bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of substance P and thyrotropin-releasing hormone on sympathetic preganglionic neurones in the upper thoracic intermediolateral nucleus of the cat
Authors: Backman S. B. , Henry J. L.
Published: April 2011

When applied by iontophoresis onto single sympathetic preganglionic neurones in the intermediolateral nucleus of spinal segments T1–T3 in the cat, substance P and thyrotropin-releasing hormone (TRH) each had a weak excitatory effect. Two-thirds of the neurones studied were excited by substance P while one-fifth were excited by TRH. The time courses of the responses to substance P and to TRH were similar, and consisted of an increase in the rate of discharge with a latency of approximately 30 s from the onset of application. They were also prolonged (30–320 s) in afterdischarge following termination of application. These results indicate that substance P and TRH exert excitatory effects on single sympathetic preganglionic neurones, and support the possibility that they may be chemical mediators of synaptic transmission in the intermediolateral nucleus.
Charges fixes du protoplasme des fibres musculaires de balane; effet de la longueur des sarcomères
Authors: Caillé Jean-Pierre
Published: April 2011

The thermodynamically effective charge density [Formula: see text] of myoplasm was measured on barnacle muscle fibers. A small section of a muscle cell formed a liquid junction between two electrolyte solutions and the electrical potential between the solutions permitted to evaluate [Formula: see text]. If the sarcomere length was kept constant (Ls = 12.5 μm), [Formula: see text] increased from 0.068 to 0.090 equiv./L when the water content was reduced from 75 to 65 g/100 g wet weight. This increment of X resulted from an increase of X when the concentration of macromolecules is raised in the sample of cytoplasm. But it also indicates that the counterions of the fixed charges concur less to the activity of the counterions when X is increased by lowering the water content. If the water content is maintained constant, [Formula: see text] increased from 0.068 to 0.084 equiv./L for sarcomere lengths equal to 9.6 and 11.5 μm but [Formula: see text] remained constant for Ls > 12 μm. Thus, when the length of the sarcomere is > 12 μm the contribution of the counterions of the fixed charges to the activity of the counterion is larger than for Ls = 9.6 μm.
Blockade of Ca2+ channels inhibits K+ contractures but not twitches in skeletal muscle
Authors: Frank George B.
Published: April 2011

The effects of the voltage-sensitive, calcium channel blocking agents, D-600 and verapamil, on twitches and K+-induced contractures were studied using frog's toe muscles. K+-contracture tension was reduced by concentrations as low as 10−8 M and the contractures were blocked by 10−6 M. There was no significant difference in the effects of the two drugs. Twitches were potentiated by 5 × 10−5 M D-600 and blocked only at 3 × 10−4 M. The latter concentration also produced contractures in the toe muscles. As shown by other workers, the higher concentration also blocks action potential production and this is probably the way in which it blocks the twitch. Raising the bathing solution Ca2+ concentration from 1.08 to 10 or 20 mM, produced only a small, inconsistent, noncompetitive antagonism of the D-600 block of K+ contractures.
Effect of diuretics on the tubuloglomerular feedback response
Authors: Gutsche Hans-Ulrich , Brunkhorst Reinhard , Müller-Ott Klaus , Franke Holger , Niedermayer Walter
Published: April 2011

To study the influence of diuretics on the tubuloglomerular feedback mechanism, early proximal stop-flow pressure (SFP) was measured during loop exposure to different drug concentrations. SFP was recorded continuously during arrested flow and at a perfusion rate of 50 nL/min. The perfusate consisted of isotonic saline, to which varying amounts of furosemide, bumetanide, piretanide, or hydrochlorothiazide were added to obtain final concentrations between 10−6 and 10−4 M. The loop diuretics furosemide, bumetanide, and piretanide showed inhibition: an inverse log–linear relation between the luminal concentration and the respective feedback response. No differences between the dose–response curves of furosemide, bumetanide, or piretanide could be demonstrated. The effective concentration range was between 10−6 and 10−4 M, the mean effective dose (ED50) was close to 10−5 M for each of them. In contrast, hydrochlorothiazide did not alter the feedback response. The effect of loop diuretics was rapidly and repeatedly reversible.
The action of some analogues of the excitatory amino acids in the dentate gyrus of the rat
Authors: Collingridge G. L. , Kehl S. J. , McLennan H.
Published: April 2011

We have confirmed that γ-D-glutamylglycine and the L-isomer of 2-amino-4-phosphonobutyric acid, and have shown also that L-2-amino-5-phosphonovaleric (L-APV) acid, are antagonists of synaptic excitations of dentate granule cells induced from both lateral and medial perforant paths. The N-methyl-D-aspartic acid (NMDA) antagonist D-APV is without effect. The synaptic antagonists reduce the presynaptic fibre volley particularly in the lateral path, suggesting that a reduced transmitter output contributes to their action. NMDA receptors exist upon the granule cells, but they are not involved with these synaptic processes.
Ion channels and membrane potential in stimulus–secretion coupling in adrenal paraneurons
Authors: Kilpatrick Daniel L.
Published: April 2011

Cultured bovine adrenal medulla cells have been shown to contain several different ion channels (Na+, Ca2+ acetylcholine receptor regulated) whose activation leads to the secretion of catecholamines. The pharmacology of these ion channels and their interactions during secretion have been examined. The mechanisms of agonist-induced calcium influx are of particular interest since this is an early obligatory event during secretion from the adrenal medulla. Data obtained on catecholamine release and 45Ca2+ uptake indicate that both voltage-dependent and voltage-independent calcium influx mechanisms operate in cultured bovine adrenal medulla cells. The significance of these results in understanding the mechanism of action of the physiological stimulus acetylcholine (Ach) will be discussed. The alkaloid channel neurotoxins D-600, batrachotoxin, veratridine, and aconitine were shown to exert a noncompetitive inhibitory effect on Ach-induced ion flux in adrenal medulla cells, presumably through an interaction with the nicotinic receptor regulated channel. Lipid-soluble neurotoxins may interact with multiple ion channels in nerve and muscle membrane.
Decrease in calcium carbimide (calcium cyanamide)-induced inhibition of rat hepatic aldehyde dehydrogenases by multiple ethanol administration
Authors: Loomis C. W. , Brien J. F.
Published: April 2011

Ethanol (0.3 g/kg) was administered intravenously to adult, male rats at 3 h or at 1 and 3 h after gastric intubation of 7 mg/kg calcium carbimide (CC). For animals administered CC and two ethanol doses, blood ethanol concentration was similar for the two doses; however, blood acetaldehyde concentration was significantly less for the second ethanol dose compared with the first dose as determined by the area-under-curve data. Hepatic aldehyde dehydrogenase activity was determined over the 3.5-to 5-h interval after CC pretreatment. The inhibition of low Km and high Km aldehyde dehydrogenase activity in liver homogenate and in hepatic mitochondrial, cytosolic, and microsomal fractions was significantly less for rats administered CC followed by two ethanol doses compared with that for animals administered CC alone or CC followed by one ethanol dose. The data demonstrate that increased acetaldehyde concentration, produced during the CC – ethanol interaction, can augment the recovery of hepatic aldehyde dehydrogenase activity following CC pretreatment and indicate the existence of a displaceable enzyme inhibitor derived from CC.
Decreased plasma testosterone and total thyroxine in desalivated male rats
Authors: Dean Dwane H. , Hiramoto Raymond N.
Published: April 2011

Plasma testosterone and total thyroxine were decreased by 50 and 35%, respectively, in submandibular gland extirpated or parotid duct ligated rats treated 27 days earlier. Sixty-two days after surgery, testosterone and total thyroxine were decreased by 20 and 40%, respectively. These changes occurred in the absence of evidence of nutritional impairment or signs of stress, such as adrenal enlargement or thymic involution.
Stability of dopamine in an in vitro incubation system using Medium 199
Authors: Marien M. R. , Shin S. H. , Cooper G. R. , Jhamandas K.
Published: April 2011

This study investigated the stability of exogenous dopamine (DA) in vitro in a commercially available medium (Medium 199), with and without additional ascorbic acid, during incubation with pituitary halves in prolactin secretion experiments. After a 3-h incubation period, 26 and 15% of the starting concentrations of DA were degraded in the absence and presence of 1 mM ascorbic acid, respectively; in the absence of pituitary tissue, these reductions in DA concentration were 19% and 0%, respectively. In contrast, 98% of DA was degraded after 3 h of incubation in Krebs–Henseleit bicarbonate buffer which contained no tissue or no antioxidants. A number of antioxidants (including a low concentration of ascorbic acid) which are already present in Medium 199 are most likely responsible for the relative stability of DA in this medium. The loss of DA during incubation in Medium 199 is considered small for this type of study, and additional ascorbic acid only marginally improves DA stability in this medium. We have concluded that there is no need to be overly concerned about the degradation of exogenous DA in vitro for some incubation experiments using Medium 199, and the addition of extra ascorbic acid (which may be deleterious) is not necessary.
Opioid receptors in bovine adrenal medulla
Authors: Dumont Michel , Lemaire Simon
Published: April 2011

Using prototypic ligands for each type of opioid receptors (μ, δ, κ, and σ) as well as compounds derived from each class of endogenous opioid peptides (β-endorphin, enkephalins, and dynorphins), we have undertaken the characterization of adrenomedullary opioid binding sites. The specific binding of [3H]etorphine ([3H]ET) to a membrane preparation of bovine adrenal medulla was greatly increased when the incubation temperature was raised from 22 to 37 °C. Characterization of the opioid binding sites was obtained at 37 °C with [3H]ET (nonspecific opioid ligand), [3H]ethylketocyclazocine ([3H]EKC; κ), [3H]dihydromorphine ([3H]DHM; μ), [3H]-[D-Ala2,D-Leu5]enkephalin ([3H]DADLE; δ), and N-[3H]allylnormetazocine ([3H]SKF-10047; σ) in the absence or presence of blocking agents for cross-reacting receptors. [3H]ET had a high affinity binding site (KD = 0.98 nM) with a Bmax of 119 pmol/g protein. All the other opioid compounds showed biphasic saturation curves with KD ranging from 0.6 to 1.29 nM for the high affinity binding site and from 2.49 to 12.1 nM for the low affinity binding site. The opioid μ-receptor was characterized by the high affinity binding site for [3H]DHM (KD = 1.29 nM; Bmax = 38 pmol/g protein). Blockade of the cross-reacting receptor sites for [3H]EKC, [3H]DADLE, and [3H]SKF-10047 revealed the presence of κ (KD = 0.66 nM; Bmax = 12 pmol/g protein), κ2 (benzomorphan site; KD = 11.1 nM; Bmax = 56 pmol/g protein), δ (KD = 0.67 nM; Bmax = 4.7 pmol/g protein), and σ (KD = 4.54 nM; Bmax = 32 pmol/g protein) opioid receptors. The ability of various opioid ligands to displace the binding of [3H]ET indicates a high potency for (−)-(1R,5R,9R,2″S)-5,9-dimethyl-2′-hydroxy-2-tetrahydrofurfuryl-6,7-benzomorphan hydrogen D-tartrate (MR-2034, a κ-opioid ligand; Ki = 6.2 nM), dihydromorphinone (DHMone; Ki = 6.9 nM), oxymorphone (Ki = 8.6 nM), DADLE (Ki high affinity = 8.4 nM) EKC (Ki = 31.8 nM), SKF-10047 (Ki = 75 nM), and opioid agonists/antagonists. trans-(+)-3,4-Dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide methanesulfonate hydrate (U-50,488H), the most specific κ-agonist, was a poor competitor (Ki = 5150 nM). However, the presence of κ-opioid receptors was supported by the ability of U-50,488H to displace [3H]EKC binding (Ki high affinity = 2.5 nM). The relative potency of various endogenous opioid peptides in displacing [3H]ET binding was as follows: β-endorphin [Formula: see text] dynorphin(1-17) > dynorphin(1-13) > [Arg6,Phe7)Met-enkephalin > Met-enkephalin > Leu-enkephalin. In addition, the presence of a high affinity binding site for dynorphin was demonstrated by the high potency of dynorphin (1-13) to displace [3H]EKC binding (Ki high affinity = 2.3 nM). These data provide further insights into the characterization of adrenal opioid receptors and suggest an in situ physiological role for adrenal opioid peptides.
Recovery of function in sympathetic nerves of interscapular brown adipose tissue of rats treated with 6-hydroxydopamine
Authors: Depocas Florent , Foster David O. , Zaror-Behrens Gloria , Lacelle Suzanne , Nadeau B.
Published: April 2011

Twenty-four hours after subcutaneous administration of 6-hydroxydopamine (6-OHDA) at a dose of 10 mg/kg body weight in warm-acclimated rats, noradrenaline (NA) content and dopamine β-hydroxylase (DBH) activity of interscapular brown adipose tissue (IBAT) were reduced to about 10 and 35% of control values. Corresponding values for cold-acclimated rats, similarly treated, were 12 and 32%. In both groups of animals, calorigenic function in IBAT assessed by measurement of the effect of cold exposure on rate of blood flow through the tissue was lost almost completely. Twenty-four hours after treatment of rats with various doses of 6-OHDA, calorigenesis in IBAT was directly related to residual NA. Measurements of noradrenaline content and DBH activity from 1 to 10 days after 6-OHDA and the increase in IBAT blood flow of cold-exposed animals from 1 to 7 days after 6-OHDA indicated marked differences in the extent to which each of these indicators of the integrity and function of sympathetic nerve endings recovered with time and with the acclimation temperature of the animals. Regeneration of macromolecuiar components of noradrenergic vesicles in IBAT appeared to occur more rapidly in cold than in warm-acclimated animals. Thus, moderate doses of 6-OHDA may acutely sympathectomize IBAT, but as previously reported for other tissues, full recovery of function of IBAT occurs long before noradrenaline stores are replenished.
Relation between fetal arterial and oxytocin-induced uterine contractions in pregnant sheep
Authors: Lye Stephen J. , Wlodek Mary E. , Challis John R. G.
Published: April 2011

The relation between oxytocin-induced type A uterine contractions and fetal arterial [Formula: see text], measured continuously with an intravascular oxygen electrode, was studied in nine chronically catheterized sheep during late pregnancy. Oxytocin provoked dose-related increases in intrauterine pressure (IUP) and decreases in fetal [Formula: see text]. There was a significant positive relationship between changes in IUP and the maximum decrease in fetal [Formula: see text] (average r = 0.696, df = 92; P < 0.001). We conclude that changes in uterine activity contribute to transient fetal hypoxemia, and that administration of exogenous oxytocin provides an experimental paradigm to examine the consequences of this relationship.
Proteins of fast axonal transport in the regenerating hypoglossal nerve of the rat
Authors: Redshaw J. D. , Bisby M. A.
Published: April 2011

The composition of proteins conveyed by fast axonal transport in growing or regenerating axons is different from that of intact, mature axons. Consistent alterations have been observed in several different types of neurons, but adult peripheral axons (rabbit hypoglossal motoneurons) seemed to be exceptions because during their regeneration there was no increased labelling of a 23 kilodalton (kD) protein associated with the growth state. We examined the composition of fast-transported proteins, labelled by application of [35S]methionine to the hypoglossal nuclei, in intact and regenerating hypoglossal nerves of the rat. Using one- and two-dimensional electrophoresis we detected both increases and decreases in the labelling of specific polypeptides during regeneration. In particular, there was increased labelling of a 23 kD polypeptide. Changes were maximal 7 days after axotomy and subsided thereafter, coincident with reinnervation of the tongue. We conclude that hypoglossal axons show the same changes in transported protein composition which are characteristic of the growth state in other axons. Thus, we have strengthened the correlation between the growth state and changes in synthesis of a set of polypeptides of unknown function.
1983 Upjohn Award Lecture Endocrine dysfunction and cardiac performance
Authors: McNeill John H.
Published: April 2011

Studies were carried out to study the effect of endocrine changes on rat cardiac performance, biochemistry, and responses to drugs. Hyperthyroidism increased contractility in rat hearts and enhanced the phosphorylase response to catecholamine. The inotropic response may be due to an increase in cardiac mass while the enzyme changes may be due to several factors. Hypothyroidism decreased force of contraction, enhanced α-adrenergic inotropic and chronotropic responses, and decreased β-adrenergic responses in isolated atrial preparations. An interaction between cyclic AMP and cyclic GMP is suggested as a possible explanation. Diabetes induced by alloxan or streptozotocin produced a decrease in cardiac performance after 42 days which was correlated with a decrease in sarcoplasmic reticulum (SR) Ca2+ uptake. Insulin treatment reversed or prevented both SR and functional changes; other treatments were not as successful. Responses to cardiotonic drugs were altered by the diabetic state. The phosphorylase response to isoproterenol was enhanced while the inotropic response was not affected. An initial subsensitivity to carbachol at 30–100 days of diabetes subsequently converted to a supersensitivity to the muscarinic agent. Ouabain responses were decreased in atrial and papillary preparations from diabetic animals. Studies are continuing to elucidate the mechanisms involved in the altered pharmacological responses seen in hearts from diabetic animals.
Inhibition of progesterone secretion by a 3β-hydroxysteroid dehydrogenase inhibitor in late pregnant sheep
Authors: Jenkin Graham , Thorburn Geoffrey D.
Published: April 2011

The role of progesterone in the initiation of parturition in the sheep is unclear. Whether a decrease in plasma progesterone is the essential prerequisite for the initiation of parturition or whether other factors also maintain uterine quiescence until delivery is not known. The effect of withdrawal of progesterone on the initiation of parturition has been investigated by intravenous administration of trilostane, a 3β-hydroxysteroid dehydrogenase Δ5−4 isomerase inhibitor, to late pregnant sheep. Twenty-five or 100 mg trilostane caused a precipitous decrease in plasma progesterone to about 30% of preinjection levels. Progesterone remained depressed for up to 7 days after treatment. 13,14-Dihydro-15-keto-prostaglandin F2α (PGFM) became elevated between 7 and 36 h after trilostane injection but gradually returned to preinjection levels during the subsequent 36 h, at a time when plasma progesterone was still depressed. Four of 11 animals treated with 100 or 200 mg trilostane aborted prematurely at a time when plasma PGFM was maximal and plasma progesterone minimal. There were no consistent changes in plasma estradiol-17β or ovine placental lactogen concentrations after treatment with trilostane. It is suggested that a decrease in plasma progesterone will cause a transient increase in plasma PGFM concentrations which can lead to the premature initiation of parturition. In some instances the myometrium does not appear to respond to the elevated PGFM concentrations even when the estrogen:progesterone ratio is elevated by a decrease in plasma progesterone.
Dopamine production by isolated glomeruli and tubules from rat kidneys
Authors: Baines A. D. , Drangova R. , Hatcher C.
Published: April 2011

To locate the sites of dopamine (D) production in rat renal cortex, we separated glomeruli and proximal tubules by sieving or centrifugation in Percoll after collagenase digestion. After centrifugation layer I contained 60–80% glomeruli and 20–40% tubule fragments, half of which did not stain with alkaline phosphatase, layer II contained 0–5% glomeruli, 10–25% tubule fragments other than proximal tubules, and 70–85% proximal tubule fragments. Layer IV contained 85–95% proximal tubules. Gluconeogenic rates were (micromoles per hour per gram wet weight) as follows: I, 4 ± 1; II, 7 ± 2; and IV, 16 ± 1. Norepinephrine (NE) content was (picomoles per gram wet weight) I, 310 ± 30; II, 540 ± 40; IV, 195 ± 60. D content was (picomoles per gram wet weight) I, 26 ± 6; II, 46 ± 13; IV, 33 ± 7. Surgical denervation 4–6 days previously reduced the norepinephrine content of layers I and II to 35 ± 10 (p < 0.001) and of IV to 60 ± 20 (p < 0.05) and the D content of layers I and II to 13 ± 6 and 6 ± 6 pmol/g, respectively (p < 0.01); D content of layer IV was unchanged. D production from 10−7 M 3,4-dihydroxyphenylalanine (DOPA) was (nanomoles per gram per minute) I, 0.2 ± 0.03; II, 0.7 ± 0.1; IV, 1.0 ± 0.04. DOPA consumption was (nanomoles per gram per minute) I, 0.6 ± 0.1; II, 1.4 ± 0.3; and IV, 1.8 ± 0.2. Denervation did not change D production or DOPA consumption. Glomeruli without arterioles or tubules, obtained by sieving, contained no D or NE and did not produce D from DOPA. We conclude that proximal tubules produced at least five times more D from DOPA than glomeruli and distal tubules. Renal nerves did not contribute significantly to D production. We found no evidence of specific D-containing nerves associated with rat glomeruli.
Measurement and characterization of swine uterine estradiol receptors: the effects of puberty induction on estradiol receptors and corpus luteum function
Authors: Tolton Alexander D. , Grinwich Daniel L. , Belke Carl J. , Buhr Mary M.
Published: April 2011

Two types of cytoplasmic 17 β-estradiol (E2) binding activity were identified and characterized in the uteri of pregnant, cycling and prepubertal, cycle-induced (400 IU pregnant mare's serum gonadotrophin (PMS) + 200 IU human chorionic gonadotropin (hCG)) gilts. Overall, type I affinity and capacity were Kd 1.94 ± 0.51 nM and 5.410 ± 1.09 pmol/mg protein, respectively; type II apparent dissociation constant and capacity were Kd 21.34 ± 6.83 nM and 62.58 ± 15.96 pmol/mg protein, respectively. Cytoplasmic luteal E2 receptors were undetectable in all groups. Uterine E2 receptor activity was eluted from diethylaminoethyl columns by a 0.05–0.15 M KCl gradient. Sodium dodecyl sulfate polyacrylamide gel electrophoresis indicated a molecular weight of 70 400–79 000. Excluding gilts with cystic ovarian follicles (16.67%), prepubertal gilts treated with PMS + hCG versus cycling sows had lower serum progesterone on days 6 and 9–13 of the estrous cycle and lower 13,14-dihydro-15-keto prostaglandin F2α levels on days 0–9 and 13–17 of the cycle. Implants, containing 200 mg estrone inserted subcutaneously on days 12–19 after PMS + hCG treatment in gilts, had no discernible effects on these parameters. These results indicate that the diminished reproductive capacity of the gilt, in which cycle activity is induced by PMS + hCG, is likely due to decreased luteal progesterone secretion. Preliminary data also suggest that the lack of E2 receptors may contribute to the low reproductive performance in gilts with cystic ovarian follicles.
Plasma vasopressin during increases and decreases in blood volume in anaesthetized dogs
Authors: Ledsome J. R. , Wilson N. , Courneya C. A.
Published: April 2011

In chloralose-anaesthetized dogs, plasma vasopressin concentration was measured by radioimmunoassay during step changes in blood volume of 4 mL/kg over a range of blood volume from +20 to −12 mL/kg. Blood volume was both increased and decreased over this range. There was a logarithmic relationship between blood volume and plasma vasopressin concentration over the range of blood volume examined. There was also a logarithmic relationship between blood volume and mean left atrial pressure. Linear regression between the natural logarithm of plasma vasopressin concentration and mean arterial pressure, heart rate, and mean left atrial pressure gave the highest correlation coefficient (r = 0.94) between vasopressin and mean arterial pressure. The results support the hypothesis that there are sensitive mechanisms controlling the release of vasopressin in response to changes in blood volume. Observations were also made of changes in atrial pressure and activity of left atrial receptors during changes in blood volume over the same range. The results suggest that changes in atrial receptor activity are unlikely to be the major cause of the large increases in plasma vasopressin concentration associated with hypovolemia.
The regulation of steroidogenesis is different in the two types of ovine luteal cells
Authors: Hoyer P. B. , Niswender G. D.
Published: April 2011

Ovine luteal tissue contains two distinct steroidogenic cell types, small (8–20 μm) and large (>20 μm), which differ based on morphological and biochemical criteria. Unstimulated small cells secrete low levels of progesterone, respond to LH or dibutyryl cAMP (dbcAMP) with enhanced secretion of progesterone, and contain most of the receptors for LH. The unstimulated large cells, conversely, secrete high levels of progesterone, have few, if any, receptors for LH, and do not respond to LH –or dbcAMP with increased progesterone secretion. The lack of response to dbcAMP by large cells was investigated. Large cells incubated in the presence of cholesterol, ram serum, or 25-hydroxycholesterol did not demonstrate substrate limitation. Hormone-independent stimulation of adenylate cyclase by cholera toxin or forskolin resulted in increased adenylate cyclase activities (P < 0.01), cAMP accumulation (P < 0.05), and the binding of endogenous cAMP (P < 0.05) by type 1 cAMP-dependent protein kinase in both small and large cells. These treatments were accompanied by enhanced secretion of progesterone (P < 0.05) in small cells. In contrast, large cells did not respond with an increase in progesterone secretion under these conditions. These observations suggest that the high rate of secretion of progesterone in unstimulated large cells is not regulated by cAMP.
The role of plasma lipoproteins in steroidogenic response of rat luteal cells during gonadotropin-induced refractory states
Authors: Rajendran K. G. , Menon M. , Peegel H. , Hwang J. , Menon K. M. J.
Published: April 2011

Administration of human chorionic gonadotropin (hCG) to pregnant mare's serum gonadotropin – hCG primed rats results in the loss of in vitro responsiveness of the ovaries to exogenous gonadotropins for progesterone production. This state is associated with a loss of membrane receptors for hCG and a concomitant increase in lipoprotein receptors. Although lipoproteins potentiated gonadotropin response in ovaries from saline-injected rats, no stimulation was observed in hCG-desensitized ovarian cells. Examination of the time course for the loss of lipoprotein response after hCG injection revealed that injection with 50 IU of hCG results in a loss of gonadotropin response as early as 1 h after injection, but exogenous cholesterol-carrying lipoprotein fractions, LDL and HDL, were capable of stimulating progesterone production up to 4 h after hormone injection. Measurement of endogenous cholesteryl ester content showed that there was a 72% decline during this period with a concomitant increase in the basal progesterone production. One hour after hCG injection there was no stimulation of steroidogenesis by hCG in the presence or absence of exogenous lipoproteins. The refractoriness to exogenous hCG appeared only 4 h later when the hCG dose was reduced to 10 IU, whereas with 25 IU of hCG, the effect was similar to that observed using 50 IU of hCG. Such diverse steroidogenic stimuli as hCG, LH, LDL, cAMP, and cholera enterotoxin failed to stimulate progesterone synthesis in vitro in luteal cells of rats injected with 50 IU of hCG 48 h prior to sacrifice. Cellular uptake of reconstituted LDL bearing [3H]cholesterol linoleate was increased twofold in hCG-desensitized rat ovarian cells, whereas incorporation of [3H]cholesterol into progesterone from this reconstituted LDL was not stimulated by exogenous hCG. Examination of the binding of [125I]iodoLDL and [125I]iodoHDL to isolated plasma membrane from luteal cells showed that the binding of both these lipoproteins was increased twofold within 12 h after hCG injection, but returned to control levels by 72 h. From these results it is concluded that during hCG-induced loss of progesterone production in the ovary, the cells are fully capable of binding and transporting exogenously supplied plasma lipoprotein tractions. The steroidogenic lesion arises from the loss of hCG receptor mediated responsive system, but is not related to loss of the substrate pool needed for steroidogenesis.
Methoxyphenamine metabolism in rat models of human debrisoquine phenotypes
Authors: Roy S. D. , Hawes E. M. , McKay G. , Hubbard J. W. , Midha Kamal K.
Published: April 2011

The metabolism of the β2-adrenoceptor agent methoxyphenamine was investigated in rats of the Lewis and Dark Agouti strains, which are proposed models for human extensive and poor metabolizers of debrisoquine, respectively. Following oral ingestion of 20 mg kg−1 of methoxyphenamine, Dark Agouti excreted, on the average, significantly more methoxyphenamine and less (O-demethylmethoxyphenamine and 5-hydroxymethoxyphenamine in 0- to 24-h urine than Lewis. In contrast, the N-demethylation of methoxyphenamine showed no interphenotype differences between the two strains. It is possible that in rats, the form of cytochrome P-450, which controls the 4-hydroxylation of debrisoquine, may also control the O-demethylation and aromatic 5-hydroxylation of methoxyphenamine.
Very low density lipoprotein binding to cultured aortic endothelium
Authors: Desai Kappu S. , Gotlieb Avrum I. , Steiner George
Published: April 2011

Because of very low density lipoprotein's (VLDL) potential atherogenicity and the demonstration that VLDL can bind to other cells, we examined the interaction of human VLDL with cultured porcine aortic endothelium. The lipoprotein–cell interaction had many properties similar to those seen with the binding of a ligand to a cell surface receptor. It was time and temperature dependent, saturable, and reversible. Scatchard analysis of competition data suggested that there may be more than one class of binding site. The affinity of the low affinity site was similar to that for low density lipoprotein (LDL). Also, the capacity of endothelial cells to bind VLDL was similar to that for LDL, when related to apo B (i.e., particle) concentration. Not only was unlabelled VLDL able to compete for VLDL binding sites, but so was LDL and high density lipoprotein (HDL). The maximal competition either by LDL or by HDL was less than that by VLDL. The maximal competition by HDL was more than by LDL. The VLDL binding was dependent on Ca2+. It was not changed by the content of lipoprotein in the medium in which cells were grown prior to the binding studies. These observations suggest that VLDL binding to endothelial cells is similar in some respects, but not in all, to the binding of LDL. Comparison of the data with endothelial cells to previous data with adipocytes also indicated differences between the interaction of these two cell types with VLDL. It is possible that this binding process may be involved in the formation of atherogenic remnants of triglyceride-rich lipoproteins on the endothelial surface of large blood vessels.
Effect of paraventricular nucleus lesions on cardiovascular responses elicited by stimulation of the subfornical organ in the rat
Authors: Gutman Michael B. , Ciriello John , Mogenson Gordon J.
Published: April 2011

It has recently been reported that stimulation of the region of the subfornical organ (SFO) elicits an increase in arterial pressure. However, the mechanisms and forebrain neural circuitry that are involved in this cardiovascular response have not been elucidated. The present study was done in urethane-anaesthetized rats to determine whether selective activation of SFO neurons elicit cardiovascular responses and whether these responses were mediated by a pathway involving the paraventricular nucleus of the hypothalamus (PVH). Stimulation sites which required the lowest threshold current (30 μA) to elicit a pressor response and at which the largest rise in mean arterial pressure (MAP; 22 ± 2 mmHg) was elicited at a constant current intensity (150 μA) were histologically localized in the region of the SFO. Short (mean peak latency; 4 ± 2 s) and long (mean peak latency; 61 ± 8 s) latency increases in MAP were observed during and after electrical stimulation of the SFO, respectively. Cardiac slowing accompanied the short latency pressor response and cardioacceleration was observed in most (57%) of the cases to accompany the late pressor response. Microinjection of L-glutamate into the SFO consistently elicited cardiovascular responses qualitatively similar to those observed during electrical stimulation. Ganglionic blockade abolished the short latency increase in MAP and the accompanying bradycardia. However, the long latency pressor and cardioacceleratory responses were not altered by ganglionic blockade and adrenalectomy. Selective bilateral electrolytic or kainic acid lesions of the region of the PVH significantly attenuated the cardiovascular responses elicited by stimulation of the SFO. These data suggest that activation of neurons in the SFO elicit cardiovascular responses partially mediated by sympathetic outflow through a neural pathway involving the PVH.
Enhanced neuronal K+ conductance: a possible common mechanism for sedative-hypnotic drug action
Authors: Carlen P. L. , Gurevich N. , Davies M. F. , Blaxter T. J. , O'Beirne M.
Published: April 2011

It is commonly thought that central nervous system depressant drugs exert their actions through enhancement of γ-aminobutyrate (GABA)-mediated mechanisms. Recently, the cellular electrophysiological evidence from this laboratory and others suggests that both sedative hypnotics and general anaesthetics inhibit central neurons by increasing potassium conductance (GK). We have utilized the mammalian in vitro hippocampal and cerebellar slice preparations at 34 – 36 °C. Intracellular recordings from CA1, CA3, and cerebellar Purkinje cells were obtained. Low dose (sedative) concentrations of ethanol (≤20 mM), two different benzodiazepines (midazolam and clonazepam in low nanomolar concentrations), and pentobarbital (10−6 to 10−4 M) were applied by pressure ejection or were bath perfused. All drugs caused a hyperpolarization with decreased spontaneous activity, and enhanced post spike afterhyperpolarizations (AHPs). These long-lasting AHPs are presumably due to enhanced calcium-mediated GK. Increased responsiveness to focally applied GABA was only seen at higher doses (ethanol, 100 mM; midazolam, 10−7 M; pentobarbital, 10−4 M). These data suggest that the above neurodepressant drugs, when applied at sedative doses to hippocampal pyramidal cells, enhance GK and not the actions of GABA.
Perturbational actions of barbiturate analogues on erythrocyte and synaptosomal membranes
Authors: Godin David V. , McGinn Peter
Published: April 2011

The membrane perturbational actions of pentobarbital, methohexital, and phenobarbital were analyzed in terms of their effects on the incorporation of group-specific chemical probes into protein and phospholipid structural components and on the activity of various functionally distinct ATPases in erythrocyte and brain synaptosomal membranes. When compared at concentrations producing similar degrees of antihemolysis in red cells, the three analogues differed most markedly in the nature and degree of the structural and functional alterations induced in membrane proteins, with the most highly lipophilic agent, methohexital, being frequently, although not invariably, the most potent. Comparison of the effects of pentobarbital on characteristics of trinitrobenzenesulfonic acid and 5,5′-dithiobis-(2-nitrobenzoic acid) incorporation into erythrocyte membranes with results previously obtained using other anaesthetics at concentrations producing 50% antihemolysis showed that pentobarbital behaves similarly to neutral general anaesthetics but differently from cationic local anaesthetics. Our findings suggest that the membrane perturbational characteristics of barbiturates may contribute to their diverse and complex actions on excitable tissues.
Characterization studies of a rat hepatie cytosolic androgen-binding protein
Authors: Sunahara G. I. , Finlayson M. J. P. , Warren B. L. , Bellward G. D.
Published: April 2011

A rat hepatic cytosolic [3Hjmethyltrienolone (R1881) binding protein was studied under various conditions. This protein was also compared with the male-specific high capacity – low affinity estrogen-binding protein derived from the same cytosolic fraction. Analysis of the R1881 binding protein in adult (60–85 days old) male rat liver cytosol indicated the presence of a high affinity – low capacity binding site (Kd = 0.3 nM; Bmax = 5.9 fmol/mg) and a lower affinity – higher capacity component (Kd = 10.4 nM; Bmax = 131 fmol/mg). The latter component was eliminated by addition of triamcinolone or cortisol to the assay mixture. Steroid binding to the high affinity R1881 site was specific for testosterone, dihydrotestosterone, androstenedione, and mibolerone, with a moderate specificity to cyproterone acetate, flutamide hydroxide, and estradiol. Saturation studies indicated that these steroids were binding to the same or a similar high affinity component except for flutamide hydroxide which produced nonsaturable displacement. The high affinity site had no specificity for progesterone, diethylstilbestrol, or cortisol. Like the high capacity – low affinity protein, this protein was not present in the immature, adult, or 10-day ovariectomized adult female. However, unlike the high capacity – low affinity protein, it was present in low quantities in the immature male. In addition, castration of the adult for 18 h, 4 days, or 10 days or hypophysectomy for 10–17 days did not have a significant effect on the high affinity component compared with the controls. Testosterone administration to these animals did not alter this protein binding. These studies indicate that a specific, high affinity – low capacity androgen-binding protein exists in rat hepatic cytosol. Furthermore, this protein shows age and sex dependency, but its presence is not affected by altering gonadal or hypophyseal factors in the adult male.
The therapeutic use of heroin: a review of the pharmacological literature
Authors: Sawynok Jana
Published: April 2011

Heroin is currently being advocated by some as a superior therapeutic agent for use in terminal illness. However, a review of the literature on heroin presently available does not support this contention. Administered orally, heroin is approximately 1.5 times more potent than morphine in controlling chronic pain in terminal cancer patients. Its effects on mood and the incidence and nature of side effects do not differ from those of morphine except in males where poorer pain control probably accounts for the worse effect on mood. Given parenterally for acute pain, heroin is 2–4 times more potent than morphine and faster in onset of action. When the potency difference is accounted for, the pharmacological effects of heroin do not differ appreciably from those of morphine. Heroin is metabolized to 6-acetylmorphine and morphine. After oral administration of heroin, morphine but not heroin or 6-acetylmorphine is detected in blood. In this case, heroin is a prodrug for the delivery of systemic morphine. Following acute i.v. administration, heroin appears transiently in blood with a half-life of about 3 min. The half-life of heroin exposed to blood or serum in vitro is 9–22 min, indicating that organ metabolism is involved in blood clearance as well. Direct renal clearance of heroin is less than 1% of the administered dose. In animal studies, heroin and 6-acetylmorphine are both more potent and faster acting than morphine as analgesics, effects attributed to their greater lipid solubility and subsequent penetration of the blood-brain barrier. Given centrally, morphine is more potent than heroin and 6-acetylmorphine in producing analgesia. In in vitro receptor binding assays, morphine is slightly more potent than 6-acetylmorphine but considerably more potent than heroin in displacing the radioactive ligand from binding sites. The weak activity of heroin could be accounted for by breakdown to 6-acetylmorphine during the experiment. On the basis of such animal and in vitro data, it has been suggested that heroin could be viewed as a lipid soluble prodrug which determines the distribution of its active metabolites. In addition to its enhanced potency and faster onset of action compared with morphine, heroin is considerably more water soluble than morphine and this property confers a practical advantage when drugs must be injected intramuscularly. There are presently other drugs available which share this property (e.g. hydromorphone, Dilaudid®, about twice as potent and half as soluble as heroin). There is therefore little scientific justification for the support of the legalization of heroin for use in terminal illness. The issue of diversion of heroin into the illicit market is separate from and not relevant to its relative therapeutic effectiveness.
Studies of angiotensin I converting enzyme: effects of kinins, bacitracin, γ-aminobutyric and ε-aminocaproic acids, and related compounds on substrate binding and catalysis in vitro
Authors: Odya Charles E. , Wilgis Ford P.
Published: April 2011

Bradykinin and 22 of its analogs were evaluated for their abilities to inhibit the hydrolysis of [3H]hippurylglycylglycine by purified porcine kidney angiotensin I converting enzyme. The mean inhibitory concentration (IC50) for bradykinin was 1.2 ± 0.2 × 10−6 M. Except for Ile-Ser-bradykinin and [Sar4]-bradykinin, none of the kinin analogs were more potent in this regard than bradykinin. Bacitracin, γ-aminobutyric acid, ε-aminocaproic acid, and structurally related compounds were also tested. The IC50 value for bacitracin was 1.9 ± 0.4 × 10−4 M, γ-aminobutyric acid, 83.4 ± 7.2 mM, and for ε-aminocaproic acid, 7.0 ± 1.4 mM. Compounds were also evaluated for their abilities to prevent 125I-labelled [Tyr1]-kallidin binding to angiotensin I converting enzyme inhibited by EDTA. The IC50 values for bradykinin, bacitracin, γ-aminobutyric acid, and ε-aminocaproic acid were 1.6 ± 0.3 × 10−8 M, 2.6 ± 0.9 × 10−6 M, >291 mM, and 13.2 ± 3.9 mM, respectively.
Effect of length changes on sensitivity of helical artery strips to adenosine
Authors: Foley Duane H.
Published: April 2011

The relationship between length and the responses of helical strips of rabbit femoral and coronary arteries to vasoactive agents was investigated by conducting concentration–response determinations at the length for maximum active force (Lmax) and a shorter length. The mean effective dose (ED50) values for norepinephrine (NE) were smaller when femoral artery strips were set at Lmax, in comparison to the values at the shorter length. Maximal relaxation of femoral artery strips by adenosine was greater when the strips were set at Lmax. However, adenosine ED50 values were smaller at Lmax only in groups of strips in which responses at Lmax were obtained prior to those at the shorter length. Experiments with coronary artery strips did not demonstrate consistent relationships between strip length and ED50 values for acetylcholine (ACh) or adenosine. The results of experiments with artery strips from normotensive and those from one-kidney, one-clip hypertensive rabbits were similar. Thus, the femoral artery data indicate that helical artery strip preparations may exhibit length-dependent sensitivity to a vasodilator agent as well as vasoconstrictor agents under certain experimental conditions. However, the coronary artery data suggest that length may not affect sensitivity of isolated artery preparations from all vascular beds in the same manner.
Acetaminophen in the guinea pig: metabolite identification in blood, urine, and bile
Authors: Hidvegi S. , Ecobichon D. J.
Published: April 2011

The biotransformation of single acute oral doses of acetaminophen (100 mg/kg body weight) in adult male guinea pigs was studied by collecting serial blood, urine, and bile samples post-treatment and identifying and quantitating the concentrations of parent drug and excretory products by high performance liquid chromatography. The plasma half-life (βt/2) (mean ± SD) of acetaminophen was 1.87 ± 0.30 h, while that of the only metabolite detected in plasma, the glucuronide, was 2.41 ± 0.64 h. In 24-h urine samples, the predominant product was the glucuronide (90%) with a small amount of the sulphate conjugate (7.0%) and approximately 3.0% acetaminophen. In bile, the glucuronide was the major metabolite detected initially but, with time, this product decreased concomitantly with an increase in the cysteinyl conjugate. No sulphate was detected in bile but two unidentified metabolites were detected, having distinct column retention times and comprising approximately 6–10% of the total excretory products. The results demonstrated that glucuronidation is a high capacity biotransformation pathway for acetaminophen in this species, only small amounts of other conjugated products being detectable under usual circumstances.
Decreased velocity of shortening in arterial smooth muscle from older (28- to 31-week-old) spontaneously hypertensive rats
Authors: Packer C. S. , Kagan M. L. , Stephens N. L.
Published: April 2011

An increased maximum velocity of shortening (Vmax) and increased shortening ability (ΔLmax) have been reported for caudal arterial smooth muscle from 16- to 18-week-old spontaneously hypertensive rats (SHR) compared with age-matched Wistar-Kyoto (WKY) control rats. It is known that hypertension results in hypertrophy of vascular smooth muscle. It is plausible that the faster Vmax of 16- to 18-week-old SHR arterial smooth muscle may slow down with age due to hypertrophy. The force–velocity (F–V) study done previously on caudal arterial strips from 16- to 18-week-old SHR and WKY rats was repeated on preparations from 28- to 31-week-old rats. An electromagnetic muscle lever was employed in recording force–velocity data. Analysis of these data revealed that the 28- to 31-week-old SHR (n = 7) mean F–V curve was not different from the 28- to 31-week-old WKY (n = 5) mean F–V curve (p > 0.05), and the shortening ability of 28- to 31-week-old SHR arterial muscle was significantly depressed compared with 28- to 31-week-old WKY arterial muscle (p < 0.01). In conclusion, (i) although Vmax is faster in younger (16- to 18-week-old) SHR compared with age-matched WKY caudal arterial smooth muscle, SHR Vmax is not different from WKY Vmax in the older (28- to 31-week-old) rats, (ii) Shortening ability is greater in 16- to 18-week-old SHR caudal arterial strips compared with 16- to 18-week-old WKY strips, but is significantly depressed in 28- to 31-week-old SHR compared with 28- to 31-week-old WKY preparations. It can also be concluded that the decrease in SHR Vmax from once elevated speeds is not due simply to ageing, for if this were the case, the WKY Vmax should also decline with age and the relative difference between SHR and WKY F–V curves seen in younger rats should not have been obliterated when comparing the older rats.