Prostaglandin A2 (PGA2) increases the coronary vascular resistance in the guinea-pig isolated heart preparation

Summary Prostaglandin A₂ (PGA₂) in concentrations of 1.5·10^–8 to 3·10^–6 M was found to produce concentration-dependent increase in the coronary vascular resistance of the guinea-pig isolated heart without alterations in myocardial contractile force and oxygen consumption.Supported by the Deutsche Forschungsgemeinschaft.     

Effect of enkephalins in the presence of the antibiotic bacitracin in the longitudinal muscle strip preparation from guinea-pig ileum

Summary The antibiotic bacitracin (5×10^–5–4×10^–4 M) increases the inhibition of the contractile response caused by both enkephalin release and direct application of Met-enkephalin 5×10^–7 M in the longitudinal muscle strip preparation from guinea-pig ileum. This effect is attributed to an inhibition of enkephalin degrading peptidases by bacitracin.     

Über die Wirkung von Prostaglandin E1 auf den Ca-Haushalt isolierter Meerschweinchenherzen

Summary The stimulatory effect of PGE₁ on different functions of isolated guinea-pig hearts (Langendorff method, Tyrode solution) was coupled with an increase in the rate of⁴⁵Ca uptake from the perfusion medium. The total myocardial Ca content and the amount of exchangeable cellular Ca were not affected. This action of PGE₁ on the myocardial Ca metabolism seems to be related to the positive inotropic action of PGE₁ and can most probably be explained by an increase in the membrane permeability to Ca ions (similar to the action of epinephrine).     

Opposite effect of PGE2 on cAMP levels in human adrenal medulla and pheochromocytoma

Summary PGE₂ (10^–7 M) caused increased cAMP accumulation in 5 pheochromocytomas, while in 3 human adrenal medullae PGE₂ caused a significant decrease of cAMP level on incubating slices in vitro. This finding is discussed in relation to the opposite effect of PGE₂ on catecholamine release from human medulla and pheochromocytoma slices in vitro.Acknowledgment. This paper is part of a Ph. D. thesis of Punya Boonyaviroj.Established Investigator of the Chief Scientist's Bureau, Israeli Ministry of Health.     

Effects of bunaphtine on45Ca movements in rat aortic smooth muscle

Summary The effect of bunaphtine (BNA, 5×10^–5 M) on La³⁺-resistant⁴⁵Ca content and⁴⁵Ca efflux was studied on rat aortic smooth muscle. BNA decreased both control and norepinephrine-stimulated, La³⁺-resistant⁴⁵Ca content and increased the⁴⁵Ca efflux. These effects could explain the inhibition of the contractile responses induced by BNA.     

Electrophysiological actions of chlorimipramine on guinea-pig ventricular fibres

Summary Chlorimipramine (CMI, 1×10^–5M to 7×10^–5M) decreased the amplitude, overshoot and rate of rise of ventricular action potentials and abolished the Ca-mediated action potentials elicited in guinea-pig papillary muscles. These results indicates that CMI inhibits the rise in sodium and calcium conductances during the cardiac action potential.     

Über die Beeinflussung der Ca-Aufnahme in Lipidextrakte aus Mikrosomen und Mitochondrien des Herzens durch Digitoxin

Summary Lipids were isolated by chloroform-methanol extraction from mitochondrial and microsomal fractions of guinea-pig hearts. In the presence of digitoxin (10^–9-10^–6 g/ml) 15–30% more radioactive Ca was taken up by the lipid extracts than under control conditions, but the total amount of Ca in this phase remained unchanged. Thus, digitoxin produced an increase in the specific activity of the lipid-bound Ca which may be explained by an increased exchangeability of this Ca fraction. This effect of digitoxin might result in an improved availability of the lipid-bound Ca for Ca-dependent functions (e.g. contraction) of the heart muscle cell.     

Prostaglandin production by human polymorphonuclear leucocytes during phagocytosis in vitro

Summary Human polymorphonuclear leukocytes were found to be able to synthetize and release substantial amounts of PGE₂, when stimulated by a phagocytic stimulus such as zymosan particles coated with complement. Hydrocortisone, at a concentration of 10^–5 M, which proved to be effective in other biological systems, failed to inhibit phagocytosis and PG release.     

Differential sensitivity of the two phases of ear artery contraction to intimal and adventitial norepinephrine

Summary The biphasic contraction of the rabbit ear artery to norepinephrine (NE) was investigated in the normal (adventitial stimulation) and the everted (intimal stimulation) segment of ear artery. The 2nd phase response showed an intimal ED₅₀ of 8.2×10^–8 M which was significantly (p<0.05) lower than the adventitial ED₅₀ of 42.6×10^–8 M. This difference was abolished by inhibition of neuronal and extraneuronal uptake for NE. The 1st phase response also showed an ED₅₀ for the intimal stimulation (6.9×10^–8 M) which was significantly (p<0.05) lower than adventitial (65.5×10^–8 M). This difference was reduced but not abolished by NE uptake inhibition. This suggsets that some feature of the adrenergic neuroeffector apparatus is asymmetrically arranged to favor fast responses to blood borne NE.Supported by American Heart Association-Greater Los Angeles Affiliate Grant No. 602. We wish to thank Dr John Bevan and Dr Alasdair MacLean for helpful advice.     

Differences in luteinizing hormone release stimulated in rat anterior pituitary cells by leukotriene C4 and by gonadotropin-releasing hormone in vitro

Summary Continuous administration of leukotriene C₄ (LTC₄, 10^–10 M) to superfused rat anterior pituitary cells increased LH release for 40 min only, whereas in a parallel experiment gonadotropin-releasing hormone (GnRH, 10^–9 M) evoked a continuous increase in hormone secretion. In contrast to GnRH, LTC₄ did not desensitize rat anterior pituitary cells. The secretory action resulting from the administration of LTC₄ (10^–10 M) was abolished for 40 min after previous stimulation. The results documented the dual action of LTC₄ on LH exocytosis.     

Fatty acid modulation of antiestrogen action and antiestrogen-binding protein in cultured lymphoid cells

Summary Nonsteroidal antiestrogens reversibly and specifically inhibited the proliferation of two estrogen receptornegative lymphoid cell lines (EL4 and Raji) in a dose-dependent manner. [³H]Thymidine incorporation of concanavalin A-stimulated primary splenocytes was also inhibited by 10^–6 M clomiphene (1-[4-(2-diethylaminoethoxy)phenyl]-1,2-diphenyl-2-chloroethylene). The antiproliferative effect could be prevented by the simultaneous presence in the growth medium of 10^–5 M linoleic acid or 10^–5 M arachidonic acid but not by 10^–6 M estradiol. Both lymphoid cell lines had high affinity antiestrogen-binding sites whose affinity could be altered by conditions of growth. Growth of EL4 cells in RPMI 1640 medium supplemented with charcoal-pretreated 5% fetal calf serum (charcoal-stripped medium) resulted in significantly higher affinity (K_d 0.54 nM±0.11 nM; n=6) than growth in medium supplemented with untreated serum (complete medium) (K_d=1.68 nM±0.48 nM; n=6) (p<0.001). This change in affinity was partly due to removal of fatty acids from the growth medium by charcoal pretreatment, since addition of 10^–5 M linoleic acid or 10^–5 M gamma-linolenic to charcoal-stripped medium decreased the affinity of the antiestrogen-binding protein. In contrast, growth in 10^–5 M stearic acid or 10^–5 M oleic acid did not significantly alter the affinity of the antiestrogen-binding protein, whereas 10^–5 M palmitic acid significantly increased its affinity. The same fatty acids were also tested for their intrinsic effects on EL4 cell proliferation. Oleic, linoleic and gamma-linolenic acids were growth stimulatory while stearic and palmitic acids were not. Thus linoleic and gamma-linolenic acids whose presence in the growth medium was associated with decreased affinity of [³H]tamoxifen (1-[4-(2-dimethylaminoethoxy)phenyl]-1,2-diphenylbut-1(Z)-ene) binding to the intracellular antiestrogen-binding protein were also growth stimulatory. Unsaturated fatty acids have previously been shown to inhibit binding of [³H]tamoxifen to the antiestrogen-binding protein in a cell-free system. The present observations demonstrate that unsaturated fatty acids also modify the affinity of the antiestrogen-binding protein in intact cells.     

Ouabain-induced release of extraneuronal catecholamine in the isolated guinea-pig vas deferens

Summary It was found that ouabain (10^–5 M) was effective in releasing the extraneuronal catecholamine which was taken up by uptake₂ process in the guinea-pig vas deferens. This result shows that a Na–K ATPase is essential for the storage of catecholamine in the extraneuronal site.     

Role of adenosine A1 and A2 receptors in the regulation of aldosterone production in rat adrenal glands

Summary To investigate the roles of adenosine A₁ and A₂ receptors in the regulation of aldosterone production, we examined the effects of adenosine and adenosine agonists (N⁶-cyclohexyl adenosine; selective adenosine A₁ receptor agonist and 5-N-ethylcarboxamine adenosine; selective adenosine A₂ receptor agonist) on aldosterone and cyclic AMP production in rat adrenal capsular cells. Neither adenosine nor 5-N-ethylcarboxamine adenosine caused significant effects on basal aldosterone or cyclic AMP production. Also, adenosine (10^–3M) showed no consistent effects on aldosterone and cyclic AMP production induced by ACTH. On the other hand, N⁶-cyclohexyl adenosine exhibited a significant inhibition of basal aldosterone and cyclic AMP production at doses of 10^–4 M and 10^–3 M; furthermore, 10^–3 M N⁶-cyclohexyl adenosine inhibited aldosterone and cyclic AMP production stimulated by ACTH. These results suggest that adenosine A₁ receptors are coupled to and inhibit adenylate cyclase and may be involved in the inhibition of aldosterone production.     

VIP and histamine H2 receptor activity in human fetal gastric glands

Summary Vasoactive intestinal peptide (VIP, EC₅₀=6.4×10^–10 M) and histamine (EC₅₀=3×10^–6 M) activated the cyclic AMP generating system in gastric glands isolated from two human fetuses at 23 weeks gestation. Histamine antagonism by the H₂ receptor blockers cimetidine (Ki=0.35×10^–6 M) and ranitidine (ki=0.51×10^–7 M) clearly characterized the histaminic activation as being of the H₂ type. It is suggested that these two vasoactive hormones may operate as neurocrine/paracrine regulators of the differentiation and/or function of the human gastric mucosa in utero.     

Evidence of a direct action of triiodothyronine (T3) on the cell membrane of GH3 cells: an electrophysiological approach

Summary Electrophysiological experiments demonstrate that triiodothyronine (T₃) exerts a direct effect on the membrane of a strain of cultured rat pituitary tumor cells, GH₃/B₆. These cells respond to pressure application of T₃ (2–5 nl, concentration 1·10^–10 M) with an increase in the membrane resistance (R_m) and a hyperpolarization. Spontaneously firing cells become silent.     

An analysis of the effects of urethane on cardiovascular responsiveness to catecholamines in terms of its interference with Ca++ mobilization from both intra and extracellular pools

Summary Urethane (1×10^–2–1×10^–1 M) reduced, in a concentration-dependent manner, both intra and extracellular Ca⁺⁺ dependent noradrenaline-induced contractions of perfused rabbit ear artery as well as the tonic contractions produced by perfusion with high K⁺ solution. However, a quantitative analysis of the data indicated that for urethane concentrations similar to those found in plasma during anesthesia urethane antagonism is confined to noradrenaline-induced contractions which depend upon the mobilization of Ca⁺⁺ from intracellular storage sites. In KCl-contracted arteries, urethane enhanced the relaxant effects of isoprenaline.—Urethane reduced the amplitude of contractions of spontaneously beating guinea-pig right atrium at concentrations which have only a limited effect on frequency. In addition, it decreased in a concentration-dependent manner the amplitude of isoprenaline-activated electrically driven, and K⁺ depolarized guinea-pig right ventricular strips. Urethane had no effect on the chrono and inotropic actions of isoprenaline on cardiac preparations. In in vivo experiments the chronotropic response to low doses of isoprenaline was significantly higher in urethane-treated as compared to unanesthetized rats. The higher dose of isoprenaline tested produced a significant fall in systolic blood pressure in urethane-anesthetized rats. A significant correlation exists between the chronotropic response to isoprenaline and resting heart rate values in urethane-anesthetized rats. These results indicate that urethane, at concentrations similar to those found in plasma during anesthesia selectively interferes with mobilization of Ca⁺⁺ from intracellular storage sites. In addition, the interference of urethane anesthesia with the isoprenaline chronotropic effect in vivo cannot be explained by a direct interference of urethane with -adrenoceptors at cardiac level.     

Phosphoramidon enhances allatostatin-mediated inhibition of juvenile hormone biosynthesis in the corpora allta of the cockroach,Diploptera punctata

Use of the enkephalinase inhibitor phosphoramidon in the in vitro radiochemical assay for juvenile hormone biosynthesis enhanced allatostatin-mediated inhibition of hormone production by corpora allata of the cockroach,Diploptera punctata. Significant increases in inhibition in day 2 virgin female CA by AST 1 (at 10^–7 M) and AST 4 (10^–8–10^–7 M) were observed in the presence of phosphoramidon (10^–5M or greater). No significant increases in inhibition were seen in CA from day 6 mated females with AST 4 (10^–9–10^–7M) and phosphoramidon combined. Phosphoramidon alone had no effect on JH biosynthesis. Analysis of allatostatin content of the CA, as determined by ELISA, revealed that addition of phosphoramidon to the medium increased the endogenous allatostatin conten in CA of virgin and mated females. The similarity in primary structure between allatostatins and enkephalin-like peptides and their similar distribution makes it probable that phosphoramidon acts by preventing breakdown of allatostatins within the CA.     

Induction of the in vitro p-hydroxylation of14C-amphetamine stereoisomers in phenobarbital-treated rats

Summary The rate of p-hydroxylation of¹⁴C-(-)-amphetamine by liver microsomes was higher than that of (+)-isomer in phenobarbital-treated male rats. The apparent K_m values for (-)- and (+)-amphetamine hydroxylation were 4.54×10^–5 M and 2.27×10^–5 M respectively, in both treated and control animals.     

Monoclonal antibodies to L-asparaginase

Summary Five hybridomas secreting monoclonal antibody toE. coli L-asparaginase were isolated. These monoclonal antibodies were classified into 3 different subclasses; Ig G₁ (1 clone), Ig G₂ (2 clones) and Ig G₃ (2 clones). One of them possessed anti-L-asparaginase neutralizing activity. Four antibodies examined demonstrated a linear Langmuir binding plot and binding affinities, with equilibrium dissociation constant (K_d) ranging between 2.5×10^–9M and 6.3×10^–10 M. The monoclonal antibodies should be useful probes for investigation of the enzyme activity.     

Growth ofNostoc muscorum mutants in the presence of diuron (DCMU) and L-methionine-DL-sulfoximine

Summary Diuron (DCMU) is inhibitory to the photoautotrophic and photoheterotrophic growth of the N₂-fixing blue-green algaNostoc muscorum at concentrations of 1.0×10^–5 M and 2.0×10^–5 M, respectively. A mutant of this organism resistant to 5.0×10^–5 M DCMU under its photoheterotrophic growth conditions, with the ability to utilize DCMU as a carbon and nitrogen source for growth, and complete inability to grow photoautotrophically has been isolated. With the apparent defect in its photosynthetic ability, it is suggested that theDCMU ^r mutant lacks the step inhibited by 1.0×10^–5 M DCMU, and metabolizes DCMU by an existing enzyme system in the absence of such inhibition. That this enzyme may be glutamine synthetase (GS) is explained with the help of a L-methionine-DL-sulfoximine (MSO)-resistant mutant ofN. muscorum which is able to grow faster with 2.0×10^–5 DCMU and is known to contain an altered GS.Thanks are due to the Council of Scientific and Industrial Research, CSIR Complex, Govt. of India, New Delhi-110012, for appointing the author to the Scientists' Pool for undertaking researches on the physiological and genetic controls of nitrogen metabolism in blue-green algae, a part of which is presented in this literature.