Transmural pressure as a determinant of basic intrinsic heart rate

Summary It was observed the heart rate was minimum at zero transmural pressure. The mean heart rate at zero transmural pressure was 23±5/min. This mean heart rate increased from 23±5/min to a peak value of 40±6/min (74% acceleratin) when the transmural pressure was raised from 0 to +4 mm Hg and to a similar peak value of 36±8/min (56% acceleration) when the transmural pressure was lowered from 0 to –4 mm Hg. The peak values attained at ±4 mm Hg were higly significant (p<0.001). It is concluded that the heart rate at zero transmural pressure represents the basic intrinsic pacemaker frequency independent of neural, humoral, thermal and haemodynamically induced mechanical influences.     

Reduced deformability of erythrocytes exposed to hypercapnia

Summary The effect of hypercapnia on the deformability of erythrocytes was studied by means of a nuclepore membrane filter method. A decrement of the deformability by 20–40% was observed when was increased from 50 mm Hg to 200 mm Hg, accompanied with an increment of 5% in hematocrit value.     

Intravital measurement of arteriolar pressure and tangential wall stress in normotensive and spontaneously hypertensive rats (established hypertension)

Summary Under intravital conditions, intravascular pressures of mesenteric resistance vessels were measured in normotensive (NR, mean blood pressure 92 mm Hg) and spontaneously hypertensive rats (SHR, 161 mm Hg) being elevated over all by about 75%; the tangential wall stress (=p·r/h; p represents the intravascular pressure and r/h the ratio of internal radius to wall thickness) was found to be increased by 120–140% in SHR.Supported by the DFG.     

Conduction velocity of peristaltic waves in the in vivo ureter: application of a new diameter gauge

Summary The conduction velocity of peristaltic movements of the canine ureter was measured under anaesthesia with a new type of diameter gauge using an image sensor. The peristaltic velocity was 34.1±6.2 mm/sec in 10 experiments. Noradrenaline at a low dosage of 1 g/kg i.v. reduced the resting diameter, increased the conduction velocity to 47–56 mm/sec, and approximately doubled the frequency of contraction. The application of acetylcholine also caused an increase in both frequency and conduction velocity (42–46 mm/sec). A plot of the conduction velocity against the mean period of peristaltic contraction was hyperbolic in shape.     

Denaturation map of the ribosomal DNA ofLytechinus variegatus sperm

Summary Electron microscopy of the partially heat denatured ribosomal DNA (rDNA) from sea urchin (Lytechinus variegatus) sperm has demonstrated that it consists of repeating units of 3.6±0.2 m, corresponding to a mol.wt of 7.2±0.4×10⁶. Based on differential denaturability, each repeat unit is divided into 2 regions. The larger region of 2.47±0.11 m (mol.wt 4.9±0.22×10⁶) corresponds in length to the ribosomal precursor RNA of sea urchins and the smaller, GC-rich, subunit of 1.16±0.09 m (mol.wt 2.3±0.18×10⁶) is presumed to contain non-transcribed spacer sequences.Acknowledgments. This paper is dedicated to the memory of Dr D. P. Costello whose insprration made this work possible. I gratefully acknowledge the valuable advice of Drs D.W. Stafford and M.A. Bleyman.     

Effect of dipyridamole on glomerular mesangial cell ecto-5′-nucleotidase expression

Although dipyridamole has been extensively studied as an anti-aggregating agent, its mechanism of action has not been elucidated. Cultured mesangial cells were treated with dipyridamole 1–100 M from 6–72 h. Ecto-5-nucleotidase activity approximately doubled (from 115±11 to 226±14 nmol/min/mg) after treatment with 100 M dipyridamole for 72 h. This effect was concentration- and time-dependent. Cycloheximide, an inhibitor of protein synthesis, did not alter basal 5-nucleotidase activity. However, it prevented stimulation by 5 M dipyridamole. Adenosine availability at the receptor sites was increased by dipyridamole and S-(p-nitrobenzyl)-6-thioinosine (NBTI), which inhibit adenosine uptake into the cell. Addition of dipyridamole or NBTI to the adenosine-treated mesagial cells produced an additive increase in ecto-5-nucleotidase activity. Dipyridamole, through its effect on extracellular adenosine and ecto-5-nucleotidase, may have an influence upon regulation of the glomerular microcirculation.     

Nachweis einer physiologischen Spontanaktivität in Einzelfasern des N. opticus der Katze

Summary Spike potentials were recorded with metal micro-electrodes from single fibers in the intracranial part of the cat's optic nerve with the retina left completely intact. All units studied as yet showed a marked spontaneous activity irrespective of differences in their response to light stimuli. The spontaneous activity in the intracranial part of the optic nerve could be suppressed reversibly by increasing the intraocular pressure up to 200 mm Hg. Thus spontaneous activity has been verified as a normal feature of the retina. A spontaneous firing rate of 22±11/s after 1 h dark adaptation was found in altogether 12 well-isolated fiber units.     

Thyroid function parameters during a selenium repletion/depletion study in phenylketonuric subjects

Phenylketonuric (PKU) subjects have a limited supply of selenium (Se) in their phenylalanine-restricted diet. A Se repletion (1 g Se/kg/day)/depletion study was conducted in PKU children to determine the effect of Se on thyroid function parameters.The initial plasma Se concentration (mean±SD: 0.26±0.12 mol/L, p<0.00003, n=10) and glutathione peroxidase (GSH-Px) activity (140±58 U/L, p<0.00003, n=10) were significantly lower compared to agematched controls. After 14 weeks of supplementation, the plasma Se concentration (mean ±SD: 0.74±0.20 mol/L) normalized (normal range: 0.57–1.15 mol/L, mean ±SD: 0.76±0.13 mol/L, n=32) and remained stable thereafter during repletion. Plasma GSH-Px activity reached normal values after 18 weeks of supplementation (312±57 U/L; normal range: 238–492 U/L, mean ±SD: 345±54 U/L, n=32) and increased significantly for up to eight weeks thereafter (332±52 U/L). Individual and mean thyroid parameters were initially normal in all cases. The mean concentrations of plasma thyroxine (T₄: p<0.025), free T₄ (FT₄: p<0.01) and reverse triiodothyronine (rT₃: p<0.005) decreased to 75% of their initial value within three weeks of Se supplementation and remained stable thereafter, within a normal physiological range during selenium supplementation. They increased back to their initial values three weeks (T₄: p<0.05, FT₄: p<0.05) and six weeks (rT₃: p<0.025) respectively, after the end of the supplementation. In conclusion, Se supplementation modifies thyroid function parameters in Se-deficient PKU subjects most likely by an increase in activity of type I 5-deiodinase (5-DIase I).Preliminary results of this study were presented as posters on the 4th International Congress on Trace Elements in Medicine and Biology, Chamonix, France (1993) and the 4th Joint Meeting of the Lawson Wilkens Pediatric Endocrine Society and the European Society for Paediatric Endocrinology, San Francisco, California, Ped Res (1993) 33: S93 (abstract 537). Support in part by Research Grants of Nutricia BV, (The Netherlands).     

α1-Adrenergic stimulation of ketogenesis and fatty acid oxidation is associated with inhibition of lipogenesis in rat hepatocytes

Summary The effect of norepinephrine on fatty acid synthesis (³H₂O incorporation into fatty acids), on fatty acid oxidation to CO₂ and on ketogenesis was studied in isolated hepatocytes of fed rats. After incubation with norepinephrine (50 M), lipogenesis was lower (5.7±1.1 nmoles³H₂O incorporated into fatty acids/mg dry weight/30 min) than in controls (7.5±1.7; n=6, p<0.02). In contrast, (1-¹⁴C) palmitate conversion into total ketone bodies was increased to 10.9±1.8 nmoles/mg/30 min with norepinephrine, vs 8.5±1.6 in controls (p<0.05), and more (1-¹⁴C) palmitate was converted to¹⁴CO₂ with norepinephrine than in controls (1.48±0.10 nmoles/mg/30 min vs 1.06±0.11, p<0.05). The inhibitory effect of norepinephrine on lipogenesis was abolished by addition of the ₁-receptor blocker prazosin, but not by ₂ or -blockers. The results demonstrate that the ketogenic effect of norepinephrine is coupled with an inhibitory effect on lipogenesis which may be explained by diminished activity of acetyl-CoA carboxylase, diminished formation of malonyl-CoA and decreased activity of carnitine palmitoyl transferase I.     

Comparison of X-prolyl dipeptidyl-aminopeptidase activity in human cerebrospinal fluid with that in serum

Summary X-Prolyl dipeptidyl-aminopeptidase activities in cerebrospinal fluid and serum from the same patients without neurological diseases, undergoing surgery under lumbar anesthesia, were assayed fluorometrically with a newly synthesized fluorogenic substrate, 7-glycylproline-4-methylcoumarinamide; the values were 129.1±19.5 nmoles/min/1 and 54.17±3.11 moles/min/1 (mean±SEM, n=23), respectively, and there was no correlation between both activities (r=0.0894).     

The excretion of urea by the larvae ofSpodoptera mauritia boisd. (Noctuidae: Lepidoptera) during development

Summary The concentration of urea in the excreta of the 6th instar larvae ofSpodoptera mauritiavaries from 4.017±0.541 to 31.052±1.193 moles/g dry excreta (mean±SE). The observation confirms that urea excreted is of metabolic origin.     

The conduction velocity,number and diameter of unmyelinated fibers in Remak's nerve

Summary Remak's nerve in the chicken was examined ultrastructurally and electrophysiologically to determine the characteristics of fibers in the nerve trunk. The ratio of unmyelinated fibers to myelinated ones was 1111. The mean number of unmyelinated fibers was 3555±232 (SEM, n=5) and they had a mean diameter of 0.502±0.034 (SEM) m. The compound action potential consisted almost entirely of a large diphasic waveform which had a mean peak conduction velocity of 0.62±0.031 (SEM, n=5) m·s^–1 at 37°C.     

Age distribution of circulatingα-interferon

Summary A sensitive radioimmunoassay showed that circulating -interferon in the plasma of healthy individuals was low in children and reached the highest level in the young adult, then declined gradually with age. Circulating -interferon was 0.201±0.059 ng/ml in males (n=19) and 0.184±0.076 ng/ml in females (n=14) at ages 30–39 years old. It was noted that circulating -interferon was maintained up to a certain level even in elderly individuals.     

The determination of extracellular space using hemoglobin

Summary The ECS of guinea-pig atria and frog sartorii can be determined using hemoglobin. For guinea-pig atria an ECS of (32.2±2.6)% wet wt for frog sartorii an ECS of (12.4±1.0)% wet wt can be measured.This work was supported by the Deutsche Forschungsgemeinschaft SFB 114 Bionach.     

HCN channels contribute to the intrinsic activity of cochlear pyramidal cells

A hyperpolarization-activated current recorded from the pyramidal cells of the dorsal cochlear nucleus was investigated in the present study by using 150- to 200-m-thick brain slices prepared from 6- to 14-day-old Wistar rats. The pyramidal neurones exhibited a slowly activating inward current on hyperpolarization. The reversal potential of this component was –32 ± 3 mV (mean ± SE, n = 6), while its half-activation voltage was –99 ± 1 mV with a slope factor of 10.9 ± 0.4 mV (n = 27). This current was highly sensitive to the extracellular application of both 1 mM Cs⁺ and 10 M ZD7288. The electrophysiological properties and the pharmacological sensitivity of this current indicated that it corresponded to a hyperpolarization-activated non-specific cationic current (I_h). Our experiments showed that there was a correlation between the availability of the h-current and the spontaneous activity of the pyramidal cells, suggesting that this conductance acts as a pacemaker current in these neurones. Immunocytochemical experiments were also conducted on freshly isolated pyramidal cells to demonstrate the possible subunit composition of the channels responsible for the genesis of the pyramidal h-current. These investigations indicated the presence of HCN1, HCN2 and HCN4 subunits in the pyramidal cells.Received 15 May 2003; received after revision 26 June 2003; accepted 21 July 2003     

Asscorbic acid portects against male infertility in a teleost fish

An animal unable to synthesize ascorbic acid uniquely minicks human and non-human primates. Therefore, in this study we used the rainbow trout, a teleost fish, as the model animal to study the importance of dietary ascorbic acid on the fertilizing ability of sperm. A high concentration of ascorbic acid in semen plays a key role in maintaining the genetic integrity of sperm cells, by preventing oxidative damage to sperm DNA. This study will show that the concentration of asorbic acid in seminal plasma refelcts the dietary fed either an ascorbate-free diet (from 4.74±0.9 to 0.16±0.08 g ml^–1) or an ascorbate-rich diet (from 37.9±4.7 to 17.7± 3.2 g ml^–1) during the sperimnation season. The relationship between ascrobate status and fertility was studied in six groups of fish fed graded levels of ascorbic acid, which sperimated over a 150-day-period. Sperm from individual males was used to fertilize several batches of eggs. When the seminal plasma ascorbate concentration decreased to 7.3 g ml^–1 a significant decrease of fertilization rate and the hatching rate of embryos resulted. This is the first evidence that dietary ascorbate level directly affected sperm quality and influenced male fertility in a scruvy-prone vertebrate.     

Temperaturabhängigkeit der elektrischen Leitfähigkeit einiger Tocopherole

Summary The electrical dark conductivity of several tocopherols has been measured and found to be analogous to that of organic semiconductors. Conductivity at 25°C varies between 10^–14 and 10^{–11 –1} cm^–1. The temperature dependence of the tocopherols yields a thermal activation energy of 1.6 ± 0.15 eV for most of the substances.     

β-Endorphin in normozoospermic and pathologic human semen

Summary -Endorphin was estimated in normozoospermic, oligozoospermic and azoospermic human semen. The mean amount in normozoospermic specimens was 278.6±43.6 (SE) pg/ml while in the others only 191.1±25 pg/ml. Both values are significantly higher than those present in the blood.     

Immunocytochemical localization of hyperglycemic hormone (HGH) in the neurosecretory system of the eyestalk of the crayfishAstacu leptodactylus

Summary Hyperglycemic hormone (HGH) fromAstacus leptodactylus can be visualized by an immunocytochemical procedure using a specific antiserum against HGH and the peroxidase-anti-peroxidase (PAP) method. HGH containing cells are localized in the most distal portion of the x-organ in the medulla terminalis. Their cell diameter is about 47±7 m; the nucleus measures about 22±2 m. They form a subgroup of neurosecretory cell type 1, already described for the crayfish. A large amount of this HGH material is homogeneously stored in the sinus gland. A group of fibres in the x-organ — sinus gland — tractus can be followed, due to their positive reaction with the PAP-reagent.     

A new method for measuring guanidine in uremia

Riassunto Si descrive un metodo per la determinazione della guanidine nei liquidi biologici e si rileva che essa aumenta nel siero uremico fino a 30 volte la norma (valore medio normale: 1.41±0.49 g/100 ml) e che nei cani uremici la concentrazione muscolare è di quasi 3 volte superiore a quella plasmatica. La eliminazione urinaria non è diversa fra normali ed uremici: 382±221 e 459±229 g/24 h, rispettivamente.

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Aknowledgments. This investigation was supported by Public Health Service, Research Contract No. PH-43-68-1466.