vasodilator action of acetylcholine 300-3000 ng kg(-1)) but did not modify 5-HT-induced vasodilatation. The vasodilator effect produced by intra-arterial administration of 5-HT in the hindquarters was significantly inhibited both 30 min after denervation of the lumbar sympathetic chains and 1 h after bilateral adrenalectomy. Our data suggest that in the in-situ autoperfused hindquarters of the rat 5-HT-induced vasodilatation is mediated by a local 5-HT(1D) or 5-HT(1D/1B) activation, which in turn mediates the adrenal release of adrenaline, which then produces beta2-activation and vasodilatation.

Receptor changes in cerebral arteries after subarachnoid haemorrhage

Subarachnoid haemorrhage (SAH), occurring with a delay of 4-10 days is linked to cerebral vasospasm (CVS), a pathological constriction of the cerebral arteries. Several agents have been suggested as being responsible - amongst these perhaps 5-hydroxytryptamine (5-HT) and endothelin-1 (ET-1) are the most prominent, given their ability to elicit powerful constriction of arteries. Investigating both 5-HT and ET receptors we observed distinct changes in the receptor phenotype after experimental SAH - namely upregulation of the ETB and 5-HT1B receptors - linked to a higher sensitivity to the endogenous agonists. This multiple receptor upregulation may explain the failure in treating CVS using single receptor antagonists, and may also significantly change our understanding of the effector mechanism behind CVS. So far only the ET and 5-HT receptors have been studied in this regard, but other receptor systems may also undergo changes.

Attenuated agonist evoked vasoconstrictor responses in the perfused mesenteric vascular bed of streptozotocin diabetic rats

We compared agonist-evoked responses in the perfused mesenteric vascular bed (MVB) of streptozotocin (STZ) diabetic Sprague-Dawley rats 2 and 14 weeks after induction of diabetes. Endothelin-1 (ET-1)-, methoxamine (MTX)-, and KCl-evoked vasoconstrictor responses were unchanged in 2-week-old diabetic rats. In contrast, both the sensitivity (P < 0.01) and the maximal vasoconstrictor responses (P < 0.05) to ET-1 were attenuated in 14-week-old diabetic rats, whereas endothelin plasma levels were increased (P < 0.05). Although no differences were observed in responses to KCl in either the 2- or 14-week-old diabetic groups, MTX-evoked maximal responses were attenuated in the 14-week-old group (P < 0.01). Changes in agonist-evoked responses in the 14-week-old diabetic group were unaffected by the protein kinase C (PKC) inhibitor, staurosporine, the phospholipase C (PLC) inhibitor, U73122, the calcium channel blocker, nifedipine, the calcium pump inhibitor, cyclopiazonic acid (CPA), or by endothelial denudation. Sodium fluoride (NaF), an activator of guanosine triphosphate binding proteins (G proteins) normalized the responses in the 14-week-old diabetic group. These data suggest that advanced stages of STZ are associated with alterations in G protein receptor coupling and/or activity leading to the attenuation of responses to vasoconstrictor agonists.