N-aryl-3,3,3-trifluoro-2-hydroxy-2-methylpropanamides: KATP potassium channel openers. Modifications on the western region

A subset of antiandrogen compounds, the N-aryl-3,3,3-trifluoro-2-hydroxy-2-methylpropanamides 1, were found to activate ATP sensitive potassium channels (KATP) and represent a new class of potassium channel openers (PCOs). A structure-activity relationship was carried out on the western region of this series with the goal of obtaining an activator of the ATP sensitive potassium channel suitable for use in the treatment of urge urinary incontinence. In particular three large 4-(N-aryl) substituents, the (N-phenyl-N-methylamino)sulfonyl, benzoyl, and 4-pyridylsulfonyl moieties, yielded non-antiandrogen, KATP potassium channel openers (39, 41, and 64, respectively) that are bladder selective in an in vivo rat model that simultaneously measures bladder contractions, heart rate, and blood pressure. Substitutions of the aryl rings of 41 and 64 gave several derivatives that also display selectivity in the in vivo rat model; however, none appear to offer a substantial advantage over 41 and 64. The PCO activity of 41 and 64 resides in the (S)-(-) enantiomers. ZD6169, 41(S), has been selected into development for the treatment of urge urinary incontinence.

Telesurgery. Acceptability of compressed video for remote surgical proctoring

OBJECTIVE

To determine the clinical acceptability of various levels of video compression for remote proctoring of laparoscopic surgical procedures.

DESIGN

Observational, controlled study.

SETTING

Community-based teaching hospital.

PARTICIPANTS

Physician and nurse observers.

INTERVENTIONS

Controlled surgical video scenes were subjected to various levels of data compression for digital transmission and display and shown to participant observers.

MAIN OUTCOME MEASURES

Clinical acceptability of video scenes after application of video compression.

RESULTS

Clinically acceptable video compression was achieved with a 1.25-megabit/second data rate, with the use of odd-screen 43.3:1 Joint Photographic Expert Group compression and a small screen for remote viewing.

CONCLUSION

With proper video compression, remote proctoring of laparoscopic procedures may be performed with standard 1.5-megabit/second telecommunication data lines and services.

The acid metabolite of ZD7114 is a partial agonist of lipolysis mediated by the rat beta 3-adrenoceptor

Experiments were performed to characterise the lipolytic effects of the acid metabolite, ZM215001, ((S)-4-[2-hydroxy-3-phenoxy-propylamino-ethoxy] phenoxyacetic acid) of the putative beta 3-adrenoceptor agonist, ZD7114 ((S)-4-[2-hydroxy-3-phenoxy-propylamino-ethoxy]-N-(2-methoxyethyl) phenoxyacetamide) on isolated rat white adipocytes. ZM215001 was used for these studies since it is the predominant moiety after in vivo administration of ZD7114. The agonist properties of ZM215001 were assessed in comparison to the standard nonselective beta-adrenoceptor agonist (+/-)-isoprenaline and the beta 3-adrenoceptor-selective agonist BRL 37344. Isoprenaline, BRL 37344 and ZM215001 all stimulated the rate of free fatty acid release from isolated adipocytes with the order of potency being BRL > isoprenaline > ZM215001. The maximum effect of BRL 37344 was equivalent to that of isoprenaline, but ZM215001 achieved only 30% of the maximum isoprenaline response. ZM215001 competitively antagonised the lipolytic response to BRL 37344 (pA2 = 7.26), whereas the agonist effects of BRL 37344 were not antagonised competitively by the selective antagonists ICI 118551 and CGP 20712A, at concentrations which would be expected to block beta 1- and beta 2-adrenoceptors respectively. These results indicate that ZM215001 has low intrinsic activity at the rat adipocyte beta 3-adrenoceptor, and is a partial agonist of lipolysis in rat white adipocytes.

Effects of K+ channel blockers and cromakalim (BRL 34915) on the mechanical activity of guinea pig detrusor smooth muscle

There is strong evidence that cromakalim (BRL 34915) relaxes smooth muscle by opening cell membrane K+ channels. The aim of this study was to use relatively selective K+ channel blockers to investigate 1) the K+ channel type(s) opened by cromakalim in guinea pig detrusor and 2) the role of different K+ channel types in the control of basal tension. Cromakalim produced a concentration-related relaxation (IC50 = 0.50 +/- 0.03 microM, n = 42) of 15 mM K(+)-evoked mechanical activity. The ATP-sensitive K+ channel blocker glyburide (0.3-3 microM) antagonized the effects of cromakalim in an apparently competitive manner (pA2 = 6.76). Charybdotoxin and iberiatoxin (3-30 nM), blockers of the large conductance, Ca(++)-activated K+ channel, appeared to functionally antagonize cromakalim. Apamin (1 microM) and leiurotoxin I (0.3 microM), blockers of the small conductance, Ca(++)-activated K+ channel, and noxiustoxin (0.3 microM), a blocker of squid axon delayed rectifer K+ channels, all failed to antagonize cromakalim. Cumulative administration of charybdotoxin and iberiatoxin produced marked, concentration-related stimulation of mechanical activity per se whereas glyburide, noxiustoxin, apamin and leiurotoxin I had no effect. Apamin and leiurotoxin I did stimulate mechanical activity to a small extent when administered noncumulatively, however. The results suggest that cromakalim opens ATP-sensitive K+ channels in detrusor and suggest that cromakalim does not open CA(++)-activated K+ channels and noxiustoxin-sensitive, delayed rectifier K+ channels. The marked stimulatory effects of charybdotoxin and iberiatoxin per se suggest an important role for large conductance, Ca(++)-activated K+ channels in the control of basal tension and, presumably, membrane potential in detrusor smooth muscle cells.

Comparison of the effects of the K(+)-channel openers cromakalim and minoxidil sulphate on vascular smooth muscle

1 The actions of the potassium channel openers, cromakalim and minoxidil sulphate, were compared in a range of isolated blood vessel preparations. 2 Cromakalim and minoxidil sulphate inhibited spontaneous mechanical activity of the guinea-pig portal vein and relaxed the noradrenaline precontracted rat aorta with similar potency. In contrast, minoxidil sulphate was less potent than cromakalim in inhibiting spontaneous activity in the rat portal vein and was essentially inactive in the noradrenaline precontracted rat mesenteric artery and rabbit aorta. 3 Minoxidil sulphate did not antagonize the effects of cromakalim in the rabbit aorta indicating it was not acting as a partial 'agonist'. 4 Charybdotoxin, noxiustoxin and rubidium failed to discriminate between cromakalim and minoxidil sulphate indicating that the apparently selective effects of minoxidil sulphate were not mediated by either Ca(2+)-activated potassium channels, delayed rectifiers or rubidium impermeable potassium channels. 5 Glibenclamide antagonized the effects of cromakalim in an apparently competitive manner whereas the effects of minoxidil sulphate were antagonized in a non-competitive manner. The involvement of subtypes of ATP-sensitive potassium channels is discussed.

Interactions between angiotensin II and alpha-adrenoceptor agonists mediating pressor responses in the pithed rat

1. The aim of the study was to investigate the interactions between angiotensin II (AII) and adrenoceptor-mediated pressor responses in the pithed rat. Emphasis was placed on the effects of AII on blood pressure per se and the possibility of differential effects on alpha 1- and alpha 2-adrenoceptor-mediated pressor responses. 2. A low concentration of the angiotensin converting enzyme (ACE) inhibitor, teprotide (1 mg kg-1) lowered the resting diastolic blood pressure (BP) and attenuated only the second phase components of pressor responses to both alpha 1- and alpha 2-adrenoceptor agonists. Infusion of AII (50 ng kg-1 min-1) did not reverse the attenuating effect of teprotide and did not reliably restore the basal diastolic BP. 3. Although teprotide (10 mg kg-1) did not produce a greater fall in diastolic BP than did the low dose (1 mg kg-1), it attenuated the peak and second phase pressor responses to alpha 1- and alpha 2-adrenoceptor agonists but had no effect on pressor responses to AII or 5-hydroxytryptamine (5-HT). Infusion of AII reversed the effects of teprotide (10 mg kg-1) provided that rats were pretreated with flurbiprofen (5 mg kg-1), confirming that the depressor effects of the higher dose of teprotide are AII-dependent but that demonstration of this was complicated by products of cyclo-oxygenase. 4. The AII-receptor antagonist, saralasin (4 micrograms kg-1 min-1) attenuated alpha 1- and alpha 2-adrenoceptor-mediated pressor responses in a manner similar to that of teprotide (10 mg kg-1), suggesting that in this pithed rat model the alpha-adrenoceptor-mediated responses were selectively facilitated by endogenous AII. 5. Infusion of AII (50 ng kg-1 min-1) over a 60 min period did not produce a pressor response in the absence of other drugs but did facilitate pressor responses to alpha-adrenoceptor agonists. This confirms that AII can modulate alpha-adrenoceptor-mediated responses independently of basal blood pressure. 6. Overall the results indicate a facilitatory role for endogenous AII on alpha-adrenoceptor-mediated pressor responses. This is discussed in relation to the failure to demonstrate this convincingly under similar conditions on sympathetic nerve-mediated pressor responses.

Interactions between angiotensin II, sympathetic nerve-mediated pressor response and cyclo-oxygenase products in the pithed rat

1. The influence of angiotensin II (AII) on resting blood pressure and on sympathetic nerve-mediated pressor responses in the pithed rat was investigated either by inhibiting the renin-angiotensin system or by infusing AII. 2. Plasma AII levels in the pithed rat were approximately 20 fold higher than in normotensive rats. 3. Infusion of a subpressor dose of AII (50 ng kg-1 min-1) had no effect on sympathetic nerve mediated pressor responses but a pressor dose of AII, (200 ng kg-1 min-1) facilitated nerve-mediated pressor responses. 4. The angiotensin converting enzyme inhibitor, teprotide, and the AII-receptor antagonist, saralasin, lowered the diastolic blood pressure and attenuated sympathetic nerve-mediated pressor responses. There was no difference in the effects of teprotide at 1 mg kg-1 and 10 mg kg-1. Infusion of sodium nitroprusside at concentrations producing a fall in diastolic blood pressure of similar magnitude to that produced by teprotide and saralasin significantly attenuated nerve-mediated pressor responses. 5. After teprotide, AII 50 mg kg-1 min-1 increased diastolic blood pressure. The inhibitory effect of teprotide on nerve-mediated pressor responses was antagonized by this infusion of AII only if the rats were pretreated with the cyclo-oxygenase inhibitor, flurbiprofen. 6. It is concluded that AII is a major determinant of vascular tone in the pithed rat and that inhibition of the renin-angiotensin system attenuates sympathetic nerve-mediated pressor responses at least in part through the fall in blood pressure per se. The demonstration of this is complicated by an excessive release of vasodilator prostaglandins possibly due to the infused AII. Since plasma All levels are high, the effects of blockade of the renin-angiotensin system will be exaggerated and so the importance of All as a modulator of sympathetic responses will be overestimated in this model.

The effects of arterial blood gas tensions on pressor responses to angiotensin II in the pithed rat

The influence of arterial blood gas tensions on angiotensin II-mediated pressor responses in the pithed rat was studied by altering the inspired gas mixture at a fixed tidal volume. When rats were ventilated to produce physiological Pa, CO2 levels (35-40 mmHg) responses to boluses of angiotensin II were greater with increasing Pa, O2 over the Pa, O2 range of 65-460 mmHg. There was no difference in response to angiotensin II over the Pa, CO2 range studied (18-50 mmHg). All variations in response to angiotensin II were attributable to changes in Pa, O2. Since arterial blood gas tensions, especially the Pa, O2, modulate pressor responses to boluses of angiotensin II, the physiological effects of this hormone may be most fruitfully explored in rats ventilated to produce normal arterial blood gas tensions.

Analysis of the alpha-adrenoceptor-mediated, and other, components in the sympathetic vasopressor responses of the pithed rat

The vascular receptors activated following sympatho-adrenal stimulation were determined by analysing the effects of 'selective' antagonists on the vasopressor response to spinal sympathetic nerve activation in the pithed rat. The net vascular response to adrenal stimulation was a balance between alpha-adrenoceptor-mediated vasoconstriction and beta-adrenoceptor-mediated vasodepression. Part of the alpha-adrenoceptor-mediated response was 'prazosin-sensitive' (alpha 1) and the remainder was abolished by rauwolscine (alpha 2). As with adrenal stimulation, direct sympathetic nerve stimulation of the vasculature evoked pressor responses which were partly resistant to prazosin. Rauwolscine only partly blocked the prazosin-sensitive component. Reserpine pretreatment led to smaller responses than prazosin plus rauwolscine. Thus, the response resistant to alpha-adrenoceptor antagonists could be mediated, in part, by adrenoceptors distinct from alpha-adrenoceptors, as currently defined. alpha, beta-Methylene ATP reduced the nerve-mediated pressor response after alpha-adrenoceptor blockade or reserpine pretreatment but not in drug-free controls. The results suggest that stimulation of the adrenal medulla can produce a vasopressor response which consists of summating alpha 1- and alpha 2-adrenoceptor-mediated components, and is identical to the effect of injected adrenaline. In contrast, the response to vasopressor nerve stimulation appears to be essentially mediated by alpha 1-adrenoceptors, with a facilitatory influence from alpha 2-adrenoceptors. A further response obtained after alpha-adrenoceptor blockade may contain a purinergic component and another which is adrenergic but not mediated by stimulation of alpha-adrenoceptors.

The influence of blood gases on alpha 1- and alpha 2- adrenoceptor-mediated pressor responses in the pithed rat

The influence of blood gases on alpha 1- and alpha 2-adrenoceptor-mediated pressor responses was studied in the pithed rat by varying the inspired gas mixture or the ventilation stroke volume. Acidosis favoured the peak responses to the alpha 2-adrenoceptor agonist, xylazine, while alkalosis favoured the peak responses to the alpha 1-adrenoceptor agonist, phenylephrine. A combination of hypoxia and hypercapnia greatly depressed the alpha 1 response to phenylephrine whereas the alpha 2 response to xylazine remained relatively unaffected. When Pao2 was varied in either acidotic or alkalotic conditions the response to the phenylephrine increased as Pao2 increased. To prevent hypoxia in air ventilated rats, large stroke volumes were required. This caused alkalosis and hence decreased responsiveness to xylazine. Consequently, air ventilated pithed rats gave poorer responses to xylazine than did those ventilated on 100% O2. The results show that alpha 1- and alpha 2-adrenoceptor-mediated pressor responses can be differentially affected by blood gases. The relative contribution of alpha 1- and alpha 2-adrenoceptors to vascular tone may be either under- or over-estimated depending on the arterial blood gases.

Attempts to uncover subtypes of alpha-adrenoceptors and associated mechanisms by using sequential administration of blocking drugs

By the sequential administration of alpha 1- and alpha 2-blockers it can be shown, in the pithed rabbit, that the dose/pressor response curve to noradrenaline consists of two separate curves, one for each receptor. alpha 2-mediated responses predominate at low doses and alpha 1-mediated responses predominate at high doses. Pressor responses to sympathetic nerve stimulation have, similarly, an alpha 2 component at low frequencies and a dominant alpha 1-mediated response at high frequencies: a residual response is resistant to combined alpha 1- plus alpha 2-blockade. This alpha-blocker-resistant pressor nerve response was further analysed in the pithed rat and was found to be partly susceptible to alpha,beta-methylene ATP, which desensitizes purinergic responses. However, reserpine pretreatment produced a greater reduction of nerve-mediated pressor responses than did alpha-blockade, suggesting that part of the 'alpha-blocker resistant' response might be adrenergic. It is concluded that sympathetic vasopressor nerve transmission is mediated for the greater part by alpha 1- and alpha 2-adrenoceptors but that there is evidence for contributions from non-alpha-adrenergic and 'purinergic' elements. An even greater proportion of the responses to circulating catecholamines is attributable to the alpha-receptors with a relatively small but significant 'resistant' component.

Influence of blood gases, Ca2+-entry blockade and angiotensin converting enzyme inhibition on pressor responses to alpha-adrenoceptor agonists: evidence in vivo for subtypes of response independent of receptor subtype?

The pressor responses in the pithed rat to alpha-adrenoceptor agonists can be modified by alterations in arterial blood gas levels or by drugs which interfere with excitation-contraction coupling processes in the vascular smooth muscle, e.g. Ca2+-entry blockers or angiotensin converting enzyme (ACE) inhibitors. However, the extent of these influences depends on which agonist is used. The pressor response to intravenous injection of alpha-adrenoceptor agonists consists of two phases: an initial rapid but transient response (phase I) is followed by a response of slower onset but longer duration (phase II). We have examined the effects of manipulation of arterial blood gases, a Ca2+-entry blocker, nifedipine, and an ACE inhibitor, teprotide, on the pressor responses to a series of alpha-adrenoceptor agonists. In each case, the effects showed selectivity for one or other of the two phases and the differences in susceptibility between agonists could be explained by the relative sizes of the two phases in their responses. In general, phase II was more susceptible to alkalosis, nifedipine and teprotide, so that drugs in which this component predominated were more susceptible to these factors. In contrast there was no direct correlation with the receptor subtypes activated by the agonists.