bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulation of carotid sinus baroreceptor reflex by sciatic nerve stimulation
Authors: Kumada M , Nogami K , Sagawa K
Published: December 2017

In anethetized, immobilized, and vagotomized cats we analyzed the effect of sciatic nerve stimulation (SNS) on the relationships between intrasinus pressure (ISP) and arterial pressure (AP) and between ISP and heart rate (HR). At each of seven ISP levels between 60 and 240 mmHg, AP and HR before and 20 s after the onset of SNS were plotted against ISP to obtain the ISP-AP and ISP-HR relationships before and during SNA. SNA caused increases in AP, HR, and total peripheral resistance (TPR) and a decrease in cardiac output (CO). SNS raised the equilibrium pressure (the value of AP at which AP equaled ISP), but it significantly (P smaller than 0.005) decreased the slope (or gain) of the ISP-AP relationship at ISP's between 90 and 150 mmHg. SNS also significantly (P smaller than 0.05) diminished the gain of ISP-HR relationship at ISP's between 120 and 210 mmHg. Modulation of the gain of ISP-AP relationship was ascribable to that of CO but not of TPR. We conclude that in vagotomized cats 1) SNS attenuates the sensitivity of AP and HR responses in the carotid sinus baroreceptor reflex, and 2) the inhibition of the reflex AP response was caused by modulation of the reflex CO response.
Effects of hypothalamic stimulation on gluconeogenesis and glycolysis in rat liver
Authors: Shimazu T , Ogasawara S
Published: December 2017

Hypothalamic effects on gluconeogenesis and glycosis in rat liver were studied byelectrical stimulations of the ventromedial hypothalamic nucleus (LH) without disturbing the animal's behavior. Stimulation of VMH caused a increase in the activity of phosphoenolpyruvate carboxykinase (PEPCK), a key gluconeogenic enzyme, and marked suppression of pyruvate kinase (PK), a key glycolytic enzyme, of the liver. Stimulationof LH, on the other hand, resulted in a decrease in PEPCK activity but did not alterPK activity. The maximal responses of these enzymes to hypothalamic stimulations were obtained after intermittent stimulations for 4 h. Differential estimations of thetwo isozymes of liver PK (types L and M) were made using antibody against typeM PK. The level of type M enzyme was not altered significantly on stimulation of either VMH or LH. The content of type L enzyme greatly decreased on stimulation of VMH but was not affected by stimulation of LH. The reciprical influences of VMH and LH on hepatic carbohydrate metabolism and their relation to neural-hormonal responses are discussed.
Renal autoregulation: evidence for the transmural pressure hypothesis
Authors: Raeder M , Omvik P , Kiil F
Published: December 2017

Autoregulation of glomerular filtration rate (GFR) was examined during uteral orarterial constriction in anesthetized dogs after renal denervation. GFR was sustaineduntil ureteral pressure greater than 80 mmHg, provided renal arterial pressure exceeded 180 mmHg, but fell at ureteral pressure less than 54 mmHg when arterial pressure averaged 127 plus or minus 5 mmHg; renal blood rose as GFR declined. Ethacrynic acid, saline, or mannitol infusion increased tubular pressure without reducing GFR,but during subsequent ureteral constriction GFR fell at uteral pressure less than 40mmHg. During arterial constriction GFR was maintained at lower arterial pressures in hydropenic than in diuretic dogs. Because of thisdifference in the range of autoregulation, saline infusion increased GFR more in hydropenic than in diuretic dogs except at high arterial pressure. This response to reduced plasma oncotic pressure and the constancy of GFR over a wide range of proximal tubular and arterial pressure indicate constancy of thehydrostatic transmural pressure of glomerular capillaries. Afferent arteriolar resistance is, in addition to a regulation by transmural pressure, perhaps controlled by vascular stretch receptors in the glomeruli.
Epidermal thermal conductivity and stratum corneum hydration in cat footpad
Authors: Holmes KR , Adams T
Published: December 2017

Epidermal thermal conductivity (k) was calculated for the cat footpad by measuringtransepidermal heat flux and temperature gradient ( inverted question markT) while changes in stratum corneum water content were produced by "internal hydration" (IH; eccrine sweat gland activity by nerve stimulation) or by "external hydration" (HH; exposure to air saturated with water vapor). In some experiments, cutaneous vasoconstriction accompanying IH was prevented by an alpha-adrenergic receptor blocking agent, phenoxybenzamine (POB), 3.52 mg/kg iv. For dry skin k=0.167 plus or minus 0.023 (SE) W.m (-1) degree C (-1). With and without POB, IH produced 49.5% and 17.2% increases in k, respectively; HH after IH did not increase k more. With POB, IH increased k more than did HH alone (49.5% and 15.5%, respectively) and at a higher rate (4.22 times 10 minus 3 and 0.63 times 10 minus 3 W.m minus 1.degree C minus 1. min minus 1, respectively.) As k increased, usually deltaT decreased. Increasing k and decreasing deltaT with skin hydration explain the phenominon that air temperature is felt to be lower the more humid a cold exposure, since the temperature of thermoreceptors at the dermoepidermal junction is closer to that of the skin surface when the corneum is hydrated than when it has a low water content.
Reversibility of mechanical and biochemical changes in smooth muscle due to anoxia and substrate depletion
Authors: Knull HR , Bose D
Published: December 2017

The effect of temporary glucose and oxygen deprivation on isometric tension as well as content of glycogen, creatine phosphate (CP), adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), and adenylate pool (AP) were studied in potassium-contracted guinea pig isolated taenia coli. Under aerobic conditions glucose removal caused a decrease in tension, glycogen, CP, ATP, and energy charge; ADP and AMP increased, keeping the adenylate pool size unchanged. During rigor caused by additional anoxia, there was an increase in tension associated with further decrease in ATP and marked reduction of adenylate pool. Restoration of oxygen supply caused only a small increase in ATP that, though sufficient for abolishing rigor, was insufficient to support potassium contraction. Restoration of both glucose and oxygen did not restore tension even though ATP stores were increased further. Elevation of extracellular calcium caused partial restoration of tension, suggesting that the defect was in calcium metabolism rather than energy metabolism. During recovery AP remained low, possibly due to deamination of AMP. Anoxia in the presence of glucose reduced ATP to a concentration similar to that due to aerobic glucose deprivation but tension decreased much less. This result is consistent with different degrees of ATP depletion in various functional (Ca pump vs. contractile mechanism) compartments.
Action of 1,25-dihydroxyvitamin D3 and a diphosphonate on calcium metabolism in rats
Authors: Bonjour JP , Trechsel U , Fleisch H , Schenk R , DeLuca HF , Baxter LA
Published: December 2017

The effect of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) on Ca balance, 45Ca kinetics, and bone morphology has been studied in control rats and rats given disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP), 10 mg P/kg sc per day. This large dose of EHDP is known to inhibit bone mineralization and intestinal calcium absorption and to depress the endogenous production of 1,25-(OH)2D3. In conctrol rats, 1,25-(OH)2D3 increased intestinal calcium absorption. However, in contrast to the enhanced calcium absorption that results from an augmentation of dietary calcium, the 1,25(OH)2D3-induced augmentation of calcium absorption does not lead to a rise in calcium retention, the intestinal effect being matched by an increased excretion of urinary calcium. The EHDP-induced decrease of intestinal calcium absorption could be completely prevented by the concomitant administration of 1,25-(OH)2D3 but not the inhibition of bone mineralization. Therefore, in contrast to the impairment of calcium absorption, that of bone mineralization brought about by large doses of EHDP cannot be merely attributed to a decreased production of 1,25-(OH)2D3.
Temporal changes in growth hormone, cortisol, and glucose: relation to light onset and behavior
Authors: Natelson BH , Holaday J , Meyerhoff J , Stokes PE
Published: December 2017

Plasma growth hormone (GH), cortisol, and glucose were measured every 20 min in the last 2 h of a 12-h dark cycle and the first 4 h of a 12-h light cycle in eight environmentally limited rhesus monkeys; additionally, ongoing behavior was scored every 20 min in the last 4 h when the lights in the booths housing the monkeys were on. Episodic fluctuations in levels of GH, cortisol, and glucose occurred. Onset of booth illumination was associated with a significant number of GH secretory bursts (6 of 18), and more than twice as many bursts per hour occurred in the light than in the dark (L:D = 0.44:0.19). The onset of illumination was also associated with significant increases in glucose for the eight animals. In addition, plasma glucose increased concurrently with the onset of 13 of 18 bursts of GH secretion. Monkeys were rated as significantly more alert or aroused when plasma levels of GH and glucose were increasing than when they were decreasing. In contrast plasma cortisol showed small, rhythmic fluctuations over time that did not correlate with booth illumination or degree of behavioral arousal. This latter finding challenges the traditional assumption that cortisol is a sensitive index of behavioral arousal.
Adaptation of actomyosin ATPase in different types of muscle to endurance exercise
Authors: Baldwin KM , Winder WW , Holloszy JO
Published: December 2017

Higher concentrations of actomyosin were found in the red portion of the vastus lateralis and in the white portion of the vastus lateralis muscle than in the soleus or heart in rats. A strenuous program of treadmill running lasting 18 wk or longer did not significantly affect the amount of actomyosin recovered from the different types of muscle. No changes in actomyosin ATPase occurred in fast-twitch white (white vastus) or heart muscles in response to the exercise training. In contrast, a decrease of approximately 20% occurred in the specific activity of actomyosin ATPase of fast-twitch red (red vastus) muscle (0.635 +/- 0.029 mumol Pi/min per milligram for sedentary vs. 0.529 +/- 0.021 mumol Pi/min per milligram for trained), while the actomyosin ATPase activity of slow-twitch red (soleus) muscle increased about 20% (0.209 +/- 0.033 vs. 0.257 +/- 0.031 mumol Pi/min per milligram). There was a close correlation (r = 0.99, P less than 0.001) between actomyosin ATPase activity and phosphofructokinase activity in the three types of skeletal muscles and in heart muscle of exercise-trained and untrained animals, providing further evidence in support of the concept that the glycogenolytic capacity of a muscle and its actomyosin ATPase activity are regulated in parallel.
Thyroid activity in desert rodents: a mechanism for lowered metabolic rate
Authors: Yousef MK , Johnson HD
Published: December 2017

Desert rodents are known to exhibit three different levels of metabolic rate (MR) when related to the mouse-elephant equation. Several species have an MR that is either higher, lower, or similar to that predicted from the equation. The role of thyroid function as a possible mechanism associated with these different MR was examined in 12 species of desert rodents, representing 3 families and 3 different biotic communities. Thyroidal 131I uptake, ratio of neck-to-thigh 131I counts per minute (N/T ratio), thyroxine secretion rate (TSR), and plasma protein binding sites were used as indices of thyroid function. When relating thyroid function to MR, TSR was found to be low in species exhibiting low MR and vice versa. Other thyroid indices did not show a consistent relationship to MR. Also, TSR seems to be related to ecologic distribution: low TSR in desert areas and high TSR in arid woodland and montane forest areas. TSR was found to be correlated to body weight. The low TSR associated with reduced MR represents a useful adaptive mechanism for survival of desert rodents under their natural stressful environment.
Interaction of O2 diffusion and O2 metabolism in cat urinary bladder tissue
Authors: Van Liew HD , Chen PY
Published: December 2017

We measured oxygen exchange across the inside surface of excised urinary bladders that were inflated with gas mixtures. By using a range of Po2 differences between the two sides of the tissue and relatively simple mathematical models, we could infer the exchanges across the outside surface and the total O2 economy of the tissue so that we could evaluate the interaction between diffusion and metabolic O2 consumption. The estimate of the Krogh diffusion constant or permeation coefficient with this preparation avoids errors due to O2 consumption and unstirred layers. At 37 degrees C, the value of bladder tissue O2 consumption was 4.4 times 10(-3) min-1 and the value of the Krogh constant for O2 was 2.22 times 10(-5)cm2min-1atm-1.
Effect of heparin on chronically induced intravascular coagulation in dogs
Authors: Owen CA  , Bowie EJ
Published: December 2017

When intermediate-strength thromboplastin was continuously infused into dogs for 10 days or more, platelet counts decreased sharply and factor VIII concentrations decreased by more than 50%. There was little change in plasma fibrinogen, prothrombin, factor V, antithrombin III, plasminogen, prothrombin time, and thrombin time values. When heparin was infused (25-50 U/kg per h) along with the same thromboplastin, there was no change in onset or degree of thrombocytopenia. However, the decrease in factor VIII was abolished and there were significant increases in fibrinogen, prothrombin, and factor V. The absolute concentrations of the various clotting factors seemed to give no indication of their turnover rates. Unexplained is the remarkable heparin tolerance that developed in these dogs.
Uric acid excretion by the rat kidney
Authors: Cook MA , Adkinson JT , Lassiter WE , Gottschalk CW
Published: December 2017

The renal excretion of uric acid was studied in nondiuretic (ND) male Wistar rats and in the same animals subsequently made diuretic (D) by the infusion of hypertonic saline. Clearances of endogenous urate and of inulin, determined chemically, were compared with the simultaneous clearance of 14C infused as [6(-14)C]urate or [2(-14)C]urate. In rats infused with [6(-14)C]urate the isotope/inulin clearance ratios were 0.29 +/- 0.09 (ND) and 0.31 +/- 0.11 (D) ml/min; the simultaneous urate (chemical)/inulin ratios were 0.21 +/- 0.07 (ND) and 0.24 +/- 0.08 (D) ml/min. In rats infused with [2(-14)C]urate the isotope/inulin clearance ratios were 1.02 +/- 0.5 (ND) and 1.13 +/- 0.9 ml/min (D); the simultaneous urate (chemical)/inulin clearance ratios were much lower-0.19 +/- 0.09 (ND) and 0.32 +/- 0.19 (D) ml/min. Thin-layer chromatography of urine after [6(-14)C]urate inl uric acid. In contrast, a similar analysis of urinary radioactivity after [2(-14)C]urate infusion revealed that more than 70% of the 14C was excreted as allantoin and not as uric acid.
Bile acid kinetics and bile secretion in the pony
Authors: Anwer MS , Gronwall RR , Engelking LR , Klentz RD
Published: December 2017

Bile acid pool size and synthesis rate were determined by both isotope-dilution and washout methods in ponies with chronic external biliary fistulas. Bile acid pool size (10.9 mumol/kg) and synthesis rate (11.2 mumol/day per kg) estimated by the isotope-dilution method did not differ significantly from pool size (9.4 mumol/kg) and synthesis rate (9.5 mumol/day per kg) estimated by washout method. Bile acid-dependent and -independent fractions of bile flow, determined by a method that circumvents any inevitable correlation of flow to bile acid secretion due to common factors in both parameters, did not differ from those values obtained by linear regression of bile flow versus bile acid secretion. The choleretic effect of infused chenodeoxycholic acid was higher than that of both endogenous bile acid and infused taurocholic acid.
Phase lock of electrical slow waves and spike bursts in cat duodenum
Authors: Sancholuz AR , Croley TE  , Christensen J , Macagno EO , Glover
Published: December 2017

The phase relationship between slow waves and spike bursts was studied in vitro in the cat duodenum. Electrodes were arranged radially about the duodenum. Records were read for T1, the time between the slow-wave "valley" and the first spike, and T2, the time between successive valleys. The distributions of the ratio T1/T2 showed very small differences, not uniquely attributable to radial electrode position. The distribution of T1/T2 indicated that spike bursts began 58.8% of the way through a slow-wave cycle, measured from the valley. Also, electrodes were arranged longitudinally and records were read to determine deltaSW, the slow-wave delay time between adjacent electrode positions, and deltaS, the spike burst delay time between adjacent electrode positions. The correlation of deltaS and deltaSW suggested a linear relation, and a regression resulted in a good linear description. These results are consistent with an assumed phase lock of spike bursts to slow waves.
Isotonic relaxation in cardiac muscle
Authors: Strobeck JE , Bahler AS , Sonnenblick EH
Published: December 2017

The force-velocity-length determinants of isotonic relaxation were studied in 12 cat papillary muscles. Isotonic relaxation velocity (VL) was found to be a function of total load (preload + afterload), with peak VL increasing to a maximum at loads approximately .3 to .4 Po(L') (Po(L') defined as maximum isometric force developed during a twitch at the experimental length) and falling with increasing loads. Initial muscle length (ML) had no effect on the peak VL with constant load. Increasing the initial length at which isotonic relaxation occurred (LL) decreased peak VL but did not alter the unique length-velocity trajectory at constant load. This unique length-velocity trajectory occurred, despite a wide variation in time during the contraction when peak VL was measured. Increasing Ca++ from 2.5 to 7.5 mM increased peak VL (1.73 +/- .16 to 2.32 +/- .20 ML/s) and shifted the entire length-velocity trajectory toward higher velocities of lengthening. The addition of 10 mM caffeine increased peak VL also (1.67 +/- .18 to 2.54 +/- .20 ML/s) and had a similar effect on the length-velocity trajectory during lengthening as Ca++. Both increased Ca++ and caffeine (10 mM) augmented the maximum VL measured on addition of load.
ADP, thrombin, and Bothrops atrox thrombinlike enzyme in platelet-dependent fibrin retraction
Authors: Niewiarowski S , Stewart GJ , Nath N , Sha AT , Lieberman GE
Published: December 2017

Clots formed upon the addition of thrombin to human platelet-rich plasma (PRP) retracted readily but the clotting enzyme from Bothrops atrox venom did not cause retraction in PRP unless ADP, collagen, epinephrine, or low concentrations of thrombin (0.1 U) were added. The latter type of retraction was inhibited by apyrase and creatine phosphate kinase in the presence of creatine phosphate, but that induced with higher concentration of thrombin (2 U) was not. In a system composed of washed human platelets and purified fibrinogen, Bothrops marajoensis (BM) thrombinlike enzyme (highly purified preparations of viper venom) did not cause clot retraction. Addition of ADP to the platelet-fibrinogen mixture prior to BM enzyme resulted in stimulation of clot retraction that could be dissociated from the release of platelet constituents. Addition of low concentrations of thrombin (0.1 U/ml) caused retraction associated with a considerable release of adenine nucleotides that was inhibited by potato apyrase. Electron micrographs showed platelet-fibrin aggregates in all types of retracted clots. Nonretracted clots formed in the presence of potato apyrase contained discoidal platelets that were not in close association with fibrin. It has been postulated that platelet-dependent fibrin clot retraction induced by collagen, epinephrine, and low concentration of thrombin is mediated by ADP. High concentrations of thormbin may possibly promote clot retraction independently of ADP.
Role of luminal hydrostatic pressure in proximal tubular fluid reabsorption in the rat
Authors: Grandchamp A , Scherrer  , Scholer D , Bornand J
Published: December 2017

The effect of small changes in intraluminal hydrostatic pressure (P) on the tubular radius (r) and the net fluid reabsorption per unit of surface area of the tubular wall (Js) has been studied in the proximal tubule of the rat kidney. The split-drop method was used to simultaneously determine Js and r. Two standardized split-drop techniques A and B allow selective change in P. P was 31.6 +/- 1.3 mmHg in technique A and 15.5 +/- 1.5 in technique B. The pressure difference significantly affected the tubular radius; r was 21.9 +/- 0.4 and 18.6 +/- 0.5 mum in the split drop A and B, respectively. In contrast, net transepithelial fluid reabsorption Js was unchanged. Js amounted to 2.72 +/- 0.20, and 2.78 +/- 0.33 10(-5) cm3 cm-2 s-1 in split drop A and B. The absence of variations in Js could result from two opposite effects of pressure. P might enhance Js by increased ultrafiltration. However, the rise in r might decrease the density of the intraepithelial transport paths per unit area of tubular wall and therefore might decrease Js.
Effects of synthetic buffers on reflexes in the isolated frog spinal cord
Authors: Davidoff RA , Sears ES
Published: December 2017

Substitution of synthetic buffers (Tris, TES, HEPES, or 3,3-dimethylglutarate) for CO2-bicarbonate buffer in Ringer solution perfusing the isolated in vitro frog spinal cord preparation altered membrane properties and reflex activity. Perfusion with Ringer solution gassed with O2 and containing synthetic bu,fers consistently produced a depolarization of motoneurons and dorsal root fibers, decreased the amplitude (and usually the duration) of ventral and dorsal root potentials, and had variable effects on motoneuron and dorsal root reflex discharges. With Tris-Ringer these discharges decreased in amplitude; with Ringer containing one of the other synthetic buffers, these discharges were augmented. All changes were reversible when the cord was returned to bicarbonate-buffered Ringer aerated with 95% O2/5% CO2. The use of a combined buffer system-one containing a synthetic buffer and bicarbonate-induced smaller or minimal changes in bioelectric activity. At present the data are insufficient to allow firm conclusions concerning the mechanisms underlying these results; but it is evident 1) that changes in PCO2 and bicarbonate concentration and 2) that the pharmacological properties of synthetic buffers are important variables.
Metabolic and hemodynamic consequences of mannitol following myocardial anoxia
Authors: Smithen C , Christodoulou J , Killip T , Brachfeld N
Published: December 2017

The mechanism of action of hyperosmolal mannitol was evaluated by hemodynamic and metabolic studies in 79 isovolumic nonrecirculating paced perfused rat hearts during sequential 15-min periods of aerobic, anoxic, and reoxygenated perfusion. Hyperosmolality induced by addition of mannitol significantly decreased myocardial water content (wet/dry wt ratio). It improved recovery of hemodynamic function during reoxygenation. With isomolal perfusion (290 mosmol/kg) left ventricular systolic peak pressure (LVSP) decreased 32% (127 +/- 5 to 86 +/- 6 mmHg) and maximum dP/dt fell 50% (3,513 +/- 328 to 1,758 +/- 172 mmHg/s) during the postanoxic recovery period. With hyperosmolal perfusion (350 mosmol/kg), LVSP decreased 23% (132 +/- 5 to 102 +/- 7 mmHg) and dP/dt fell 21% (3,817 +/- 215 to 2,998 +/- 234 mmHg/s) (P less than .01). Hyperosmolal perfusion did not affect postanoxic total coronary flow, lactate and glucose metabolism, tissue glycogen, creatine phsophate, or adenine nucleotide concentrations. Coronary perfusion with hypersmolal solution aided recovery, enhanced postanoxic myocardial performance, and minimized tissue swelling. The most tenable explanation for the locus of action of hyperosmolal mannitol during anoxia under our experimental conditions is its direct effect on myocardial water content.
Glutamine transport by mitochondria isolated from normal and acidotic rats
Authors: Goldstein L
Published: December 2017

The transport of L-glutamine by isolated rat renal mitochondria was studied by means of a rapid-filtration (Millipore Filter Corp.) technique. The movement of glutamine from the incubation medium into the inner mitochondrial compartment (matrix) was inhibited by structural analogues (6-diazo-5-oxo-L-norleucine and glutamic acid), sulghydryl-binding agents (p-chloromercuri-benzoate and mersalyl), and inhibitors of mitochondrial oxidative metabolism (azide, antimycin A, and uncouplers of oxidative phosphorylation). These results suggest that glutamine is transported across the inner membrane of renal mitochondria by a carrier-mediated system that is linked to the processes of oxidative metabolism. The transport of glutamine by isolated renal mitochondria was increased two- to threefold by chronic (5-7 days) metabolic acidosis. However, short-term metabolic acidosis did not increase the glutamine transport capacity of isolated mitochondria. A hypothesis is presented for the regulation of mitochondrial glutamine transport, in vivo, during short-term and chronic acidosis.
In vivo toxic effects of halothane on canine cerebral metabolic pathways
Authors: Michenfelder JD , Theye RA
Published: December 2017

The effects of high concentrations of halothane on cerebral metabolism were examined in dogs with the aid of an extracorporeal circuit to support the systemic circulation. At blood levels exceeding those representing equilibration with 2.3% halothane, a dose-related decrease in cerebral oxygen consumption (CMR02) occurred that was unrelated to the presence or absence of an active electroencephalogram. In this circumstance, despite adequate oxygen delivery, a dose-related alteration in oxidative phosphorylation also occurred as evidenced by progressive decreases in cerebral concentrations of ATP and phosphocreatine and concomitant increases in cerebral lactate and lactate/pyruvate ratio. These effects were totally reversible, except for persistence of increased of increased CMR02, after return to low halothane concentrations. It is concluded that the mechanisms of the cerebral metabolic effects of halothane differ from those of thiopental and, at high concentrations, are at least in part related to interference with oxidative phosphorylation. These in vivo studies confirm the potentially detrimental effects of high halothane concentrations on cerebral metabolic pathways as demonstrated by others in vitro.
Intra-SA-nodal pacemaker shifts induced by autonomic nerve stimulation in the dog
Authors: Goldberg JM
Published: December 2017

Pacemaker shifts in the canine heart were inferred during stimulation of thoracic cardiac nerves and following norepinephrine from changes in the initial site of activation of bipolar electrodes sutured over the rostral, middle, and caudal regions of the sinus node, over the internodal pathways, and His bundle. During control periods, pacemaker activity was localized within the sinoatrial (SA) node 87% of the time, with the middle electrode most frequently showing initial activation. Stimulation of the right-sympathetic nerves enhanced sinus node pacemaker dominance, shifting it rostrally within the node. Right-vagal stimulation shifted the pacemaker caudally within the SA node, to nonnodal sites, and to the lower atrioventricular node and His bundle. Left-sympathetic stimulation shifted the pacemaker caudally within the sinus node and enhanced pacemaker activity in the vicinity of the internodal pathway electrodes and His bundle. Dispersion of pacemaker activity was particularly apparent during stimulation of the ventrolateral cervical cardiac nerve. Stimulation of the left-vagal nerves produced effects similar to those of the left-sympathetic nerves. Norepinephrine enhanced pacemaker activity particularly in the rostral region of the sinus node. Slight shifts in pacemaker activity within the sinus node produced changes in pattern of atrial excitation.
Lipid and glycogen metabolism in the hypoxic heart: effects of epinephrine
Authors: Crass MF  , Pieper GM
Published: December 2017

The metabolism of cardiac lipids and glycogen in hypoxic and well-oxygenated perfused rat hearts was studied in the presence or absence of epinephrine. Heart lipids were pre-labeled in vivo with [1-14C]palmitate. Triglyceride disappearance (measured chemically and radiochemically) was observed in well-oxygenated hearts and was stimulated by epinephrine (4.1 X 10(-7)M). Utilization of tissue triglycerides was inhibited in hypoxic hearts in the presence or absence of added epinephrine. Hypoxia resulted in a small increase in tissue 14C-free fatty acids and inhibition of 14C-labeled triglyceride fatty acid oxidation. Epinephrine had no stimulatory effect on fatty acid oxidation in hypoxic hearts. Utilization of 14C-labeled phospholipids (and total phospholipids) was similar in well-oxygenated and hypoxic hearts with or without added epinephrine. These results suggested that the antilipolytic effects of hypoxia were predominant over the lipolytic effects of epinephrine. Glycogenolysis was stimulated threefold by epinephrine in well-oxygenated hearts. Hypoxia alone was a potent stimulus to glycogenolysis. Addition of epinephrine to perfusates of hypoxic hearts resulted in a slight enhancement of glycogenolysis.
Microvascular control in intestinal mucosa of normal and hemorrhaged rats
Authors: Bohlen HG , Hutchins PM , Rapela CE , Green HD
Published: December 2017

The mucosal microcirculation in innervated and denervated small intestine was studied using anesthetized rats. Denervation did not cause significant (P greater than 0.05) diameter changes in the precapillary vasculature; however, venules did constrict significantly. These results indicate minimum neural control in the precapillary vasculature during the resting state. The innervated precapillary vasculature constricted during both the carotid occlusion reflex and hemorrhagic hypotension. The diameter of the denervated precapillary vasculature was unchanged during the carotid occlusion reflex and dilated during hemorrhage. The responses of innervated and denervated precapillary vasculatures were attributed to increased neural activity and autoregulatory mechanisms, respectively. Neither innervated nor denervated venules responded during the carotid occlusion reflex. During hemorrhage, however, innervated venules constricted and denervated vessels dilated. The vasoconstriction of the innervated vasculature during hemorrhage contributed to a stoppage of blood and epithelial detachment; these responses did not occur in the dilated, denervated vasculature. Therefore, neural vasoconstriction, qualitatively similar to that in normal animals during the baroreceptor reflex, is a contributing cause to the vascular and tissue impairment in the intestinal mucosa during hemorrhage.
Effect of parathyroid hormone secretion on sodium reabsorption by the proximal tubule
Authors: Schneider EG
Published: December 2017

To determine if an increase in the endogenous secretion of parathyroid hormone could decrease sodium reabsorption by the proximal tubule, the ionized calcium concentration of blood perfusing the parathyroid gland of eight unilaterally thyroid parathyroidectomized dogs (TPTX) was reduced by infusion of an isotonic sodium citrate plus sodium chloride solution into the blood supply of the parathyroid gland. The fractional clearance of phosphate increased significantly (+9.3 +/- 2.8 ml/min per 100 ml GFR), while fractional sodium reabsorption by the proximal tubule decreased (-.06 +/- .02; P less than .025). In seven normal control dogs that received isotonic sodium chloride infusion, neither fractional sodium reabsorption by the proximal tubule nor the fractional clearance of phosphate was significantly altered. In five bilaterally TPTX dogs that received a sodium citrate plus sodium chloride infusion, sodium reabsorption by the proximal tubule was not significantly altered. There were no significant changes in glomerular filtration rate or renal plasma flow in any of these groups. The data demonstrate that alterations in endogenous parathyroid hormone secretion can play a significant role in the regulation of sodium reabsorption by the proximal tubule.
Distal tubular tracer microinjection study of renal tubular potassium transport
Authors: Fowler N , Giebisch G , Whittembury G
Published: December 2017

Renal tubular potassium (K) transfer was studied in rats using a tracer microinjection technique in which [14C]inulin and 42K were simultaneously injected into early distal tubules during osmotic diuresis. Experiments were carried out in 1) animals on a control diet, 2) animals in which K secretion had been stimulated (high-K diet + KC1, Na2SO4, Diamox infusions), and 3) animals in which K excretion had been reduced by a low-K or low-Na diet or by amiloride. 42K excretion into the urine coincided closely in time with the excretion pattern of [14C]inulin. Efflux of 42K out of the lumen was stimulated during reduced K secretion along the distal nephron and decreased during enhanced K secretion when small tubular K loads were given. These experiments demonstrate bidirectional K movement across the distal nephron and show that changes in reabsorptive K efflux participate in the regulation of tubular net K movement.
Effects of veratrine on repolarization in the canine right bundle branch
Authors: Arbel ER , Lazzari J , Glick G
Published: December 2017

Superfusion of Purkinje fibers in the canine right bundle branch with Tyrode solution containing veratrine, less than or equal to 1 mug/ml, prolonged repolarization phases 2 and 3 and induced a long-lasting negative after-potential that ended in some experiments with a slightly hyperpolarized resting transmembrane potential. The alterations in repolarization time were reversed by washout with veratrine-free Tyrode solution or by adding tetrodotoxin to the veratrine-containing Tyrode solution to a concentration of 0.1 and 1 mug/ml. The effect of veratrine on the repolarization time was more prominent at slower driving rates. Its effect on repolarization of ventricular muscle cells was smaller than that on the repolarization of Purkinje fibers. In the concentrations used, veratrine did not induce multiple responses.
Quantitative aspects of insulin secretion and its hepatic and renal removal in sheep
Authors: Brockman RP , Bergman EN
Published: December 2017

The secretion of insulin into the portal blood and its removal by the liver and kidneys in conscious fed sheep were determined by simultaneously measuring venoarterial plasma concentration differences and portal, hepatic, and renal plasma flows. The basal secretory rate of insulin was 0.43 +/- 0.03 U/h or 7.8 mU/kg-h. The secretory rate of insulin and the amount of insulin presented to the liver also were altered by 2-h intraportal infusions of glucagon (150 mug/h), insulin (1.17 U/h), and insulin (1.17 U/h) lus glucose (2.2 g/h). Hepatic removal under all conditions was about 50% of the insulin secretory rate, although the extraction ratio was only 0.08. Renal removal was 35% of the insulin secretory rate. The renal extraction ratio was 0.35. During insulin-induced hypoglycemia and also during starvation, the hepatic extraction ratio of insulin increased significantly, but the removal as a percentage of insulin secretion did not change. It appears that in sheep on a maintenance diet the basal secretory rate of insulin is less than that of nonruminant species and that, within physiological limits, the liver disposes of about one-half and the kidney about one-third of the insulin. Other tissues, presumably, remove the remaining 10--20%.
Effect of secretin and cholecystokinin on small intestinal blood flow distribution
Authors: Fara JW , Madden KS
Published: December 2017

The relative blood flow distribution within the small intestine of anesthetized cats was investigated during resting conditions and when superior mesenteric blood flow was increased 15--85% by the intravenous infusion of secretin, cholecystokinin (CCK), or isoproterenol. Radioactive microspheres of 15 mum diameter were injected into the superior mesenteric artery and shortly thereafter intestinal segments were removed and dissected into mucosal, submucosal, and muscularis fractions. Tissue weights and the radioactivity of each were determined. During secretin-induced mesenteric vasodilatation there was a significant redistribution of blood away from the jejunal mucosa to the submucosa. During CCK and isoproterenol infusions there were significant increases in mucosal and decreases in submucosal blood flow. No significant changes were observed in muscularis flow. There was no apparent relationship between the percent increase in SMBF and the relative blood flow distribution changes observed. The results indicate that while secretin, CCK, and isoproterenol increase superior mesenteric blood flow, they also affect blood flow distribution within the mucosa and submucosa.
Interstitial fluid pressure in canine gastric mucosa
Authors: Altamirano M , Requena M , Perez TC
Published: December 2017

Guyton's capsules were implanted in the submucosa of the gastric corpus of dogs. The pressure of the fluid inside the capsule (ICP) was measured between 12 and 42 days later after mounting the piece of the corpus in a Plexiglas chamber. The capsule was always filled with saline. In two out of three experiments, the ICP did not change significantly when the saline was replaced by isotonic glucose or blood plasma. Changes of pressure exerted on the surface of the stomach were accurately monitored by the ICP recordings. Changes of circulation produced by compression of the artery or the vein connected to the piece of mucosa, or by intra-arterial injections of epinephrine, norepinephrine, isoproterenol, or hypertonic mannitol, modified the ICP as predicted by Starling's law of capillary filtration. Spontaneous activity of the gastric muscles or the activity, which followed intra-arterial injections of acetylcholine, prostigmine, or histamine, changed the ICP significantly. Intra-arterial atropine usually decreased the ICP by 3--5 mmHg. The mean value of the ICP in 49 animals was 0.53 +/- 0.34 mmHg (SEM); it was negative in 43% of the experiments.
Effect of hypotonic medium on K and Na content of proximal renal tubules
Authors: Grantham J. J. , Lowe C. M. , Dellasega M. , Cole B. R.
Published: December 2017

The intracellular content of K and Na was measured in isolated nonperfused proximal straight renal tubules (PST) in order to determine the mode of cell volume regulation in hypotonic bathing media. Immersion in hypotonic medium caused PST to lose K and Na (with anions) in a magnitude sufficient to account for the regulation of cell volume. Hypothermia (10 degrees C) blocked cell volume regulation in hypotonic medium by promoting net accumulation of Na, although K loss was equivalent to that observed at 37 degrees C. Ouabain (10(-5) M) caused rapid loss of cell K and gain of Na in an isotonic bath, but the glycoside did not inhibit the subsequent adjustment of cell volume in hypotonic medium. In hypotonic medium ouabain-treated tubules lost Na, but not K, to account for hypotonic volume adjustment of PST in ouabain. We conclude that proximal straight tubules extrude electrolytes (K, Na, and anions) in the adjustment of cell volume in hypotonic media; in normal tubules K and Na are lost whereas Na moves primarily in ouabain-treated tubules. The adjustment of size through the extrusion of intracellular solutes in dilutional states appears to be a general property of mammalian cells.
Evidence for a peritubular-to-luminal flux phosphate in the dog kidney
Authors: Schneider E. G. , McLane L. A.
Published: December 2017

The possible presence of a direct influx of phosphate into the tubular lumen of the dog kidney was examined by two different techniques. A 0.3-ml bolus of 32PO4 and [3H]inulin was injected into the renal artery of dogs with and without phosphate loading. The mean urinary transit time (TT) for PO4 was consistently less than the TT for inulin in nonphosphate-loaded dogs. Following phosphate loading the TT for phosphate approached but did not equal the TT for inulin. In contrast, after microinjections of 32PO4 and [3H]inulin into proximal tubules, the urinary TT of PO4 was significantly longer than the TT of inulin. The application of 32PO4 and [3H]inulin to the surface of the left kidney was associated with a greater recovery of 32PO4 from the left kidney compared to that from the right kidney. The recovery of [3H]inulin was proportional to the glomerular filtration rate for both kidneys. Application of the 32PO4 and [3H]inulin to the surface of a muscle resulted in an equal recovery of phosphate and inulin from both kidneys. The results demonstrate the presence of a detectable tubular influx of phosphate.
Renal clearance studies in fetal and young guinea pigs: effect of salt loading
Authors: Merlet-Benichou C. , de Rouffignac C.
Published: December 2017

The maturation of renal function was investigated by clearance studies in 11 fetal, 9 young, and 4 adult guinea pigs undergoing salt loading (NaCl 1.5%, 75 mul min-1 100 g-1) and in 10 young and 4 adult animals under nondiuretic conditions. The fetal preparation described makes it possible to obtain two to four steady clearance periods for each animal. In the fetus, GFR increased significantly with age, but less than in the newborn. Fractional water and sodium reabsorption was generally low, and net renal secretion of potassium was observed in some cases. Fetal urine was sometimes slightly hypertonic. The effectiveness of the diuretic and natriuretic response following saline expansion was smaller in young than adult animals. The fractional excretion rate of solutes and water increased as a function of age in the young animal and the urinary Na/K concentration ratio showed a marked drop around birth. This latter observation suggests that during the first days of life the effect of saline expansion on the proximal tubule is partially blunted by enhanced sodium reabsorption from the distal nephron due to the high concentration of circulating aldosterone.
Inhibition of probenecid uricosuria by pyrazinamide and para-aminohippurate
Authors: Meisel A. D. , Diamond H. S.
Published: December 2017

Both para-aminohippurate (PAH) and pyrazinamide inhibited the uricosuric response to probenecid administration. The mechanism of this inhibition of probenecid uricosuria was assessed in 18 male subjects. The decrease in uricosuria was assessed in 18 male subjects. The decrease in uricosuric response to probenecid observed after pyrazinamide administration or PAH infusion occurs by different mechanisms. Administration of PAH and probenecid together resulted in reduced excretion of both drugs. PAH was weakly uricosuric and did not appear to inhibit urate secretion. PAH inhibition of probenecid uricosuria is accounted for by inhibition of probenecid secretion. Probenecid excretion was not affected by pyrazinamide administration. Inhibition of probenecid-induced uricosuria by pyrazinamide is most likely due to inhibition of urate secretion. The urate secretory carrier inhibited by pyrazinamide appears to be independent of that responsible for secretion of probenecid and PAH. Probenecid secretion appears to be required for its uricosuric effect.
Absence of significant secretory flux of phosphate in the proximal convoluted tubule
Authors: Greger R. F. , Lang F. C. , Knox F. G. , Lechene C. P.
Published: December 2017

The presence of phosphate secretion by the renal tubule in mammals has been controversial. Recently, in a micropuncture and microperfusion study, net secretion of phosphate was reported for the proximal tubule of rats which were infused with parathyroid hormone (PTH) and phosphate. Since the finding of net secretion of phosphate by the proximal tubule is in contradiction to other reports, the question was reinvestigated with the use of microperfusion techniques that were modified to allow identification of sample contamination. Studies were performed in intact dogs, phosphate- and PTH-loaded intact rats, and phosphate-loaded, acutely thyroparathyroidectomized rats. After exclusion of contaminated samples, no significant influx of phosphate was found in any of the three groups. Neither increased plasma phosphate concentration nor the infusion of parathyroid hormone unmasked a secretory process for phosphate. It is concluded that phosphate transport in the proximal tubule is essentially a unidirectional phenomenon, i.e., reabsorption is not opposed by significant backflux of phosphate.
Renin stimulation by isoproterenol and theophylline in the isolated perfused kidney
Authors: Viskoper R. J. , Maxwell M. H. , Lupu A. N. , Rosenfeld S.
Published: December 2017

The intrarenal mechanisms of renin release were studied in the isolated perfused rabbit kidney during stimulation by isoproterenol, 0.01 mug/kg per min, and by theophylline, 0.87 mg/kg per min. In the absence of urinary flow during the early stages of perfusion, isoproterenol caused a 17% increase of renal vein serum renin concentration (RVSRC) (P less than 0.001) without changing renal blood flow, renal vascular resistance, or serum potassium. dl-Propranolol, 2.0 mg/kg per min. abolished this isoproterenol-induced renin release. A moderate reduction in perfusion pressure prior to the infusion of isoproterenol resulted in a marked additional stimulation of renin release. Studies during and following ureteral occlusion demonstrated that theophylline stimulates renin release by decreasing renal vascular resistance, whereas the concomitant increase in sodium transport to the macula densa exerted an opposite effect. dl-Propranolol did not affect theophylline-induced renin secretion. It is concluded that single exogenous stimuli may activate more than one intrarenal mechanism simultaneously. Isoproterenol has a direct renin-stimulatory effect on intrarenal beta-adrenergic receptors that may be reinforced by baroreceptor stimulation. Theophylline stimulates renin via a baroreceptor mechanism, with simultaneous renin suppression via a sodium-macula densa effect.
Vasopressor role of ADH in the pathogenesis of malignant DOC hypertension
Authors: Mohring J. , Mohring B. , Petri M. , Haack D.
Published: December 2017

During the onset of malignant hypertension (MH) in rats treated with deoxycorticosterone trimethylacetate (DOC), plasma arginine vasopressin (AVP) concentrations increase tenfold as a consequence of hypovolemia and hyperosmolality. In benign hypertensive (BH) rats, plasma AVP is increased threefold in comparison with control animals. Plasma renin is markedly suppressed in both BH and MH animals. In MH rats, biologically active AVP antiserum lowers blood pressure (BP) transiently to normal or subnormal levels; in BH rats, a small BP-lowering effect of the AVP antiserum is seen. (Biologically active angiotensin II antiserum does not lower BP in MH rats.) The relationship between the height of BP and plasma AVP concentration in DOC hypertensive rats indicates, when compared with that relationship in diabetes insipidus rats infused with AVP, a marked enhancement of the vasopressor effect of AVP. These findings and the earlier observation of vasopressin-induced vascular damage by Byrom (F. B. Byrom, The Hypertensive Vascular Crisis. London: Heinemann, 1969) strongly suggest that ADH is involved as a vasopressor hormone in the pathogenesis of malignant DOC hypertension.