Verapamil prevents the effect of calcium-sensing receptor activation on the blood glucose and insulin levels in rats.

BACKGROUND: The Ca2+ triggered insulin exocytosis in ß cells of the pancreatic islets may be the result of Ca2+ influx through L-type voltage dependent calcium channels (VDCC) localized in the plasma membrane, as well as of liberation of Ca2+ from intracellular storages, induced by activation of the calcium receptor (CaR) coupled with the PLC enzyme present in the pancreatic islets. The present study was designated to determine, in in vivo experiments, the effects of CaR activation by R-568 and inhibition of the receptor by NPS 2143 on the plasma glucose and insulin levels in the presence of verapamil, a calcium channel blocker. METHODS: Wistar rats, after fasting for 14 h before the experiment, were anesthetized with inactin and loaded ip with 1 g/kg glucose. RESULTS: In comparison to the control group, the verapamil-induced blockade of the calcium channels in glucose loaded animals increased the blood glucose level and decreased the insulin level, whereas CaR activation with R-568 induced opposite effects. However, in the presence of verapamil, R-568 did not change the concentration of glucose or insulin versus the control animals. Verapamil infusion did not alter elevated glucose concentration in the NPS 2143 animals. At the same time, verapamil reduced the plasma insulin level and potentiated the drop of insulin concentration induced by NPS 2143. CONCLUSION: The observations suggest that under the in vivo conditions, calcium channel blockade may prevent changes in the blood glucose and insulin concentrations induced by the CaR activation.

Activity of the calcium-sensing receptor influences blood glucose and insulin levels in rats.

BACKGROUND: The calcium-sensing receptor (CaR) has been found not only in parathyroid glands but also in other tissues, e.g. in ß cells of the pancreatic islets. Therefore, CaR might likely mediate the mechanism of insulin secretion. The present study was designed to examine the in vivo effects of R-568, a CaR agonist, and NPS2143, a CaR inhibitor, on plasma insulin and blood glucose concentrations. METHODS: Wistar rats, after fasting for 14h before the experiment, were anesthetized with inactin and loaded ip with 1g/kg glucose. RESULTS: 20, 120 and 180min after iv R-568 administration, plasma insulin increased markedly (by approximately 30%), in glucose-loaded rats, as compared to the control animals. Simultaneously, 180min after R-568 administration, a significant drop by approximately 12% in blood glucose was observed. In contrast, administration of R-568 in rats not given glucose, did not influence the blood glucose or plasma insulin concentrations vs. the control group. Administration of NPS2143 increased the blood glucose level markedly (by about 18% vs. control group) at 180 and 210min of the experiment. Simultaneously, a significant decrease of insulin concentration was observed vs. control group (by about 18 and 23%, respectively). CONCLUSION: We suggest that modulation of the CaR activity may participate in the mechanisms which mediate insulin secretion in rats.

1-[(Imidazolidin-2-yl)imino]-1H-indoles as new hypotensive agents: synthesis and in vitro and in vivo biological studies.

A series of 1-[(imidazolidin-2-yl)imino]-1H-indole analogues of hypotensive α2 -AR agonists, 1-[(imidazolidin-2-yl)imino]-1H-indazoles, was synthesized and tested in vitro for their activities at α1 - and α2 -adrenoceptors as well as imidazoline I1 and I2 receptors. The most active 1-[(imidazolidin-2-yl)imino]-1H-indoles displayed high or moderate affinities for α1 - and α2 -adrenoceptors and substantial selectivity for α2 -adrenoceptors over imidazoline-I1 binding sites. The in vivo cardiovascular properties of indole derivatives 3 revealed that substitution at C-7 position of the indole ring may result in compounds with high cardiovascular activity. Among them, 7-fluoro congener 3g showed the most pronounced hypotensive and bradycardic activities in this experiment at a dose as low as 10 µg/kg i.v. Metabolic stability of the selected compounds of type 3 was determined using both in vitro and in silico approaches. The results indicated that these compounds are not vulnerable to rapid first-phase oxidative metabolism.

COMPARISON OF THE EFFECTS OF MARSANIDINE DERIVATIVES ON RAT CARDIOVASCULAR SYSTEM.

Since clonidine was introduced in clinical practice, attempts are still made to obtain substances capable of centrally controlling blood pressure, however with pharmacological profile better than currently avail- able, such as moxonidine and rilmenidine. Recently synthesized indazole derivatives exert promising action on blood pressure and heart rate in Wistar rats. In the present study, our aim was to check which of tested substituted compound exerts the best effect on basic circulatory parameters. Effects of marsanidine (M), 7-Me- marsanidine (7-Me-M), 7-Cl-marsanidine (7-Cl-M) and 7-F-marsanidine (7-F-M) on blood pressure, heart rate and diuresis were compared. Male Wistar rats were receiving iv. tested compounds in two doses: 10 or 100 pg/kg b.w. Mean arterial pressure (MAP), heart rate (HR) and ECG were recorded continuously. Urine samples were collected before and after administration of tested imidazolines. Obtained data were filtered and subjected to statistical analysis. All tested compounds caused a profound decrease of MAP. 7-M-M reduced blood pressure to the highest extent when used in 10 µg/kg b.w. dose. 7-F-M in dose of 100 µg/kg b.w. caused the strongest drop of MAP. The weakest and the shortest effect in duration was observed after M administration. HR was reduced after administration of each compound while the strongest effect was observed after 7-M-M administration in dose of 10 µg/kg b.w. and after 7-Cl-M administered in dose of 100 µg/kg b.w. Again, the weakest and the shortest in duration effect was observed after M administration. The highest increase of diuresis was observed after 7-M-M administration. These data suggest that methyl substituent in 7 position of indazole ring is the most effective in improving hypotensive effects of newly synthesized imidazolidine derivatives.

Circulatory effect of TCS-80, a new imidazoline compound, in rats.

BACKGROUND: Synthesis and hypotensive properties of centrally acting imidazoline agents: 1-[(imidazolidin-2-yl)imino]-1H-indazole (Marsanidine) and 7-chloro-1-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-1H-indazole (TCS-80) were tested in rats. We have recently synthesized two novel Marsanidine analogues which decrease blood pressure and heart rate in rats: 1-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-1H-indole (TCS-54), and 7-chloro-1-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-1H-indole (TCS-213). Among all these analogues, compound TCS-80 exhibits the highest affinity to I1-imidazoline receptors and the lowest α2/I1 selectivity ratio. The observed cardiovascular effects of the compounds might be mediated through α2-adrenergic and I1-imidazoline receptors and subsequent decrease of the symphathetic nerve activity. The present studies were performed to determine whether α2-adrenergic and/or I1-imidazoline receptors are involved in the decrease of blood pressure and heart rate induced by Marsanidine, TCS-54, TCS-80, and TCS-213 in rats. METHODS: Anesthetized rats were infused iv with the tested compounds and selective α2-adrenoceptor antagonist, RX821002, or nonselective α2-adrenergic/I1-imidazoline receptor antagonist, Efaroxan. The mean arterial blood pressure and heart rate were monitored directly and continuously throughout the experiment. RESULTS: Efaroxan inhibited the hypotensive effect of TCS-80 stronger than RX821002. The degree of inhibition of the hypotensive effect of the remaining compounds was similar for both antagonists. The presence of Efaroxan and RX821002 diminished the heart rate decrease induced by all compounds administration, though the influence on the maximal chronotropic effect was attenuated significantly in the TCS-80 and TCS-213 treated animals only. CONCLUSION: Our results indicate that hypotensive and negative chronotropic activities of all tested compounds are mediated by both the α2-adrenergic and I1-imidazoline receptors. Moreover, the circulatory effect of TCS-80 might be mediated to relatively higher degree by the I1-imidazoline receptors than by the α2-adrenergic ones.

Transfer of SAR information from hypotensive indazole to indole derivatives acting at α-adrenergic receptors: In vitro and in vivo studies.

In a search for novel antihypertensive drugs we applied scaffold hopping from the previously described α1-adrenergic receptor antagonists, 1-[(imidazolin-2-yl)methyl]indazoles. The aim was to investigate whether the α-adrenergic properties of the indazole core were transferable to the indole core. The newly obtained 1-[(imidazolin-2-yl)methyl]indole analogues were screened in vitro for their binding affinities for α1-and α2-adrenoceptors, which allowed the identification of the target-based SAR transfer (T_SAR transfer) as well as structure-based SAR transfer (S_SAR transfer) events. However, when screened in vivo with use of anaesthetized male Wistar rats, the new indole ligands showed a different hemodynamic profile than expected. Instead of the immediate hypotensive effect characteristic of peripheral vasodilatator α1 blockers, a biphasic effect was observed, reminiscent of clonidine-like centrally acting antihypertensive agents. This was supported by subsequent in vitro functional studies in [(35)S]GTPγS binding assay, where the indole analogues displayed partial agonist properties at α2-adrenergic receptors. Since no correlation was found between the in vitro binding to α-adrenoceptors and the in vivo hemodynamic effects of the two series of indazole and indole bioisosteric compounds, in a search for new imidazoline-containing adrenergic drugs, the structure-based SAR transfer information obtained from in vitro binding studies should be treated with caution.

1-[(IMIDAZOLIN-2-YL)AMINO]INDOLINE AND 1-[(IMIDAZOLIN-2 YL)AMINO] 1,2,3,4-TETRAHYDROQUINOLINE DERIVATIVES: NEW INSIGHTS INTO THEIR CIRCULATORY ACTIVITIES.

N-[(Imidazolin-2-yl)amino]indolines and N-[(imidazolin-2-yl)amino]-1,2,3,4-tetrahydroquinolines, previously described in patent literature as hypertensive agents, were synthesized and tested in viny for their affinities to α1- and α2-adrenoceptors as well as imidazoline I, and I2 receptors. The compounds most potent at either α1- or α2-adrenoceptors were administered intravenously to normotensive Wistar rats to determine their effects on mean arterial blood pressure and heart rate. Upon intravenous administration at dose of 0.1 mg/kg to normotensive male Wistar rats, the initial transient pressor effect was followed by long-lasting hypotension and bradycardia. In view of the above results the 1-[(imidazolin-2-yl)amino]indolines and [(imidazolin-2-yl)amino]-1,2,3,4-tetrahydroquinolines are now found to possess circulatory profile characteristic of the centrally acting clonidine-like hypotensive imidazolines.

Fluorinated analogues of marsanidine, a highly α2-AR/imidazoline I1 binding site-selective hypotensive agent. Synthesis and biological activities.

The aim of these studies was to establish the influence of fluorination of the indazole ring on the pharmacological properties of two selective α2-adrenoceptor (α2-AR) agonists: 1-[(imidazolidin-2-yl)imino]-1H-indazole (marsanidine, A) and its methylene analogue 1-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-1H-indazole (B). Introduction of fluorine into the indazole ring of A and B reduced both binding affinity and α2-AR/I1 imidazoline binding site selectivity. The most α2-AR-selective ligands were 6-fluoro-1-[(imidazolidin-2-yl)imino]-1H-indazole (6c) and 7-fluoro-1-[(imidazolidin-2-yl)imino]-1H-indazole (6d). The in vivo cardiovascular properties of fluorinated derivatives of A and B revealed that in both cases the C-7 fluorination leads to compounds with the highest hypotensive and bradycardic activities. The α2-AR partial agonist 6c was prepared as a potential lead compound for development of a radiotracer for PET imaging of brain α2-ARs.

Vagotomy reveals the importance of the imidazoline receptors in the cardiovascular effects of marsanidine and 7-ME-marsanidine in rats.

BACKGROUND: The recently synthesized novel benzazole derivates - marsanidine (1-[(imidazolidin-2-yl)imino]indazole) and 7-Me-marsanidine (1-[(imidazolidin-2-yl)imino]-7-methylindazole) display promising effects on the circulatory system. We previously indicated that i.v. administration of both compounds decreased the mean arterial blood pressure (MAP) and heart rate (HR) in rats. The cardiovascular effect of the tested compounds may consist not only in inhibiting the sympathetic, but also in activating the parasympathetic pathways related to vagal nerves. Present experiments were performed to determine how vagotomy, with or without an α2 adrenoreceptor blockade, may affect hypotensive and HR limiting actions of marsanidine and 7-Me-marsanidine. METHODS: Both compounds were infused i.v. (10 µg/kg b.w.) to anesthetized rats, half of which underwent vagotomy. Half the intact, and half the vagotomised rats received RX821002, an α2 adrenorereceptor inhibitor. MAP and HR were monitored directly throughout the experiment. RESULTS: Vagotomy enhanced hypotension observed after marsanidine administration. The α2 adrenergic blockade abolished the action of marsanidine in both the intact and vagotomised rats. Vagotomy did not affect the 7-Me-marsanidine-induced decrease of MAP or HR. However, it abolished the reducing effect of the α2 adrenergic receptor blockade on the hypotension triggered by 7-Me-marsanidine. CONCLUSION: The results show that although cardiovascular effects of marsanidine and 7-Me-marsanidine are not mediated by the vagal nerves, vagotomy enhanced sensitivity of the sympathetic pathways for the tested compounds. While the action of marsanidine in vagotomised and intact rats may be explained by activation of the α2 adrenoreceptors, the effects of 7-Me-marsanidine seem to be α2 adrenoreceptor-independent. It seems likely that activation of I1 imidazoline receptors could mediate the observed effects.

Marsanidine and 7-Me-marsanidine, the new hypotensive imidazolines augment sodium and urine excretion in rats.

BACKGROUND: We have recently described the synthesis and circulatory properties of two novel centrally acting imidazoline agents: marsanidine (1-[(imidazolidin-2-yl)imino]indazole) and 7-Me-marsanidine (1-[(imidazolidin-2-yl)imino]-7-methylindazole). Marsanidine has proven to be a highly selective α2-adrenoceptor ligand with the α2/I1 selectivity ratio of 3879, while 7-Me-marsanidine has been shown to be a mixed a2-adrenoceptor/imidazoline I1 receptor agonist with the a2/I1 selectivity ratio of 7.2. In the same paper, we indicated that iv administration of both compounds to Wistar rats induced a decrease in blood pressure and heart rate. The hypotensive effect of the iv administered imidazolines might be mediated not only through activation of the central α2 and/or I1 receptors but also through subsequent decrease of the renal sympathetic nerve activity and a direct effect on peripheral receptors. The present studies were performed to determine whether the newly synthesized compounds might influence the diuresis and sodium excretion in rats. METHODS: Both compounds were infused iv to anesthetized rats in the dose of 100 µg/kg b.w. The diuresis and sodium concentration in urine and blood samples were determined. The mean arterial blood pressure and heart rate were monitored directly throughout the experiment. RESULTS: A significant increase of diuresis and natriuresis was observed within 40 min after the administration of both marsanidine and 7-Me-marsanidine, in comparison to both the control period and the control group. However, between the 20 and 40 min of the experiment the natriuretic and diuretic effect of 7-Me-marsanidine was markedly higher than that of marsanidine. CONCLUSION: Our study indicates that the new hypotensive imidazoline compounds of marsanidine and 7-Me-marsanidine increase diuresis and natriuresis in rats. However, the effect of 7-Me-marsanidine is markedly more potent, probably due to its moderate affinity to the I1-imidazoline receptor.

N-(Imidazolidin-2-ylidene)-1-arylmethanamine oxides: synthesis, structure and pharmacological evaluation.

A high yielding three-step procedure was applied for the synthesis of N-(imidazolidin-2-ylidene)-1-arylmethanamine oxides 3 (α-aminonitrones) starting from the easily accessible imidazolidin-2-one O-benzyl oxime 1. The α-aminonitrone-α-iminohydroxyloamine tautomerism of these products was studied theoretically and the structures of the synthesised compounds were confirmed by single crystal X-ray crystallographic analysis. The compounds were evaluated in vitro for their binding affinities to α(1) and α(2) adrenoceptors as well as imidazoline I(1) and I(2) receptors. The highest potencies at the α(2) adrenergic receptors were observed for compounds bearing biphenyl (4h, K(i) = 9 nM) and naphthyl (4i, K(i) = 92 nM) moieties. Compounds 4h and 4i were further tested in vivo for their cardiovascular and sedative-hypnotic effects in rats.

Synthesis and biological activities of 2-[(heteroaryl)methyl]imidazolines.

A series of 2-[(heteroaryl)methyl]imidazolines was synthesized and tested for their activities at α(1)- and α(2)-adrenoceptors and imidazoline I(1) and I(2) receptors. The most active 2-[(indazol-1-yl)methyl]imidazolines showed high or moderate affinities for α(1)- and α(2)-adrenoceptors. However, their intrinsic activities at α(2A)-adrenoceptors proved to be negligible. A selected 7-chloro derivative behaved as a potent α(1)-adrenoceptor antagonist and exhibited peripherally mediated hypotensive effects in rats.

3-[(Imidazolidin-2-yl)imino]indazole ligands with selectivity for the α(2)-adrenoceptor compared to the imidazoline I(1) receptor.

A series of 3-[(4,5-dihydroimidazolidin-2-yl)imino]indazoles has been synthesized as positional analogues of marsanidine, a highly selective α(2)-adrenoceptor ligand. Parent compound 4a and its 4-chloro (4c) and 4-methyl (4d) derivatives display α(2)-adrenoceptor affinity at nanomolar concentrations (K(i)=39.4, 15.9 and 22.6nM, respectively) and relatively high α(2)/I(1) selectivity ratios of 82, 115 and 690, respectively. Evidence was obtained that these compounds act as partial agonists at α(2A)-adrenoceptors. Compound 4d with intrinsic activity comparable with that of marsanidine, but lower than that of clonidine, elicited pronounced cardiovascular effects in anesthetized rats at doses as low as 0.01mg/kg iv.

Hypertensive activity of synthesized PTH(25-34) and Ac-PTH(25-30)-NH2 in rats.

Parathyroid hormone (PTH) is secreted by parathyroid glands and is the main known factor that control plasma calcium concentration. There are many indications that PTH or products of PTH degradation influence the mean arterial blood pressure (MAP). These observations might be important in diseases accompanied with the overproduction of PTH such as primary hyperparathyroidism (PHPT). It was shown that the six amino acids PTH precursor-PRO-PTH with reversed sequence (PRO-rs), which contains a rare tripeptide -Arg-Lys-Lys- fragment, induces significant hypertensive response in rats. This strong alkali tripeptide is also present in the position 25-27 of the PTH molecule. The aim of the present study was to synthesize, by the solid phase peptide synthesis method, PTH fragments including the -Arg-Lys-Lys- sequence and test their influence on blood pressure and calcium plasma concentration in rats. Our study demonstrated that PTH(25-34) and the acetylated amide analogue of PTH(25-30), (Ac-PTH(25-30)-NH(2)) were hypertensive in the physiological doses. The presence of strong alkali sequence -Arg-Lys-Lys- in PTH(25-30) fragment is not sufficient to induce hypertension either in physiological or pharmacological doses in rats. Therefore, both the proximity of the -Arg-Lys-Lys- sequence and length of the peptide might also play roles as pressure factors.

1-[(Imidazolidin-2-yl)imino]indazole. Highly alpha 2/I1 selective agonist: synthesis, X-ray structure, and biological activity.

Novel benzazole derivatives bearing a (imidazolidin-2-yl)imino moiety at position 1 or 2 were synthesized by reacting 1-amino- or 2-aminobenzazoles with N, N'-bis( tert-butoxycarbonyl)imidazolidine-2-thione in the presence of HgCl 2. Structures of 1-[(imidazolidin-2-yl)imino]indazole (marsanidine, 13a) and free base of the 4-Cl derivative 12e were confirmed by X-ray single crystal structure analysis. Compound 13a was found to be the selective alpha 2-adrenoceptor ligand with alpha 2-adrenoceptor/imidazoline I 1 receptor selectivity ratio of 3879, while 1-[(imidazolidin-2-yl)imino]-7-methylindazole ( 13k) proved to be a mixed alpha 2-adrenoceptor/imidazoline I 1 receptor agonist with alpha 2/I 1 selectivity ratio of 7.2. Compound 13k when administered intravenously to male Wistar rats induced a dose-dependent decrease in mean arterial blood pressure (ED50 = 0.6 microg/kg) and heart rate, which was attenuated following pretreatment with alpha 2A-adrenoceptor antagonist RX821002. Compound 13a may find a variety of medical uses ascribed to alpha 2-adrenoceptor agonists, and its 7-methyl derivative 13k is a good candidate for development as a centrally acting antihypertensive drug.

Hypertensive effect of calcilytic NPS 2143 administration in rats.

Secretion of parathormone (PTH), the main parathyroid hormone, which is under the control of the calcium sensing receptor, might be inhibited by calcimimetics and stimulated by calcilytics. Parathyroid glands also secrete parathyroid hypertensive factor. Recently, it was shown that calcimimetic NPS R-568 induced decreased blood pressure in spontaneously hypertensive rats (SHR) in the presence of parathyroid glands. Therefore, the aim of this study was to determine whether administration of the calcilytic NPS 2143 provoked an increase of mean arterial blood pressure (MAP) in normotensive rats. We used male Wistar rats anaesthetized with thiopental. Clearance experiments were performed and the effect of bolus, 1 mg/kg body weight i.v. of NPS 2143 on MAP in the presence and absence of thyroparathyroidectomy (TPTX) was monitored continuously. Calcilytic properties of NPS 2143 were confirmed directly by a significant (P < 0.05) increase of plasma PTH concentration, and indirectly by a rise of plasma Ca(2+) concentration and urinary fractional phosphate excretion (FE Pi). NPS 2143 administration markedly (P < 0.05) increased MAP, calculated as the difference ( Delta ) in MAP between sequential measurements and the time of bolus injection of calcilytic. The observed increase of blood pressure in the NPS 2143 group was also significant (P < 0.05) compared with the control group. Performance of TPTX prevented the hypertensive effect of NPS 2143. We conclude that NPS 2143 is responsible for increased blood pressure in rats in the presence of parathyroid glands.

Pharmacological activity of calcimimetic NPS R-568 administered intravenously in rats: dose dependency.

Calcimimetics administered orally cause "pharmacological parathyroidectomy" confirmed by a decrease in parathyroid hormone secretion (PTH) and in plasma Ca(2+) concentration. Parathyroids are also the source of parathyroid hypertensive factor (PHF). The aim of this study was to determine the dose-dependent effect of an intravenously (iv) applied calcimimetic, NPS R-568, on plasma Ca(2+) concentration, urinary phosphate excretion and mean arterial blood pressure (MAP) in rats. Clearance experiments were performed on male Wistar rats anesthetized with thiopental and infused iv with saline supplemented with (3)H inulin for glomerular filtration rate (GFR) determination. NPS R-568 was administered iv as a bolus at the doses: 0.5, 1.0, 2.5 and 5.0 mg/kg. Control group of rats received vehicle only. MAP was monitored continuously in the carotid artery. Urine was collected from cannulated urinary bladder. NPS R-568 applied iv dose-dependently decreased plasma Ca(2+) and fractional phosphate excretion (FE(Pi)). In the control group, no significant changes in plasma Ca(2+) and FE(Pi) were observed. The most efficient hypotensive effect vs. control group was induced by the NPS R-568 of a dose of 1.0 mg/kg. Our results indicate that the dose of 1 mg/kg of the calcimimetic NPS R-568 administered iv is sufficient to induce the decrease in plasma Ca(2+) and urinary phosphate excretion accompanied with hypotensive effect in Wistar rats.

Calcimimetic NPS R-568 induces hypotensive effect in spontaneously hypertensive rats.

BACKGROUND: The discovery of calcium receptors and calcimimetics created the possibility of "pharmacologic parathyroidectomy" (phPTX), which decreased secretion of parathormone (PTH). Parathyroid glands of spontaneously hypertensive rats (SHR) and of patients with primary hyperparathyroidism and hypertension secrete parathyroid hypertensive factor (PHF). Parathyroidectomy decreases blood pressure in these rats and in patients. The present study determined whether phPTX induced by calcimimetics decreases mean arterial blood pressure (MAP) in hypertensive rats. METHODS: Hypertensive SHR and normotensive Wistar Kyoto (WKY) rats were used. Clearance experiments were performed and the effect of 1 mg/kg body weight (given intravenously) synthesized NPS R-568 (NPS) on MAP in the presence or absence of thyroparathyroidectomy (TPTX) was monitored. RESULTS: The success phPTX and TPTX were proven by a significant decrease in plasma Ca(2+) concentration and a decrease in urinary fractional phosphate excretion (FE Pi). The administration of NPS significantly decreased blood pressure in SHR versus SHR/control: Delta(0-50 min of experiment) MAP -16.5 +/- 2.5 mm Hg v -3.2 +/- 1.5 mm Hg (P < .002). The TPTX decreased blood pressure in SHR versus SHR/control and was not different versus SHR/TPTX/NPS (DeltaMAP: -10.2 +/- 1.6 mm Hg v -3.2 +/- 1.5 mm Hg (P < .01) and v -8.3 +/- 2.2 mm Hg (P = not significant). In normotensive WKY rats application of NPS did not reach significance in DeltaMAP: -6.7 +/- 1.8 mm Hg v -2.6 +/- 2.8 mm Hg (P = not significant) in WKY/control. The TPTX lowered blood pressure in WKY versus WKY/control and remained unchanged versus WKY/TPTX/NPS (DeltaMAP: -11.3 +/- 1.7 mm Hg v -2.6 +/- 2.8 mm Hg (P < .04) and v -11.4 +/- 2.6 mm Hg (P = not significant). CONCLUSIONS: We conclude that phPTX with NPS R-568 is responsible for a decrease of MAP in SHR.