bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of age and long-term diet on exocrine pancreas of the rat
Authors: Snook JT
Published: December 2017

Effects of age and long-term nutritional treatment on pancreas composition and digestive function were determined in rats fed a cereal-type chow after weaning (experiment 1) or diets with 30% casein and 34% butterfat, 54% starch, or 54% sucrose after 9 mo (experiment 2). The rats were adapted for 1-2 wk to a 15% whole-egg protein diet before killing. In experiment 1, pancreas size, nucleic acid, and digestive enzyme content increased significantly with age up to 3 mo. Values for pancreatic weight and DNA were significantly greater in 28-mo-old rats than in 12-mo-old rats. Pancreatic digestive enzyme content was 65-100% lower in rats with and without gross pathologic lesions. In experiment 2, mortality was higher and pathologic changes were more pronounced by 24 mo in rats fed the butterfat or sucrose diet. Usually, pancreatic enzymes were not reduced as much as in experiment 1, although chymotrypsinogen and trypsinogen concentrations were significantly and negatively correlated with the degree of pathologic change. Apparent digestibility of dietary nitrogen and food energy content was not reduced in rats with reduced enzyme reserves. The rate of incorporation in vitro of label into pancreatic protein and RNA did not differ significantly among aged and control rats.
Control of hepatic glycogen metabolism in the rhesus monkey: effect of glucose, insulin, and glucagon administration
Authors: Curnow RT , Rayfield EJ , George DT , Zenser TV , De Rubertis F
Published: December 2017

The effects of intravenous glucose, insulin and glucagon admininistration on the hepatic glycogen synthase and glycogen phosphorylase systems were assessed in the anesthetized rhesus monkey. Results were correlated with measurements of hepatic cyclic AMP (cAMP) concentrations and plasma glucose, insulin, and glucagon concentrations. Both glucose and insulin administration promoted significant inactivation of phosphorylase by 1 min, which was followed by more gradual activation of synthase. Neither glucose nor insulin caused significant changes in hepatic cAMP. Marked hyperglucagonemia resulting from insulin-induced hypoglycemia did not cause increases IN in hepatic cAMP, suggesting that the elevated insulin levels possibly inhibited glucagon action on the hepatic adenylate cyclase-cAMP system. Glucagon administration caused large increases in hepatic cAMP and activation of phosphorylase within 1 min, followed by more gradual inactivation of synthase when it had been previously activated by glucose. Concomitant glucose infusion, with resulting increased plasma insulin concentrations, markedly diminished the duration of hepatic cAMP elevations following glucagon adminstration, again suggesting an insulin inhibition of glucagon action on the hepatic adenylate-cAMP system.
Effects of coronary hypotension on myocardial substrate utilization
Authors: Spitzer JJ , Bechtel AA , Archer LT , Black MR , Greenfield LJ , Hinshaw LB
Published: December 2017

Changes in myocardial substrate utilization were studied after experimental coronary hypotension in the isolated dog heart perfused with the blood of a large donor animal. After a control period (100 mmHg) the afterload of the isolated heart was adjusted to 50 mmHg and kept at that level for 4 h. After this period, a second control observation was made at a 100-mmHg afterload. Coronary sinus blood flow and oxygen consumption decreased during hypotension and returned to normal during the second control period. Myocardial free fatty acid (FFA) uptake and oxidation did not change significantly. Lactate uptake and the percentage of CO2 derived from myocardial lactate utilization were both diminished during hypotension. These changes were not present during the second control period. Glucose uptake and myocardial respiratory quotient were decreased during the hypotensive period. Half the hearts exhibited elevated end-diastolic pressure after hypotension, but no metabolic differences were detectable between the failing and nonfailing hearts. Thus, prolonged severe hypotension caused a relative preference of FFA oxidation and diminished lactate and glucose uptakes by the myocardium. These changes were quite different from those obtained during experimental hemorrhagic or endotoxic shock.
Modulation of leucine transaminase activity by dietary means
Authors: Adibi SA , Peterson JA , Krzysik BA
Published: December 2017

The specific activity of leucine transaminase was measured in supernatants of liver, skeletal muscle (gastrocnemius), and kidney homogenates obtained from fed, starved, and protein-deprived rats. After 12 h of starvation, there were slight reductions in leucine transaminase activity of both muscle and kidney tissues. When starvation was prolonged to 1 full day, the activity of this enzyme increased by approximately twofold in both muscle and kidney. Prolongation of fasting to 5 days resulted in an additional increase in specific activity of leucine transaminase in muscle. During the entire 5 days of starvation, leucine transaminase activity remained unaltered in liver of starved rats. Protein deprivation for 1 or 5 days resulted in significant reductions in specific activity of leucine transaminase in skeletal muscle. Protein deprivation did not produce a remarkable effect on the activity of this enzyme in kidney or liver tissue. The results of this study, together with those previously obtained, indicate that within our experimental conditions increased oxidation of leucine in skeletal muscle of starved rats is not initially related to an alteration in activity of leucine transaminase. When caloric deficiency is prolonged, the potential for transamination is also increased. These adaptive changes increase the ability of skeletal muscle to use leucine as a metabolic fuel.
Cardiopulmonary baroreflexes: effects of staircase, ramp, and square-wave stimulation
Authors: Lloyd TC
Published: December 2017

Anesthetized dogs were pump perfused in a system that held systemic arterial pressure constant. Pulmonary arterial beds were pressurized, and the induced transient falls of systemic vascular resistance (SVR) were measured. An approximately linear relationship between percent fall of SVR and pulmonary artery pressure was obtained. Left atria and pulmonary venous beds were pressurized using square-pulse, staircase, and ramp wave forms, and changes in SVR were measured. The effect of varying the interval between stimuli was appraised. An approximately linear relationship was obtained for responses to square-wave left atrial forcing pressure (Pla). With staircase forcing, the change of SVR per unit change of Pla depended upon prestimulus Pla. With ramp forcing, responses increased approximately linearly with respect to the logarithm of the rate of pressure rise. Responses to square-wave stimulation varied directly with respect to the interstimulus interval. This study shows that left atrial-pulmonary vein baroreflexes are capable of producing substantial short-term falls of SVR, and that the response depends upon stimulus pressure, rate of pressure change, base-line pressure, and pressure history.
Comparative evaluation of the specificity and sensitivity of isometric indices of contractility
Authors: Parmley WW , Chuck L , Yeatman L
Published: December 2017

It is generally held that a useful mechanical index of contractility is one that is unchanged by changes in initial muscle length, but that changes in appropriate direction and magnitude with a change in contractile state. A number of isometric indices were measured in vitro in isolated cat papillary muscles to quantitate their relative dependence on initial muscle length and contractile state. Results indicate that no one isometric index completely fulfills the definition of an ideal index of contractile state. In particular, indices that change considerably with alterations in contractile state (e.g., maximum dF/dt) are also moderately dependent on preload. Conversely, indices that are moderately insensitive to changes in contractile state (e.g., time-to-peak force) are also insensitive to changes in contractile state. Changes in extrapolated maximum velocity and peak VCE were similar and were less sensitive to changes in contractile state than maximum dF/dt. The most sensitive in vitro index of contractility appears to be maximum dF/dt at a constant preload.
Steady-state glucose oxidation by dog kidney in vivo: relation to Na+ reabsorption
Authors: Garza-Quintero R , Cohen JJ , Brand PH , Kook YJ
Published: December 2017

In eight experiments at normal or slightly elevated blood glucose concentration we quantified the steady-state renal glucose oxidation rate (see article) during control, at reduced Naomega absorptive rates (raised ureteral pressure), and during respiratory alkalosis. A tracer amount of either [1-14C]glucose or or [U-14C]D(omega)-glucose was infused at a constant rate into one renal artery. (see article) was calculated from the renal 14CO2 production rate (corrected for recirculation) and the specific activity of glucose in renal arterial blood. The control (see article) (n equals 8) equals 4.40 plus or minus 0.9 mumol/100 g-min (mean plus or minus SE). When net Naomega reabsorption was decreased by 45% (n equals 6), or when the pH of extracellular fluid was raised (n equals 2), no significant effect on (see article) (9.1 plus or minus 4.2 and 3.9 plus or minus 2.3 mumol/min-100 g, respectively) occurred. The mean glucose oxidation rate for all experiments was 5.65 plus or minus 1.73 mumol g-1-min-1 and required similar to 13% of the renal O2 utilization. Glucose oxidation provides energy either for basal renal work or for some portion of renal transport work not affected by increased ureteral pressure.
Induction of a myogenic response in tonic airway smooth muscle by tetraethylammonium
Authors: Stephens NL , Kroeger EA , Kromer U
Published: December 2017

In multi-unit tracheal smooth muscle (TSM), quick stretches applied at a velocity of 5 times the measured maximum velocity of isotonic shortening of the muscle, of a magnitude 3 times the measured extension of the series-elastic component when the muscle contracts maximally, and at optimal muscle length (L-o) were unable to elicit any myogenic response (MR). Experimental conditions such as hypoxia (P-O2 smaller than 60 mmHg) and acidosis (pH equals 6.8) or the presence of Ba2+ (2 mM), acetylcholine (10-6 M), or high (K+)-o (59 mM) were also unable to elicit the MR. However, tetraethylammonium chloride (TEA, 0.4-67 mM) produces 1) spontaneous phasic contractions and 2) a MR to quick stretch. The ionic basis for these changes was then investigated by studying the Ca and Mg dependence of the response to TEA. The dose-response relationship to TEA was shifted to the left by decreasing external Mg2+ from 2.5 to 0.5 mM. The ability of TSM to produce a MR was absolutely dependent on external Ca, but the threshold concentration required shifted from 2.5 times 10-5 M at normal external Mg (2.5 mM) to 5 times 10-4 M at the reduced external Mg (0.5 mM). The effects of TEA on spontaneity and the MR were abolished by D-600. These results suggest that 1) TEA functionally converts multiunit smooth muscle into a single unit one and leads to the development of a MR and 2) the MR results from a depolarization-activated mobilization of Ca and is inhibited by ionic conditions known to increase membrane permeability.
The kidney in regulation of plasma choline in the chicken
Authors: Acara M
Published: December 2017

Exogenous choline was administered into the wing vein of chickens until steady-state plasma choline levels were achieved. Both plasma and urine were analyzed for free choline by a choline kinase, radiochemical microassay that did not require prior extraction of choline from the biological fluids. Choline was infused at rates from 0.5 to 20.0 mumol/kg-min. Total and urinary clearance were assessed at the steady state reached in each experiment. At the endogenous level of plasma choline of 0.019 mM, total clearance of choline from the plasma was about 50 ml/kg-min and urinary clearance was 0.06 ml/kg-min. There was no significant increase in urinary clearance of choline produced by infusion loads from 0.5 to 1.0 mumol/kg-min. However, as the infusion of choline was increased further, extraurinary clearance decreased while the contribution of the kidneys to total clearance of choline from the plasma increased. At the choline infusion rate of 12.5 mumol/kg-min, plasma choline was 0.5 mM and urinary choline clearance had reached a maximum value of 18.5 ml/kg-min for two kidneys, removing more than 70% of the infused choline.
Plasma and hepatic binding of indocyanine green in guinea pigs of different ages
Authors: Hwang SW
Published: December 2017

Binding of indocyanine green (ICG) to the proteins in plasma and bile of guinea pigs ranging in age from 1 day old to adult was studied. The ICG in plasma was almost totally bound to the protein and there was no significant difference in the binding between newborn and adult animals. Binding of ICG to biliary protein was similar in all age groups. Particulate fractions of liver from adult guinea pigs had a higher ICG binding capacity than that from the newborn at all concentrations tested. The uptake of ICG by liver slices involved mostly active processes. The slice-to-medium (S/M) ratio of ICG was lowest in liver preparations from the newborn; however, the S/M ratio for adult animals was lower than that for 10-day-old animals. Liver slices from adult guinea pig showed the fastest ICG efflux rate, and the efflux rate with liver slices from the newborn was the slowest. Processes of hepatic uptake and release of ICG were incompletely developed in the newborn guinea pig.
Operant conditioning of heart rate in curarized rats: hemodynamic changes
Authors: Gliner JA , Horvath SM , Wolfe RR
Published: December 2017

Three groups of curarized rats were subjected to operant heart rate conditioning with use of a shock-avoidance procedure while cardiac output, mean arterial pressure, and total peripheral resistance were measured. Heart rate changes in the control group remained constant during the entire 90-min experimental period, while cardiac output decreased significantly. Those rats that were reinforced for increasing their heart rate had a small but statistically significant increase in heart rate, but cardiac output decreased to approximately the same extent as in the control group. The group reinforced for decreasing their heart rate demonstrated a large, significant decrease in heart rate and an even larger drop in cardiac output, which was significantly greater than that of either of the other two groups. Operant conditioning of a single facet of the cardiovascular system resulted in significantly larger changes in other cardiovascular parameters, which may have been partly masked by the physiological effects of d-tubocurarine. Therefore, only when these other measures of cardiovascular function are taken into consideration can interpretation of operant heart rate conditioning become meaningful.
Liver uptake of amino acids and carbohydrates during a single circulatory passage
Authors: Pardridge WM , Jefferson LS
Published: December 2017

The uptake of 14C-labeled amino acids and carbohydrates by liver following rapid injection into the portal vein was measured relative to a simultaneously injected highly diffusible reference, tritium-labeled water, (3HOH). A 0.25-ml bolus of buffered Ringer solution containing 1-2 muCi of the 14C-labeled test substance and 3-6 muCi of 3HOH was administered by rabid portal injection in anesthetized rats. Circulation was terminated after a single passage of the bolus through the hepatic microvasculature and the tissue was immediately macerated, solubilized, and subjected to liquid scintillation counting. Liver uptake indices (LUI) were calculated from the ratio of 14C to 3H in liver tissue relative to the same ratio in the injection mixture. LUI's of five carbohydrates were measured: sucrose (24.3 percent), inulin (27.7 percent), D-mannitol (80.2 percent), D-glucose (96.8 percent) and L-glucose (26.7 percent). The LUI for cholic acid was 127.1 percent. Among 18 amino acids tested, the LUI's were the highest for the acidic ones (L-aspartic acid, 100.0 percent and L-glutamic acid, 86.4 percent) and lowest for the basic ones (L-arginine, 37.4 percent and L-lysine, 31.4 percent). Stereospecificity for glucose and alanine uptake, saturation kinetics for glutamic acid (Km equal to 4.8 mM) and aspartic acid (Km equal to 2.7 mM), and cross-inhibition among uptake of the acidic amino acids were observed. These findings confirmed the applicability of a technique which was originally developed for studies of amino acid uptake in brain to characterization of transport systems in liver.
Free amino acids of sex organs of the mouse: regulation by androgen
Authors: Kochakian CD
Published: December 2017

Male mice were castrated at 2 mo and a pellet of testosterone propionate was implanted subcutaneously 2 wk later. Mice were killed after 11 days and tissue extracts were analyzed. All the common 20 amino acids were present in widely varying concentrations. Castration uniformly increased the concentration of all free amino acids of the seminal vesicle, excepy proline, cystine/2, and tryptophan; androgen restored values to normal. These changes were not entirely due to changes in quantity of seminal vesicle fluid. Concentrations of amino acids of the prostate were not significantly changed by castration or testosteronepropionate. Fifteen other ninhydrin-postive compounds were detected. Hypotaruine, taurine alpha-aminobutyric acid, and cysteic acid in seminal vesicles were greatly decreased and several other compounds were slightly decreased by castration and restored tp normal by testosterone propionate. In the prostate, hypotaurine, alpha-aminobutyric acid, cysteic/cysteinessulfinic acids, glycerophosphoethaniomine, cystathionine, and phosphoethanolamine were decreased and alpha-amino-n-butyric acid was increased by castration and restored to normal by testosterone propionate. Concentrations of taurine and 5 other compounds were not affected. Epidiymis and testis also contained appreciable pools of amino acids and the other compounds. Amino acids concentrations were lower in cauda than in caput epididymis; in the testis values were intermidate, with much higher concentrations of glutamic and aspartic acids. Taurine concentrations were twice as great in cauda as in caput epidiymis; concentrations of hypotaurine and the other sulfur-containing compounds were similar in both parts of the epidiymis. The most striking result in the testis was the high concentration of reduced glutathione.
Hemodynimic effects of systemic and central administration of clonidine in the monkey
Authors: Bolme P , Forsyth RP , Ishizaki T , Melmon KL
Published: December 2017

Systemic and regional hemodynamic changes were measured in restrained, conscious rhesus monkeys with indwelling arterial and venous catheters before and after clonidine (5 and 15 mug/kg) was slowly infused intravenously or smaller doses (2 mug/kg) were injected into a lateral cerebral ventricle. Dye-dilution cardiac outputs and the complete distribution of cardiac output were obtained intermittently with the use of the radioactive microsphere method. After the higher intravenous dose and the intraventricular injection, systemic arterial pressure was significantly lowered for 30-45 min. Both of these groups had similar changes in the redistribution of cardiac output and blood flow that outlasted the hypotensive period. Blood flow was maintained or increased in the hepatic and renal arteries at the expense of skin; flow to skeletal muscle and brain also decreased during the first hour. These data support previous studies that indicate that the primary action of clonidine is in the central nervous system and, in addition, add new information about the regional blood flow changes evoked by clonidine.
Myo-inositol transport in the central nervous system
Authors: Spector R , Lorenzo AV
Published: December 2017

Free myo-inositol (inositol) transport into the cerebrospinal fluid (CSF), brain, and choroid plexus and out of the cerebrospinal fluid was measured in rabbits. In vivo, inositol transport from blood into choroid plexus, CSF, and brain was saturable with an apparent affinity constant (K-t) of approximately 0.1 mM. The relative turnover of free inositol in choroid plexus (16 percent/h) was higher than in CSF 4percent/h) and brain (0.3percent/h) when meausred by tissue penetration of tracer [3-H]-labeled inositol injected into blood. However, the passage of tracer inositol was not greater than the passage of mannitol into brain when measured 15 s after a rapid injection of inositol and mannitol into the left common carotid artery. From the CSF, the clearance of inositol relative to inulin was saturable after the intraventricular injection of various concentrations of inositol and inulin. Moreover, a portion of the inositol cleared from the CSF entered brain by a saturable mechanism. In vitro, choroid plexuses, isolated from rabbits and incubated in artificial CSF, accumulated [3-H-labeled myo-inositol against a concentration gradient by a specific, active, saturable process with a K-t of 0.2 mM inositol. These results were interpreted as showing that the entry of inositol into the central nervous system from blood is regulated by a saturable transport system, and that the locus of this system may be, in part, in the choroid plexus.
Effect of infusion of insulin into portal vein on hepatic extraction of insulin in anesthetized dogs
Authors: Harding PE , Bloom G , Field JB
Published: December 2017

Hepatic extraction of insulin was examined in anesthetized dogs before and after constant infusion of insulin (20 and 50 mU/min) with use of samples from the portal vein, mesenteric vein, left common hepatic vein, and the femoral artery. In 19 dogs, measurement of portal vein insulin concentration indicated an overall recovery of 110% of the insulin infused. The range varied from 9 to 303%, indicating the potential for serious error in sampling the portal vein. Equilibrium arterial insulin concentrations were achieved 20 min after starting the infusion. Prior to insulin infusion, hepatic extraction of insulin averaged 4.56 plus or minus 0.43 mUmin, representing an extraction coefficient of 0.42 of the insulin presented to the liver. The proportion of insulin extracted by the liver did not change significantly during insulin infusion despite a 10-fold increase in portal vein insulin concentrations. During the infusion of insulin, a significant proportion of the extraheptic clearance of insulin occurred in the mesenteric circulation. Infusion of insulin was associated with a significant increase in insulin extraction by tissues other than the liver and splanchnic beds. Initially, hepatic glucose output average 36 plus or minus 3 mg/min; by 20 min after insulin infusion, it was 16 plus or minus 5 mg/min. Despite continuation of insulin infusion, hepatic glucose output returned to control values even though arterial glucose concentration continued to fall. Hepatic glucose output increased with termination of insulin infusion.
Micropuncture study of uric acid transport in rat kidney
Authors: Abramson RG , Levitt MF
Published: December 2017

Free-flow micropuncture studies were perfromed to evaluated uric acid transport in the rat kidney. In all studies (a-minus 14C) uric acid and (methoxy-3H) inulin wereadministered. A simple two-step, column-chromatographic technique was utilized to separate (2-minus 14C) uric acid from its labeled oxidation product in plasma, urine, and tubular fluid. Tubular fluid collections were obtained from the early-and late-proximal tubule under control conditions and during subsequent volume expansion induced with 0.9 per-cent sodium chloride. These studies indicate bidirectional, possible active, uric acidtransport in the proximal tubule undr control conditions, with net reabsorption evident early and net decretion apparent late in this nephron segment. In association with volumeexpansion net uric acid reabsorption and secretion both decreased. No significant nettransport was evident beyond the accessible portion of the late-proximal tubule in either experimental state.
Magnesium-neurohypophyseal hormone interactions in contraction of vascular smooth muscle
Authors: Altura BM
Published: December 2017

The contractile responses of helically cut rat aortic strips to neurohypophyseal hormones and synthetic analogues in the presence and absence of 1.2 mM external magnesium ions [Mg++]o was studied. These experiments demonstrate that 1) [Mg++]o potentiates the contractile actions of a variety of neurohypophyseal peptides on vascular smooth muscle. 2) [Mg++]o can alter both the ED50s (i.e., hormone-receptor affinities) and intrinsic activities (or maximum contractile responses) of these molecules on vascular muscle. 3) The amino acid moieties in positions 1, 2, 3, and 8 of the vasopressin molecule interact, differentially, with [Mg++] to produce contraction of vascular muscle. 4) The length of the side chain, and basicity, in position 8 of the vasopressin molecule are probably important in Mg potentiation in mammalian vascular muscle. 5) Interaction of Mg with an aromatic group in position 3 might be critical for potency of vasopressin hormones of mammalian vascular muscle; the ED50 for oxytocin is not shifted to lower concentrations in the presence of [Mg++]o. Collectively, these data suggest that Mg probably acts at more than one site in vascular smooth muscle in the production of neurohypophyseal peptide-activated contractions. In addition, the present findings indicate that the Mg dependence of these peptides on at least one vascular muscle, rat aorta, is a direct function of the rat pressor potency of the molecules.
Effect of chronic preoptic lesions on the renal excretion of sodium in rats
Authors: Keeler R
Published: December 2017

Rats with bilateral lesions in the preoptic area showed a normal pattern of urineand electrolyte excretion under resting conditions but complete absence of a natriuretic response to unilateral carotid baroreceptor stimulation and also a significant reduction in the rate of sodium excretion after saline loading and after a high-sodium intake. Measurements of renal clearance did not show any significant differences in glomerular filtration rate, renal plasma flow, or filtration fraction between normal and preoptic-lesion rats. Apart from the test situations used above, rats with preoptic lesions were apparently able to regulate their sodium metabolism normally because after 3 wk on a high-sodium intake their plasma and extracellular fluid volumes, plasma electrolytes, osmolaity, and mean arterial pressures were indistinguishable from normal rats.It is suggested that the preoptic component of the baroreceptor reflex pathway mighthave an input into a hypothalamic area controlling sodium excretion.
Longitudinal contractions in the duodenum: their fluid-mechanical function
Authors: Melville J , Macagno E , Christensen J
Published: December 2017

The hypothesis examined was that contractions of the longitudinal muscle layer occurin the duodenum which are independent of those of the circular muscle layer and that they induce flow of duodenal contents. A segment of opossum duodenum isolated in vitro was marked and photographed during periods of longitudinal muscle contraction, when the circular muscle layer appeared inactive. The prequency of longitudinal oscillation of the marked points was 20.5 cycles/min. The longitudinal displacement wave spread caudad with an average velocity of 3.27 cm/s. Frequency and velocity of electrical slow waves were determined in similiar duodenal segments. Slow-wave frquencywas 18.9 cycles/min. In a two-dimensional mechanical model, flow induced by simulatedlongitudinal muscle layer appear to be driven by the electrical slow waves of the duodenum. They are capable of inducing a pattern of flow in which ocntents flow betweenthe core and the periphery of the intestinal conduit.
Analysis of coronary vascular beta receptors in situ
Authors: Gross GJ , Feigl EO
Published: December 2017

Observations were conducted in the isolated potassium-arrested dog heart to determine the direct vasodilator effects of adrenergic agonists and antagonists on the coronaryvascular beta receptors, independent of cardiac inotropic and chronotropic influences.Practocol (a selective beta-1-receptor antagonist) blocked coronary vasodilation activated by isoproternol (a combined beta-1-and beta-2-receptor agonist) only at the very high dose of 10-minus 3 M, whereas propranolol (a combined beta-1- and beta-2-receptor antagonist) blocked coronary vasodilation at 10-minus 7 to 10-minus 5 M. Salbutamol (a selective beta-2-receptor agonist) was one-eighth as potent as isoproterenol in producing coronary vasodilation. The potency ratio (1/8) is similiar to valuesreported for other beta receptors classified as type 2. It is concluded that the coronary vasodilator beta receptors are type 2, similiar to those found in peripheral bloodvessels.
Effects of water load on renal glomerular and tubular function in desert quail
Authors: Braun EJ , Dantzler WH
Published: December 2017

Effects of an acute intravenous water load on glomerular and tubular function were studied in the anesthetized desert quail Lophortyx gambelii. Total-kidney glomerular filtration rate (GFR) and single-nephron glomerular filtration rates (SNGFR) of reptilian-type and mammalian-type nephrons increased by more than 50% compared with the GFR and SNGFRs measured during a control mannitol diuresis. Despite the increase in GFR, urine flow rate was only 56% of that in control mannitol diuresis, free-water clearance (CH2o) remained at 1-2% of GFR, and the animals excreted only about 79% of the water load. More than 99% of the filtered sodium and 93% of the filtered water were reabsorbed during the water load. Possible reasons for the increased GFR and the failure to produce a dilute urine or excrete the water load are discussed.
Interaction of O2 and CO2 in sustained exercise hyperemia of canine skeletal muscle
Authors: Stowe DF , Owen TL , Anderson DK , Haddy FJ , Scott JB
Published: December 2017

The relative contribution of O2 and CO2 to the metabolic control of blood flow in long-term exercise was examined in the denervated gracilis muscle of the anesthetized dog. The data show that 1) on initiation of heavy exercise, the effluent blood PO2 and pH fall markedly and then rise slowly but remain depressed relative to control during 60 min of exercise hyperemia, while the initial increases in [K+] and osmolality rapidly approach and eventually reach preexercise levels. 2) The enhanced vasodilator activity of venous blood from exercising muscle is attenuated when effluent blood PO2 or pH is corrected to preexercise levels; it is completely abolished when both are corrected. 3) Induced reduction PO2 or pH in the arterial inflow, and thus venous outflow, of resting muscle produces a fall in resistance; simultaneous reductions of both to levels seen in heavy exercise produce a fall in resistance to near that observed during exercise. Since the enhanced vasodilator activity of venous blood from the contracting muscle was abolished by simultaneous correction of the PO2 and pH, it seems likely that these factors, acting directly or indirectly, are the principal chemicals responsible for the maintenance of the vasodilation seen in canine skeletal muscle during heavy exercise.
Effect of aldosterone on potassium transport in the toad bladder
Authors: Rodriguez HJ , Wiesmann WP , Klahr S
Published: December 2017

The effect of aldosterone on potassium uptake by the toad bladder is described. The hormone stimulated the uptake of potassium across the serosal border of the bladder. The increased uptake was the consequence of an increase in the rate of potassium influx. An effect on potassium uptake was characterized by a latent period of approximately 60 min; it was evident for periods as long as 5 h, and it was abolished by addition of actinomycin D. The time course of the aldosterone effect on potassium closely resembled the effect of the hormone on sodium transport. It is suggested that aldosterone influences potassium transport in the toad bladder via DNA-dependent RNA synthesis. In addition, it is suggested that the effect of the hormone on potassium and sodium may be in some way related.
Coronary artery cyclic AMP content during adrenergic receptor stimulation
Authors: Seidel CL , Schnarr RL , Sparks HV
Published: December 2017

The purpose of this study was to test the hypothesis that the mechanical response of coronary smooth muscle following adrenergic receptor stimulation was mediated by changes in cyclic AMP content. Dibutyryl cyclic AMP caused relaxation of coronary artery strips. Aminophyline caused relaxation and a 254% elevation of cyclic AMP content (P less than 0.005). Phenylephrine caused contraction but no significant change in cyclic AMP content (P greater than 0.4). Epinephrine alone caused contraction and a 99% elevation of cyclic AMP content (P less than 0.001). The alpha blocker, phentolamine, reversed the mechanicaal response to epinephrine, but it did not significantly (P greater than 0.15) reduce the effect of epinephrine on cyclic AMP content. Propranolol enhanced the contractile response to epinephrine and attenuated the epinephrine-induced increase in cyclic AMP content. These results suggest that the contraction of coronary arteries associated with alpha-receptor stimulation is not mediated by changes in cyclic AMP content; however, relaxation associated with beta-receptor stimulation may be mediated by an increase in cyclic AMP content.
Hypercholesterolemia of total starvation: its mechanism via tissue mobilization of cholesterol
Authors: Swaner JC , Connor WE
Published: December 2017

After the establishment of a relatively linear decay curve for plasma [4-14C]cholesterol, rabbits were starved for 26-32 days. The plasma cholesterol concentration increased 400% during starvation. Concurrently, the plasma triglyceride level declined by 50%. While the plasma cholesterol was rising, the cholesterol specific radioactivity of the plasma remained unchanged in starved animals, but in control animals the plasma cholesterol specific radioactivity declined substantially. The cholesterol content of the liver and adipose tissue increased with starvation. The cholesterol specific radioactivities relative to plasma for adipose tissue were lower in the starved animals versus controls. These results support the hypothesis that cholesterol stored in the lipid droplet of the adipose tissue cell is released into plasma and is the chief source of the hypercholesterolemia observed during complete caloric starvation. Cholesterol metabolism in the starved animal can be depicted as a virtually closed system in both the input from biosynthesis and diet being low or zero and the output likewise being close to zero.
Effect of KCl infusion on renin secretory rates and aldosterone excretion in dogs
Authors: Flamenbaum W , Kleinman JG , McNeil JS , Hamburger RJ , Kotchen TA
Published: December 2017

The effects of unilateral intrarenal arterial KCl infusion in dogs (12 mueq/kg per min) on bilateral renal function, renin secretory rates, and aldosterone excretion were studied. During KCl infusion, infused-side renal arterial plasma [K+] increased by 2.2 +/- 0.6 meq/liter. Systemic plasma [K+] simultaneously rose by 0.6 +/- 0.1 meq/liter. Plasma renin activity decreased 29 +/- 9%, and the decrease correlated with the increases in plasma [K+]. Renin secretory rate decreased bilaterally, the decrease being greater in each experiment on the infused side. Aldosterone excretion increased during KCl infusion by 72 +/- 17%, despite a decrease in plasma renin activity. With KCl infusion there was a bilateral increase in K+ excretion, and a positive correlation was observed between the net alterations in K+ and Na+ excretion. No significant alterations in systemic blood pressure, glomerular filtration rate, total renal blood flow, or intracortical renal blood flow distribution were observed. These studies suggest that K+ inhibits the release of renin by an intrarenal mechanism, which may be related to a K+-induced alteration in Na+ absorption.
Comparison of hilar and capsular renal lymph
Authors: O'morchoe CC , Omorchoe PJ , Donati EJ
Published: December 2017

The sites of origin of renal lymph were studied by analysis of simultaneously collected samples of lymph and plasma. The samples included renal hilar (HL) and capsular lymph (CL), thoracic duct lymph (TD), renal venous (RVP) and arterial plasma (AP), and were analyzed for Na+, Cl-, K+, urea, glucose, inulin, and PAH concentrations. The glucose concentrations of HL (76 mg/100 ml, SE +/- 1.9), and CL (92 mg/100 ml, SE +/- 2.5) were significantly different (P less than 0.01) from that of RVP (86 mg/100 ml, SE +/- 2.2). Concentrations of both inulin and PAH in CL and HL fell between the AP and RVP values. The concentration of inulin in CL (CL/RVP = 1.27) exceeded that in HL (HL/RVP = 1.10), but no such difference was detected for PAH. The Na+ (152 meq/liter) and Cl- (129 meq/liter) concentrations in HL were significantly (P less than 0.01) higher than those in CL (Na+ = 148 meq/liter; Cl- = 120 meq/liter), in TD (Na+ = 146 meq/liter; Cl- = 121 meq/liter), and in RVP (Na+ = 144 meq/liter; Cl- = 114 meq/liter. These differences remained highly significant when the electrolyte concentrations were converted to milliequivalents per kilogram H2O. In contrast, no significant differences were detected between the concentrations of urea in the various fluids sampled. It is concluded that CL and HL do not drain a perfectly homogeneous intrarenal pool, and that they do not equilibrate with RVP or AP within the kidney. The results also indicate that CL and HL derive a small component from tubular reabsorbate; that for CL stemming from the cortex, and that for HL from the deeper cortex and outer medulla.
Folate transport in the central nervous system
Authors: Spector R , Lorenzo AV
Published: December 2017

Methyltetrahydrofolic acid or folic acid was infused intravenously at a constant rate into conscious untreated or methotrexate-pretreated rabbits. After 150 min, at equivalent plasma concentrations, folic acid or methyltetrahydrofolic acid readily entered the cerebrospinal fluid and probably brain by a saturable transport system. In contrast, after intraventricular injections, folic acid but not methyltetrahydrofolic acid was cleared from cerebrospinal fluid to blood by a saturable system. Intraventribular injection of folic acid at concentrations that saturated folic acid clearance from cerebrospinal fluid did not affect the transport of methyltetrahydrofolic acid from blood into cerebrospinal fluid. These results suggest that the transport system for mehtyltetrahydrofolic acid, which is about half-saturated at normal plasma concentrations, helps maintain the cerebrospinal fluid and probably brain methyltetrahydrofolic acid concentrations within relatively narrow limits. Moreover, folic acid, which the brain cannot utilize, is transported from cerebrospinal fluid. A possible locus for the systems that transport folic acid from and methyltetrahydrofolic acid into the cerebrospinal fluid is the choroid plexus.
Arterial wall mechanics and composition and the effects of smooth muscle activation
Authors: Cox RH
Published: December 2017

A comparison of passive mechanics and the effects of smooth muscle (SM) activation has been made in canine carotid and iliac arteries. Measurements of external diameter and axial force were made on isolated cylindrical segments in response to internal pressure variations. Data were obtained during maximal norepinephrine (NE) and potassium (K) activation, and following metabolic inhibition of SM. These data were used to determine wall tangential stress-strain relations. The maximum increase in wall stress after K and after NE was greater for the iliacs and occurred at smaller values of wall strain. Passive stress-strain curves for the iliacs were likewise shifted to smaller strains, suggesting an important role of passive wall elements in setting the length of contractile elements. Diameter responses to K at low values of pressure were the same for iliacs and carotids, but were better maintained at higher pressure levels for the iliacs. Similar findings were found for iliac responses to NE and K. The results suggest that at low values of wall stress, active diameter responses are not strongly dependent on the maximum isometric stress development. However, higher pressure-diameter responses are also determined by the force-generating capacity of SM.
Characteristics of sodium and potassium transport in the lung
Authors: Sayeed MM , Senior RM , Chaudry IH , Baue AE
Published: December 2017

Freshly prepared lung slices were incubated in an oxygenated Krebs-Ringer bicarbonate medium for 90 min at 0.5 degrees C (chilling) followed by 60 min at 38 degrees C (rewarming). Fresh tissue cation contents (mean +/- SE) in mmol/kg dry wt were: sodium, 431 +/- 7; potassium, 416 +/- 10. After chilling, tissue sodium increased to 757 +/- 11 and potassium decreased to 113 +/- 6. Upon rewarming there was a net increase in tissue potassium of about 150 (mmol/kg dry wt) and a net decrease in tissue sodium of about 130. Tissue extrusion of sodium and reaccumulation of potassium observed at 37 degrees C were abolished when 1 mM ouabain, dinitrophenol, or iodoacetamide was added to the incubation medium. Similar results were obtained when the medium contained no potassium or when medium Na was replaced by choline. The data indicate the presence of active Na+-K+ transport in lung cells somewhat similar to that found in other mammalian tissue.
Control of tissue manganese: initial absence and sudden emergence of excretion in the neonatal mouse
Authors: Miller ST , Cotzias GC , Evert HA
Published: December 2017

All adult animals and humans tested up to this time have controlled their tissue manganese concentrations by controlling primarily the rate of the metal's excretion. In sharp contrast, neonatal mice did not excrete manganese for the first 17-18 days of life, although absorption of the natural 55Mn as well as distribution, tissue accumulation, and mitochondrial accumulation of the radioactive 54Mn were vigorous. This suggested as initially avid accumulation of this essential micronutrient, supplied in scarce traces in mouse milk (54 ng/ml) by mothers consuming very much higher dietary concentrations (55,000 ng/g). The tissue accumulation was demonstrated analytically and was particularly impressive in the brain, which can be susceptible to both manganese poisoning and deficiency.
Factors affecting O2 transfer in sheep and rabbit placenta perfused in situ
Authors: Power GG , Jenkins F
Published: December 2017

In these experiments we have studied three factors that affect placental O2 transfer. The fetal artery of an isolated cotyledon of the sheep placenta (or one of the umbical arteries in flow studies in rabbits) was perfused in situ with blood of varying PO2 and at different flow rates while the ewe was administered varying inspired O2 concentrations. Measurements were made of the PO2 of inflowing and outflowing umbilical blood, and the O2 transfer rate was calculated by the Fick principle. Changes in individual factors could be studied, since most compensations tending to maintain normal O2 delivery were not operative in the isolated preparation. Results indicate that a 20% change in umbilical arterial PO2, a 14% change in umbilical blood flow, and a 20% change in maternal arterial PO2 would be equivalent in causing a 10% change in placental O2 transfer. Small changes in umbilical arterial PO2 are sufficient to maintain the rate of placental O2 transfer equal to the rate of fetal consumption. Maternal arterial PO2 becomes progressively more critical to fetal oxygenation as its level falls. The experimental results are compared to those predicted by a mathematical model of placental exchange.
Determination of the ENa of from skin from studies of its current-voltage relationship
Authors: Helman SI , O'Neil RG , Fisher RS
Published: December 2017

Studies were done to test the idea that the emf of the sodium pump (ENa) of isolated frog skin could be estimated directly from studies of its current-voltage relationship. ENa was estimated in two ways: a) from the bidirectional sodium flux ratio according to Ussing and Zerahn, and b) from the values of open-circuit voltage, short-circuit current, and the shunt resistance estimated when the [Na] of the outer solution was reduced to zero. When the values of ENa were compared with the values of E1 obtained from the current-voltage relationships, they were found to be the same despite considerable variability in the values of ENa between skins (77-168 mV). In general, the values of ENa were considerably higher when the skins were bathed with sulfate-Ringer as compared with chloride-Ringer solution. These data are compatible with the idea that in nonedge-damaged frog skin, the unidirectional sodium fluxes were confined primarily to active transport pathways alone, and, accordingly, they may be excluded from parallel-shunt pathways.
Adrenergic receptor and epinephrine-induced hyperglycemia and glucose tolerance
Authors: Skikama H , Ui M
Published: December 2017

Intravenous glucose tolerance in fasting rats was improved by phentolamine, an alpha-adrenergic blocking agent, and diminished by propranolol, a beta-adrenergic blocking agent. These effects of adrenergic blockers were dependent on the action of insulin, secretion of which is controlled by an adrenergic mechanism. Epinephrine caused by hyperglycemia and impaired glucose tolerance. Both actions of epinephrine were partly inhibited by either an alpha or beta blocker and completely abolished by combination of both blockers in normal rats. However, in rats treated with anti-insulin serum or 5-methoxyindole-2-carboxylic acid, a potent inhibitor of gluconeogenesis, both actions of epinephrine were blocked by propranolol alone, but not by phentolamine. It is concluded that beta-receptor-mediated inhibiton of peripheral glucose utilization is primarily responsible for epinephrine-induced hyperglycemia and impairment of glucose tolerance. Furthermore, the reduction of glycemic action of epinephrine observed after alpha blockade is due to the hypoglycemic action of insulin secreted by the stimulation of beta receptors in pancreatic beta cells.
Uptake and supply of purine compounds by the liver
Authors: Pritchard JB , O'Connor N , Oliver JM , Berlin RD
Published: December 2017

We have analyzed for purine compounds entering and leaving the liver in lightly anesthetized rabbits and rats and for the export of utilizable purine from liver perfused with oxypurine. The in vivo results indicate that roughly 80% of hypoxanthine, xanthine, and urate is removed in a single passage of blood through liver. Conversely, the adenosine concentration of hepatic venous blood is increased 10-fold over portal or arterial levels. When the liver is isolated and perfused with hypoxanthine there is significant release of adenosine, whether measured quantitatively by microbiological assay or qualitatively by analysis of the radioactive purines released from liver that has been prelabeled with [14C]hypoxanthine. These results provide direct evidence for the clearance of hydroxylated purines and the release of utilizable adenine derivatives by liver.