Hair Loss in Patients with Gastroparesis: A Sign of Nutritional Deficiency in Gastroparesis?

INTRODUCTION

Some patients with gastroparesis (Gp) report hair loss. The aim of this study was to investigate the prevalence of patient-reported hair loss in Gp patients, analyze hair loss association to severity of Gp and nutritional deficiencies, and study effects of multivitamin treatment on hair loss.

METHODS

Patients with Gp were questioned about hair characteristics, Gp symptoms, and diet. Patients with hair loss had blood drawn for vitamin levels. Patients with hair loss were treated with daily multivitamin and assessed 8 weeks later.

RESULTS

Hair loss was reported in 65 of 143 patients with Gp (45.5%), occurring similarly in idiopathic and diabetic Gp. Hair loss was most commonly noticed while washing and/or combing hair. Patients with hair loss had more severe nausea, abdominal pain, stomach fullness, loss of appetite, abdominal discomfort, bloating, retching, stomach distension, vomiting, early satiety, postprandial fullness, and constipation. Hair loss patients lost more weight over prior 6 months. Patients with hair loss had similar gastric retention on gastric emptying scintigraphy. Overall, 29 of 61 (47.5%) patients with hair loss had at least one abnormal bloodwork result. After 8 weeks of treatment with a daily multivitamin, 17 of 41 (41%) patients had improvement in hair loss.

CONCLUSION

Hair loss occurred in 46% of patients with Gp, being associated with more severe symptoms, loss of weight, and several vitamin deficiencies, although not a specific one. Treatment with multivitamins improved hair loss in 40% of patients. Presence of hair loss in patients with Gp should prompt nutritional evaluation and supplementation.

Proximal and distal intragastric meal distribution during gastric emptying scintigraphy: Relationships to symptoms of gastroparesis

BACKGROUND

Total gastric retention (TGR) from gastric emptying scintigraphy (GES) is used for diagnosing gastroparesis (Gp), but correlates poorly with patients' symptoms. Regional intragastric meal distribution (RIMD) can also be assessed from GES. This study classified patients' meal distribution as proximal or distal to relate RIMD to symptoms of Gp.

METHODS

GES studies in patients (n = 193) and control subjects (n = 21) were selected for RIMD analysis. Patients completed Patient Assessment of Upper Gastrointestinal Symptoms (PAGI-SYM) for symptom severity before GES. TGR was analyzed using % TGR, and RIMD used a proximal/distal gastric count ratio (PDCR). Results were classified as proximal or distal RIMD at 0, 1, 2, and 4 h postprandially based on their PDCR being above or below the median value of the patients.

RESULTS

Patients with delayed GE and immediate post-meal ingestion distal distribution had more severe early satiety and regurgitation. Distal distribution at 1 h had more severe early satiety and loss of appetite compared to proximal distribution. Patients with delayed GE and proximal distribution at 4 h had more severe nausea, retching, and vomiting compared to 4 h distal distribution. Severely delayed 4 h proximal distribution had more nausea than severely delayed 4 h distal distribution.

CONCLUSIONS

Increased early distal IMD in patients with delayed GE was associated with regurgitation and early satiety whereas increased late proximal IMD was associated with nausea, retching, and vomiting. Differentiating proximal from distal meal distribution patterns helps to relate symptoms to gastric dysfunction and may be helpful for directing therapy.

Gastric half emptying time (T½ ) for 4-h gastric emptying scintigraphy simplifies reporting but reduces detection of gastroparesis

BACKGROUND

Gastric emptying scintigraphy (GES) reports percent retention at 1, 2, and 4 h. Time to empty half the meal (T_½ ) could simplify GE reporting.

AIMS

To compare the performance of GES T_½ to 1-, 2-, and 4-h retention.

METHODS

GES studies were reviewed; results determined according to retention at 1, 2, and 4 h. T_½ was determined using 3 methods: (1) GES curve fitting using 0, 0.5, 1, 2, 3, and 4 h data; (2) linear interpolation using 0, 0.5, 1, 2, 3, and 4 h data; and (3) linear interpolation using only 0, 1, 2, and 4 h data.

RESULTS

Of 495 patients, 265 had normal GE, 4 rapid GE (<30% retention at 1 h), and 226 delayed GE: 17 delayed only at 2 h (>60% ret); 94 delayed only at 4 h (>10% ret); and 115 delayed at both 2 h and 4 h. Strong correlations were seen between each T_½ method and 1, 2, 3, and 4 h %-empty values: curve-fit T_½ (r = -0.851, -0.942, -0.864, -0.744), linear T_½ using all imaging times (r = -0.848, -0.972, -0.878, -0.763), and linear T_½ using standard imaging times (r = -0.853, -0.974, -0.868, -0.760). The 132 min cutoff for delayed GE captures 99.1% to 100% of delayed GE at both 2 h and 4 h, 76.5% to 94.1% delayed at 2 h only, but only 36.7% to 39.4% delayed at 4 h only; 3.5 to 11.3% of patients with normal GE miscategorized as delayed.

CONCLUSIONS

GES T_½ correlates more strongly with retention at 2 h than at 4 h. T_½ alone may misclassify patients, particularly those with late-phase (4 h only) delays, reducing its utility for diagnosing gastroparesis.

IBT 9302 (Heparinase III): a novel enzyme for the management of reperfusion injury-related vascular damage, restenosis and wound healing

IBT 9302 (heparinase III, EC 4.2.2.8), purified from Flavobacterium heparinum, selectively cleaves heparan sulfate proteoglycans (HSPGs) from cellular surfaces and extracellular matrices. HSPGs serve as binding sites for P- and L-selectins, as well as for pro-inflammatory chemokines, such as interleukin (IL)-8. IBT 9302 reversibly removes these binding sites and inflammatory mediators, thereby limiting tissue damage following reperfusion of ischaemic areas by reducing leukocyte rolling, adhesion and extravasation. In models of myocardial ischaemia/reperfusion injury, infusion of IBT 9302 the time of transport and reperfusions, reduces the area of necrosis/area at risk ratios relative to vehicle-treated animals. Cardioprotection is accompanied by a reduction in serum creatine kinase levels and neutrophil adherence to coronary vessels, and the preservation of endothelial relaxation responsiveness to acetylcholine. HSPGs also serve as accumulation sites for most growth factors and IBT 9302 limits both proliferation and migration of vascular smooth muscle cells to platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF) and endothelial growth factor (EGF). In vivo, the application of IBT 9302 at the time of vascular injury significantly reduces arterial medial proliferation. External application of IBT 9302 to wounds in a steroid-impaired wound healing model increases tensile strength by releasing mitogenic growth factors and HSPGs from the surrounding extracellular matrix. Pharmacokinetic studies show a simple monoexponential decay following iv. bolus dosing of IBT 9302, with a half-life of 5 - 6 min. The majority of [(125)I]-IBT 9302 goes to the liver (60%) and kidneys (25%), following iv. dosing. Preliminary toxicology studies in rats following single iv. bolus (10 mg/kg) or infusion (10 mug/kg/min) dosing show no untoward effects. These results suggest that IBT 9302 may have therapeutic utility in treating myocardial ischaemia/reperfusion injury, ischaemic stroke, restenosis or in healing diabetic ulcer wounds, by virtue of its ability to selectively cleave HSPGs.

Anti-tumor activities of chondroitinase AC and chondroitinase B: inhibition of angiogenesis, proliferation and invasion

In the current study, two specific glycosaminoglycan lyases, chondroitinase AC and chondroitinase B, were utilized to examine the roles of chondroitin sulfates and dermatan sulfate in tumor metastasis and angiogenesis. Melanoma cells (SK-MEL) or endothelial cells were treated with either medium or chondroitinase enzyme. Chondroitinase AC inhibited melanoma invasion and proliferation as well as endothelial proliferation and angiogenesis. Apoptosis of melanoma and endothelial cells, as measured by the activity of caspase-3, was also increased by chondroitinase AC, but not by chondroitinase B. Chondroitinase B inhibited endothelial and melanoma proliferation and invasion, but to a lesser extent than chondroitinase AC. Neither chondroitinase had a detectable effect on gelatinase secretion by melanoma cells. These results indicate that both chondroitin and dermatan sulfates regulate many cellular activities related to metastasis.

Synthetic heparin pentasaccharide depolymerization by heparinase I: molecular and biological implications

A synthetic pentasaccharide (SR90107/ ORG31540) representing the antithrombin III (ATIII) binding sequence in heparin is under clinical development for the prophylaxis and management of venous thromboembolism. This pentasaccharide exhibits potent anti-factor Xa (AXa) effects (>750 IU/mg) and does not exhibit any anti-factor IIa (AIIa) activity. Previous reports have suggested that synthetic heparin pentasaccharides are resistant to the digestive effects of heparinase I. To investigate the effect of heparinase I on the AXa activity of pentasaccharide SR90107/ORG31540, graded concentrations (1.25-100 microg/ml) were incubated with a fixed amount of heparinase I (0.1 U/ml). Heparinase I produced a strong neutralizing effect on this pentasaccharide, as measured by AXa activity. This observation led to further studies where high performance liquid chromatography (HPLC) analysis was employed to determine the potential breakdown products of the pentasaccharide. The experiment with the pentasaccharide included incubation (37 degrees C) at 1 mg/ml and exposure to graded concentrations of heparinase I (0.125-1 U/ml). After 30 min of incubation, the enzymatic activity was stopped by heat treatment and the mixture was analyzed using high performance size exclusion chromatography (HPSEC). Heparinase I concentration-dependent cleavage of the pentasaccharide was evident. The breakdown products exhibited a mass of 1,034 d and 743 d, respectively, suggesting the generation of a trisaccharide and a disaccharide moiety. The extinction of a disaccharide moiety in the UV region was high, indicating the presence of a double bond in this molecule. These data clearly suggest that pentasaccharide SR90107/ORG31540 is digestible by heparinase I into its two components. Furthermore, these data support the hypothesis that heparinase I can be used as a neutralizing agent for pentasaccharide overdose. Additionally, a highly methylated analog of the previously mentioned synthetic pentasaccharide. SanOrg34006, which has also been subjected to similar experiments, has shown complete resistance to the depolymerizing function of heparinase I; therefore, its use may be appropriate in chronic situations as a long-acting form of the pentasaccharide.

Comparison of urinary desmosine excretion in patients with chronic obstructive pulmonary disease or cystic fibrosis

Neutrophil elastase is involved in the pathogenesis of several pulmonary diseases; a strategy for monitoring in vivo elastase activity is to measure changes in biochemical markers. The objective of this study was to determine whether differences in the urinary excretion of the elastin crosslinks, desmosine and isodesmosine (which are unique amino acid products of elastase activity), could be discerned between groups of patients with chronic obstructive pulmonary disease (COPD) or cystic fibrosis (CF), and non-diseased, age-matched controls. Twenty-four-hour urine collections were analysed to eliminate variations in excretion throughout the day, and urine was collected on four separate days in 29-31 subjects/group to investigate the variability in desmosines excretion among the groups. Both sets of patient populations had significantly more variable desmosines readings (higher standard deviations) relative to their respective age-matched control group. The means for three adult groups (COPD, controls and a COPD-smoker subset) ranged from 28.4 to 35.5 pmol desmosines/mg creatinine and there were no differences among the groups. Values in children were higher: 55 pmol desmosines/mg creatinine in the non-CF children and 77 pmol desmosines/mg creatinine for the CF group (P<0.01 vs. age-matched controls). The results of this study show that urinary desmosines, as a surrogate marker for enhanced elastase activity, are more highly variant in both patient populations relative to age-matched controls, and an overall increase in the mean value is further observed in patients with cystic fibrosis.

Inhibition of human dermal fibroblast proliferation by removal of dermatan sulfate

In the current study, a glycosaminoglycan lyase, chondroitinase B, was used to study the role of dermatan sulfate proteoglycans on human dermal fibroblast proliferation. Pretreatment with chondroitinase B significantly decreased fibroblast proliferative responses to serum (20% to 55%). In contrast, heparinase III and chondroitinase AC were less effective in inhibiting fibroblast proliferation to serum. Analysis of glycosaminoglycans on chondroitinase B-treated fibroblasts confirmed that dermatan sulfate was removed from fibroblasts by this enzyme. Chondroitinase B treatment also decreased proliferation to basic fibroblast growth factor (bFGF) by 20% and reduced receptor binding by 25%. Heparinase III inhibited bFGF binding by 73%, but decreased proliferation to bFGF by only 21%. Chondroitinase AC had no effect on bFGF proliferation or binding. These data suggest that dermatan sulfate proteoglycans play a significant role in the control of human dermal fibroblast proliferation.

Interaction of the beta adrenergic receptor antagonist bucindolol with serotonergic receptors

Bucindolol is a nonselective beta-adrenergic receptor antagonist that has additional vasodilating properties. Because some beta-adrenergic receptor antagonists such as cyanopindolol are used as 5-HT1A/5-HT1B receptor antagonists, we tested the hypothesis that bucindolol can interact with 5-HT receptors. Both in vitro and in vivo methods were used to examine the interaction of bucindolol with 5-HT receptors relevant to the cardiovascular system-the 5-HT1A, 5-HT1D, 5-HT2A, and 5-HT2B receptors-and with alpha1-adrenergic receptors. In binding studies, bucindolol displayed high affinity for the 5-HT1A receptor (Ki, 11 nM), modest affinity for the 5-HT2A receptor (Ki, 382 nM), and no measurable affinity for the 5-HT1D receptor; binding affinity for the 5-HT2B receptor was not studied. Bucindolol also displayed significant binding affinity (Ki, 69 nM) for the alpha1-adrenergic receptors. Alpha1-Adrenergic receptor antagonist activity was confirmed by the ability of bucindolol (1 mg/kg) to act as a competitive antagonist against 0.01-30 microg/kg phenylephrine-induced pressor responses in conscious rats. In conscious permanently instrumented rats, bucindolol (0.1-3.0 mg/kg, i.v.) did not cause bradycardia similar to that elicited by the 5-HT1A-receptor agonist 8-OH-DPAT (3-300 microg/kg, i.v.), nor did bucindolol (1 mg/kg) block the 8-OH-DPAT-induced bradycardia. Bucindolol (10(-9)-10(-5) M) did not cause relaxation in the PGF2alpha-contracted, endothelium-intact porcine coronary artery, nor did bucindolol (10(-5) M) block 5-HT-induced coronary artery relaxation, indicating that bucindolol does not have significant interactions at the 5-HT1D receptor. Bucindolol also displayed no agonist activity at the 5-HT2A and 5-HT2B receptor (endothelium-denuded rat thoracic aorta and rat stomach fundus, respectively), but did act as a weak 5-HT2A-receptor antagonist (-log K(B) [M] = 5.4+/-0.1) and 5-HT2B-receptor antagonist (-log K(B) [M] = 7.8+/-0.1). Thus, these data suggest that bucindolol lacks the ability to activate the 5-HT1A, 5-HT1D, 5-HT2A, and 5-HT2B receptor, but can block alpha1-adrenergic receptors and act as a weak 5-HT2A- and 5-HT2B-receptor antagonist. The relevance of these serotoninergic effects as it pertains to the mechanism of bucindolol-induced vasodilation is unknown.

Neutralase reverses the anti-coagulant but not the anti-thrombotic activity of heparin in a rabbit model of venous thrombosis

Neutralase (heparinase I; E.C. 4.2.2.7) is a heparin-degrading enzyme undergoing clinical evaluation as an alternative to protamine for reversing the anticoagulant effects of heparin in coronary bypass surgery. The objective of this study was to assess the relative effects of Neutralase and protamine on reversal of heparin-dependent elevations in coagulation parameters and inhibition of clot formation in a rabbit vena caval stasis model. Rabbits were treated with saline or heparin (300 U/kg) for 10 minutes, followed by saline, protamine (2.6 mg/kg), or Neutralase (10 or 30 microg/kg, representing 1.23 IU/kg and 3.69 IU/kg, respectively). Twenty minutes later, venous stasis was induced, and vena caval clots were excised, weighed, and characterized. Coagulation parameters [activated partial thromboplastin time (aPTT) and thrombin clotting time (TCT)] and antiFactor IIa and Xa levels were measured throughout the protocol. Both protamine and Neutralase reversed heparin-mediated increases in aPTT (>300 seconds to 26-35 seconds) and TCT (>300 seconds to 29-56 seconds) to values that were not different from saline-treated, nonheparinized animals. Thrombus weight in the nonheparinized saline group was 62+/-7 mg; heparin-treated animals had no detectable clots. Protamine reversal of heparin was associated with clot formation (89+/-20 mg) while Neutralase reversal was not (no clots). Heparin-induced increases in antiFactor IIa activity were reversed similarly by protamine and Neutralase (from 4.3-8.8 U/ml to 0.2-0.3 U/ml) while antiFactor Xa activity was differentially reversed (from 3.9-5.9 U/ml to 0.7-1.3 U/ml Neutralase; 5.5 U/ml to 0.02 U/ml protamine). These results are consistent with a hypothesis that Neutralase cleaves heparin into fragments, which are devoid of antiFactor IIa activity that retain modest antiFactor Xa activity, resulting in reversal of anticoagulant, but not antithrombotic, heparin activity. This property of Neutralase may be beneficial in reducing post-surgical thrombotic events after reversal of heparin.

Heparinase III limits rat arterial smooth muscle cell proliferation in vitro and in vivo

Heparinase III degrades heparan sulfate proteoglycans, which are co-receptors for growth factors that stimulate arterial proliferation. We assessed the ability of locally-delivered heparinase III to limit medial vascular smooth muscle cell proliferation induced by balloon catheter injury in rat carotid arteries. Whereas vehicle-treated arteries showed 12% of smooth muscle cells proliferating after 2 days, heparinase III (0.022-5.7 mg/kg) treated arteries showed 0.8-4%. Chemically-inactivated heparinase III did not limit proliferation. In isolated rat A10 vascular smooth muscle cells, heparinase III (1 IU/ml) inhibited both PDGF-BB and bFGF mediated increases in proliferation and migration. These results suggest that heparinase III can limit proliferation by affecting heparan sulfate proteoglycan binding growth factors following arterial injury.

Cardiovascular activity of WIN 65579, a novel inhibitor of cyclic GMP phosphodiesterase 5

This study describes the phosphodiesterase inhibitory potency and cardiovascular actions of WIN 65579 (1-cyclopentyl-3-ethyl-6-(3-ethoxy-4-pyrridyl)-1H-pyrazolo[3,4-d]p yrimidin-4-one), a potent, new cGMP phosphodiesterase 5 inhibitor. WIN 65579 is a competitive inhibitor of phosphodiesterase 5, with IC50 values of 2-3 nM for phosphodiesterase 5 from human or canine vascular sources. WIN 65579 has low affinity for phosphodiesterases 1, 2 and 3 (IC50 > 3-10 microM), and is somewhat selective for phosphodiesterase 4 (IC50 approximately 100 nM). WIN 65579 is an endothelial-dependent relaxant of rat aortic smooth muscle (EC50 = 60 nM) and lowers mean arterial blood pressure in conscious spontaneous hypertensive rats following intravenous or oral dosing. WIN 65579 also increases plasma cGMP levels, and reinstates vascular responsiveness to nitroglycerin in conscious rats that are nitroglycerin-tolerant. These data show that WIN 65579 is one of the more potent phosphodiesterase 5 inhibitors, and that WIN 65579 possesses cardiovascular activities consistent with vascular phosphodiesterase 5 inhibition in vivo.

Zaprinast, but not dipyridamole, reverses hemodynamic tolerance to nitroglycerin in vivo

Hemodynamic tolerance to nitroglycerin was developed in spontaneously hypertensive rats following 2-3 days of pretreatment with 100 mg/kg of nitroglycerin administered s.c. 3 times/day. Tolerance was evaluated both in vivo, by administering ascending bolus doses of nitroglycerin of 1-300 micrograms/kg i.v., and ex vivo in isolated, denuded aortic vascular rings by exposure to ascending concentrations of nitroglycerin of 0.0003-100 microM. Tolerance was observed as a significant blunting of the hypotensive and vasorelaxant effect of nitroglycerin. Co-incubation of tolerant aortic rings and pretreatment of tolerant SHR with 10 microM and 0.1-10 mg/kg zaprinast, respectively, resulted in full restoration of the vasorelaxant and hypotensive effect of nitroglycerin. Zaprinast partially reversed hemodynamic tolerance at 0.01 mg/kg. Conversely, dipyridamole (10 microM) reversed tolerance ex vivo, but was ineffective in reversing tolerance in vivo at pretreatment doses of 30 and 60 mg/kg. Following a 100-micrograms/kg i.v. challenge dose of nitroglycerin, aortic cyclic guanosine monophosphate (cGMP) levels were lower in nitroglycerin tolerant SHR when compared to non-tolerant SHR. Pretreatment of tolerant SHR with 10 mg/kg zaprinast restored the increase in cGMP levels to nitroglycerin to that seen in non-tolerant SHR. Conversely, dipyridamole (30 mg/kg) pretreatment was not effective in restoring cGMP levels. These data therefore suggest that reversal of hemodynamic tolerance in vivo is related to restoration of changes in vascular cGMP levels. Zaprinast, a selective cGMP phosphodiesterase inhibitor, effectively reverses tolerance and dipyridamole, a rather non-selective inhibitor, does not.

In vitro characterization of a novel series of platelet-derived growth factor receptor tyrosine kinase inhibitors

In this report, we describe the discovery and characterization of a novel biarylhydrazone series of platelet-derived growth factor (PDGF) receptor tyrosine kinase inhibitors typified by the prototype WIN 41662 (3-phenyl-N1-[1-(4-pytidyl)pyrimidine]hydrazone). WIN 41662 inhibited PDGF-stimulated autophosphorylation of PDGF receptors from human vascular smooth muscle cells (hVSMC) with an IC50 value of 60 nM. The inhibitor appeared to be competitive with respect to substrate (Mn(2+)-ATP), having a calculated Ki of 15 +/- 5 nM. WIN 41662 was approximately 500-fold more potent in inhibiting the PDGF receptor tyrosine kinase than the p56lck tyrosine kinase. It was inactive against other serine/threonine and tyrosine kinases tested. WIN 41662 produced concentration-dependent inhibition of PDGF-stimulated receptor autophosphorylation in intact hVSMC with an IC50 < 100 nM. Intracellular Ca2+ mobilization and cell proliferation were events that occurred in hVSMC subsequent to PDGF receptor activation. WIN 41662 inhibited PDGF-stimulated Ca2+ mobilization and cell proliferation ([3H]TdR incorporation) with IC50 values of 430 nM and 2.3 microM, respectively. These effects appeared to be specifically related to PDGF receptor tyrosine kinase inhibition since WIN 41662 was not cytotoxic (in vitro) and since WIN 72039, a close structural analog that does not inhibit PDGF receptor tyrosine kinase, also did not inhibit PDGF-stimulated receptor autophosphorylation, Ca2+ mobilization, or hVSMC proliferation. Thus, WIN 41662 is representative of a novel class of selective PDGF receptor tyrosine kinase inhibitors that inhibit PDGF-regulated secondary events in intact cells.

4,5-Dihydro-3-(methanesulfonamidophenyl)-1-phenyl-1H-2,4-benzodiazepines: a novel class III antiarrhythmic agents

A series of 4,5-dihydro-3-[2-(methanesulfonamidophenyl)ethyl]-1-phenyl- 1H-2,4-benzodiazepines has been identified as potential antiarrhythmic agents that interact at the delayed rectifier myocardial potassium channels (IKr) and prolong the ventricular effective refractory period (ERP) in rabbit isolated Langendorff heart preparations. Structure-activity relationship (SAR) studies based upon prolongation of ERP indicate that placement of the sulfonamido group is important for potent activity in this model. Furthermore, methanesulfonamido has enhanced activity over its ethyl or trifluoromethyl analogs. Slightly greater activity was observed in compounds that had a heteroatom in the ethyl bridge that connects the methanesulfonamidophenyl to the benzodiazepine. Further incremental improvements in activity were noted when the 1-phenyl ring was substituted with a variety of substituents. Chirality of the compounds of interest in this series does not appear to influence activity in this model. Several of these compounds were chosen for advanced evaluation, and all possess high selectivity for blockade of potassium current in hearts relative to other ion channels. In addition, these compounds prolong cardiac refractoriness in dogs following oral dosing. Thus, these agents may represent potential new class III agents, but with the potential liability of myocardial IKr blockers.

Species-dependent pharmacodynamic effects of the selective low Km cyclic AMP phosphodiesterase III inhibitors WIN 58993 and WIN 62005

We describe the biochemical and pharmacologic effects of two novel fused pyridinones derived from milrinone: WIN 58993 and WIN 62005. Both WIN 58993 and WIN 62005 competitively inhibit cyclic GMP-inhibitable low Km cyclic AMP phosphodiesterase (PDE III) from rat heart and canine aorta with Ki values of 25 +/- 3 and 26 +/- 5 nM, respectively, and are selective (at least 160-fold) for PDE III inhibition relative to other PDE isozymes. WIN 58993 and WIN 62005 were given to conscious, chronically instrumented rats and dogs intravenously (i.v.) or perorally (p.o.). Because the doses of WIN 58993 and WIN 62005 required to decrease mean arterial blood pressure (MAP) by 20% were estimated to be 0.9 and 0.7 mg/kg, respectively, the compounds appear to be equipotent after acute i.v. administration in rats. However, the duration of the depressor responses in rats apparently differs since MAP remained significantly decreased 6 h after i.v. or p.o. administration of WIN 58993, but returned to control levels < or = 4 h after administration of WIN 62005. WIN 58993 may be slightly less potent than WIN 62005 after acute i.v. administration to dogs since significant increases in left ventricular (LV)dP/dtmax first occurred at doses of 0.1 and 0.03 mg/kg, respectively. LVdP/dtmax significantly increased in 30 min and returned to baseline 3 h after p.o. administration of 1 mg/kg WIN 58993. After p.o. administration of 1 mg/kg WIN 62005. LVdP/dtmax was significantly increased in 30 min and remained increased for at least 6 h. These data suggest that WIN 58993 and WIN 62005 are potent, selective, p.o.-active inhibitors of PDE III.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic GMP potentiation by WIN 58237, a novel cyclic nucleotide phosphodiesterase inhibitor

The objectives of this study were to determine the potency and selectivity of the structurally novel cyclic nucleotide phosphodiesterase (PDE) inhibitor, WIN 58237 (1-cyclopentyl-3-methyl-6-(4- pyridyl)pyrazolo[3,4-d]pyrimidin-4-(5H)-one), and to determine if this compound possesses cyclic GMP (cGMP) PDE inhibitory activity in vitro and in vivo. WIN 58237 is a competitive inhibitor of cGMP PDE V from canine aorta, with a Ki value of 170 nM. It is a relatively less potent inhibitor of calmodulin-sensitive PDE I and cGMP-inhibitable cyclic AMP PDE III; but does inhibit cyclic AMP PDE IV with an IC50 value of approximately 300 nM. In vitro, WIN 58237 is a functional cGMP PDE inhibitor at submicromolar concentrations as evident by potentiation of both sodium nitroprusside- and atrial natriuretic factor-mediated vasorelaxation of contracted, endothelial-denuded rat aortic rings. Moreover, WIN 58237 possesses vasorelaxant activity in the presence of an intact endothelium or nitric oxide. Similar results are evident in vivo, as WIN 58237 (0.3-3.0 mg/kg i.v.) decreases mean arterial pressure in conscious spontaneously hypertensive rats with an associated increase in vascular (aortic) cGMP content in vivo. Both the decrease in mean arterial blood pressure and increase in aortic cGMP content are attenuated by the nitric oxide synthase inhibitor, N omega-nitro-l-arginine. However, WIN 58237 may possess an additional depressor mechanism of action. WIN 58237 restores vasorelaxation responsiveness to nitroglycerin in vitro and in vivo in models of vascular tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologic and pharmacodynamic effects of the selective low Km cyclic AMP phosphodiesterase III inhibitors WIN 63291 and WIN 62582

We describe the biochemical, pharmacologic, and in vivo pharmacodynamic profiles of two novel inhibitors of the cyclic GMP-inhibitable, low Km cyclic AMP phosphodiesterase (PDE) III; WIN 63291, a 6-quinolinyl analogue of the prototypic PDE III inhibitor milrinone and WIN 62582, an imidazopyridinone. Both WIN 62582 and WIN 63291 competitively inhibit PDE III from rat, dog, and human heart and from rat and canine aorta with IC50 values of 5-37 and 55-80 nM, respectively; the IC50 values for milrinone ranged from 300 to 520 nM. WIN 62582 and WIN 63291 are at least 1,000-fold selective for PDE III relative to inhibition of PDE isozymes I, II, IV, and V. We evaluated WIN 62582 and WIN 63291 in conscious rats and dogs after intravenous (i.v.) and oral (p.o.) administration. The dose of WIN 62582 required to reduce mean arterial blood pressure (MAP) by 20% (ED20) in rats was 1.8 mg/kg, with a pharmacodynamic duration of action of approximately 2 h. In comparison, the estimated i.v. ED20 for WIN 63291 in rats was 0.4 mg/kg, with a pharmacodynamic duration of action > 6 h. In conscious dogs, the i.v. doses of WIN 62582 and 63291 required to increase left ventricular (LV)dP/dtmax significantly were 0.1 and 0.01 mg/kg, respectively. In dogs, WIN 63291 0.1 mg/kg p.o. increased LVdP/dtmax by 86% in 30 min; LVdP/dtmax remained increased by 60% for at least 6 h. In comparison, WIN 62582, 0.3 mg/kg p.o., increased LVdP/dt by 56% in 30 min and remained increased by 40% at 6 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological modulation of human cardiac Na+ channels

Pharmacological modulation of human sodium current was examined in Xenopus oocytes expressing human heart Na+ channels. Na+ currents activated near -50 mV with maximum current amplitudes observed at -20 mV. Steady-state inactivation was characterized by a V1/2 value of -57 +/- 0.5 mV and a slope factor (k) of 7.3 +/- 0.3 mV. Sodium currents were blocked by tetrodotoxin with an IC50 value of 1.8 microM. These properties are consistent with those of Na+ channels expressed in mammalian myocardial cells. We have investigated the effects of several pharmacological agents which, with the exception of lidocaine, have not been characterized against cRNA-derived Na+ channels expressed in Xenopus oocytes. Lidocaine, quinidine and flecainide blocked resting Na+ channels with IC50 values of 521 microM, 198 microM, and 41 microM, respectively. Use-dependent block was also observed for all three agents, but concentrations necessary to induce block were higher than expected for quinidine and flecainide. This may reflect differences arising due to expression in the Xenopus oocyte system or could be a true difference in the interaction between human cardiac Na+ channels and these drugs compared to other mammalian Na+ channels. Importantly, however, this result would not have been predicted based upon previous studies of mammalian cardiac Na+ channels. The effects of DPI 201-106, RWJ 24517, and BDF 9148 were also tested and all three agents slowed and/or removed Na+ current inactivation, reduced peak current amplitudes, and induced use-dependent block. These data suggest that the alpha-subunit is the site of interaction between cardiac Na+ channels and Class I antiarrhythmic drugs as well as inactivation modifiers such as DPI 201-106.

Zaprinast increases cyclic GMP levels in plasma and in aortic tissue of rats

The purpose of this study was to determine if significant relationships exist between plasma and aortic cyclic GMP (cGMP) levels and pharmacodynamic effect after the i.v. administration of the cGMP-selective phosphodiesterase inhibitor zaprinast to conscious, spontaneously hypertensive rats. Zaprinast dose-dependently increased plasma and aortic cGMP levels at 10, 18 and 30 mg/kg and decreased mean arterial blood pressure (MAP) at 18 and 30 mg/kg. The concentrations of cGMP in the plasma and in the aorta were significantly correlated (r = 0.765, P < 0.0001). The changes in MAP were significantly correlated to aortic (r = -0.750, P < 0.0001) and plasma (r = -0.762, P < 0.0001) cGMP levels. We conclude that plasma cGMP may be an index of cGMP-selective phosphodiesterase inhibition in vivo.

Reversal of nitroglycerin tolerance in vitro by the cGMP-phosphodiesterase inhibitor zaprinast

Following in vitro exposure of rat aortic rings to 550 microM nitroglycerin for 1 h, tolerance was demonstrated by a significant increase in EC50 values for nitroglycerin-induced relaxation. However, cross-tolerance to sodium nitroprusside was not observed. Co-incubation of aortic rings with the cGMP-phosphodiesterase (cGMP-PDE) inhibitor zaprinast (10 microM), during incubation with 550 microM nitroglycerin, did not prevent the development of tolerance. However, the addition of 0.30 or 10 microM zaprinast to tolerant aortic rings did restore responsiveness to nitroglycerin. The increase in cGMP in tolerant aortic rings in response to 300 nM nitroglycerin (2-4 fmol/micrograms) was significantly less than that observed for non-tolerant rings (6.6-12 fmol/micrograms), but cGMP levels were restored in tolerant rings by zaprinast (7-12 fmol/micrograms). These data suggest that inhibition of vascular cGMP-PDE activity does not prevent the development of tolerance in vitro, but does reverse the loss of vasorelaxant potency to nitroglycerin via restoration of intracellular cGMP levels.

Ocular effects of topical administration of the phosphodiesterase III inhibitor milrinone in rabbits and cats

Increases in intracellular cAMP levels have previously been shown to decrease intraocular pressure (IOP) and increase ocular blood flow (OBF). However, the ocular effects of milrinone, which increases intracellular cAMP levels via selective cAMP PDE III inhibition, have not been investigated. The purpose of this study was to investigate the ocular effects of topically administered milrinone at different concentrations in rabbits and cats. When compared to vehicle in conscious rabbits, topical administration of milrinone at 0.03% decreased IOP (-14.1 +/- 2.6% vs. -7.4 +/- 3.7%, max. changes expressed as mean +/- SEM), at 0.1% increased IOP (10.4 +/- 8.5% vs. -1.7 +/- 4.1%), and at 0.01% and 1% did not significantly affect IOP. Neither pupil size nor central corneal thickness were affected by milrinone. Additionally, there were no signs of inflammation and no effects on corneal clarity. In anesthetized cats, topical administration of milrinone at 0.01-0.3% increased OBF (38.9 +/- 6.0% for milrinone vs. -7.4 +/- 4.4% for vehicle), and at 0.03%-0.3% decreased mean arterial pressure (-19.0 +/- 5.6 vs. 3.0 +/- 4.1 mmHg) in a dose-related manner. The durations of OBF enhancement (1.5-2.5 h) and MAP reduction (less than 30 min to 2 h) were also dose-dependent. In conclusion, milrinone induced biphasic IOP effects: IOP was decreased at 0.03% but increased at 0.1%. Milrinone at 0.01% increased OBF, possibly via a local vasodilator effect, and at 0.03-0.3% increased OBF, possibly via local and systemic effects. These data suggest that cAMP PDE III inhibitors such as milrinone may have efficacy as agents which enhance ocular blood flow following topical ocular application.

Lack of cross-tolerance between nitroglycerin and endothelium-derived relaxing factor-mediated vasoactive agents in spontaneously hypertensive rats

The purpose of this study was to determine whether cross-tolerance develops between nitroglycerin and endothelium-derived relaxing factor (EDRF)-mediated vasoactive agents in vivo. Spontaneously hypertensive rats (SHR) were made tolerant by pretreatment with high doses of nitroglycerin (100 mg/kg s.c., 3 times/day, for 3 consecutive days). The hypotensive effect of challenge doses of nitroglycerin (1, 10, 300, 100 micrograms/kg i.v.) was completely abolished in nitroglycerin-pretreated SHR. To evaluate cross-tolerance, the effects of the following EDRF-dependent vasoactive agents on blood pressure were determined in groups of nitroglycerin-pretreated and vehicle-pretreated SHR: acetylcholine, bradykinin and L-arginine. In addition, the hypotensive effects of zaprinast (M & B 22,928), a cyclic guanosine monophosphate (cGMP) phosphodiesterase inhibitor, and the hypertensive effects of the nitric oxide-synthase inhibitor N omega-nitro-L-arginine were also evaluated. In all cases, there was no difference in the effects of these agents on blood pressure when compared in nitroglycerin-pretreated (tolerant) and vehicle-pretreated (non-tolerant) SHR. The use of a variety of agents which modulate EDRF release or its effects by several different mechanisms suggests that cross-tolerance does not occur between nitroglycerin and EDRF in vivo.

Identification of a specific radioligand for the cardiac rapidly activating delayed rectifier K+ channel

Class III antiarrhythmic drugs show promise as effective treatments for the suppression of potentially lethal cardiac arrhythmias. Dofetilide (UK-68,798), is a potent class III antiarrhythmic agent that is presently under clinical investigation. The objective of this study was to determine whether [3H]dofetilide could be used as a specific radioligand for the rapidly activating delayed rectifier K+ channel of the heart. We find that [3H]dofetilide binds to high-affinity sites on guinea pig cardiac myocytes. Competition studies using unlabeled dofetilide indicate that binding is characterized by an IC50 of 100 +/- 30 nM (mean +/- SD, n = 13). Scatchard analyses of binding indicate a Kd of 70 +/- 6 nM and a maximal binding capacity of 0.30 +/- 0.02 pmol/mg protein. [3H]Dofetilide is displaced from guinea pig myocytes by dofetilide, clofilium, quinidine, sotalol, and sematilide with a rank order of potency that correlates with functional blockade of the rapidly activating delayed rectifier K+ current (correlation coefficient, 0.951; slope, 0.99 +/- 0.19; p = 0.014). High-affinity [3H]dofetilide binding is not detected in rat myocytes, which are devoid of delayed rectifier K+ current. We conclude that [3H]dofetilide specifically binds to sites associated with the rapidly activating delayed rectifier K+ channel of guinea pig myocardium.

Novel cAMP PDE III inhibitors: 1,6-naphthyridin-2(1H)-ones

Two series of medorinone (3) analogs were prepared by modifications at C(2) and C(5). The C(2)-series was prepared from 2-chloro-5-methyl-1,6-naphthyridine (4) by replacement of the chloro group with various nucleophiles. The C(5)-series was prepared from 5-acyl-6-[2-(dimethylamino)-ethenyl]-2(1H)-pyridinone (11), 5-bromo-1,6-naphthyridin-2(1H)-one (17), and 1,3-diketones 19 and 27. 1,6-Naphthyridin-2(1H)-ones are novel inhibitors of cAMP PDE III. Modification of the carbonyl group of 3 or N-methylation at N(1) resulted in a dramatic loss of enzyme activity. Absence of the C(5)-methyl group of medorinone (3) or its shift to C(3) or C(7) also resulted in reduced activity. Substitution at C(3) also diminished activity. However, substitution at C(5) by a wide variety of substituents led to improvement of enzyme activity and several C(5)-substituted analogs were more potent than milrinone.

Calcium transport by sarcoplasmic reticulum of vascular smooth muscle: II. Effects of calmodulin and calmodulin inhibitors

The role of calmodulin (CaM) in modulating calcium (Ca) uptake by sarcoplasmic reticulum (SR) of vascular smooth muscle was studied in saponin skinned strips of rat caudal artery. Exogenous CaM concentrations ranging from 0.3-1.8 microM did not statistically change the steady state MgATP-dependent Ca content, the MgATP-independent Ca content, or the oxalate-stimulated Ca influx. Calmidazolium (CDZ), W-7, and trifluoperazine (TFP) were used to examine the potential effect of an endogenous CaM pool on inward Ca transport. The IC50 of these antagonists for inhibition of Ca-CaM-stimulated phosphodiesterase activity and Ca-activated superprecipitation of canine aortic actomyosin was measured and found to be in the low micromolar range with a rank order of potency for inhibition of CDZ greater than TFP greater than W-7. In skinned tissues, micromolar concentrations of antagonists that inhibited CaM-mediated reactions in isolated enzyme systems did not reduce Ca content or oxalate-stimulated Ca influx. At higher concentrations of 100-200 microM, the MgATP-dependent Ca content was significantly reduced by TFP and W-7 but not by CDZ. The order of potency for inhibition of Ca uptake was TFP greater than W-7 greater than CDZ. The MgATP-independent Ca content was significantly decreased only by 200 microM TFP. Although none of these inhibitors significantly altered Ca efflux at concentrations up to 100 microM, Ca release was significantly stimulated by all three at 200 microM. The TFP-stimulated Ca release was partially inhibited by ruthenium red. The results indicate that neither exogenous CaM nor an endogenous CaM pool directly modulates inward Ca transport by the SR of saponin skinned caudal artery. The inhibition of Ca uptake produced by hundred micromolar concentrations of CaM antagonists fails to correlate with the order of and with the potency of inhibition measured in isolated enzyme systems. This suggests that the inhibition of Ca uptake produced by high concentrations of these antagonists may be independent of a specific interaction with CaM. The activation of Ca release by high concentrations of CaM antagonists may involve a nonspecific increase in membrane permeability as well as modulation of a membrane Ca channel.

Hemodynamic and renal effects of the protein kinase inhibitor staurosporine in conscious rats

To evaluate the pattern of hemodynamic responses produced by an inhibitor of protein kinase C (PKC), staurosporine 0.03-0.55 mg/kg was administered intravenously (i.v.) to conscious, normotensive rats chronically instrumented with vascular catheters for direct measurement of blood pressure (BP) and i.v. administration of drugs and either an aortic flow probe for measurement of cardiac output (CO) or miniaturized pulsed Doppler flow probes for measurement of hindquarter, renal, and mesenteric vascular resistances. Staurosporine decreased mean arterial pressure (MAP) and total peripheral resistance (TPR) and increased heart rate (HR) in a dose-dependent manner. Because staurosporine decreased resistance in all three vascular beds monitored (hindquarter, renal, and mesenteric), staurosporine is probably a nonselective vasodilator that decreases MAP by decreasing resistance in a number of peripheral vascular beds. Staurosporine produced biphasic effects on CO, dF/dtmax and peak aortic blood flow; these parameters were significantly increased at doses less than 0.3 mg/kg and decreased to levels equal to or significantly less than control values at doses greater than 0.3 mg/kg. In comparison, the calcium channel blocker nitrendipine decreased MAP and TPR and increased HR, CO, dF/dtmax, and peak aortic flow in a dose-dependent manner over the entire dose range (0.01-1 mg/kg i.v.). Staurosporine (0.3 mg/kg) and nitrendipine (1 mg/kg) produced similar changes in MAP (-44 +/- 3 and -33 +/- 2 mm Hg, respectively), yet staurosporine affected dF/dtmax to a lesser extent than nitrendipine (-5 +/- 36 and 390 +/- 46 ml/s/s, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular protein kinase C in Wistar-Kyoto and spontaneously hypertensive rats

Phorbol esters which activate protein kinase C (PKC) produced concentration-related force development in aorta from spontaneously hypertensive rat (SHR) and Wistar-Kyoto rat (WKY); all were 2-7 x more potent in SHR. However, total PKC activity in aortas, as well as carotid, caudal and renal arteries, was not different, when SHR was compared with WKY. Binding of phorbol dibutyrate to particulate aortic PKC was similar in SHR and WKY (same apparent Kd and Bmax values), as was potency for displacement of phorbol dibutyrate by phorbol myristate acetate. Furthermore, there was no difference in potency with staurosporine, H-7, and calmidazolium in inhibiting SHR and WKY aortic PKC. These data demonstrate enhanced contractile sensitivity to PKC-activating phorbol esters in SHR aortic smooth muscle that is not related to activity, phorbol ester binding, or sensitivity to inhibitors when SHR PKC is compared with WKY PKC. Thus, signal transduction events distal to PKC activation may be responsible for enhanced vascular contractile sensitivity to phorbol esters in SHR.

Cardiovascular cyclic nucleotide phosphodiesterases and their role in regulating cardiovascular function

We have described five phosphodiesterase (PDE) isozymes that can be found in cardiac and vascular smooth muscle of animals and humans. Much of the evidence for the role that these isozymes have in the regulation of cellular processes has been generated through, or awaits, the identification of selective and potent PDE inhibitors. While selective inhibitors of the cGMP-inhibitable (cGi)-PDE isozyme have been approved for use in the acute treatment of heart failure, selective inhibitors of the cGMP-PDE have not been extensively explored as potential candidates for the treatment of cardiovascular diseases. More potent selective inhibitors of the cGMP-PDE isozyme are needed to determine whether these pharmacological potentiators of EDRF and ANP will be useful in the therapy of angina, hypertension or heart failure.

The effects of iodixanol and iopamidol on hemodynamic and cardiac electrophysiologic parameters in vitro and in vivo

Iodixanol is a new, nonionic, dimeric contrast medium which, in concentrations appropriate for radiographic use, is hypotonic with respect to plasma. The purpose of these in vivo and in vitro studies was to compare the effects of iopamidol, iodixanol formulated to isotonicity with sodium salts (sodium formulation), and iodixanol formulated to isotonicity with sodium, calcium, and magnesium salts (cationic formulation) on hemodynamic and electrophysiologic parameters. In vitro, the spontaneous rate of contraction by guinea pig right atrial and force development by right ventricular papillary muscles were evaluated in the presence of 1% to 100% (v/v) of the three contrast media. Iopamidol significantly (P less than .05) decreased the rate of atrial contraction to a greater extent than either formulation of iodixanol. Iopamidol decreased papillary muscle force development more than the sodium formulation of iodixanol (P less than .05). The cationic formulation of iodixanol had little effect (less than 30% change) on papillary muscle force development at concentrations up to 100%. The contrast media were also injected into the left coronary arteries of open-chest, anesthetized dogs at 0.8 mL/second for 5 to 30 seconds. All contrast media increased (P less than .05) systolic blood pressure (SBP), mean arterial pressure (MAP), and peak left ventricular pressure (LVP). Iopamidol increased LVP and LV end diastolic pressure to a greater extent (P less than .05) than the cationic formulation of iodixanol. We conclude that iopamidol affected cardiovascular parameters more than iodixanol.

Inhibition of low Km cGMP phosphodiesterases and Ca+(+)-regulated protein kinases and relationship to vasorelaxation by cicletanine

In the present studies we sought to determine if cicletanine, which is an antihypertensive agent of unknown mechanism, could alter cGMP metabolism via inhibition of cGMP phosphodiesterases (PDE) in vascular smooth muscle. Cicletanine was determined to be a mixed (competitive, noncompetitive) inhibitor of both calmodulin-regulated and cGMP-specific PDEs from monkey aortic smooth muscle with Ki values of 450 to 700 microM. Cicletanine also potentiated vasorelaxation by the guanylate cyclase activators sodium nitroprusside and atrial natriuretic peptide in isolated rat aortas. Potentiation was not dependent upon the contractile agonists nor was it indomethacin-sensitive. Neither potentiation nor inhibition of cGMP PDEs was stereoselective. Methylene blue attenuated a component of cicletanine-induced vasorelaxation, but did not completely obviate relaxation. Both cicletanine and the cGMP-PDE inhibitor zaprinast potentiated sodium nitroprusside-mediated cGMP formation and relaxation, although the increase in cGMP content was markedly greater with zaprinast compared to cicletanine. In further studies, cicletanine did not potentiate cGMP activation of cGMP-dependent protein kinase, but did inhibit calmodulin-activated myosin light chain kinase and protein kinase C at relatively high concentrations (approximately 1 mM). In summary, these data demonstrate that cicletanine inhibits vascular cGMP PDEs, potentiates vasorelaxation, and to a limited extent, cGMP formation by guanylate cyclase activators in vascular smooth muscle. However, these relationships for cicletanine are dissimilar from the reference cGMP PDE inhibitor, zaprinast. Thus, other mechanisms may also contribute to the vasorelaxant action of cicletanine.

Protein kinase inhibitors and blood pressure control in spontaneously hypertensive rats

Considerable evidence suggests that protein kinase C activation participates in the regulation of vascular smooth muscle tone. The objective of the current study was to examine the relations between inhibition of protein kinase C (PKC) and myosin light-chain kinase (MLCK) and vasorelaxation and blood pressure regulation in spontaneously hypertensive rats (SHR). Putative PKC inhibitors from two chemical classes, staurosporinelike (staurosporine and K252A) and isoquinolinesulfonamides (H7 and HA1004), were tested for their ability to 1) inhibit PKC and MLCK from SHR aorta, 2) relax isolated SHR aorta, and 3) lower blood pressure in conscious SHR. A rank order of potency for the inhibition of PKC and MLCK was established, with the staurosporinelike compounds (staurosporine PKC IC50 = 54 nM) clearly more potent than the isoquinolinesulfonamides (H7 PKC IC50 = 128 microM). The rank order of potency for inhibition of PKC was retained for inhibition of MLCK for all compounds. Staurosporine (EC50 = 75 nM) and H7 (EC50 = 2 microM) caused concentration-dependent relaxation of SHR aorta, but only staurosporine produced vasorelaxation at concentrations consistent with the inhibition of PKC or MLCK. Dose-dependent reductions in arterial pressure of SHR were demonstrated after intravenous injection of staurosporine and HA1004. A single intravenous injection of staurosporine (0.3 mg/kg) lowered blood pressure for more than 10 hours. Staurosporine also lowered blood pressure after oral administration. The depressor response to staurosporine was unaffected by sympathetic beta-adrenergic blockade. In conclusion, the vasorelaxant and antihypertensive actions of staurosporine in SHR are consistent with the inhibition of PKC but could also be equally related to inhibition of MLCK. Not all PKC inhibitors produce vasorelaxation and lower blood pressure. Moreover, the lack of correlation between in vitro vasodilation and PKC or MLCK inhibition for the isoquinolinesulfonamide protein kinase inhibitors H7 and HA1004 suggests that these agents do not cause vasorelaxation in SHR by inhibition of these enzymes.

Inhibition of low Km cyclic GMP phosphodiesterases and potentiation of guanylate cyclase activators by cicletanine

Cicletanine is an antihypertensive/vasorelaxant/natriuretic agent of unknown mechanism. We wished (a) to determine if cicletanine interacts with guanylate cyclase activators that modulate vasomotor tone and sodium balance [i.e., atriopeptin II (AP II), endothelium-derived relaxing factor (EDRF), and sodium nitroprusside (SNP)], and (b) to define the subcellular basis for this interaction by quantitating the effects of cicletanine on low Km cyclic GMP phosphodiesterase (PDE) activity. In phenylephrine-contracted rat aortic smooth muscle, the vasorelaxant potency of cicletanine was increased twofold in the presence of a threshold-relaxant concentration of AP II, and functional cyclic GMP PDE inhibition was also evident from the three- to sixfold potentiation by cicletanine of AP II- or SNP-induced vasorelaxation. Vasorelaxation produced by cicletanine was not endothelium dependent, however. In further studies, intravenous (i.v.) administration of cicletanine or the low Km cyclic GMP PDE inhibitor, zaprinast, decreased blood pressure (BP) greater than or equal to 20% in conscious spontaneously hypertensive rats (SHR). These results are consistent with the additional finding that cicletanine inhibited Ca2(+)-calmodulin (CaM) cyclic GMP PDE and zaprinast-sensitive cyclic GMP specific PDE over a concentration range (10-600 microM) similar to that for vasorelaxation. Thus, inhibition of low Km cyclic GMP PDEs by cicletanine may be partly responsible for the vasorelaxant effect of cicletanine as well as the potentiation by cicletanine of the vasorelaxant actions of guanylate cyclase activators. The extent to which this mechanism contributes to the antihypertensive efficacy of cicletanine has not yet been fully determined.

Sodium nitroprusside potentiates the depressor response to the phosphodiesterase inhibitor zaprinast in rats

To determine if the presence of an activator of guanylate cyclase alters the depressor response to a selective inhibitor of low Km cyclic GMP (cGMP) phosphodiesterase (PDE), zaprinast (3-30 mg/kg) was given i.v. to conscious, spontaneously hypertensive rats during a steady state of i.v. infusion of sodium nitroprusside (15 micrograms/kg per min). Sodium nitroprusside significantly increased the magnitude of the depressor response to zaprinast. In contrast, fenoldopam (20 micrograms/kg per min), an activator of adenylate cyclase, did not affect the depressor response to zaprinast. Zaprinast (10 mg/kg) significantly decreased mean arterial pressure (MAP) in rats given an infusion of sodium nitroprusside, an activator of soluble guanylate cyclase, at doses of 15 and 25 micrograms/kg per min but not at a dose of 5 micrograms/kg per min. However, in rats given atrial natriuretic peptide (ANP; 0.5, 1 and 2 micrograms/kg per min), an activator of particulate guanylate cyclase, zaprinast (10 mg/kg) did not affect MAP. In contrast to the potentiation of the depressor response to zaprinast, sodium nitroprusside (15 micrograms/kg per min) significantly attenuated the reductions in MAP produced by CI-930, a selective inhibitor of low Km cAMP PDE. It is concluded that sodium nitroprusside, but not ANP or fenoldopam, potentiates the depressor response to zaprinast. Furthermore, the potentiation of the depressor response to zaprinast is dependent upon the dose of sodium nitroprusside and is selective for zaprinast; the depressor response to CI-930 is attenuated by sodium nitroprusside.