Direct immuno-electron microscopy and some morphological features of hog cholera virus

Summary Characteristic particles of hog cholera virus were identified by direct immuno-electron microscopy. The virion is 40–50m, often asymmetrically shaped, and is enveloped in a membrane that bears 12–15 m surface projections. The surface projections are shear-sensitive and are antigenically different from the virion's envelope. They may represent hog cholera virus soluble antigen.     

On the regulation of the expressed L-type calcium channel by cAMP-dependent phosphorylation

The Ca²⁺ channel subunits _1C-a and _1C-b were stably expressed in Chinese hamster ovary (CHO) and human embryonic kidney (HEK) 293 cells. The peak Ba²⁺ current (I _Ba) of these cells was not affected significantly by internal dialysis with 0.1 mM cAMP-dependent protein kinase inhibitor peptide (mPKI), 25 M cAMP-dependent protein kinase catalytic subunit (PKA), or a combination of 25 M PKA and 1 M okadaic acid. The activity of the _1C-b channel subunit expressed stably in HEK 293 cells was depressed by 1 M H 89 and was not increased by superfusion with 5 M forskolin plus 20 M isobutylmethylxanthine (IBMX). The _1C-a·₂·₂/ complex was transiently expressed in HEK 293 cells; it was inhibited by internal dialysis of the cells with 1 M H 89, but was not affected by internal dialysis with mPKI, PKA or microcystin. Internal dialysis of cells expressing the _1C-a·₂·₂/ channel with 10 M PKA did not induce facilitation after a 150-ms prepulse to +50 mV. The Ca²⁺ current (I _Ca) of cardiac myocytes increased threefold during internal dialysis with 5 M PKA or 25 M microcystin and during external superfusion with 0.1 M isoproterenol or 5 M forskolin plus 50 M IBMX. These results indicate that the L-type Ca²⁺ channel expressed is not modulated by cAMP-dependent phosphorylation to the same extent as in native cardiac myocytes.     

Structure and mechanics of growing arterial microvessels from hypertrophied urinary bladder in the rat

Rat bladder hypertrophy, induced by a partial ligation of the urethra, was used to study the accompanying changes of microvascular smooth muscle mechanics, pharmacology and morphology. A segment of a microarterial vessel to the bladder was taken from a defined anatomical location and studied in a wire myograph in vitro at the length for maximal isometric force development (L _max). After 10 days of ligation, bladder hypertrophy resulted in a microvascular growth response compared to non-operated controls which was characterized by (i) an increase of the calculated diameter at L _max from 134±5 m to 222±19 m; (ii) an increase of the media thickness from 22.4±1.9 m to 32.2±3.0 m; (iii) an increase of the active tension from 1.42±0.28 mN/mm to 3.06±0.33 mN/mm; (iv) no change of the wall/lumen ratio (from 0.83±0.10 to 0.79±0.15). Normalized length/force relations (active, passive and total) did not differ significantly between microarteries from control and hypertrophic bladders. Microvascular smooth muscle growth was also associated with a decreased sensitivity to K⁺-induced depolarization and an increased sensitivity to ₁-adrenergic stimulation. No differences were noted regarding the Ca²⁺ sensitivity of force during K⁺-induced depolarization. The results suggest that microvascular growth (1) is immediately and positively influenced by the organ growth; (2) results in a functional resetting of the microvascular segments towards larger diameters without gross morphological or mechanical alterations; and (3) is accompanied by pharmacological alterations of the smooth muscle reactivity.     

Freeze-fracture study of the mechanoreceptive digital corpuscles of mice

Summary The freeze-fracture replication technique was used to study the mechanoreceptive digital corpuscles in toe pads of mice. The axon terminal plasmalemma had intramembranous particles (IMPs) at a density of 2367 ± 517 m^–2 (mean ±s.e.m.) in the P-face and 84 ± 4 m^–2 in the E-face. Particles were 10 ± 1.8 nm in diameter in the P-face and 10 ± 1.5 nm (mean ±s.d.) in the E-face. Particle-rich and particle-free areas were noted in the P-face. The lamellar cell plasmalemma had IMPs at a density of 3359 ± 224 m^–2 in the P-face and 265 ± 95 m^–2 in the E-face. Particles were 10 ± 1.4 nm in diameter in the P-face and 10 ± 1.6 nm in the E-face. Non-terminal unmyelinated fibres in the connective tissue compartment of toe pads were also examined: the P-faces of the axolemma and Schwann cell plasmalemma had IMPs at a density of 1356 ± 283 m^–2 and 1514 ± 514 m^–2, respectively, while the E-face of these membranes had only a few particles. Particles were 9 ± 1.2 nm and 10 ± 1.6 nm in diameter in the P-faces of axon and Schwann cell plasmalemmata, respectively.The results show that the IMPs in terminal axolemma and in lamellar cell plasmalemma have a much higher density than those of non-terminal axons or Schwann cells in myelinated and unmyelinated fibres. In addition, IMPs in the terminal axolemma are larger than those in non-terminal axolemma except for the nodal axolemma. It can be said that plasmalemmata of both the axon terminals and lamellar cells of digital corpuscles are specialized in terms of IMPs, suggesting that they have specific physiological properties in mechanoreceptive functions including mechano-electric transduction.     

Synthesis and release of platelet-activating factor and eicosanoids in human endothelial cells induced by different agonists

Production of platelet-activating factor (PAF) and eicosanoids by human umbilical vein endothelial cells (HUVEC) after stimulation with different agonists has been studied. Significant amounts of PAF were measured in the cellular fraction after treatment with thrombin (2 NIHu/ml), calcium ionophore A23187 (2 M) and histamine (100 M) (110.3±14.3, 80.7±19.2 and 119.2±22.4 pg/10⁵ cells, respectively). Only thrombin caused a partial release of PAF into the supernatant. IL-1 (0.1 nM), TNF (1 nM), arachidonic acid (10 M) and endothelin (0.1 M) were not able to induce any PAF synthesis. High levels of 6-keto-PGF₁ were found after stimulation with thrombin and calcium ionophore A23187 (8641±2575 and 6715±3340 pg/10⁵ cells, respectively). Cytokines IL-1 and TNF were also able to stimulate PGI₂ synthesis, although to a lesser extent. PGE₂ production increased after treatment with thrombin and calcium ionophore A23187 three- and two-fold, respectively. Our results confirm that stimulated HUVEC are able to synthesize PAF and eicosanoids simultaneously, the relative amounts depending upon the agonist used. None of the agonists studied showed any significant effect on 15-HETE production.     

Isoproterenol sensitivity in heat tolerant and relatively heat intolerant men

Summary Recent research has demonstrated that pharmacologic blockade of -adrenoceptors predisposes to hyperthermia during prolonged exercise. To investigate the hypothesis that -adrenoceptor sensitivity to catecholamines may be an important determinant of exertional heat tolerance, we performed a cross-sectional study comparing the heart rate responses to graded doses of isoproterenol in 6 heat tolerant and 6 relatively heat intolerant men. We observed no significant difference (p>0.1) between the heat tolerant (0.9±0.68 g) and heat intolerant (1.19±0.61 g) subjects in the dose of isoproterenol that produced a 25 beat · min^–1 increment in heart rate. Although the possibility of a relationship between -adrenoceptor sensitivity and the ability to tolerate exercise in heat cannot be entirely excluded on the basis of these data, our study clearly demonstrates the lack of a correlation between cardiac pacemaker sensitivity to isoproterenol and exertional heat tolerance.Study supported by grants from ICI Pharmaceuticals and the Exercise Heart Research Fund     

Effects of inhibitors and ion substitutions on oscillations of cell membrane potential in cells expressing the RAS oncogene

Previous studies revealed that in NIH fibroblasts expressing the ras oncogene but not in other NIH fibroblasts, bradykinin leads to sustained, calcium dependent oscillations of cell membrane potential by repetitive activation of calcium-sensitive K⁺ channels. The present study has been performed to test for ion and inhibitor sensitivity of these oscillations. Both, Lys-bradykinin (kallidin) and bradykinin, but not any shorter peptide tested, maintained the oscillations. The oscillations are abolished in the presence of the K⁺ channel blocker barium (10 nmol/l). The amplitude but not the frequency of the oscillations is dependent on the extracellular potassium concentration. The oscillations are not dependent on the presence of extracellular sodium, bicarbonate or chloride. The oscillations are abolished in the absence of extracellular calcium and their frequency is significantly decreased at reduced extracellular calcium (to 0.2 mmol/l). The oscillations are not inhibited by acute administration of ouabain (0.1 mmol/l), by dimethylamiloride (100 mol/l), furosemide (1 mmol/l) and hydrochlorothiazide (100 mol/l), by cobalt (100 mol/l), zinc (100 mol/l), gadolinium (100 mol/l), verapamil (10 mol/l) and diltiazem (10 mol/l), but are abolished in the presence of 100 mol/l lanthanum, 1 mmol/l cadmium, 10 mol/l nifedipine, 25 mol/l SK & F 96365 and 200 mol/l TMB-8. Stimulation of calcium entry by 10 mol/l ionomycin is frequently followed by oscillations of cell membrane potential even in the absence of bradykinin. In conclusion, in cells expressing the ras oncogene bradykinin leads to sustained activation of calcium channels at the cell membrane, which cause oscillations of the cell membrane potential by triggering intracellular calcium release.     

Comparison of disk diffusion,the E test,and detection ofmecA for determination of methicillin resistance in coagulase-negative staphylococci

The aim of this study was to find a reliable, fast, and simple alternative to the methicillin disk method for determination of methicillin resistance in coagulase-negative staphylococci, since results of this method are often difficult to read due to growth within the zone of inhibition. The sensitivity of 319 strains of coagulase-negative Staphylococci to a 5 g methicillin disk on Mueller-Hinton agar using an incubation period of 48 h was compared with that of 1 (1 g and 5 g oxacillin disks on Mueller-Hinton agar with or without 2% NaCl, using an incubation period of 24 h. The detection ofmecA (MecAgen) by the polymerase chain reaction was used as a standard. Minimum inhibitory concentrations were determined by means of the E test. Of the 225mecA-positive strains, 190, 215, and 193 were resistant to 5 g methicillin, 1 g oxacillin and 5 g oxacillin disks on Mueller-Hinton agar, respectively, and 216, 218, and 223 were resistant on Mueller-Hinton agar with 2% NaCl. Of the 94mecA-negative strains, 89, 93, and 94 were susceptible to 5 g methicillin, 1 g oxacillin, and 5 g oxacillin disks on Mueller-Hinton agar, respectively, and 92, 93, and 94 were susceptible on Mueller-Hinton agar with 2% NaCl. Using breakpoints of 2 g/ml for oxacillin resistance and 8 g/ml for methicillin resistance, the E test yielded sensitivities of 99.6 and 99.1% and specificities of 97.9 and 98.9% after 48 h of incubation. The 5 g oxacillin disk was faster and easier to read than the methicillin disk and correlated better with detection ofmecA than the methicillin disk or the 1 g oxacillin disk.     

Tubular transport processes in proximal tubules of hypothyroid rats. Lack of relationship between thyroidal dependent rise of isotonic fluid reabsorption and Na+−K+-ATPase activity

Hypothyroid rats reconstituted with 10 g/kg b.w. per day of tri-iodothironine (T₃) for 4 days resulted in normal free T₃ and TSH levels. FT₃ levels were: 0.53±0.3 pg/ml in hypothyroid rats; 2.78±1.21 pg/ml in hormone reconstituted rats and 2.90±0.90 pg/ml in euthyroid rats. TSH levels were 3,508±513 g/ml in hypothyroid rats; 1,008±204 g/ml in reconstituted rats and 270±184 ng/ml in euthyroid rats.When hypothyroid rats were reconstituted with 50 g T₃/kg b.w. per day, TSH levels were nearly normal after 4 days (1,157±621 ng/ml). However FT₃ levels after 1–4 days were always higher than in euthyroid rats.Hypothyroid rats show a decrease in isotonic fluid reabsorption (J _v) in the proximal tubule (1.50±0.08 versus 4.96±0.23 10^–2 nl·mm^–1·s^–1 in euthyroid animals). 1 day after T₃ (10 g/kg b.w./day) injectionJ _v was increased significantly to 2.05±0.20 10^–2 nl·mm^–1·s^–1 and continued to increase during 4 days of T₃ reconstitution.When 50 g T₃/kg b.w./day was used,J _v increased to 2.75±0.07 after 1 day and to 3.10±0.42 10^–2 nl·mm^–1·s^–1 after 4 days.J _v was never reaching a value close to that of euthyroid rats because the tubular radius in hypothyroid rats (14.7±1.8 m) is less than that of euthyroid rats (19.2±0.5 m). The radius in hypothyroid rats treated with T₃ was unchanged over a 4 day course with either high or low doses of T₃.Na⁺–K⁺-ATPase activity was found to be 2.91±0.16 M P_i/h×mg protein in homogenates of kidney cortex from hypothyroid rats. Treatment of hypothyroid rats with 10 g or 50 g of T₃ resulted in an initial decrease in ATPase activity, followed by an increase to base level in hypothyroid rats with 10 g and a significantly higher level with 50 g. This decrease in ATPase activity was contrasted to the increase inJ _v.These data indicate that there is a dissociation between the effects of physiological doses of thyroid hormones on proximal tubular reabsorption and the effects of T₃ on Na⁺–K⁺-ATPase activity of kidney cortex. This leads to question the relationship between sodium transport and ATPase activity under physiological doses of thyroid hormones. An early effect of physiological doses of thyroid hormones on brush border Na⁺ permeability is suggested.     

Pyramidal tract of the cat: axon size and morphology

Summary The purpose of this work was to determine the number and morphology of pyramidal tract (PT) axons in the cat, using electron microscopy, modern methods of fixation, and computer-assisted morphometric analysis. Sections taken at the level of the medullary pyramids in three animals were fixed and magnified up to 10,000 x to produce photomicrographs. Morphological data were entered into computer files for analysis by tracing axon perimeters on micrographs mounted on a digitizer tablet. The number of axons per PT averaged 415,000, of which 88% were myelinated and 12% were unmyelinated. 90% of the myelinated axons fell in the diameter range 0.5–4.5 m. Axons larger than 9 m diameter accounted for 1% of the total; the largest were 20–23 m. Myelinated axon mean diameter was 1.98 m; because of the skewed distribution, with many small axons and a few very large axons, median diameter was 1.60 m. Size distribution was relatively uniform throughout the PT cross section, with all sizes represented in all regions. However, the more medial regions had a higher proportion of small fibers than the more lateral regions: mean medial diameter was 1.85 m while mean lateral diameter was 2.09 m. Myelin sheath thickness averaged 7.9% of fiber diameter for axons up to 11 m, but was constant at 0.9 m for larger fibers. Myelinated fibers were distorted from the circular shape in cross section, with a mean circularity index (or form factor) of 0.85, which implies that the fibers could swell about 15% without rupture of the cell membrane. Unmyelinated fibers averaged 0.18 m diameter (range 0.05–0.6 m); the largest unmyelinated axons were larger than the smallest myelinated axons. It is concluded that previous work greatly underestimated the number of axons in the cat pyramidal tract.     

The distribution of single P2x1-receptor clusters on smooth muscle cells in relation to nerve varicosities in the rat urinary bladder

The distribution of purinergic (P2x1) receptors on smooth muscle cells in relation to autonomic nerve varicosities in the rat urinary bladder has been determined using immunofluorescence and confocal microscopy. P2x1 receptors were visualized using rabbit polyclonal antibodies against the extracellular domain of the P2x1 receptor, and varicosities were visualized using a mouse monoclonal antibody against the ubiquitous synaptic vesicle proteoglycan SV2. Two size classes of P2x1 receptor clusters were observed on the smooth muscle cells of the detrusor, namely, a large ellipse of mean long axis 1.23 ± 0.21 m and short axis 0.92 ± 0.17 m and a smaller spherical cluster with a mean diameter of 0.40 ± 0.04 m. The latter occured in much greater numbers than the former in selected areas, with a density as high as 0.8 per m2 or two orders of magnitude more than the larger-sized clusters. The large clusters are in general located beneath varicosities, with only 4.5% of P2x1 clusters not possessing an overlying varicosity. None of the small clusters was associated with varicosities. Three-dimensional reconstruction of the P2x1 and SV2 labelling at individual varicosities showed that the varicosities were immediately apposed to the P2x1 receptor clusters. On occasions, two or more small SV2-labelled varicosities about 0.7 m in diameter each with a receptor patch were found juxtaposed to each other; these might represent the splitting up of a single large varicosity. These observations are discussed in relation to the identity of the autonomic neuromuscular junction.     

Tetrodotoxin exerts a large frequency-dependent depression of the maximum rate of rise of action potentials in guinea pig ventricular myocytes

The action potential configuration in guinea pig ventricular myocytes was unaffected by low concentrations (0.3–1 M) of tetrodotoxin (TTX); high concentrations (10–30 M) depressed both the overshoot (5–10 mV) and duration (5–10%). Although the control was unaffected by stimulation rate (0.1–5 Hz), the depression of by TTX was greatly potentiated at rates above 1 Hz: on dose-response curves, 50% control occurred at 4.3 M (5 Hz) versus 22 M ( 1 Hz). The frequency dependent component of the depression reported here is much larger than the extra block of Na channels observed by others in voltage clamp studies on Purkinje strands. This is not a discrepancy; rather it is a consequence of a non-linear relation between and available Na conductance.     

Stimulus-specific patterns of myosin light chain phosphorylation in smooth muscle of rabbit thoracic artery

When the rabbit thoracic artery was stimulated with submaximal concentrations of agonist [40 mM K⁺, 30 M prostaglandin F₂ (PGF₂) or 7 M histamine], about 90% of a maximal contraction occurred. Each agonist induced a rapid development of contraction followed by a sustained response. The maximal rate of force generation stimulated with PGF₂ was twice that seen with K⁺ or histamine. Stimulation with 40 mM K⁺ increased the extent of monophosphorylated 20 kDa myosin light chain (MLC-P) for up to 1 min to a maximal value of 38.8±1.0%, there was a subsequent rapid decrease and the MLC-P level remained just above the basal value for 40 min (6.8±3.0%). In the case of stimulation with 7 M histamine, MLC-P level increased rapidly and was sustained for up to 40 min (28.0±4.9%). In contrast to the stimulation with K⁺ or histamine, PGF₂ induced both mono- and diphosphorylated MLC₂₀ (MLC-P and MLC-P 2 respectively) at a low concentration (3 M). The monophosphorylation of MLC₂₀ induced by 30 M PGF₂ reached the maximal value of 32.8±5.2%, and was sustained for up to 40 min (15.2±5.4%). The diphosphorylation of MLC₂₀ increased rapidly (7.4±4.0% at 5 min), then decreased to the basal value within 40 min. These results suggest that different modes of stimulation of smooth muscle contraction produce different profiles of MLC₂₀ phosphorylation. The implications of these observations are that the diphosphorylated form, specifically induced by certain agents, may modify the mode of contraction of the aortic artery.     

Characterization of two components of the N-like,high-threshold-activated calcium channel current in differentiated SH-SY5Y cells

Retinoic acid differentiated SH-SY5Y cells exhibit only a high-threshold-activated (–30 to –20 mV) whole cell calcium channel current. When barium was used as the charge carrier, the high-threshold-activated current showed bi-exponential inactivation kinetics during a 500 ms voltage step from –90 to +10mV. The time constants of inactivation were approximately 75 and 750 ms. The fast inactivating component was more sensitive than the slow inactivating component to steady-state inactivation at depolarized holding potentials. The calcium channel current was inhibited by externally applied cadmium (10–300 M) and gadolinium (10–30 M) as well as by high concentrations of nickel and cobalt, Conus toxin (1 M) irreversibly blocked the calcium channel current. However, the dihydropyridine agonist, BAY K 8644 (3–10 M) and antagonists, nifedipine (3–10 M) and nimodipine (10 M) did not affect either component of the calcium channel current. Agents which blocked the calcium channel current did not exhibit any selectivity for the fast inactivating over the slow inactivating component of the current. These results indicate that whilst the calcium channel current recorded in differentiated SH-SY5Y cells can be classified on the basis of the blocking agents as being of the N type, the current shows more than one form of inactivation.     

Inhibitory effects of E-5110 on interleukin-1 generation from human monocytes

Effects of E-5110, a novel non-steroidal antiinflammatory drug, on interleukin-1 (IL-1) generation from human monocytes were studiedin vitro. E-5110 reduced the amounts of extra- and intracellular IL-1 activity induced by lipopolysaccharide (LPS, 1 g/ml) in a dose-dependent manner (1–10M). E-5110 also inhibited the IL-1 generation induced by antigen-antibody complexes, opsonized zymosan and silica particles. It was suggested that the inhibition of IL-1 generation by E-5110 was independent of the inhibitory effects on arachidonate cyclooxygenase and/or lipoxygenase because indomethacin, piroxicam, BW755C and AA861 had no effects on IL-1 generation. Hydrocortisone (IC₅₀:0.084 M), aurothioglucose (11.5 M) and lobenzarit (75.0 M), which are clinically effective antirheumatic drugs, also inhibited IL-1 generation, like E-5110 (1.21 M). It is expected that E-5110 will be superior to classical non-steroidal antiinflammatory drugs in medical treatment of rheumatoid arthritis.     

The use of local anaesthetic microinjections to identify central pathways: a quantitative evaluation of the time course and extent of the neuronal block

Summary The time course and extent of local anaesthetic blocks within the spinal cord of cats were evaluated. A monopolar stimulation electrode with the tip lowered into the dorsal columns (DC) 1000 m below cord surface was used to activate antidromically DC fibers at the T13 level and evoke cord dorsum potentials at the level of the lumbar spinal cord. The amplitude of the negative deflection, the N-wave, was determined for various stimulation intensities (stimulation-response-function, SRF). Lidocaine (1%) was microinjected in volumes of 0.5 or 1.0 l into the DC from a glass micropipette 1 mm caudal to the stimulation site. Conduction block was characterized by a reversible shift of the SRFs to higher stimulation intensities. The diameter of the blocked area in the transverse plane was evaluated from threshold intensities and was found to be 0.9±0.1 mm 4 to 30 min after the injection of 0.5 l lidocaine and 1.6±0.36 mm 10 to 45 min after the injection of 1.0 l lidocaine. In the sagittal plane, the diameter of the blocked area following 1.0 l lidocaine was found to be up to 2.8 mm. The DC-block was reversible within 92 min following injection of 1.0 l and 69 min after the injection of 0.5 l lidocaine. The application of the present findings for blocks in other CNS structures is discussed.     

Transient improvement of polymorphonuclear leukocyte function by splenectomy in β-thalassemia

Host defense mechanisms in transfusion-dependent non-splenectomized patients with -thalassemia were studied. Polymorphonuclear leukocytes (PMNLs) of non-splenectomized patients responded poorly to zymosan generated chemotactic factors. Chemotactic indices were 22.1 m ± 2.8 (mean ± S.D.) using zymosan activated serum (ZAS) as the attractant in comparison to 20.4 m ± 2.6 when fresh untreated serum was used. In contrast, chemotactic indices of normal PMNLs increased from 21.1 m to 33.6 m ± 3.1 in response to ZAS. Normal PMNL responses to a mixture of normal ZAS and thalassemic serum were inhibited; the mean chemotactic index was 18.1 m ± 5.1 with use of ZAS alone. Splenectomy temporarily reverses these alterations. Adherence to nylon wool of PMNLs suspended in fresh thalassemic serum prior to splenectomy was 3.1% ± 1.1 (mean ± S.D.); 20 days after splenectomy adherence increased to 14.0% ± 2.8 (P = 0.0001) and remained at this level for 90 days. At 120 and 150 days after splenectomy adherence decreased to 1.5% ± 0.8 and 1.0% ± 0.85 respectively. Splenectomy also transiently abrogated the failure of zymosan to generate chemotactic factors in thalassemic serum.This study was presented in part at the American Federation for Clinical Research, Central Society, Infectious Diseases, Chicago, Illinois, November 3, 1983     

Mechanical properties of mammalian single smooth muscle cells I. A low cost large range microforce transducer

Summary A transducer has been developed for measuring the minute forces generated during isometric contractions (1.0–10.0N) of single smooth muscle cells from the pig urinary bladder and the human uterus. In addition to its high sensitivity, resolution and stability (100 mVN^–1, <0.1N and <2.0N h^–1), the transducer features a very wide range (100–140N) with good linearity, enabling measurement of contractions as well as passive force-length characteristics within one uninterrupted measurement session. Since the transducer features an independent and interchangeable force to displacement conversion system, different force ranges can be realized by inserting force conversion systems with different compliances.     

The effects of TRH analogues on cerebral ischaemia produced by middle cerebral artery occlusion in the rat

Summary This study examined the effects of two stabilised analogues of TRH, RX 77368 and CG 3509, in a rat cerebral ischaemia model produced by unilateral occlusion of the middle cerebral artery. The analogues were given intraventricularly after artery occlusion. The extent of the cortical ischaemia was evaluated after 10 days by somatosensory evoked potential (SEP) recording, followed by tetrazolium staining of brain slices for NADH-diaphorase activity. RX 77368 (2×10 g; 15 min, 24 h) significantly improved the survival rate, protected the SEP and reduced the area of infarct. In contrast, neither a smaller dose of RX 77368 (2×3 g) nor a 4 h delay in the treatment had any significant beneficial effects. Although CG 3509 (2×10 g) resulted in an apparent improvement in survival, its overall effects were not statistically significant. The findings indicate that stabilised TRH analogues may have beneficial effects when given to animals with focal cerebral ischaemia.     

Transient effects of norepinephrine on myocardial oxygen balance

Summary In conscious dogs with experimental atrioventricular block and with ventricles paced at constant rate the effects of norepinephrine (NE) and isoproterenol (ISO) on coronary flow, coronary resistance, and myocardial O₂-balance were investigated. Myocardial O₂-s balance, as estimated from continuous measurement of coronary venous O₂-s saturation, was used for the discrimination of coronary dilation induced either directly by vascular -adrenoreceptor stimulation or indirectly by increased myocardial metabolism.Following bolus injection of NE (0.3 g/kg) or ISO (0.1 g/kg) into the pulmonary artery, coronary venous O₂-s saturation increased from a control of 25±2% O₂-s saturation (mean±S.D.) transiently to 51±5 and 62±5% O₂-s saturation respectively. After ₁-adrenoreceptor blockade these increases were reduced to 33±4 and 41±3% O₂-s saturation, respectively. The remaining increase after NE was abolished when atropine was given in addition to ₁-b blockade. After ₁+2-adrenoreceptor blockade neither NE nor ISO injection had an effect on coronary venous O₂ saturation. After ₁-b blockade was superimposed on ganglionic blockade NE injection led to a decrease in coronary venous O₂-s saturation indicating a ratent -a activity of NE.NE seems to act directly via ₁-a adrenoreceptors, since no differences were observed in the time courses of changes in coronary venous O₂-s saturation after left atrial injection of NE when compared to adenosine.It is concluded that circulating NE like ISO is able to improve myocardial oxygen balance by a direct vasodilating effect on canine coronary vessels mediated by vascular ₁-adrenoreceptors.