bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of theophylline and heat-stable enterotoxin of Escherichia coli on transcellular and paracellular ion movement across isolated porcine colon
Authors: Argenzio R. A. , Whipp S. C.
Published: April 2011

The effect of theophylline and a heat-stable enterotoxin of Escherichia coli (ST) on ion transport was examined using an in vitro, short-circuited preparation of the porcine colon. Theophylline abolished net Na absorption and elicited net Cl secretion, which quantitatively accounted for the increase in short-circuit current (Isc) observed. In contrast, a maximal dose of ST elicited an Isc response about one-half that of theophylline and only partially reduced the net absorption of Na and Cl. A significant residual ion flux, consistent with HCO3 secretion, was elicited by ST and was sustained after theophylline addition. Ion replacement experiments showed that the Isc and net ion transport response to ST was abolished when either Cl or HCO3 were removed from the bathing solutions. Voltage clamp experiments to evaluate the contribution of the paracellular and transcellular transepithelial pathways from serosa to mucosa showed that approximately one-half of the total serosa-to-mucosa flux (Jsm) of both Na and Cl was through the cells. Theophylline and ST both significantly reduced transcellular.[Formula: see text], but did not affect [Formula: see text]. Theophylline, but not ST, caused an increase in paracellular conductance of both ions. These results demonstrate significant differences in the effects of ST or theophylline on both transcellular and paracellular ion movement, and suggest that ST induces a Cl-dependent HCO3 secretion which is unobserved under control or theophylline-stimulated conditions. In addition, results are consistent with the operation of a neutral NaCl secretory process which is normally masked by the greater net rates of the neutral Na and Cl absorptive mechanisms. Thus, both ST and theophylline appear to reduce or abolish the neutral processes and convert the neutral secretory process into an electrogenic one. This latter effect could be explained simply by an increase in the anion conductance of the mucosal membranes.
Chronotropic actions of bPTH-(1–34) in the right atrium of the rat
Authors: Tenner Jr. Thomas E. , Ramanadham Sasanka , Yang May C. M. , Pang Peter K. T.
Published: April 2011

Bovine parathyroid hormone and its N-terminal (1–34) peptide fragment (bPTH-(1–34)) are known to possess direct hypotensive activity in the rat. The purpose of the present study was to determine if bPTH-(1–34) possessed a direct chronotropic action as well. In vivo studies revealed that bPTH-(1–34) did produce a chronotropic effect in the rat comprising both a direct component as well as a reflex tachycardia related to its hypotensive actions. In vitro studies of isolated right atria indicated that while bPTH-(1–34) had no positive inotropic effect, it did produce significant chronotropic effects which were direct and dose-dependent. The potency of bPTH-(1–34) was found to be similar to that of isoproterenol, however, it was only one-third as effective as isoproterenol in maximally increasing atrial rate. A slight but significant increase in atrial cyclic AMP was generated prior to the chronotropic actions of bPTH-(1–34).
A fluorometric study of the possible role of calcium in synchronizing substrate metabolism with contractile performance in rabbit papillary muscle
Authors: Snow T. Russell
Published: April 2011

Based on the hypothesis that Ca2+ plays an important role in coordinating the rates of substrate catabolism with those of mechanical power utilization, experiments were designed to answer two questions. First, to what extent do the separate Ca2+ pools (e.g., Na+–Ca2+ exchange, sarcoplasmic reticulum (SR)) contribute to this messenger Ca2+ pool; and second, are the three catabolic pathways (glycolysis, β-oxidation, and tricarboxylic acid (TCA)) equally sensitive to regulation by Ca2+. To answer these questions, an assessment of the dynamic relation between metabolism and mechanical performance in rabbit papillary muscle was employed which used the slope (coupling coefficient: Mc) of the linear relation between the maximum oxidation of NADH accompanying an increase in contractile activity and the product of the peak isometric tension times the stimulation rate. Except for ketones, changes in superfusate [Ca2+] significantly decreased the coupling coefficient, suggesting a greater sensitivity of metabolism to mechanical requirement. Studies using ouabain indicated that this response was not attributable to Na+–Ca2+ exchange. Experiments with theophylline yielded two important results. First, the redox response of the respiratory chain can be significantly influenced by the available substrate. Second, the glycogenoltic complex associated with the SR may play an important role in ensuring adequate supplies of reducing equivalents and therefore may be a prime site for coordinating metabolism with mechanical performance. The data also suggest that glycolysis and β-oxidation are more sensitive to regulation by messenger Ca24 than the TCA cycle.
Natriuretic effect of atrial extract on isolated perfused rat kidney
Authors: Baines A. D. , DeBold A. J. , Sonnenberg H.
Published: April 2011

To examine the mechanisms underlying the natriuretic action of a partially purified extract of rat atria (AE) we injected the equivalent of one atrium into isolated perfused rat kidneys. Some kidneys received an infusion of angiotensin II at 0.5 ng/min throughout the experiment. In the absence of angiotensin AE had a variable effect on renal vascular resistance (RVR) but, in the presence of angiotensin II, AE consistently decreased RVR by 3% for 5 min followed by a slight increase. Inulin clearance and filtration fraction increased slightly but significantly. AE increased sodium, chloride, phosphate, and free water clearance but not potassium excretion. Ventricular extract had no effect on any of these variables. Furosemide (50–250 μg) increased sodium, chloride, and potassium but not phosphate or free water excretion. AE did not alter dopamine or norepinephrine excretion. We conclude that AE increases the glomerular filtration rate (GFR) and inhibits tubular reabsorption by mechanisms which differ, at least in part, from those affected by furosemide.
Secretory bursts of growth hormone secretion in the dog may be initiated by somatostatin withdrawal
Authors: Cowan John S. , Gaul Penney , Moor Bruce C. , Kraicer Jacob
Published: April 2011

In 28 6-h experiments on 10 conscious resting trained male dogs, plasma growth hormone (GH) was determined at 5-min intervals by radioimmunoassay. For all experiments, the basal GH concentration in plasma was 0.80 ± 0.06 ng mL−1. In each experiment, 1–3 secretory bursts of GH occurred, raising plasma GH 2.4 to 15.3 times basal concentrations (for all 43 bursts, 6.6 ± 0.4 times the basal value). Metabolic clearance rates (MCR) and apparent distribution volumes (V) were determined, using stepwise infusions of canine GH. The MCR (3.99 ± 0.30 mL kg−1 min−1) and V (57.9 ± 5.5 mL kg−1) were used to transform the GH concentration versus time data into GH secretion rates, using a single compartment approach. Basal GH secretion rates for all 28 experiments were 3.12 ± 0.24 ng kg−1 min−1. The secretory bursts yield peak GH secretion rates of 9.4 ± 0.8 times basal secretion and these steep-sloped bursts last 25.1 ± 1.2 min. Six-hour infusions of 0.15 μg kg−1 min−1 of somatostatin (SRIF) abolished all secretory bursts but did not lower basal secretion rates. In five of seven SRIF infusion experiments in which samples were taken after the infusion ceased a secretory burst was seen in the hour following cessation of infusion (in four cases within 10 min). These secretory bursts lasted 23.0 ± 2.9 min and were similar to those seen in control experiments. Infusions of SRIF at 0.05 μg kg−1 min−1 had no effect. These results imply that during basal GH secretion, a surfeit of SRIF impinges on the somatotrophs, as extra SRIF does not further lower basal secretion. However, during secretory bursts, very little SRIF must be present, as exogenous SRIF blocks these bursts. The bursts are similar in duration to overshoots provoked in perifused dispersed rat somatotrophs by removal of an SRIF signal. It seems likely that their cause in vivo is similar. (All values are means ± SEM.)
Influence of bran on bioavailability of chloramphenicol administered orally to pigs
Authors: Buéno L. , Fioramonti J. , Alvinerie M. , Bardon T.
Published: April 2011

The present study was undertaken to determine if bran added to a fiber-free diet (milk) would modify the absorption of orally administered chloramphenicol (cmp) compared with that observed on a standard concentrates diet in pig. The plasma chloramphenicol level was maximal (0.47 ± 0.26 μg/mL), 3.5 h after a meal of concentrates containing 8 g of chloramphenicol palmitate; this highest concentration represented only 30% of that observed 12 h after a meal of substituted milk and 14% of the maximal plasma concentration of chloramphenicol detected 14 h after a milk meal when supplemented with bran (100 g). Over 24 h, the plasma availability of chloramphenicol with the three tested diets represented, respectively, 11.4% (concentrates), 17.2% (milk), and 74.1% (milk + bran) of that obtained for intravenous administration; similar oral–caecal transit times were observed for these three diets. It was concluded that the presence of bran in the regimen strongly increases the intestinal absorption of chloramphenicol palmitate, with the lowest rate of absorption on standard concentrates, and it is tempting to speculate that this increase is due to a more rapid intestinal hydrolysis by an increased pancreatic lipase activity on bran.
Diet-induced thermogenesis with relation to training state in female subjects
Authors: LeBlanc Jacques , Mercier Pauline , Samson Pierre
Published: April 2011

The purpose of this study was to investigate the effect of exercise training on meal-induced thermogenesis in 30 female subjects with an average age of 26 years, an average weight of 53.5 kg, and an average height of 162.4 cm. Three groups of 10 subjects were formed with an average maximum aerobic capacity [Formula: see text] of 57.5 mL∙kg−1∙min−1 and a percent body fat of 17.5% for group 1 (competition athletes), of 49.9 mL∙kg−1∙min−1 and 21.2% for group 2 (moderately active), and 38.9 mL∙kg−1∙min−1 and 22.2% for group 3 (sedentary subjects). Oxygen uptake [Formula: see text], respiratory quotient (R), and heart rate (HR) were measured at intervals for 45 min before and 120 min after a standard meal containing 800 kCal (1 kCal = 4.184 kJ). The increases in [Formula: see text] produced by the meal were significantly smaller (P < 0.05) in group 1 than in group 3. Following the meal, R was significantly increased (P < 0.01) from its initial value in the three groups, but it remained significantly lower in the well-trained subjects than in the nontrained. HR, which was initially higher (P < 0.01) in group 3, was slightly increased after the meal, but the response was the same for all groups. These results show a diminished meal-induced thermogenesis in exercise-trained female subjects associated with reduced carbohydrate oxidation.
Evidence for angiotensin II receptors in the urinary bladder of the rabbit
Authors: Anderson Gordon F. , Barraco Robin A. , Normile Howard J. , Rosen Todd N.
Published: April 2011

Dose–response (DR) curves for several angiotensin analogs were examined on isolated rabbit detrusor strips with washout and rest between each addition. The order of potency was [Val5]-angiotensin II > [IIe5]-angiotensin II > [IIe5]-angiotensin I > [Val4]-angiotensin III. Repeated cumulative DR to [Val5]-AII resulted in a gradual increase in potency and intrinsic activity for four DR. However, the maximum force generated occurred at lower agonist concentrations and was less than that of the single methods, suggesting tachyphylaxis. Atropine (1.0 μM) shifted the cumulative DR curve downward, suggesting some cholinergic component possibly involving a presynaptic site of action. The magnitude of field-stimulated atropine-resistant contractions was reduced by both 1.0 and 10 μM saralasin as well as 10 μM naloxone. Tissue binding with 125I-labelled angiotensin II on isolated detrusor smooth muscle membranes indicated specific binding saturation occurred at 14.3 fmol/mg with a KD of 0.72 nM in EDTA–Tris buffered saline. Thus our results show that angiotensin II (AII) receptors can be demonstrated in detrusor muscle by ligand binding experiments on ceil membranes and that saralasin and naloxone partially block atropine-resistant contractions. However, it seems unlikely that AII serves as a neurotransmitter because of the delay in onset of action of exogenous AII in isolated bath experiments and the apparent inability of saralasin to totally abolish the atropine-resistant field-stimulated preparation. If AII serves a role in neurotransmission it most probably is as a neuromodulator.
Morphine diesters. I. Synthesis and action on guinea pig ileum
Authors: Owen J. A. , Elliott J. , Jhamandas K. , Nakatsu K.
Published: April 2011

3,6-Dipropanoylmorphine (DPM), 3,6-dibutanoylmorphine (DBM), and 3,6-dihexanoylmorphine (DHM) were prepared as prospective long-acting narcotic analgesics. The purity and structure of these compounds were authenticated by high pressure liquid chromatography and direct probe mass spectrometry. In aqueous solution the stability of the HCl salts of these compounds decreased with increasing alkyl chain length such that DHM underwent rapid hydrolysis to 6-monohexanoylmorphine (MHM). A comparison of DPM, DBM, and MHM with morphine (MO) and 3,6-diacetylmorphine (DAM, heroin) in the electrically stimulated guinea pig ileum myenteric plexus longitudinal muscle strip preparation (GUPIL) revealed similar potencies and efficacies for all compounds, but marked differences in the onset of drug action (MO > DAM > MHM > DPM > DBM, faster to slower). In a periodically washed GUPIL preparation DBM and MHM were five times longer acting than MO, DAM or DPM.
Morphine diesters. II. Blood metabolism and analgesic activity in the rat
Authors: Owen J. A. , Nakatsu K.
Published: April 2011

The kinetics of hydrolysis of dipropanoylmorphine (DPM) and dibutanoylmorphine (DBM) in human blood fractions and for diacetylmorphine (DAM) and DBM in rat blood fractions were investigated. In each case the hydrolysis of morphine diesters terminated with the production of the corresponding 6-monoester derivative. Generally, decreases in Km and Vmax were observed for the plasma, red blood cell (RBC) cytosol, and RBC membrane esterases responsible for morphine diester hydrolysis as the alkyl chain length of the ester moiety increased. This resulted in an overall decrease in the rate of hydrolysis of morphine diesters by human or rat blood with longer chain homologs of DAM. The analgesic potency and duration of morphine, DAM, and DBM were assessed at various i.v. dosages in the rat by means of the tail-flick latency test. A comparison of equianalgesic doses of morphine, DAM, and DBM indicated that DAM and DBM were 11.5 and 6 times as potent and 0.8 and 1.2 times as long acting, respectively, as morphine.
Receptors and receptor modulation in cultured chromaffin cells
Authors: Livett B. G. , Boksa P.
Published: April 2011

The colocalization of acetylcholine (ACh) and neuropeptides (e.g., substance P and enkephalins) in the splanchnic nerve terminals suggests that these compounds might interact to modulate adrenal catecholamine release. Use has been made of primary monolayer and suspension cultures of bovine adrenal chromaffin cells to investigate postsynaptic receptor interactions between acetylcholine and a number of neuropeptides endogenous to the adrenal medulla and splanchnic nerve. The cells have both nicotinic and muscarinic acetylcholine receptors, but only the nicotinic receptors stimulate catecholamine release. Substance P, somatostatin, and the enkephalins all produced an inhibition of the Ach-evoked secretion of catecholamines, but their potency ranged over 100-fold. Substance P was the most potent with a mean inhibitory concentration (IC50) of 10−6 M and Leu-enkephalin the least potent with an IC50 > 10−4 M. These pharmacological effects were monitored conveniently by measuring the release of [3H] norepinephrine preloaded into the cells or alternatively, "on-line" by measuring ATP released into an incubation medium containing luciferin and firefly tail extract (luciferase). Of interest, the endogenous enkephalin heptapeptide (Met-enkephalin Arg6-Phe7) and "big" Met-enkephalin (BAM-22P) were some 100-fold more effective than Leu- or Met-enkephalin at inhibiting the nicotinic secretion of catecholamines, suggesting that a unique opiate receptor may be involved. Substance P had two distinct actions on the nicotinic response: (1) substance P inhibited acetylcholine-induced release of catecholamines; and (2) substance P protected against acetylcholine-induced desensitization of catecholamine release. With regard to (1), substance P inhibited the secretion of catecholamines and ATP evoked by acetylcholine or nicotine but not that evoked by K+ or veratridine, nor did substance P by itself affect secretion. Substance P appeared to interact with a regulatory site on the acetylcholine receptor – ionophore complex. Substance P receptors on chromaffin cells have similar structural requirements for activation as do substance P receptors in other substance P responsive tissues. With regard to (2), substance P (> 5 × 10−6 M) completely protected against desensitization of catecholamine release produced by acetylcholine (> 10−4 M) or nicotine (> 2.5 × 10−6 M) with no effect on K+-induced desensitization. Substance P protected against both a Ca2+-dependent and a Ca2+-independent component of desensitization and this protection against desensitization was a result of facilitation of catecholamine release rather than inhibition of catecholamine reuptake. These actions of substance P may help to ensure a prolonged adrenal catecholamine output during stress.
Regional myocardial blood flow during pericardial tamponade
Authors: Taichman Gerald C. , Byrne Paul , Forester George V. , Keon Wilbert J.
Published: April 2011

The relative changes in myocardial blood flows within different parts of the heart were measured in anaesthetized thoracotomized dogs during and following effusive pericardial tamponade. Blood flows measured in a group of animals bled to the same arterial hypotensive levels served as experimental controls. The results demonstrate that regional myocardial blood flows to all areas were severely reduced during tamponade. Regional differences in the relative responses were evident; right and left atrial flows decreased more than left ventricular or septal flows which in turn decreased more than right ventricular flow. Significant changes in transmural flow distributions were seen as well; on a relative basis, left and right ventricular endocardial flows decreased more than epicardial and the flow within the left side of the septal wall decreased more than the right. Although decreases in aortic pressure and ventricular volumes can account for some of these changes in flow seen in tamponade, alterations in extravascular compression appear to further reduce the myocardial perfusion and may be responsible for the differences in regional responses. In further experiments when the pericardial cavity was drained following 2 h of tamponade, a hyperemic response was seen throughout the heart indicating that the myocardial flow during tamponade may-have been insufficient to meet the cardiac demands. In conclusion tamponade appears to result in a disproportionate decrease in myocardial blood flow to various parts of the heart which cannot be explained on the basis of a decrease in blood pressure or a reduction in ventricular volume.
Quinidine and propranolol binding to very low and low density lipoproteins of human plasma
Authors: Trung A. Ho Ngoc-Ta , Sirois G.
Published: April 2011

The interaction of quinidine (Q) and propranolol (P) with human very low density lipoproteins (VLDL) and low density lipoproteins (LDL) was determined by ultrafiltration in phosphate buffer (pH 7.4) for Q and in phosphate and Tris buffers (pH 7.4–7.5) for P, respectively. The Scatchard plots of Q are curved and were best described by a model assuming two independent classes of binding sites on lipoproteins. When working with P, the Scatchard plots were also nonlinear, but positive cooperativity was observed for the VLDL fraction in phosphate buffer and apparently also for the LDL fraction in Tris buffer. These nonlinear curves were described by the model used for Q, excluding any data falling in the cooperating region. The binding parameters, primary (K1) and secondary (K2) affinity constants and the number of sites in each class of independent binding sites, were generated by a computer program. The results of this in vitro study suggest that drug binding (and possibly distribution) to lipoproteins may be affected by the nature and concentration of some ions present in serum.
Relationship of electrical slow wave and spike bursts in the dog jejunum in vivo
Authors: Mendel C. , Pousse A. , Grenier J. F.
Published: April 2011

The temporal relationship between the slow wave and the spike bursts was studied in the fasted and the fed states in conscious dogs implanted with serosal electrodes on the jejunum. A fully automatic computerized method processed more than 225 h of recording. For each slow wave cycle that contained a spike burst, the program computed the cycle duration and the times elapsed from the beginning of the cycle to the onset and to the end of the burst. In the fasted state as well as after feeding, the spike bursts began and ended at any time within the segment of the slow wave cycle on which spike activity occurred. These results indicate that in vivo in the dog jejunum, the temporal relationship of the slow wave and spike bursts is not fixed. They suggest that the slow wave allows the spikes to occur during limited time intervals, but does not determine their precise location and duration within these intervals. Furthermore, differences existed in the patterns of the slow wave and in its relationship with spike activity (period, location, and duration of the segment on which the spike bursts occurred) between the various phases of the migrating myoelectric complex in the fasted state and the fed state.
Chronotropic, inotropic, and coronary artery blood flow responses to stimulation of specific canine sympathetic nerves and ganglia
Authors: Janes R. D. , Johnstone D. E. , Armour J. A.
Published: April 2011

Electrical stimulation of the major sympathetic cardiac nerves and ganglia in chloralose-anesthetized, open-chest dogs elicited specific changes in heart rate, coronary blood flow, regional intramyocardial pressure, or intraventricular pressure. The effects produced by stimulation of a cardiac nerve were similar to, but never greater than those produced by stimulation of the ipsilateral stellate ganglion. Coronary blood flow was increased when neural stimulation increased intramyocardial pressure. In contrast, coronary blood flow was not altered significantly when neural stimulation induced tachycardia without increasing intramyocardial pressure. It is concluded that in the intact heart, electrical stimulation of the sympathetic cardiac nerves or ganglia increases coronary blood flow by augmenting intramyocardial pressure, not chronotropism.
Interaction of prolactin (PRL) binding sites with PRL receptor antibodies in rat liver cells in suspension culture: effect of inhibitors of cellular functions
Authors: Ferland Louis H. , Rosa Alzira A. M. , Kelly Paul A.
Published: April 2011

We have recently demonstrated that prolactin is able to maintain the level of its receptors in cultured rat hepatocytes. This effect could be modulated by various inhibitors of cellular functions. We report here that an antibody developed against a partially purified prolactin receptor preparation can mimic this effect of the hormone (although to a lesser extent) and that drugs can modulate it in a similar manner. In particular, cycloheximide (50 μg/mL), which reduced basal receptor levels by approximately 40%, totally reversed the maintenance induced by the antireceptor serum. Actinomycin D (10 μg/mL), another protein synthesis inhibitor (at the transcriptional level), had no effect of basal receptor concentration, but counteracted by about one-half the antiserum-induced maintenance. This effect of actinomycin D is much clearer here than the effect previously observed on prolactin-induced receptor levels in rat liver cells in culture. The effect of dinitrophenol (1 mM) on basal levels was of limited amplitude but maintenance was again partly reversed by this drug. In accordance with previous results obtained with prolactin, chloroquine (100 μM) and colchicine (1 μM) failed to alter prolactin binding either in the absence or presence of 5% antireceptor serum. The effect of the antiserum indicates that prolactin itself is not required beyond the membrane for its effect on receptor regulation to be attained. These results also confirm our previous results with prolactin maintenance of prolactin receptor levels in rat liver cells in culture, that the mechanism of receptor maintenance appears to be due in part to a stimulation of receptor synthesis but to be independent of the internalization or of lysosomal degradation.
The release of slow-reacting substance of anaphylaxis from guinea pig lung: effects of calcium antagonists
Authors: Damiano Melissa A. , Barbieri Edward J.
Published: April 2011

The effects of three calcium antagonists, verapamil, lanthanum, and 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) were studied on the release of slow-reacting substance of anaphylaxis (SRS-A) from ovalbumin-sensitized chopped guinea pig lung parenchyma in calcium-containing and calcium-free media. The SRS-A levels (mean ± SEM) obtained from tissues incubated in normal and calcium-free Krebs–bicarbonate buffer were 51 ± 8 (N = 19) and 21 ± 4 (N = 14) U/mL, respectively. TMB-8 (0.1–10 μM) a reported intracellular calcium antagonist, reduced antigen-stimulated SRS-A release from lung tissue incubated in calcium-containing, but not calcium-free, medium; A23187-induced SRS-A release from normal guinea pig lung was not significantly altered by TMB-8 at concentrations up to 10 μM. Verapamil and lanthanum consistently reduced SRS-A release only at high concentrations (100 μM and 1 mM, respectively). The quantities of SRS-A released from lung tissue incubated in the presence of verapamil in normal medium were similar to those obtained in calcium-free medium. Tissues incubated in the presence of potassium chloride (60 and 100 mM) did not release significant quantities of SRS-A, and release which did occur was not blocked by verapamil, suggesting that antigen-induced SRS-A release is not dependent on membrane depolarization and that verapamil was not exerting inhibition via blockade of voltage-dependent calcium channels. These data suggest that although intracellular calcium is important for the regulation of SRS-A secretion from guinea pig lung tissue, extracellular calcium is necessary for optimal release of SRS-A.
Chlormadinone acetate, a progesterone derivative that binds to the digitalis receptor, inhibits the sodium pump in the isolated rat diaphragm
Authors: Bihler Ivan , LaBella Frank S. , Sawh P. C.
Published: April 2011

Rb+ uptake, intracellular Na+ and K+ levels, and the tissue–medium distribution of the nonmetabolized glucose analog, 3-O-methyl-D-glucose (3-MG) were measured in rat diaphragms incubated with chiormadinone acetate, 6-chloro-4,6-pregnadien-17-ol-3,20-dione 17-acetate (CMA), in the presence and absence of ouabain. CMA in concentrations of 5 × 10−7 M or higher significantly depressed 86Rb uptake, and promoted an increase in internal Na+ and a decrease in internal K+, indicating inhibition of the sodium pump. Sugar transport in resting muscle parallels the changes in internal Na+ levels and is an additional indicator of sodium pump activity. Equilibration of 3-MG between tissue and medium was accelerated by CMA, in parallel to the rise in internal Na+ level. Effects of CMA on Na+ levels and sugar transport, but not on Rb+ uptake, were additive to those of various concentrations of ouabain, suggesting interaction with sites not affected by ouabain. These results on diaphragm muscle confirm our previous studies on isolated cardiac muscle preparations showing that CMA, added to the aqueous bathing medium, inhibits the sodium pump in intact muscle tissues.
Force–velocity constants in smooth muscle: afterloaded isotonic and quick-release methods
Authors: Stephens N. L.
Published: April 2011

In using pharmacologic stimuli, force–velocity (FV) curves are usually obtained by the method of quick release (QR) and redevelopment of shortening at peak tetanic tension; the advantage of the method being that the active state is at maximum. However, the QR may itself reduce the intensity of the active state and result in reduced values of FV constants. We tested this by delineating FV curves in canine tracheal smooth muscle using both conventional afterloaded isotonic contractions (ALI), and redevelopment of shortening after QR methods. For both these studies a supramaximal tetanizing electrical stimulus was used. The analysis of 11 experiments revealed that the latter method resulted in statistically significant reductions of all FV constants except for Po (maximum isometric tetanic tension). The means and standard errors for the sets of constants for the ALI and QR, respectively, are as follows: Vmax (maximum velocity of shortening) = 0.275 lo (optimal muscle length)/s ± 0.024 (SE), and 0.216 lo/s + 0.023; a (hyperbolic constant with units of force) = 294 g/cm2 ± 35 and 236 g/cm2 ± 32; b (hyperbolic constant with units of velocity) = 0.059 lo ± 0.004 and 0.039 lo/s ± 0.005; a/Po = 0.214 ± 0.028 and 0.182 ± 0.026; and Po = 1.362 kg/cm2 ± 0.106 and 1.294 kg/cm2 ± 0.097. These data clearly show that the quick-release method for measuring force–velocity relationships in canine smooth muscle results in significant underestimates of muscle shortening properties.
The influence of chronic experimental diabetes on contractile responses of rat isolated blood vessels
Authors: MacLeod K. M. , McNeill J. H.
Published: April 2011

The influence of experimental diabetes induced by streptozotocin on responses of rat isolated aortae and portal veins to noradrenaline, 5-hydroxytryptamine, and KCl was examined 7, 100, 180, and 360 days after the onset of diabetes. No significant changes in reactivity were seen 7 days after the onset of diabetes. After 100 days aortae from diabetic rats were supersensitive (defined as a significant increase in the pD2 value) to noradrenaline. However, 180 days after the onset of diabetes, the sensitivity of diabetic aortae to noradrenaline was not significantly different from control, while the responsiveness (defined as the maximum developed tension ÷ cross-sectional area of aorta) to 5-hydroxytryptamine was reduced. A generalized increase in both the sensitivity and responsiveness of diabetic aortae to all three agonists was observed after 360 days of diabetes. In contrast, no changes in either the sensitivity or the responsiveness of portal veins to noradrenaline, 5-hydroxytryptamine, or KCl could be detected at any time after the onset of diabetes. These results indicate that changes in vascular reactivity can be detected with increasing duration of experimental diabetes. However, these changes do not follow a consistent pattern and are not seen in all parts of the vasculature.
Comparison of somatostatin-28 and somatostatin-14 clearance by the perfused rat liver
Authors: Seno M. , Seino Y. , Takemura Y. , Nishi S. , Ishida H. , Kitano N. , Imura H. , Taminato T. , Matsukura S.
Published: April 2011

The hepatic clearances of somatostatin (SS)-28 and SS-14 by the perfused rat liver were compared, using a recirculating, plasma-free, erythrocyte-containing perfusion system. The disappearance rate constant, half time, clearance, and hepatic extraction ratio when 1.2 nM SS-28 was added to the perfusate were 0.0221 ± 0.0051 min−1, 36.6 ± 7.6 min, 0.34 ± 0.08 mL/min, and 17.2 ± 3.9%, respectively. The corresponding values obtained when SS-14 was added to the perfusate were 0.0405 ± 0.0022 min−1, 17.3 ± 1.0 min, 0.71 ± 0.05 mL/min, and 35.4 ± 2.6%, respectively. The differences between the SS-28 and SS-14 indices were all statistically significant. In addition, the perfusates with SS-28 added were eluted on Sephadex G-25 fine columns and somatostatinlike immunoreactivity (SLI) was determined. No SS-14 was found in perfusate containing SS-28 at both 5 and 30 min after the beginning of the perfusion. To investigate whether or not the liver plays an important role in the clearance of SS-28 or the conversion of SS-28 to SS-14 in vivo, the plasma disappearance of 2 μg SS-28 was compared in the whole rat and the functionally hepatectomized model. The half time of plasma SS-28 was 1.43 ± 0.12 min in the whole rat, significantly shorter than the 2.20 ± 0.14 min in the hepatectomized model. Gel filtration of plasma extract samples at 0.5 min after the SS-28 injection showed two major peaks of SLI: a first peak corresponding to SS-28 and a second peak coeluted in the position of SS-14 in both the whole rat and the hepatectomized model. At 4 min after the SS-28 injection, the first peak disappeared and only a small second peak was observed. These results suggest that SS-28 is cleared by the rat liver in vivo and in vitro and that it is cleared more slowly than SS-14. Furthermore, we find that little, if any, conversion of SS-28 to SS-14 occurs in the liver.
Effect of food restriction on cold adaptability of rats
Authors: Kuroshima Akihiro , Yahata Takehiro
Published: April 2011

To determine the role of the nutritional state in nonshivering thermogenesis during cold adaptation, cold adaptability was compared between cold-adapted (5 °C for 4–5 weeks) rats fed ad libitum and cold-adapted rats pair fed with warm controls having the same food intake. Cold-adapted pair-fed rats suffered a significant loss in body weight during cold exposure. However, brown adipose tissue (BAT) in both cold-adapted ad libitum fed and cold-adapted pair-fed rats was enlarged to the same extent as compared with that in control rats. Fat-free dry matter in BAT also increased in cold-adapted ad libitum fed and cold-adapted pair-fed rats to the same extent. Cold tolerance as assessed by the change in the colonic temperature at −5 °C was improved relative to control rats and was the same for cold-adapted ad libitum fed and cold-adapted pair-fed rats. Nonshivering thermogenesis as estimated by the noradrenaline-induced increase in oxygen consumption was significantly greater in the cold-exposed rats and there was no significant difference between cold-adapted ad libitum fed and cold-adapted pair-fed rats. These results suggest that an improved cold tolerance by means of nonshivering thermogenesis in brown adipose tissue is closely related to the low temperature itself but not the increased food intake which occurred in the cold.
Estimates of Na+–K+ pumping in intact canine iliac arteries
Authors: Rangachari P. K.
Published: April 2011

Estimates of Na+ pumping capacity were made using Na+-loaded canine iliac arteries. Ouabain-sensitive uptake of 204Tl or 86Rb was used to measure near-maximal pump rates and [3H]ouabain binding to measure the number of pump sites. Compared with Rb+, Tl+ had the higher affinity for the pump and showed better signal-to-noise characteristics. Maximal uptakes were 0.545 μmol∙g−1∙min−1 for Rb+ and 0.40 μmol∙g−1∙min−1 for Tl+ Specific ouabain binding (Kd: 28.62 ± 0.58 nM) was inhibited by external K+, Tl+, and Rb+ and a maximal binding of 51.6 pmol/g wet weight translated into 3.2 × 1013 sites per gram wet weight. Using these values, the maximal values of K+ transported per pump site per minute lie between 7752 and 10562. If each activation of the pump moves 2K+, the turnover rates could lie between 3876 and 5281 per minute.
Effects of minoxidil on blood pressure and cardiac hypertrophy in two-kidney, one-clip hypertensive rats
Authors: FenJe Paul , Leenen Frans H. H.
Published: April 2011

Rats made severely hypertensive by renal arterial clipping were treated for 24 days with the arterial vasodilator minoxidil (40, 80, and 120 mg/L drinking water). In all three treated groups of animals, blood pressure initially decreased markedly and to a similar extent. Subsequently partial tolerance developed to the antihypertensive effects of minoxidil. All three doses induced hypertrophy of the right ventricle to a similar degree. In contrast, the hypertension-induced hypertrophy of the left ventricle was further increased in a dose-dependent fashion by minoxidil.
Functional interactions between organic calcium channel antagonists in smooth muscle
Authors: Yousif F. , Triggle D. J.
Published: April 2011

The Ca2+ channel antagonists D-600, diltiazem, and nifedipine are competitive antagonists of Ca2+ responses in K+ -depolarized guinea pig taenia coli and rat mesenteric artery preparations. pA2 values for D-600, diltiazem, and nifedipine in taenia coli were 8.28, 7.44, and 9.27, respectively and in mesenteric artery, 9.6, 7.83, and 10.4, respectively. The combination of nifedipine plus diltiazem gave in both tissues antagonism greater than that calculated on the basis of additivity. This suggests, consistent with published 3H-Sabelled radioligand binding data, that diltiazem and nifedipine interact at distinct sites. However, the combination nifedipine plus D-600 yielded antagonism consistent with additivity of response.
Mechanics of caudal artery relaxation in control and hypertensive rats
Authors: Packer C. S. , Stephens N. L.
Published: April 2011

Alterations of smooth muscle function can just as easily stem from mechanical alterations in its ability to relax as from alteration in contraction. Since a failure of arterial smooth muscle to relax may contribute to the development of hypertension, we felt it necessary to study the relaxation process in greater depth. The effect of load on the time course of relaxation of rat caudal artery smooth muscle was analyzed either by comparing afterloaded contractions against various loads or by imposing abrupt alterations in load. Unlike mammalian striated muscles in which relaxation was reported sensitive to loading conditions, relaxation in the smooth muscle of the rat caudal artery (n = 17) was found to be largely independent of loading conditions. This type of relaxation has been termed "inactivation-dependent" relaxation; it is typical of muscle tissue in which the calcium sequestering apparatus is poorly developed. Our results suggest that calcium resequestration, or some biochemical process downstream to it, is the rate-limiting step during relaxation in arterial smooth muscle and that this is not qualitatively different for hypertensive arterial smooth muscle. These analytic techniques were used in the study of relaxation of hypertensive vessels. Quantitative analysis of the relaxation curves showed that both isometric and isotonic relaxation time was prolonged in hypertensive arterial smooth muscle. Prolonged isotonic relaxation indicates that hypertensive arteries remain narrowed for prolonged periods compared with normotensive vessels. Such narrowed vessels may be a factor in the increased total peripheral resistance seen in genetic hypertension.
Prolactin as a luteotrophin
Authors: Murphy Bruce D. , Rajkumar Kadaba
Published: April 2011

This review summarizes evidence suggesting a direct luteotrophic role for the hypophyseal hormone prolactin (PRL). This direct role consists of the capability to stimulate progesterone synthesis in vitro, the capability to maintain the membrane fluidity and receptors for luteinizing hormone and the capability to import substrate for progesterone synthesis. The time required for PRL-induced luteotrophic events is in the order of hours and sometimes days, and it appears that the effects are not associated with acute intracellular changes. The relatively slow responses and the stimulation of specific protein synthesis by PRL in target tissues other than the ovary suggest that PRL may function primarily through activation of the genome. PRL may induce the synthesis of specific luteal proteins, including enzymes for the regulation of intracellular substrate pools, membrane receptors for LH, or receptor proteins for lipoproteins, a major extracellular source of substrate.
Acetylcholine supersensitivity in the rat heart produced by neonatal sympathectomy
Authors: Ishii Kunio , Ishii Norie , Shigenobu Koki , Kasuya Yutaka
Published: April 2011

Effects of neonatal sympathectomy with antiserum to nerve growth factor or 6-hydroxydopamine on the acetylcholine sensitivity of the rat left atria were investigated. Sensitivities to acetylcholine of atria from immunologically and chemically sympathectomized rats were much higher than that of control at 4 weeks of age. These results suggest possible involvement of the sympathetic nervous system in regulation of cardiac cholinergic sensitivity.
The effects of small cardioactive peptide B on the isolated heart and gill of Aplysia californica
Authors: Cawthorpe D. R. L. , Rosenberg J. , Colmers W. F. , Lukowiak K. , Drummond G. I.
Published: April 2011

Effects of small cardioactive peptide B on the physiology of the isolated heart and gill preparations from the mollusc Aplysia californica were examined. In addition, the effects of small cardioactive peptide B and FMRFamide (Phe-Met-Arg-Phe-NH2) on adenylate cyclase activity were compared in particulate fractions of heart and gill tissues, respectively. Small cardioactive peptide B was found to exert dose-dependent, reversible changes in cardiac activity when perfused through the isolated heart. The EC50 values effecting changes in heart rate and force of contraction were 3 × 10−11 and 3 × 10−10 M, respectively; minimum concentrations found to effect changes in heart rate and force of contraction were normally 10−15 and 10−12 M, respectively. However, some winter hearts demonstrated threshold sensitivity to small cardioactive peptide B at concentrations as low as 10−17 M. When perfused through the isolated gill, small cardioactive peptide B was found to suppress the gill withdrawal response amplitude with a threshold concentration of 10−14 M and an EC50 value of 3 × 10−11 M. Suppression of the gill withdrawal response amplitude by small cardioactive peptide B was found to be dose dependent and reversible up to a concentration of 10−9 M. At higher concentrations, the suppression tended to persist irreversibly. Small cardioactive peptide B stimulated adenylate cyclase activity in particulate fractions of both heart and gill tissues with an EC50 of 0.1 and 1.0 μM, respectively. In the heart, adenylate cyclase activity increased by 32-fold at a concentration of 5 × 10−6 M small cardioactive peptide B. FMRFamide stimulated comparable adenylate cyclase activity in the gill only. The evidence presented suggests that small cardioactive peptide B plays an important role in the regulation of important homeostatic functions in Aplysia.
Regulation of renal vitamin D hydroxylase activity in vitamin D deficient rats
Authors: Warner M. , Tenenhouse A.
Published: April 2011

The regulation of renal mitochondrial 1-hydroxylase activity in chronic vitamin D deficiency was studied in male rats. These rats were born of mothers who had been raised from weaning (21 days) on a vitamin D deficient diet and who had no detectable serum 1,25-dihydroxycholecalciferol (1,25-(OH)2D) at the time their offspring were weaned (28 days). In the pups, renal mitochondrial 1-hydroxylase activity was undetectable before the 3rd week of life even though the animals were severely hypocalcemic from birth. The 1-hydroxylase activity first became detectable at 26 days of age, rapidly reached a maximum at day 34, then decreased to become undetectable again by 65 days. Throughout this time serum calcium concentration was <5.0 mg/dL and serum parathyroid hormone (PTH) concentration, measured by a midmolecule radioimmunoassay, was two-to five-fold greater than that found in vitamin D replete rats. 1-Hydroxylase activity could be restored in the +65-day-old animals by administration of a single dose of 2.5 μg vitamin D3. Enzyme activity was detected within 24 h, was maximal at 72 h, and returned to undetectable levels by 96 h after administration of the vitamin. Serum 1,25-(OH)2D which was undetectable before administration of the vitamin D3, was 108 and 458 pg/mL at 16 and 40 h, respectively, after the injection. The serum concentration of this metabolite then decreased progressively to 80 pg/mL by 6 days. 24-Hydroxylase activity first became detectable 48 h after vitamin D administration, increased to a maximum at 96 h, and thereafter decreased to become undetectable by 7 days. The urinary excretion of phosphate and cyclic AMP was 10% of control values between 65 and 90 days of age. These values became normal 4 days after a single dose of 2.5 μg vitamin D3. From these data it is concluded that there are two distinct levels of regulation of 1-hydroxylase activity: a vitamin D independent induction of the activity at the time of weaning that is transient and is not associated with any detectable 24-hydroxylase activity; and the second is a vitamin D dependent induction of enzyme activity seen in animals which prior to administration of the vitamin manifest the characteristics of PTH resistance and have no detectable renal hydroxylase activity. The mechanisms of these effects remain to be determined.
Vascular actions of epidermal growth factor–urogastrone: possible relationship to prostaglandin production
Authors: Muramatsu I. , Hollenberg M. D. , Lederis K.
Published: April 2011

Epidermal growth factor–urogastrone (EGF-URO), a polypeptide of about 6000 atomic mass units present in humans, mice, rats, and other mammals that is widely recognized for its mitogenic and acid-inhibitory activities, was observed to cause contraction of helical arterial strips of the rat ileocolic artery and to potentiate the action of KCl on helical strips from the superior (cephalic) mesenteric artery. The contractile effect of EGF-URO in ileocolic preparations displayed marked tachyphylaxis at high EGF-URO concentrations (100 ng/mL). The apparent mean effective concentration for EGF-URO in these tissues was about 10 ng/mL (1.7 nM); the detection of EGF-URO degradation in the organ bath indicated that a half-maximal response may have been achieved at a concentration as low as 50% of this value (i.e., about 0.9 nM). The actions of EGF-URO were abolished by indomethacin (3 μM) and were, in part, mimicked by prostaglandin F2α (PGF2α), which contracted the ileocolic preparation and potentiated the action of KCl in the superior mesenteric preparation. In the superior mesenteric preparation, PGF2α alone, like EGF-URO, did not have an appreciable effect on resting tension. The time fag of the EGF-URO effect in the ileocolic preparation (5–6 min to reach peak contraction) corresponded closely with the time course of EGF-URO-stimulated calcium accumulation measured previously in other cell systems. Our results suggest that EGF-URO acts to modulate contractility in vascular tissue via a cyclooxygenase pathway product (possibly PGF2α). Our data point to a role for EGF-URO and possibly other growth factors in the control of vascular function.