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M Schachter

Publications and source records attributed to M Schachter.

At least 19 recordsLinked to original sources
PubMed1992

Tyrosine kinase inhibitors block calcium channel currents in vascular smooth muscle cells.

Selective inhibitors of tyrosine kinases, tyrphostin 23 and genistein, produced concentration-dependent inhibition of voltage-operated calcium channel currents in vascular smooth muscle cells isolated from rabbit ear artery. The potency of these two structurally dissimilar inhibitors was similar to that reported for their action as inhibitors of tyrosine kinases. Daidzein, an inactive analogue of genistein, had little inhibitory effect on calcium channel currents at concentrations below 300 microM consistent with an action of these agents at a tyrosine kinase. However, tyrphostin 1, a reportedly less active tyrphostin derivative, also inhibited calcium channel currents with a potency similar to tyrphostin 23. These findings suggest that voltage-operated calcium channels in vascular smooth muscle may be modulated by endogenous tyrosine kinase(s) which display different sensitivities to inhibitors compared with the epidermal growth factor (EGF) receptor. Alternatively the possibility of direct blocking actions of these inhibitors at voltage-operated calcium channels cannot be excluded.

Animals↗
PubMed1992

Direct vascular actions of hydrochlorothiazide and indapamide in isolated small vessels.

The mechanism by which thiazides lower peripheral resistance is unresolved. The aim of this study was to investigate the mechanisms of the acute vasodilator action of hydrochlorothiazide and the 'thiazide-like' diuretic indapamide on human, guinea pig and rat small arteries. Vessels were mounted on a myograph and the relaxation profile of both drugs and interactions with K+ channels and the vascular eicosanoid system were studied. Neither drug had any relaxant effect in rat mesenteric vessels and indapamide did not relax human arteries. Hydrochlorothiazide in both human and guinea pig vessels produced significantly more relaxation of noradrenaline than K(+)-constricted vessels (P less than 0.001). Relaxation to hydrochlorothiazide was reduced in the presence of charybdotoxin. Maximal-induced hydrochlorothiazide relaxation was reduced by 64% in human arteries (P less than 0.001) and by 91% in guinea pig vessels (P less than 0.001). Incubation with glibenclamide and indomethacin had no effect on the relaxant activity of hydrochlorothiazide and indapamide. Indapamide-induced relaxation was unaffected in the presence of charybdotoxin. These results show marked differences in the acute vasodilator action of hydrochlorothiazide and indapamide. There appears to be involvement of Ca(2+)-activated K+ channels in the acute vasorelaxant activity of hydrochlorothiazide.

Animals↗
PubMed1992

Celiprolol.

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Antihypertensive Agents↗
PubMed1992

Electrophysiological evidence for a role of nitric oxide in prolonged chemical nociception in the rat.

The role of nitric oxide in the periphery and the spinal cord, during acute electrically-evoked and prolonged chemically-evoked nociceptive stimulation, was investigated in rats anaesthetised with halothane. The responses of single dorsal horn neurones to electrically-evoked A beta fibre and C fibre inputs were reduced by topical application (directly onto the spinal cord) of both the nitric oxide inhibitor, nitro-L-arginine methyl ester (L-NAME; 500-1500 micrograms) and the precursor of nitric oxide, L-arginine (4500 micrograms). Administration of L-NAME, either directly into the receptive field (500-1500 micrograms) or intravenously (10-100 mg/kg) had little or no effect on the acute electrically-evoked activity. Intravenous injection of L-NAME, administered 40 min prior to injection of formalin, significantly reduced the prolonged second peak of firing, with only a small effect on the short-duration first peak. Administration of L-NAME, directly into the site of injection of formalin, as a 10 min pretreatment, significantly reduced the second but not the first peak of the response. Topical application of L-NAME onto the spinal cord, as a 30 min pretreatment, significantly reduced both the first and second peaks of the response. This inhibition was not reversed by the coadministration of L-arginine, which was inhibitory by itself. Thus, nitric oxide may be involved, in a complex way, in nociceptive events both in the periphery and within the spinal cord.

Animals↗
PubMed1992

Human pancreatic cancer cell lines do not express receptors for somatostatin.

The in vivo administration of somatostatin (SS) or its analogues is capable of suppressing the growth of pancreatic cancer in experimental animals. We examined the effects of SS-14 and its analogue RC-160 on the in vitro growth of two human pancreatic cancer cell lines MiaPaCa-2 and Panc-1 stimulated with epidermal growth factor (EGF) or insulin-like growth factor 1 (IGF-1). Neither SS-14 nor RC-160 inhibited the growth of either cell line. In contrast RC-160 did inhibit the EGF-stimulated growth of a rat pancreatic cancer cell line AR42J. Binding studies with 125I-Tyr11 somatostatin revealed the presence of a single class of high affinity binding sites with a Kd of 0.20 +/- 0.05 nM and a Bmax of 2.1 +/- 0.26 pmoles mg-1 protein on AR42J but not displaceable binding was observed on MiaPaCa-2 or Panc-1. We conclude that lack of receptors accounts for the failure of SS-14 and RC-160 to influence the growth of human pancreatic cancer in vitro. These results, taken together with other findings, lead us to question the therapeutic efficacy of somatostatin and its analogues as mono-therapy in the treatment of human pancreatic cancer.

Animals↗
PubMed1992

Mechanisms of action of cicletanine in human and guinea pig resistance arteries.

Human subcutaneous (s.c.) arteries and guinea pig mesenteric vessels (internal diameter 150-570 microns) were isolated and mounted on a microvascular myograph. Cicletanine-induced relaxation curves were constructed after preconstriction with either depolarising potassium (KPSS) or norepinephrine (NE) and in the presence and absence of indomethacin, glibenclamide, or tetraethylammonium chloride (TEA). Using only guinea pig vessels, cicletanine relaxation curves were constructed with and without charybdotoxin. In human vessels, there was no significant difference between cicletanine-induced relaxation in vessels preconstricted with either NE or KPSS, and neither ATP-sensitive or Ca(2+)-activated K channels were involved. However, with indomethacin added, in human vessels the maximal response to cicletanine (30 microM) was reduced by 51% (p less than 0.05). In guinea pig mesenteric arteries, cicletanine (30 microM) produced a 95% relaxation of the NE-constricted vessel and only 30% relaxation of the KPSS-constricted vessel (p less than 0.001). There was no evidence for any involvement of the ATP-sensitive K channel or the eicosanoid system. The relaxation to cicletanine (less than 3 microM) in with TEA added was greatly reduced (p less than 0.001) and with charybdotoxin added the concentration response curve to cicletanine was shifted approximately 3 log units to the right (p less than 0.001), suggesting an involvement of Ca(2+)-activated K channels. The acute vasodilator action of cicletanine is complex, with multiple mechanisms of action, and the relative importance of these varies in different species or at least in different vascular beds.

Animals↗
PubMed1992

Interaction between cicletanine and the eicosanoid system in human subcutaneous resistance arteries.

In human subcutaneous resistance arteries in-vitro, the relaxation produced by the novel furopyridine compound cicletanine (30 microMs) was inhibited by 51% (P less than 0.0001) in the presence of 20 microMs of the cyclo-oxygenase inhibitor indomethacin. Maximal cicletanine-induced relaxation was reduced by both the cyclo-oxygenase inhibitor mefenamic acid and the relatively specific blocker of prostacyclin synthetase, tranylcypromine by 55% (P less than 0.0005) and 43% (P less than 0.01), respectively. The potassium channel blocker, glibenclamide (100 microMs), did not affect the relaxation produced by cicletanine but did inhibit the relaxation produced by the potassium channel blocker cromakalim (P less than 0.0001). Cromakalim-induced relaxation was inhibited in the presence of indomethacin; relaxation induced by cromakalim (30 microMs) was reduced by 22% (P less than 0.02). The relaxation produced by the hypotensive agonists sodium nitroprusside, hydrochlorothiazide, bumetanide and nicardipine was unaffected by incubation with indomethacin. The results suggest that the vascular eicosanoid system, specifically prostacyclin, may be involved in the mechanism of the acute vasodilator action of cicletanine. Although at high doses, cicletanine is a diuretic, in this model it did not act like either a thiazide or a loop diuretic. The acute vasodilator action of the thiazide diuretic, hydrochlorothiazide was a novel finding of this study. Cromakalim showed a reduced response in the presence of indomethacin suggesting an involvement of the eicosanoid system in its mechanism of action.

Antihypertensive Agents↗
PubMed1992

Evidence that nitric oxide or a related substance is a neurovasodilator in the submandibular gland of the cat.

Close-arterial injection of L-NG-nitro arginine methyl ester, a compound that inhibits the synthesis of nitric oxide (NO), caused a dose-dependent reduction in both the parasympathetic and sympathetic (rebound) nerve-induced vasodilatation within the submandibular gland of the cat. At the same time, salivary secretion produced by each nerve was relatively unaffected, and the sympathetic vasoconstriction was enhanced. These results suggest that NO or a related compound may be either a neurotransmitter or neuromodulator contributing to the autonomic nerve-induced vasodilatation in the submandibular gland of the cat.

Animals↗
PubMed1991

Drug-induced modification of vascular structure: effects of antihypertensive drugs.

It has long been realized that hypertension causes alterations in the peripheral vasculature, with the arterial wall becoming thicker and the lumen relatively smaller. This is particularly true in small resistance arteries, but larger vessels are also affected. The precise mechanisms remain to be determined, although it is highly likely that growth-promoting autacoids are involved as well as mechanical forces. Numerous studies of hypertension in animal models and a few in hypertensive humans have tried to establish the reversibility of these changes after successful lowering of blood pressure. Too few data are available to form firm conclusions, but thiazides and hydralazine-like vasodilators appear to have only a minimal effect on the vasculature. On the other hand, angiotensin-converting enzyme inhibitors are clearly effective, and alpha-blockers may be active. However, it is difficult to derive even tentative conclusions from the available information on calcium antagonists and beta-blockers. These results are discussed in the context of future therapeutic and investigative approaches.

Animals↗
PubMed1991

Isradipine.

Isradipine is a potent dihydropyridine calcium channel blocker. It is highly selective for vascular smooth muscle, with very few negative inotropic or chronotropic effects. It may have minor depressant effects on the sinoatrial node, hence reducing the incidence of reflex tachycardia. The drug is extensively metabolized in the liver, with several pharmacologically inactive metabolites. As the elimination half-life is about 9 h the drug is usually given twice daily, but a once-daily modified release form is under investigation. Isradipine is effective monotherapy in essential hypertension, and has been successfully combined with pindolol and captopril. On the basis of more limited evidence it also appears to be beneficial in stable angina and in congestive cardiac failure. A trial is also under way to assess its antiatherogenic properties. Adverse effects are those predicted for a vasodilator calcium antagonist, and may be less frequent than for equivalent doses of nifedipine. This needs to be confirmed by more extensive clinical experience. Overall, isradipine can be considered favourably in essential hypertensives where a calcium channel blocker is indicated, particularly if it is desirable to avoid myocardial depression or to minimize reflex tachycardia. Its role in other cardiovascular disease awaits further evaluation.

Angina Pectoris↗
PubMed1990

Measurement of intracellular magnesium in a vascular smooth muscle cell line using a fluorescent probe.

Until recently, direct measurement of intracellular free magnesium has been complex and difficult. However, fluorescent probes are now available, based on the same principle as well-established probes for free calcium. Using one such probe, mag-fura-2, we have estimated basal intracellular magnesium concentrations in the A7r5 rat vascular smooth muscle cell line. This level was unaffected by numerous pharmacological manipulations, including agonist stimulation and depolarisation. The possible implications of these findings are discussed.

Animals↗
PubMed1990

Procedure-specific costs and savings in a mandatory program for second opinion on surgery.

Initial examination of the surgery experience of participants in a large employer-sponsored second opinion program revealed minimal savings in medical resource costs. But closer examination of relative savings for specific procedure categories showed that the greatest savings are for high-cost procedures: hysterectomy, prostatectomy, back surgery, and hip replacement. Furthermore, a nonconfirming second opinion does not dissuade patients from some procedures. Decisions about which procedures to include in a mandatory program should consider volume, costs, and effects of nonconfirmation, as well as the advantages of a mandatory second opinion for skeptical patients, or for patients for whom a controversial procedure has been recommended.

Blue Cross Blue Shield Insurance Plans↗
PubMed1989

Electrophysiological evidence for a role of bradykinin in chemical nociception in the rat.

Single nociceptive neurones were recorded in the L1-L3 region of the dorsal horn of the spinal cord in halothane anaesthetized intact rats. Subcutaneous formalin (50 microliters of 5% solution) into the peripheral receptive field produces a biphasic activation of these neurones. The initial 1st peak of the response was unaltered by any of the treatments. However, the prolonged 2nd peak of the response was significantly reduced to a similar degree by 10 min pretreatment with 50 micrograms subcutaneous B4162 (a bradykinin B2 receptor antagonist) and by prior desensitization of the receptive field with bradykinin. The putative bradykinin B1 receptor antagonist des-Arg9[Leu8]bradykinin (DALB) applied subcutaneously (50 micrograms) 10 min prior to formalin had no effect on the subsequent responses to formalin implying that the B4162 and bradykinin desensitization effects occur via the B2 receptor. Repeated subcutaneous injection of bradykinin (10 microliters of a 1 mg/ml solution) was used to elicit responses in these dorsal horn neurones and these were shown to be antagonised by 50 micrograms B4162 suggesting that the effects of this compound on the formalin response are indeed due to its ability to inhibit bradykinin induced neuronal activity. These results provide electrophysiological evidence for a physiological role of bradykinin as a mediator in prolonged chemical nociception.

Action Potentials↗