Howard A. Ball

Prevention of vascular nitroglycerin tolerance by inhibition of protein kinase C

We investigated whether in vivo inhibition of protein kinase C (PKC) can prevent the development of vascular tolerance and restore the sensitivity of isolated vessels to nitroglycerin (NTG). Tolerance was induced in male Wistar rats by a constant i.v. infusion of NTG 1 mg kg−1 h−1, a dose which did not alter blood pressure. After 72 h, the aorta was removed and the sensitivity of aortic rings to NTG tested. Chronic NTG infusion resulted in a 5.5 fold decrease in NTG‐sensitivity as compared with controls (vehicle), indicating the development of vascular tolerance. The simultaneous in vivo administration of the specific PKC inhibitor N‐benzoyl‐staurosporine (30 mg kg−1 day−1) prevented this decrease in NTG sensitivity. These results suggest a role for PKC activation in the development of vascular NTG tolerance.

Effect of cyclopiazonic acid, an inhibitor of sarcoplasmic reticulum Ca2+‐ATPase, on the frequency‐dependence of the contraction‐relaxation cycle of the guinea‐pig isolated atrium

1 The relevance of a functional sarcoplasmic reticulum (SR) membrane system to the contraction‐relaxation cycle and to the force‐frequency relationship of guinea‐pig atrial tissue was investigated. Cyclopiazonic acid (CPA) was used to inhibit selectively the activity of the SR Ca2+‐ATPase. IQo values of 0.2 μm or 1.0 μm were measured in guinea‐pig isolated SR membranes in the absence or presence of millimolar ATP, respectively. CPA (0.3–30 μm) did not inhibit the activity of the sarcolemmal Na+‐Ca2+‐exchanger as measured in isolated cardiac cell membrane preparations. 2 In guinea‐pig isolated left atrium paced at 2.5 Hz (30°C), CPA (1–100 μm) produced a concentration‐dependent reduction in developed tension and a fall in the maximum rate of tension increase (+ dT/dtmax) and decrease (‐dT/dtmax). The twitch duration was markedly increased due to a prolongation of the time to peak tension, and in particular, the relaxation phase. 3 The contraction‐relaxation cycle of the left atrium showed a marked dependence on the frequency of stimulation. The developed tension and +dT/dtmax showed a progressive increase from 0.5 Hz, reaching peak values at a stimulation rate of 1.5‐2.5 Hz, the positive staircase phenomenon. Higher frequencies of stimulation caused a fall in these parameters. Resting tension was unaffected. The time‐course of the contraction‐relaxation cycle was also frequency‐dependent, with both time to peak tension and relaxation time showing a progressive fall from 2.0–3.5 Hz. 4 The addition of CPA (30 μm) caused marked alterations in the frequency‐dependence of the contraction‐relaxation cycle. The frequency‐dependence of developed tension, + dT/dtmax, was shifted downwards, particularly at higher frequencies, and the frequency at which peak values of + dT/dtmax and — dT/dtmax were reached was shifted leftwards. The resting tension of the tissues in the presence of 30 μm CPA was increased markedly at frequencies greater than 2 Hz. The time‐course of the contraction‐relaxation cycle was markedly prolonged between 1.0 and 3.5 Hz, due to an effect on both time to peak tension and relaxation time. 5 In conclusion, these results show that CPA is a highly selective inhibitor of the cardiac SR Ca2+‐ATPase, without effect on the sarcolemmal Na+‐Ca2+‐exchanger, and suggest that a functional SR Ca2+‐ATPase is necessary for the normal contraction‐relaxation cycle of guinea‐pig cardiac tissue. Additionally, the results suggest an increasing dependence of tension development on SR Ca2+‐ATPase with increasing frequency, which may reflect either a frequency‐dependent activation of this enzyme or the diminished contribution of the Na+‐Ca2+ exchanger. These results also provide novel support for the mechanism of the depressed force‐frequency relation found in cardiac tissue of heart failure patients, in which there is a reduced expression of Ca2+‐ATPase.

Simultaneous LV and RV volumes by conductance catheter: effects of lung insufflation on parallel conductance

One aspect in the measurement of ventricular volume using the conductance catheter technique is the assessment of parallel electrical conductivity of structures extrinsic to the ventricular blood pool. Because it is sometimes necessary to make volume measurements during ventilation or spontaneous respiration, the extent to which parallel conductance may vary with lung insufflation was investigated. Anesthetized pigs (11-15 kg) were ventilated and instrumented with both left (LV) and right ventricular (RV) conductance and pressure-tip catheters and end-hole catheters for injection of hypertonic saline into the inferior vena cava and pulmonary artery. Data were recorded during ventilation with tidal volumes of 10 and 20 ml/kg, and the associated fluctuations to LV and RV end-diastolic (EDV) and stroke (SV) volumes were measured. With the use of a saline dilution technique, parallel conductance (Vc) was determined for each ventricle with the ventilator off and lungs insufflated to 0, 10, and 20 ml/kg. Whereas ventilation caused marked oscillations in LV and RV EDV and SV, these variations could not be attributed to Vc, which remained statistically unchanged from their baseline values of 34.1 +/- 3.1 in the LV and 31.1 +/- 4.4 in the RV. These results indicate that the fluctuations that occur in conductance catheter-derived LV and RV volume signals with ventilation are not caused by any significant changes to parallel conductance.

Biphenyl derivatives as novel dual NK1/NK2-receptor antagonists

In a continuation of our efforts to simplify the structure of our neurokinin antagonists, a series of substituted biphenyl derivatives has been prepared. Several compounds exhibit potent affinities for both the NK(1) receptor (<10nM) and for the NK(2) receptor (<50 nM). Details on the design, synthesis, biological activities, SAR and conformational analysis of this new class of dual NK(1)/NK(2) receptor antagonists are presented.

N-[(R,R)-(E)-1-(4-chloro-benzyl)-3-(2-oxo-azepan-3-ylcarbamoyl)-allyl]-N-methyl-3,5-bis-trifluoromethyl-benzamide: an orally active neurokinin NK1/NK2 antagonist.

The stereoselective synthesis of N-[(R,R)-(E)-1-(4-chloro-benzyl)-3-(2-oxo-azepan-3-ylcarbamoyl+ ++)-allyl]-N-methyl-3,5-bis-trifluoromethyl-benzamide (4) and its NK1 and NK2 receptor binding properties are reported. In addition the potent inhibitory effects in vivo on sar9-SP- and beta-Ala-NKA-induced airway bronchoconstriction in guinea pigs are demonstrated.

Airways pharmacology of DNK333A, a dual NK1/NK2 neurokinin receptor antagonist.

The British Pharmacological Society wish to apologise that in the above Supplement the correct abstract for 69P was omitted. Abstract 69P appears below.​below. Figure 1

CGP57698: A Structurally Simple, Highly Potent Peptidoleukotriene (PLT) Antagonist of the Quinoline Type

A number of peptido-leukotriene antagonists coming from a variety of different structural classes have been developed over the last ten years and are in clinical development as anti-asthmatic agents.1, 2, 3 Many of these compounds are complex molecules and we have aimed at developing novel compounds which combine structural simplicity with high oral potency. Compounds of the quinoline type were considered to be suitable target structures for the design of new potent and highly bioavailable LTD4 antagonists.4, 5 The clinically most advanced compound of this type is at present MK-0476 (montelukast sodium).6 The quinoline antagonists, characterized by a substituent in the 2 position consisting of a spacer with 2 atoms, an additional aromatic moiety and a terminal acidic group, show good in vitro and in vivo activity including ease of synthesis. The nature of this acidic residue is of key importance for the pLT antagonist potency of quinoline type antagonists. Combination of the required structural elements led to the synthesis of CGP57698 (4-[3-(7-fluoro-2-quinolinyl-methoxy)phenyl-amino]-2,2-diethyl-4-oxo-buta-noic acid). In CGP57698 the acidic group is derived from succinic acid with two geminal ethyl groups, which are essential for the high potency of CGP57698.

Parallel tolerance between platelet cyclic GMP and preload effects of nitroglycerin in anaesthetized mini‐pigs

The effects of acute intravenous nitroglycerin (NTG) administration on platelet cyclic GMP in relation to changes in indices of preload (end‐diastolic volume) and afterload (effective arterial elastance) were evaluated in the anaesthetized mini‐pig, using pressure‐volume analysis. NTG (1–30 μg kg‐1 min‐1, i.v.) elicited a dose‐dependent fall in preload and afterload, and an increase in arterial blood platelet cyclic GMP. Repeated doses of NTG (30 μg kg‐1 min‐1) resulted in tolerance to the preload but not afterload effects. The increases in platelet cyclic GMP were also attenuated, being highly correlated with the preload changes. Therefore, platelet cyclic GMP appears to reflect NTG‐induced venous tolerance, rather than arterial responsiveness. The measurement of platelet cyclic GMP may represent a simple approach for monitoring the degree of venous tolerance to NTG in animals or patients, facilitating further mechanistic investigations.