bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid determination of whole-body bicarbonate kinetics by use of a digital infusion
Authors: Irving C. S. , Wong W. W. , Wong W. M. , Boutton T. W. , Shulman R. J. , Lifschitz C. L. , Malphus E. W. , Helge H. , Klein P. D.
Published: December 2017

Accurate determination of substrate oxidation rates from breath 13CO2 levels often requires information on the bicarbonate status of the subject. We have developed a rapid method to obtain a complete set of bicarbonate kinetic parameters, prime bicarbonate pools with 13C, clamp breath 13CO2 levels rapidly and accurately with predetermined ranges, and provide a steady base-line enrichment of 13C for a subsequent substrate oxidation measurement. The method consists of administering NaH13CO3 intravenously as a combination of a bolus dose, an exponentially decreasing infusion, and a constant infusion. A Harvard model 2729 microprocessor-controlled syringe pump was modified for external control and coupled to a Hewlett-Packard HP-85 desk-top computer to deliver the complex infusion. An infusion algorithm that would rapidly attain and maintain an increase of 50% 13C enrichment of breath CO2 was derived by using the SAAM-27 program to interrogate a three-compartmental model of bicarbonate kinetics in normal, fasted, resting adult subjects. When the method was tested on five adult fasted subjects who had rested for 1.5 h, plateau enrichments were achieved within 10–20 min. The bicarbonate pool sizes and kinetic parameters obtained by compartmental analysis of their 13CO2 data were used to obtain a refined infusion protocol, which resulted in more rapid attainment of plateau enrichments. If carried out immediately before a substrate oxidation test, the method can provide a complete description of bicarbonate kinetics for use in the compartmental and noncompartmental analysis of substrate catabolism.(ABSTRACT TRUNCATED AT 250 WORDS)
Arterial pressure responses to increasing interstitial potassium in hindlimb muscle of dogs
Authors: Rybicki K. J. , Kaufman M. P. , Kenyon J. L. , Mitchell J. H.
Published: December 2017

Static contraction of hindlimb skeletal muscle is known to increase reflexly arterial pressure and heart rate. Potassium is known to be released by the working muscle and is thought to activate the afferents responsible for the reflex cardiovascular responses to muscular contraction. However, it is not known whether potassium, at interstitial concentrations within the range observed during static contraction, is capable of stimulating these afferents. Thus we injected potassium into the gracilis artery of chloralose-anesthetized dogs while we measured interstitial potassium concentrations in the gracilis muscle with potassium-selective electrodes. In 16 dogs, we found that potassium injections, which increased interstitial potassium concentrations by 4.7 +/- 0.3 mM, increased mean arterial pressure by 18 +/- 3 mmHg and heart rate by 12 +/- 8 beats/min; cutting the obturator nerve abolished these increases. These heart rate and blood pressure responses were of short duration (20 +/- 7 s), even though interstitial potassium remained elevated for a period of several minutes. In 5 of the 16 dogs, static contraction of the gracilis muscle for 60 s increased interstitial potassium concentration by 4.3 +/- 0.3 mM. Our data are consistent with the hypothesis that potassium plays a role in causing the reflex cardiovascular responses to static muscular contraction.
Comparison of lactate and glucose metabolism in the developing porcine placenta
Authors: Ramsay T. G. , Sheahan J. A. , Martin R. J.
Published: December 2017

The present experiment was conducted to determine whether lactate is an important metabolic substrate for the developing porcine placenta. Pregnant gilts were anesthetized with pentobarbital sodium (5 mg/kg) at 65, 85, or 110 days of gestation and underwent an abdominohysterectomy. Fetal and maternal placental tissues were obtained and isolated for enzyme analysis and tissue incubations. Tissues were incubated for 2 h in Krebs-Ringer bicarbonate buffer containing 10 mM glucose, 1.0 mM Na-palmitate, 2.0 mM L-lactate, and 2% albumin. The incorporation of glucose or lactate into CO2, total lipids, and fatty acids was examined by radioactive tracers. Lactate was shown to be at least as important a substrate as glucose for utilization through these metabolic pathways in both the fetal and maternal placentas during gestation. This ability to metabolize lactate may serve as a conservation mechanism to spare other nutrients for transfer to the fetus. Additionally, analysis of enzyme and incubation data indicated that the fetal and maternal placenta follow different developmental patterns, implying the origins for (or mechanisms of) regulation of these two tissues may differ.
Kinetics of intravenous saline infusion and selective IgG removal in rabbits
Authors: Smeby L. C. , Charlton B. , Schindhelm K.
Published: December 2017

Selective removal of approximately 60% of the plasma immunoglobulin G (IgG) mass in conscious rabbits was studied and compared with similar procedures combined with intravenous saline infusions equal to 7.5% body weight. Plasma concentrations of 125I-IgG and endogenous IgG were employed in model analysis to examine if saline infusions could be used to shift IgG from extra- to intravascular pool, thereby making more protein available for removal by extracorporeal plasma treatment. After IgG removal, the fractional metabolic clearance and the extra- to intravascular transfer coefficient were 40-50% lower than before IgG removal, and model simulations indicated that this may be caused by IgG binding. Saline infusion resulted in 40% more IgG mass in plasma 24 h after treatment compared with procedures without saline. Model analysis indicated that the increased IgG mass in plasma after saline procedures could be explained by a three- to fourfold increase in lymphatic clearance. Crystalloid infusions may be a method to increase the efficacy of repeated plasma exchange treatment.
Hypoglossal and phrenic responses to cholinergic agents applied to ventral medullary surface
Authors: Haxhiu M. A. , Mitra J. , van Lunteren E. , Bruce E. N. , Cherniack N. S.
Published: December 2017

Application of cholinergic agents on the ventrolateral surface of the medulla in areas in which the “central chemoreceptors” are believed to be located stimulates breathing. It is also known that cranial nerves, such as the hypoglossal, have respiratory modulated activity (greater in inspiration than expiration) that responds to many of the same stimuli which affect breathing. In the present study we compared effects of cholinergic agents (acetylcholine, carbachol, methacholine, eserine) directly applied to chemoreceptive areas on the ventral medullary surface on phrenic and hypoglossal nerve activity. Studies were performed in paralyzed, anesthetized, and artificially ventilated cats after vagotomy. All cholinergic agents increased hypoglossal activity significantly more than phrenic activity in animals ventilated with O2 or 7% CO2 in O2 whether or not the carotid sinus nerves were intact. Atropine applied topically to the same medullary area blocked the respiratory effects of locally administered acetylcholine. The results suggest that cholinergic agents applied centrally can increase both phrenic and hypoglossal activity. Moreover the effects of the drugs are relatively greater on XII nerve activity than on phrenic discharge, suggesting that the drive from medullary cholinergic structures is distributed with unequal weight to different respiratory motoneurons.
Mosquito circadian flight rhythms: differential effects of constant light
Authors: Clopton J. R.
Published: December 2017

The flight activity of Culiseta incidens was automatically recorded in constant darkness and constant light after entrainment to light:dark 12:12 to determine the usefulness of a formal circadian pacemaker model in which the periods of two oscillators respond reciprocally to light intensity. Period at activity onset lengthened approximately 0.4 h from darkness to 0.1 lx, whereas period at offset shortened approximately 0.4 h. Thus within this range, the onset of the nocturnal active phase obeyed Aschoff's rule for nocturnal animals, and the offset (or onset of diurnal rest phase) obeyed the rule for diurnal animals. These data supported a model in which, as light intensity increases, the period of one oscillator (evening) increases while that of another (morning) decreases. This model, with additional assumptions, also provided a framework for mutually consistent explanations of other features among the data. These included long periods at 3.5 lx, short periods at 35 lx, a progressively earlier occurrence of inactivity with increasing light intensity, and a clear example of circa-bi-dian (approximately 2 days) rhythmicity.
Responses of primate T1-T5 spinothalamic neurons to gallbladder distension
Authors: Ammons W. S. , Blair R. W. , Foreman R. D.
Published: December 2017

Extracellular unit recordings were obtained from 44 spinothalamic tract (STT) neurons in the T1-T5 segments of 15 alpha-chloralose anesthesized monkeys (Macaca fascicularis). Each cell had a somatic receptive field in the left chest region and was excited by electrical stimulation of cardiopulmonary sympathetic afferent fibers. Gallbladder distension to pressures between 20 and 100 mmHg increased activity in 16 of 44 neurons. Responses usually consisted of bursts of activity associated with increased gallbladder pressure (phasic responses) followed by maintained activity during the distension (tonic responses). Magnitude of phasic responses was linearly related to the distending pressure and was consistently greater than magnitude of tonic responses. The gallbladder-responsive and nonresponsive groups included similar proportions of wide dynamic range, high threshold, and high-threshold inhibitory cells. Nine of 10 gallbladder-responsive cells and 11 of 21 gallbladder-nonresponsive cells increased their discharge rate after injection of 2 micrograms/kg bradykinin into left atrium. Activity of cells with gallbladder input increased from 14 +/- 4 to 33 +/- 4 spikes/s. Cells without gallbladder input increased their discharge rate to a significantly less degree (10 +/- 3-23 +/- 4 spikes/s). These results indicate that upper thoracic STT neurons may increase their activity during gallbladder distension. Convergence of afferent information from the chest and gallbladder may explain chest pain occurring during gallbladder disease. Furthermore the tendency of gallbladder-responsive cells to respond to bradykinin injections with a high rate of discharge could explain how this chest pain of gallbladder origin may closely mimic pain of angina pectoris.
Role of renin-angiotensin-aldosterone system in NaCl appetite of rats
Authors: Fregly M. J. , Rowland N. E.
Published: December 2017

A variety of experimental paradigms is now known to induce an appetite for NaCl solutions in rats. These include 1) bilateral adrenalectomy; 2) hypothyroidism; 3) salivariectomy; and 4) administration of hydrochlorothiazide, metyrapone, estrogen, methylxanthines, captopril, propranolol, large doses of deoxycorticosterone acetate, and intraperitoneal isotonic glucose or subcutaneous polyethylene glycol. A point of commonality among these is that a reduction in preference threshold accompanies the appetite for NaCl in all cases thus far tested. An additional point is the fact that each paradigm inducing a salt appetite, except salivariectomy, can be linked to an effect on the renin-angiotensin-aldosterone system. The level of angiotensin II in the brain may play a role in the induction of a salt appetite in the rat. It is clear, however, that modest doses of mineralocorticoid hormones, given in conjunction with the stimulus producing the salt appetite (e.g., adrenalectomy, thyroidectomy, or treatment with captopril), reduces NaCl intake to control level. Although this effect can be partially explained in most cases by the consequent reduction in angiotensin II production, the salt appetite that occurs when mineralocorticoid concentration in blood is high and angiotensin II concentration is low, or when both are low, requires another explanation. This may be related to the effect of mineralocorticoid hormones on salivary sodium concentration. The role of the concentration of sodium in saliva on intake of NaCl solution provides an alternative explanation for the induction of a salt appetite in rats and merits additional study.
Fever-specific changes in central MSH and CRF concentrations
Authors: Holdeman M. , Khorram O. , Samson W. K. , Lipton J. M.
Published: December 2017

The concentration of melanocyte-stimulating hormone (melanotropin; MSH) within the septal region of the brain increases during the fever, and septal injections of MSH are antipyretic. Corticotropin-releasing factor (CRF), when injected intracerebroventricularly, is also antipyretic. Using sensitive radioimmunoassays of microdissected tissue extracts, we established the presence of immunoreactive MSH (IRMSH) and CRF (IRCRF) within discrete central nervous system sites of the rabbit. Leukocytic pyrogen-induced fever and hyperthermia due to heat exposure did not alter concentrations of IRMSH or IRCRF in tissue extracted from preoptic-anterior hypothalamic or midbrain central gray regions. However, significantly greater levels of IRMSH were detected in septal extracts of febrile rabbits than in similar extracts from afebrile controls or heat-stressed animals. A significant decrease in IRCRF was detected in paraventricular nucleus extracts from febrile animals compared with extracts from afebrile controls or heat-stressed rabbits. Our results support the hypothesis that these central peptides have a role in temperature control during fever. Since no changes were detected in extracts from hyperthermic rabbits, it appears that changes in concentration of these neuropeptides within particular brain regions are specific to the febrile state and are not caused by elevation of body temperature or by nonspecific stress.
Dynamic model of gonadotropin-releasing hormone receptor function
Authors: Zolman J. C.
Published: December 2017

Functioning gonadotropin-releasing hormone (GnRH) receptor is visualized as an aggregate of identical subunits (not all always functional) with the aggregate usually transformed into at least four successive structurally distinct receptor assemblies. Receptor protein, hormone molecule(s), and carrier(s) are main components of each functional subunit. During the normal lifespan of the functional subunit, each carrier is responsible for delivery of a unit amount of product, per unit time, to the cell surface (ratio between functional carrier and bound hormone, 1:1). Association of hormone with the receptor protein is essential, not only for the initial formation of the functional subunits but also for subsequent conformational changes that are in turn essential for formation of the aggregate only, or later (in the presence of sufficiently high GnRH concentrations) for a successive formation of a family of receptor assemblies (occurring one at a time). The successive assemblies differ from the aggregate by being more stable and from one another by increasing GnRH binding affinity and apparent capacity. They resist stimulation during protracted decay (desensitization).
Level of satiety: GABA and pentose shunt activities in three brain sites associated with feeding
Authors: Kasser T. R. , Harris R. B. , Martin R. J.
Published: December 2017

The hypothesis addressed was that metabolic activity within specific brain areas may be altered to depict peripheral metabolic status. Sixty-three female Sprague-Dawley rats (225 g) received 150, 100, or 50% of normal intake by gastric intubation for 7 days. The incentive for spontaneous feeding would be inhibited in 150% fed rats (anoretic), stimulated in 50% fed rats (hungry), and maintained in 100% fed rats (control). Glucose flux through the gamma-aminobutyric acid shunt of the ventrolateral hypothalamus was 32% lower in hungry rats and 35% higher in anoretic rats relative to control values. Glucose flux through the pentose shunt of the ventromedial hypothalamus was 111% lower in hungry rats and 152% higher in anoretic rats relative to control values. Pentose shunt activity in the area postrema nucleus of the solitary tract (AP NTS) was 116% lower in hungry rats and 60% higher in anoretic rats relative to control values; however, hungry and anoretic rats had AP NTS pentose shunt activities that were not different from control values but were different from each other. The data demonstrate that within selective brain sites, specific pathways for glucose oxidation are affected by energy intake and may be used by the rat to assess and respond to changes in peripheral energy status.
Autonomic modulation of refractoriness in canine specialized His-Purkinje system
Authors: Turner L. A. , Zuperku E. J. , Bosnjak Z. J. , Kampine J. P.
Published: December 2017

The effects of autonomic efferent stimulation on refractoriness of the specialized His-Purkinje system were examined in open-chest dogs anesthetized with 1.0% halothane. In eight animals submaximal bilateral stimulation of the ventral ansae subclavia decreased (P less than or equal to 0.01) the average functional refractory period for the propagation of His bundle extrastimuli to five ventricular recording sites (HP-FRP) by 10.9 +/- 0.6 ms. Submaximal stimulation of the decentralized vagal nerves that produced first degree atrioventricular block did not affect ventricular refractoriness. Combined vagosympathetic stimulation produced a smaller (P less than or equal to 0.01) decrease of the average HP-FRP (7.2 +/- 1.1 ms) than that produced by sympathetic stimulation alone. Administration of atropine abolished (P less than or equal to 0.05) vagal antagonism of the shortening effect of isoproterenol on the average HP-FRP. Treatment with propranolol reversed (P less than or equal to 0.01) the sympathetic effect on the average HP-FRP and nonuniformly increased refractoriness in the His-Purkinje system. The latter changes were abolished (P less than or equal to 0.05) by infusion of phentolamine. The autonomic nervous system modulates His-Purkinje refractoriness by actions mediated by cholinergic and both alpha- and beta-adrenergic receptors.
Cortisol dynamics during seawater adaptation of Atlantic salmon Salmo salar
Authors: Nichols D. J. , Weisbart M.
Published: December 2017

We examined plasma cortisol concentration (PCC), cortisol metabolism, and cortisol protein binding (CPB) in chronically cannulated Atlantic salmon (Salmo salar) during seawater (SW) adaptation. PCC rose significantly 2 h after freshwater (FW) to SW changeover but tended to be lower for 6 days thereafter. Plasma chloride concentrations began to stabilize 24–48 h after entry to SW. Cortisol metabolic clearance rate (MCR) was significantly higher 24 h after SW transfer than in FW; CPB and plasma protein concentration were significantly lower, but cortisol production rate was unchanged. The change in plasma chloride after 24 h in SW was negatively correlated with the change in plasma protein (r = -0.915, n = 9, P less than 0.001). The changes in CPB and plasma protein were correlated with the change in MCR (r = -0.643, n = 14, P less than 0.02; r = -0.850, n = 9, P less than 0.005). We hypothesize that these changes in protein concentration reflect an ion-induced expansion of extracellular volume and lead to increased MCR.
Morphology of isolated crustacean larval salt glands
Authors: Lowy R. J. , Conte F. P.
Published: December 2017

Larval salt glands isolated from the naupliar brine shrimp (Artemia salina) were examined using light microscopy and scanning and transmission electron microscopy. These methods demonstrated that most cellular and subcellular features of the in vitro organ compared favorably with those seen in vivo. This salt gland measures 130 micron in diameter and is comprised of 50-70 secretory cells, which are of a single epithelial cell type. Characteristic ultrastructural features that are well preserved include apical to basal cell polarity, apical plasma membrane projections, and the extent of the basolateral tubular labyrinth and its association with numerous mitochondria. Some features that have been altered are a decrease in cell-cell contact, separation of septate junctions, and expansion of tubular labyrinth lumens and mitochondrial cristae. Use of this preparation has allowed examination of the salt gland cell's hemocoelic surface for the first time and provided information about the ultrastructure of the tufts formed by the apical plasma membrane.
Gastric emptying of milk in rat pups
Authors: Lorenz D. N.
Published: December 2017

Gastric emptying of rat's milk in rat pups was investigated using two experimental procedures. In the first experiment pups were matched for age, body weight, and gastric contents after ingesting mother's milk in the natural suckling situation. Then the pups were placed in one of three different environmental conditions for the test period. They were killed at 0, 2, or 4 h, and their gastric contents were weighed. The results revealed a very consistent gastric emptying process across ages, regardless of the presence or absence of the dam or moderate alterations in the environment. Gastric volume appeared to be the only factor affecting the rate of gastric emptying. In the second experiment gastric emptying was investigated in fasted pups after intubation with one of several volumes of rat's milk. Pups were killed at 0, 1, 2, or 4 h after gavage, and their gastric contents were weighed. The results indicate that the rate of gastric emptying is directly related to the immediate gastric volume. The emptying process is described as exponential, but the distribution of halftime values indicates the kinetics are not strictly first order. The volume-related effect on gastric emptying rate also correlated highly with the volume-related suppression of ingestion reported in a previous study. A model of gastric emptying is proposed for infant mammals.
Analysis of amiloride inhibition of chorda tympani taste response of rat to NaCl
Authors: DeSimone J. A. , Ferrell F.
Published: December 2017

The kinetics of inhibition by amiloride of the integrated chorda tympani response were investigated in rats subjected to lingual stimulation with NaCl. In one series of experiments the time of exposure to amiloride was varied at fixed amiloride concentration. Exposure to 10(-4) M amiloride for 2 s reduced the response to 0.5 M NaCl by approximately 50%. The time course of recovery from amiloride inhibition was first order (relaxation time approximately equal to 4 min) for all exposure times. For exposure to 10(-4) M amiloride for less than or equal to 30 s recovery was better than 90% in 20 min. Not all of the chorda tympani response was inhibited by amiloride. With 0.5 M NaCl there was a 70% reduction in response, whereas at 0.05 M NaCl the reduction was only 30%. Parallel effects of amiloride were seen in the short-circuit current of an in vitro preparation of canine lingual epithelium. Amiloride reduced the short-circuit current by the same percentage as it inhibited the chorda tympani response. These results suggest that gustatory transduction is mediated in part by an apical membrane transport system that can be inhibited by amiloride. There exists, however, a second transducing element that is amiloride insensitive. A model is developed, assuming, in part, that the neural response reflects the flows of Na through amiloride-sensitive apical pathways.
Renal function in sea snakes. I. Glomerular filtration rate and water handling
Authors: Yokota S. D. , Benyajati S. , Dantzler W. H.
Published: December 2017

Renal clearance studies were performed on anesthetized sea snakes (Aipysurus laevis) under various salt and volume loads. The median values for the control glomerular filtration rate (GFR) and urine flow rate (V) were 0.78 and 0.11 ml X kg-1 X h-1, respectively. Acute salt loading with 1 mol/l NaCl significantly increased V to 0.68 ml X kg-1 X h-1, whereas acute water loading significantly decreased GFR to 0.17 ml X kg-1 X h-1. Acute loading with either isosmotic NaCl or seawater did not significantly alter either V or GFR. Chronic loading with water or seawater by intraperitoneal injection significantly increased both GFR and V. No consistent relationship between plasma osmolality and GFR was observed. Instead a threshold-type relationship existed between GFR and plasma K concentration. Within each treatment group, high plasma K concentrations were correlated with low GFRs. There was an abrupt increase in GFR at low plasma K concentrations, the inflection point ranging from 2.5 to 4 mmol/l K depending on the experimental treatment. A curvilinear relationship existed between V and GFR; as GFR increased, V approached a maximal limiting value. At low GFRs (less than 0.2 ml X kg-1 X h-1), V often exceeded GFR, indicating net fluid secretion that was correlated with net Na movement. In addition, there was an inverse relationship between urine-to-plasma osmolality ratio and V. At low values of V, urine osmolalities modestly exceeded those of the plasma. Overall, renal function of A. laevis appears to be adapted to conserve water.
Light effects on circadian timing system of a diurnal primate, the squirrel monkey
Authors: Hoban T. M. , Sulzman F. M.
Published: December 2017

We examined light effects on the circadian timing system of the squirrel monkey. A phase-response curve to 1-h pulses of light was constructed for the drinking rhythm of six animals. The phase-response curve was the same type as that exhibited by nocturnal rodents, with phase delays occurring early in the subjective night and phase advances late in the subjective night. The range of entrainment of 10 monkeys to days with 1 h light and x h dark was determined. Five monkeys used to generate the phase-response curve were also used in the range of entrainment determination. For short light-dark cycles the range of entrainment was smaller than that expected, with no monkey entraining to a day length of less than 23.5 h.
Atriopeptin stimulation of rectal gland function in Squalus acanthias
Authors: Solomon R. , Taylor M. , Dorsey D. , Silva P. , Epstein F. H.
Published: December 2017

The rectal gland of the shark plays a significant role in the homeostasis of extracellular volume. Regulation of rectal gland function is under hormonal control, but the precise identity of the humoral mediator is unknown. Atriopeptin stimulates rectal gland chloride secretion in vivo. This stimulation of epithelial transport is accompanied by systemic and local hemodynamic effects. Atriopeptin also stimulates chloride secretion by the in vitro perfused rectal gland, an effect that is not accompanied by hemodynamic changes. Extracts of shark heart, but not muscle, brain, kidney, or intestine, contain a heat-stable trypsin-sensitive substance capable of in vitro stimulation of rectal gland chloride secretion. Electron micrographic analysis reveals multiple neurosecretory-like granules in atrial cardiocytes that are only rarely seen in ventricular cardiocytes. By using the in vitro perfused gland as a biologic assay, serum obtained after extracellular volume expansion reveals the presence of a rectal gland stimulatory factor that is not present in serum before expansion. These results are consistent with the hypothesis that atriopeptin is present in shark cardiocytes and is released during volume expansion. The atriopeptin stimulates rectal gland chloride secretion, providing a negative feedback mechanism for the regulation of extracellular volume.
Whole-body calcium flux rates in cichlid teleost fish Oreochromis mossambicus adapted to freshwater
Authors: Flik G. , Fenwick J. C. , Kolar Z. , Mayer-Gostan N. , Wendelaar Bonga S. E.
Published: December 2017

Radiotracer techniques were used to measure influx and efflux rates of Ca2+ in freshwater-adapted Oreochromis mossambicus. The influx rate of Ca2+ is related to body weight (W) as Fin = 50W0.805 nmol Ca2+/h. For a 20-g fish the calculated influx rate was 558 nmol Ca2+/h, and this was attributed largely to extraintestinal uptake since the drinking rate was estimated to be only 28 microliter water/h, which corresponds to an intake of 22.4 nmol Ca2+/h. The Ca2+ efflux rate was calculated using the initial rate of appearance of radiotracer in the ambient water and the specific activity of plasma Ca2+. Tracer efflux rates were constant over 6-8 h, which indicated that there was no substantial loss of tracer in either the urine or the feces because this would have resulted in random bursts of tracer loss. Efflux rates then primarily represent integumentary and presumably branchial efflux rates. The efflux rate of Ca2+ is related to body weight as Fout = 30W0.563 nmol Ca2+/h, which means an efflux rate of 162 nmol Ca2+/h for a 20-g fish. The net whole-body Ca2+ influx, calculated as Fnet = Fin - Fout, was 396 nmol/h for a 20-g fish, which proves that the ambient water is an important source of Ca2+.
Energy sources in fasting grey seal pups evaluated with computed tomography
Authors: Nordoy E. S. , Blix A. S.
Published: December 2017

Grey seal pups (Halichoerus grypus) were collected at the time of weaning (early November) and starved for 31 days at thermoneutrality. During starvation body weight decreased linearly, whereas metabolic rate was stable at 1.58 +/- 0.13 (SD) W X kg-1. Metabolic rate as related to body weight was significantly higher (P less than 0.01) than predicted by Kleiber (The Fire of Life, New York: Kreiger, 1975). Respiratory quotient averaged 0.67 +/- 0.03 during the 1st wk but increased to an average of 0.76 +/- 0.04 during the final week of fasting. Body composition was evaluated three times during starvation by use of computed tomography. The area of blubber and skeletal muscle in three transverse (thoracic, abdominal, pelvic) sections of the animals decreased on average 27.6 +/- 4.8 and 18.6 +/- 8.5%, respectively, from days 3 to 31 of fasting. Caloric content of blubber and skeletal muscle was determined by bomb calorimetry, and the caloric content of catabolized tissue was estimated. Based on this information it was calculated that approximately 94% of the energy expended by grey seal pups during the first 4 wk of the postweaning fast is derived from their subcutaneous deposits of fat.
Proctolin induces rhythmic contractions and spikes in Limulus heart muscle
Authors: Watson W. H. , Hoshi T.
Published: December 2017

The Limulus heart is neurogenic. If the cardiac ganglion is removed, all spontaneous contractions of the heart are abolished. Application of the pentapeptide proctolin (greater than 1 microM) causes the deganglionated heart muscle to beat with a frequency and amplitude slightly greater than those of a normal heart with an intact cardiac ganglion. At a proctolin concentration of 1 microM, rhythmic beating requires 2–10 min to develop, and up to 1 h of continuous washing is required to reverse the effect. A contracture often precedes the rhythmic contractions. Proctolin-induced rhythmicity occurs in the presence of tetrodotoxin (TTX) and in Na+-free saline. These effects of proctolin are not mediated by residual portions of the cardiac ganglion. Contractions are inhibited by Ca2+-free EGTA saline, CoCl2, MnCl2, and CdCl2. Proctolin causes no significant long-term changes in the myocardial resting potential or apparent input resistance. However, proctolin causes rhythmic 10- to 20-mV spikes that precede each contraction of the myocardium. Production of these spikes appears to be the mechanism by which proctolin causes rhythmic contractions in normally quiescent deganglionated myocardium of Limulus.
Glucose clamping and cardiovascular function in endotoxic dogs
Authors: Kober P. M. , Thomas J. X. , Filkins J. P.
Published: December 2017

Fasted mongrel dogs were anesthetized with pentobarbital sodium and instrumented for the continuous measurement of blood glucose (BG), a lead II electrocardiogram, and pressures in the left ventricle (LV), pulmonary artery, and aorta. Cardiac output was measured every 15 min using thermodilution and LV stroke work, and pulmonary and systemic resistances were calculated. After a 30-min pretreatment period, glucose clamping was initiated. The desired glucose levels were reached within 45 min (hypoglycemic 20 +/- 1 mg/dl, n = 11; normoglycemic 85 +/- 1, n = 7; hyperglycemic 156 +/- 3, n = 7). At this point dogs were treated with either endotoxin (8 mg/kg to 6 hypoglycemic, 4 normoglycemic, and 4 hyperglycemic) or saline (5 hypoglycemic, 3 normoglycemic, and 3 hyperglycemic). All infusions were terminated after 2 h glucose clamping, and all dogs were monitored either until death or for a maximum of 10 h. Hypoglycemic clamping curtailed survival in endotoxic dogs. Hyperglycemic clamping markedly prolonged survival. Normoglycemic clamping left survival time unchanged compared with untreated dogs. The effects of glucose clamping on cardiovascular function during endotoxic shock paralleled the effects on survival. Cardiovascular function was also depressed in hypoglycemic-clamped saline dogs. It is concluded that glucose dyshomeostasis may be a crucial factor in the development of fatal cardiovascular dysfunction and shock after endotoxin administration.
GABA-mediated baroreceptor inhibition of reticulospinal neurons
Authors: Sun M. K. , Guyenet P. G.
Published: December 2017

A total of 45 cells with spinal projections, pulse-synchronous discharges, and extreme sensitivity to changes in arterial pressure were recorded in the retrofacial portion of nucleus paragigantocellularis lateralis (PGCL) in halothane-anesthetized rats. Every unit tested was inhibited by iontophoretic applications of gamma-aminobutyric acid (GABA), glycine, and taurine and excited by glutamate or the GABA receptor antagonist bicuculline methiodide. The inhibitory effect of GABA was antagonized by bicuculline methiodide but not by strychnine; the effect of glycine was eliminated by strychnine but unaffected by bicuculline. Iontophoretically applied bicuculline completely antagonized the time-locked reduction in unit activity resulting from increases in arterial pressure while strychnine was ineffective. 1-Glutamate, applied in a dose that produced a larger increase in the unit discharge rate than bicuculline, did not significantly alter the magnitude of the inhibition associated with increases in arterial pressure. It is concluded that GABA or a related substance mediates the inhibition of PGCL reticulospinal neurons resulting from the activation of arterial baroreceptors.
Impaired secretion of vasopressin and oxytocin in rats after lesions of nucleus medianus
Authors: Gardiner T. W. , Verbalis J. G. , Stricker E. M.
Published: December 2017

Regulation of posterior pituitary secretion of vasopressin (AVP) and oxytocin (OT) was studied in rats given electrolytic lesions of ventral nucleus medianus (vNM). As described previously, rats with such lesions were chronically hypernatremic and showed impaired drinking responses to an osmotic challenge. AVP secretion in response to osmotic stimuli also was significantly blunted, although sufficient increases in plasma AVP levels did occur, in association with an abnormally high range of plasma sodium concentrations, to allow urinary concentration comparable to control animals. These findings suggest that vNM lesions cause an upward resetting of the osmotic threshold for AVP secretion. In contrast, hypovolemia, produced by subcutaneous polyethylene glycol treatment, and hypotension, produced by phentolamine treatment, both evoked AVP responses in rats with vNM lesions that were equivalent to those seen in control animals. Plasma OT responses to osmotic and hemodynamic stimuli were analogous to the AVP responses. These findings reproduce the major clinical features observed in humans with the disorder of essential hypernatremia and by doing so support proposals that this disorder is caused by lesions in the vicinity of the anterior hypothalamus that result in selective destruction of afferent osmosensitive inputs to the neurohypophysis.
Hemorrhage in DOC-salt hypertensive rats: plasma and platelet vasopressin
Authors: Crofton J. T. , Share L. , Brooks D. P.
Published: December 2017

The effect of two consecutive hemorrhages, each 10% of blood volume, on plasma vasopressin concentrations was determined in conscious unilaterally nephrectomized Long-Evans rats made hypertensive by treatment for 3 wk with deoxycorticosterone (DOC) and substitution of 1% saline for drinking water (DOC-salt rats) or DOC alone (DOC rats) and in normotensive unilaterally nephrectomized rats drinking water (H2O rats) or saline (NaCl rats). In response to 20% hemorrhage, blood pressure decreased more (P less than 0.01) and plasma vasopressin increased less (P less than 0.01) in the DOC-salt rats than in the other groups. Under basal conditions, immunoreactive vasopressin was found in the platelets in NaCl, DOC, and DOC-salt rats (P less than 0.01) but not in H2O rats. Platelet vasopressin increased (P less than 0.05-0.01) in response to hemorrhage only in DOC-salt rats. In conclusion, the vasopressin response to hemorrhage in DOC-salt rats is impaired; platelet immunoreactive vasopressin is of little importance in normal rats but is increased by treatment with DOC and/or chronic salt loading; and platelet vasopressin increased in response to hemorrhage only in DOC-salt rats.
Effects of temperature and PCO2 on O2 affinity of pigeon blood: implications for brain O2 supply
Authors: Pinshow B. , Bernstein M. H. , Arad Z.
Published: December 2017

Bird heads contain paired countercurrent heat exchangers, the ophthalmic retia, which function in brain temperature regulation. Blood, cooled by evaporation from the nasal and buccal mucosa and the ocular surfaces, flows to the venous side of each rete and there gains heat from arterial blood flowing countercurrent to it. The cooled arterial blood then flows to the brain. To ascertain whether characteristics of the blood reaching the cooling surfaces and the retia favor O2 and CO2 exchange, as well as heat exchange, we studied blood O2 affinity in relation to temperature (T) and CO2 tension (PCO2) in six pigeons (Columba livia). O2 tension (PO2) at half-saturation (P50, Torr) was measured at various combinations of T and PCO2 from 36 to 44 degrees C and 9 to 33 Torr. pH was uncontrolled. O2 half-saturation of hemoglobin (P50) varied according to P50 = 1.049T + 0.573PCO2–19.444. We propose that shifts in blood O2 affinity, associated with T and PCO2 at the mucosa and eyes and in the retia, would enhance the brain O2 supply by an exchange of O2 and CO2 between air and blood at moist cephalic surfaces, thereby augmenting O2 and reducing CO2 in the venous return to the retia and diffusion of O2 from veins to arteries in the retia. This mechanism might have particular importance at high altitude; we calculate that at 7,000 m above sea level both O2 saturation and PO2 could double in blood flowing from the retia to the brain.
Effects of alpha-adrenergic blockade on cardiovascular responses to static exercise in cats
Authors: Waldrop T. G. , Bielecki M. , Gonyea W. J. , Mitchell J. H.
Published: December 2017

Static exercise performed by conscious cats elicits increases in heart rate (HR), left ventricular systolic pressure (LVSP), and the maximal rate of left ventricular pressure development [LV(dP/dt)max]. The increased HR is mediated primarily by withdrawal of parasympathetic tone, whereas a beta-adrenergic mechanism is responsible for the LV(dP/dt)max increase. In the present study the cardiovascular responses to static exercise in awake cats was recorded before and after alpha-adrenergic blockade. Pressure transducers were implanted into the left ventricle of cats who had been trained operantly to perform static exercise. Significant increases in LVSP, LV(dP/dt)max and HR occurred in all cats during static exercise before blockade. In contrast, alpha-adrenergic blockade (phentolamine, 2.5 mg/kg iv) abolished the exercise-induced increase in LVSP but did not prevent increases in HR and LV(dP/dt)max. The cats performed fewer exercise bouts per day during alpha-blockade than when unblocked. We conclude that an alpha-adrenergic mechanism mediates the increase in LVSP in response to static exercise in conscious cats.
Neurotransmitter modulation of VIP release from cat cerebral cortex
Authors: Wang J. Y. , Yaksh T. L. , Harty G. J. , Go V. L.
Published: December 2017

The cortical release of vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) in vivo was examined by superfusion of the pial surface of the cerebral cortex of the cat. The modulation of cortical VIP release by several neurotransmitters [gamma-aminobutyric acid (GABA), opioids, norepinephrine, acetylcholine, and glutamate] normally present in the cerebral cortex was studied by administering respective agonists and antagonists for their receptors. Although GABA and opiate agonists did not influence the resting release of VIP-LI, GABA antagonists (picrotoxin and bicuculline) and opiate antagonists (naloxone and naltrexone) significantly elevated the resting release. The evoked release from cortex of VIP-LI (by electrical stimulation of the cortex or mesencephalic reticular formation) was suppressed by GABA and mu- but not delta-, kappa-, or sigma-opioid receptor agonists. Glutamate and kainic acid increased the resting release of VIP-LI from the cerebral cortex. Noradrenergic (alpha 2 but not alpha 1) displayed an inhibitory effect on the evoked release of cortical VIP-LI release. Resting VIP-LI release was enhanced by cholinergic agents (carbachol). The facilitatory effects of mesencephalic reticular formation stimulation on VIP-LI release were demonstrated by atropine. These observations suggest characteristic interactions reflecting the circuitry modulating the activity of cortical VIP-releasing neurons.
Technique for continuous measurement of compliance in isolated vascular segments
Authors: Bell L. B. , Zuperku E. J. , Kampine J. P.
Published: December 2017

A method has been developed that provides an on-line (1/s) measurement of elastance [E = 1/compliance (C)] in a perfused isolated vessel segment in situ. Values of E can be obtained as a function of perfusion pressure (P) or in response to drug interventions. Noncompliant stainless steel tubes are used as inflow and outflow cannulas. Segment P is obtained from a short small-bore stainless steel catheter and miniature pressure transducer. During constant flow through the inflow cannula, an adjustable outflow resistance is used to set the segment P. Simultaneous activation of solenoid pinch valves, for 200 ms, compresses in-line Silastic tubing next to each cannula and serves to simultaneously 1) isolate the segment and 2) inject a small volume into the segment (delta V). This delta V results in a step increase in segment P (delta P). delta V is not significantly altered by changing the volume of air in the in-line windkessel reservoir (when air volume is greater than or equal to 100 ml), mean perfusion pressure (over a range of 50-150 mmHg) or compliance of the test cell. Therefore, delta P alpha E, and 1/delta P alpha C. Since this recorded variable is linearly related to C, actual C can be continuously recorded on a recorder after a simple two-point calibration process. C as determined by this method was found to be linearly related (r = 0.997) to calculated C of a test cell air bubble (range: 0.1 less than C less than 0.7 microliter/mmHg; resolution: 0.001 microliter/mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)
Attenuation of hindlimb vasodilation in heat-stressed baboons during dehydration
Authors: Thornton R. M. , Proppe D. W.
Published: December 2017

The influence of dehydration on hindlimb vasodilation during environmental heating (EH) was examined in eight unanesthetized chronically instrumented baboons. Mean iliac blood flow (MIBF), arterial blood pressure, and core temperature (Tc) were measured during EH of baboons in euhydrated and dehydrated states. EH consisted of acute exposure to high ambient temperatures (39-44 degrees C) until Tc reached 39.5 degrees C. Dehydration was produced by 68-72 h of fluid deprivation, which caused increases in plasma osmolality [291 +/- 1 (SE) to 338 +/- 6 mosmol/kg H2O] and sodium concentration (143 +/- 2 to 163 +/- 3 meq/l) and a 16% fall in plasma volume. The primary influence of dehydration was attenuation of the progressive rise in MIBF and iliac conductance (IC) during EH. Absolute MIBF and IC levels at Tc = 39.5 degrees C during EH were 44 and 52%, respectively, lower in the dehydrated state. Also, the MIBF-Tc and IC-Tc linear regression coefficients during EH were lower by 33 and 43%, respectively, in the dehydrated state. Since limb skeletal muscle blood flow does not increase during EH, we conclude that dehydration attenuates the heat stress-induced rise in skin blood flow in baboons, an influence that is similar to what occurs in humans.
Renal excretion in gull chicks: effect of parathyroid hormone and calcium loading
Authors: Clark N. B. , Mok L. L.
Published: December 2017

Renal clearance experiments were performed on herring gull (Larus argentatus) and great black-backed gull chicks (L. marinus) to test the importance of parathyroid hormone (PTH), parathyroidectomy (PTX), and calcium loading on excretion patterns of sodium, potassium, calcium, and phosphate. PTX reduced the relative clearance of phosphate to near zero within 2 h. Conversely, PTH stimulated net secretion of phosphate within 40 min. Calcium loading caused a drop in phosphate excretion identical to that of PTX, presumably by inhibiting PTH secretion by the parathyroid glands. This also could be reversed by administration of PTH. Serum phosphate values were highest in PTX gulls and lowest in calcium-loaded gulls. The relative clearance of calcium (CCa/CIn) was elevated in calcium-loaded birds. However, CCa/CIn did not change significantly in response to either PTX or PTH in the sham-operated or PTX birds. Serum calcium values were highest in calcium-loaded gulls and lowest in PTX gulls, the reciprocal of the effects on serum phosphate.
Heterogeneous mechanical response of rat knee menisci to thermomechanical stress
Authors: Zernicke R. F. , Vailas A. C. , Shaw S. R. , Bogey R. A. , Hart T. J. , Matsuda J.
Published: December 2017

Thermodilatometric, dynamic thermomechanical, and light-microscopic analyses were done on the anterior and posterior regions of the rat knee menisci to correlate regional differences in morphology and extracellular matrix composition with regional mechanical behavior. Following the administration of a general anesthetic, menisci were excised from 12 young female Sprague-Dawley rats. During thermodilatometric and thermomechanical testing, tissue temperature was increased at a constant rate of 3.5 degrees C/min from 30 to 100 degrees C. Light microscopy revealed regional differences in cell density and proteoglycan content. The anterior horn was significantly heavier (greater than 87%) and thicker (greater than 60%) than the posterior region. During thermal analyses, both the anterior and posterior horns decreased in tissue thickness as the temperature increased from 30 to 73 degrees C. After 73 degrees C, however, the posterior horn expanded significantly, whereas the anterior remained in a comparatively contracted state. The rates of linear contraction and expansion of the posterior horn were seven times those of the anterior horn, and the stiffness of the anterior horn was significantly greater than the posterior horn.