Hakan Gurdal

EFFECTS OF CALCIUM CHANNEL BLOCKERS ON FORMALIN-INDUCED NOCICEPTION AND INFLAMMATION IN RATS

The possible anti-inflammatory and antinociceptive effects of nitrendipine, nicardipine, diltiazem and verapamil were examined with formalin test in the rat paw. Pretreatment with these calcium channel blockers 1 h before formalin injection diminished formalin-induced inflammatory changes and nociceptive responses. Formalin-induced nociceptive responses were inhibited 20-90% by the calcium channel blockers. Nitrendipine and nicardipine were found to be highly effective in inhibiting the inflammatory changes, whereas the effects of verapamil and diltiazem were partial. Administration of naloxone affected neither the inflammatory changes and nociceptive responses induced by formalin nor the antiinflammatory and antinociceptive effects of the calcium channel blockers. The results suggest the possible anti-inflammatory and naloxone-insensitive antinociceptive properties of calcium channel blockers.

α1-Adrenoceptor-mediated contraction of rat aorta is partly mediated via transactivation of the epidermal growth factor receptor

Background and purpose:  High level of plasma catecholamines is a risk factor for vascular diseases such as hypertension and atherosclerosis. Catecholamines induce hypertrophy of vascular smooth muscle through α1‐adrenoceptors, which in cell culture involves the transactivation of epidermal growth factor receptor (EGFR). We hypothesized that EGFR transactivation was also involved in contractions of rat aorta mediated by α1‐adrenoceptors.

The effect of long-term resveratrol treatment on relaxation to estrogen in aortae from male and female rats: role of nitric oxide and superoxide.

Resveratrol, which is found in several foods, has vasorelaxing and estrogen-like activities. The aim of the present study was to determine whether the relaxation to estrogen is differently modified between male and female genders after long-term resveratrol treatment. To test this, we compared endothelium-dependent and -independent relaxations to estrogen in the aortae of control and resveratrol-treated male and female rats. Nitric oxide and superoxide levels were also evaluated to explain the mechanism of action of resveratrol. Concentration-response curves to estrogen (10(-10)-10(-4) M) were obtained in aortic rings with and without endothelium from control or long-term resveratrol-treated (50 mg/l in drinking water for 21 days) male and female rats. Estrogen produced mainly endothelium-dependent relaxation in aortic rings of rats, with a higher potency in females than males. Resveratrol treatment increased both endothelium-dependent and -independent relaxations to estrogen especially in aortae from males. The relaxations to estrogen in the aortae of resveratrol-treated rats were inhibited, almost to the same extent as those of control, by pretreatment with ICI 182,780 (10(-6) M), an estrogen receptor antagonist. In both genders, resveratrol treatment increased basal nitric oxide and nitrite/nitrate productions and decreased both basal and NAD(P)H-induced superoxide productions in the aortae. In addition, plasma estrogen levels were found decreased in long-term resveratrol-treated animals of both genders. The improvement in the relaxations to estrogen observed in resveratrol-treated animals could be related to elevated nitric oxide and/or decreased superoxide productions and possibly mediated by classical estrogen receptors. The modulating effect of resveratrol on estrogen responsiveness may differ between male and female.

Short-term effects of three continuous hormone replacement therapy regimens on platelet tritiated imipramine binding and mood scores: a prospective randomized trial.

OBJECTIVE To evaluate the effects of continuous hormone replacement therapy (HRT) regimens on platelet-tritiated ((3)H-) imipramine binding (Bmax) and mood. DESIGN Prospective randomized study. SETTING University hospital. PATIENT(S) Sixty postmenopausal patients. INTERVENTION(S) Randomization to 3 months of daily treatment with tibolone and conjugated equine estrogen (CEE).625 mg combined either with 2.5 or 5 mg of medroxyprogesterone acetate (MPA). The inclusion criteria-matched patients declined for HRT were prescribed daily alendronate. Pre- and posttreatment blood sampling for Bmax and mood evaluation with the Beck Depression Inventory (BDI) and the State-Trait Anxiety Inventory (STAI) were done. MAIN OUTCOME MEASURE(S) Pre- and posttreatment Bmax and mood scores. RESULT(S) As compared with baseline, both CEE+MPA regimens and tibolone significantly increased Bmax. The comparisons of percent change from baseline Bmax for the CEE+MPA and tibolone groups were similar. All three HRT regimens improved the BDI significantly, while there were no significant changes in the STAI. In the alendronate group, there were no significant changes in both pre- and posttreatment Bmax and mood scores. CONCLUSION(S) Continuous treatment with CEE+MPA and tibolone increases platelet (3)H-imipramine binding and improves mood. Mood-enhancing effects of tibolone may occur through the serotonergic system, as is the case with estrogen.

α1-Adrenoceptor responsiveness in the aging aorta

Abstract Previous studies from this laboratory have shown that aortic α 1 -adrenoceptor-mediated responsiveness is altered during maturation and aging. This study examines the possibility that there is a change in the α 1 -adrenoceptor subtypes in the aorta during maturation and aging. The apparent affinity of norepinephrine, as determined by partial receptor inactivation with the α 1 -adrenoceptor antagonist phenoxybenzamine, was found to be higher in 1-month-old rats compared to 6- and 24-month-old rats. The α 1B -adrenoceptor subtype-selective antagonist chlorethylclonidine was used to examine possible heterogeneity in aortic α 1 -adrenoceptors. The inhibitory effect of chlorethylclonidine on norepinephrine-stimulated contraction was greater in young animals compared to aged animals. Chlorethylclonidine blocked norepinephrine-stimulated inositol phosphate accumulation in 1-month-old aorta but it produced only partial inhibition in the 6- and 24-month-old aortas. The relatively non-selective α 1 -adrenoceptor antagonists phenoxybenzamine (0.1 μM) and prazosin (0.1 μM) inhibited inositol phosphate accumulation and contractile responses in all ages. The complete block of α 1 -adrenoceptor-mediated responses by chlorethylclonidine in younger animals shows that α 1 -adrenoceptor-mediated responses are mediated by the chlorethylclonidine-sensitive α 1 -adrenoceptor subtypes. The partial inhibition by chlorethylclonidine of α 1 -adrenoceptor-mediated responses in 6- and 24-month-old animals indicates an increased role of an α 1 -adrenoceptor subtype that is relatively insensitive to chlorethylclonidine.

Fatigue of cholestasis and the serotoninergic neurotransmitter system in the rat

Fatigue associated with cholestasis may impair health‐related quality of life. The pathogenesis of this symptom is largely unknown, but it has been suggested that central serotoninergic neurotransmission may be implicated and that serotonin 1A receptor agonists may yield improvement. The aim of this study was to study the central serotoninergic system, specifically the serotonin (5‐HT)1A receptor–mediated pathway of serotoninergic neurotransmission, in a bile duct resection rat model of cholestasis. Fatigue was assessed in the forced swim test in sham and bile duct–resected rats. The serotonin behavioral syndrome, which includes hyperlocomotion, was assessed in both groups of rats after escalating doses of the 5‐HT1A receptor agonist 8‐hydroxy(di‐n‐propylamine)tetralin (8‐OH DPAT). 5‐HT1A and 5‐HT2 receptor densities were explored in four brain regions using a receptor‐binding assay. Extracellular 5‐HT and 5‐hydroxyindoleacetic acid were measured via in vivo brain dialysis. Bile duct–resected rats spent more time floating in the forced swim test, and 8‐OH DPAT decreased floating time in cholestatic rats (P < .01). Dose–response curves created with 8‐OH DPAT for the serotonin behavioral syndrome were similar in bile duct–resected and sham‐operated rats. 5‐HT1A and 5‐HT2 receptor densities in most brain regions and extracellular serotonin levels were similar in both groups of rats. In conclusion, 5‐HT1A receptor agonist–induced amelioration of fatigue in cholestatic rats may be nonspecific and not linked to reversal of the pathophysiology of fatigue associated with cholestasis; however, these data do not exclude a potential role of the central serotoninergic system in the evolution of fatigue. (HEPATOLOGY 2005.)

The role of nitric oxide synthase in reduced vasocontractile responsiveness induced by prolonged α1‐adrenergic receptor stimulation in rat thoracic aorta

1 Prolonged exposure (6–12 h) of rat aorta to alpha1‐adrenergic receptor (α1AR) agonist phenylephrine (Phe) leads to a decrease in α1AR‐mediated vasoconstriction. This reduced responsiveness to α1AR stimulation was strongly dependent on the intactness of the endothelium. 2 We examined the effect of Phe on nitric oxide synthase (NOS) activity by measuring the conversion of [3H]L‐arginine to [3H]L‐citrulline in rat aorta or in endothelial cells isolated from rat aorta. Phe stimulation increased NOS activity in control aortas. This response was antagonized by prazosin. However, Phe increased neither the activity of NOS nor intracellular Ca2+ in the isolated endothelial cells from the control aortas, whereas acetylcholine (Ach) was able to stimulate both responses in these cells. This result suggests that Phe stimulates α1AR on vascular smooth muscle cells and has an indirect influence on endothelial cells to increase NOS activity. 3 In Phe‐exposed aortic rings, basal NOS activity was found to have increased compared to vehicle‐exposed control rings. Stimulation with Phe or Ach caused a small increase over basal NOS activity in these preparations. Prolonged exposure to Phe also caused an enhancement of Ach‐mediated vasorelaxation in rat aorta. 4 Immunoblot and reverse transcription–polymerase chain reaction experiments showed that prolonged exposure of rat aorta to Phe resulted in an increased expression of eNOS, but not iNOS. This increase was antagonized by nonselective antagonist prazosin. Immunohistochemical staining experiments also showed that expression of eNOS increased in endothelial cells after Phe exposure of the aortas. 5 These results, all together, showed that prolonged exposure of rat aorta to α1AR agonist Phe enhanced the expression of eNOS and basal NOS activity, which probably causes a decreased vasocontractile response to Phe or to other agonists such as 5HT (5‐hydroxytryptamine) in rat aorta. 6 This phenomenon can be considered more as a functional antagonism of vasocontractile response to agonists mediated by endothelium than a specific desensitization of α1AR‐mediated signalling in vascular smooth muscle cells.

Ligand efficacy and affinity in an interacting 7TM receptor model

Quantitative understanding of the activation of G protein-coupled receptors is based mostly on some theoretical models that describe the interaction between ligand and protein partners and the activation process of the receptor. All of these models provide different definitions for observable affinity or efficacy. However, the property common to such parameters defined in the context of these models is that they are always independent of the concentration of the receptor molecule. This is based on the assumption that receptors do not interact with each other appreciably. In this article, experimental evidence for which this assumption does not seem to apply is discussed and an oligomerization model for seven-transmembrane-domain receptors that explains the relationship between receptor concentration, apparent affinity and efficacy is provided.

Epidermal Growth Factor Receptor Inhibitor PKI-166 Governs Cardiovascular Protection without Beneficial Effects on the Kidney in Hypertensive 5/6 Nephrectomized Rats

Transactivation of epidermal growth factor receptor (EGFR) signaling by G protein–coupled receptors has been implicated in several cardiovascular (CV) conditions, including hypertension, heart failure, and cardiac and vascular hypertrophy. However, the therapeutic potential of EGFR inhibition in these conditions is currently unknown. The main objective of the present study was to investigate cardiac, vascular, and renal effects of EGFR inhibition by 4-[4-[[(1R)-1-phenylethyl]amino]-7H-pyrrolo[2,3-d]pyrimidin-6-yl]phenol (PKI-166) in the hypertensive chronic kidney disease model. Rats underwent 5/6 nephrectomy (5/6Nx) and were treated with PKI-166, lisinopril or vehicle from week 6 after disease induction until week 12. Sham animals received either PKI-166 or vehicle. Treatment with PKI-166 did not affect the development of the characteristic renal features in 5/6Nx, including proteinuria, diminished creatinine clearance, and increased glomerulosclerosis, whereas these were attenuated by lisinopril. Despite absence of effects on progressive renal damage, PKI-166 attenuated the progression of hypertension and maintained cardiac function (left ventricle end-diastolic pressure) to a similar extent as lisinopril. Also, PKI-166 attenuated the increase in phosphorylated EGFR in the heart as induced by 5/6Nx. Moreover, PKI-166 and lisinopril restored the impaired contraction of isolated thoracic aortic rings to phenylephrine and angiotensin II and impaired myogenic constriction of small mesenteric arteries in 5/6Nx rats. Blockade of the EGFR displays a CV benefit independent of limiting the progression of renal injury. Our findings extend the evidence on EGFR signaling as a target in CV disorders.

The role of gender differences in beta-adrenergic receptor responsiveness of diabetic rat heart

Since the mechanisms responsible for gender differences in cardiac contractile function have not been fully elucidated, we focused to determine the effect of gender difference on β-adrenergic receptors (β-ARs) signal transduction in ventricular cardiomyocytes from insulin-dependent diabetic (streptozotocin-induced) rats. Dose-response curves of left ventricular developed pressure (LVDP) to isoproterenol (ISO) in females showed that there was only a ∼30% decrease in the maximum response without a significant shift in EC50 in diabetic females. On the other hand, diabetes induced a clear rightward shift in the potency (5–10 folds) without a significant change in the maximum response in the males. In order to further determine of the underlying mechanism for this difference, we measured cAMP production and obtained dose-response curves with ISO stimulation in isolated cardiomyocytes. In diabetic females, there was no obvious change in the cAMP dose-response curve. On the other hand, there was a significant decrease in the maximum response without any apparent change in the potency of diabetic males. Our findings indicate that male and female rats are affected differently by diabetes in terms of LVDP responses to β-ARs stimulation. Also, the difference between their β-ARs induced cAMP responses may underlie this disparity.