bluuebunny/crossref_metadata_2025 huggingface dataset:
Water vapor absorption in insects
Authors: Machin J.
Published: December 2017

In common with other animals the principal examples of water transport in insects are to be found in processing food and in excretion. Some insects and other arthropods are able to absorb water vapor using preexisting buccal or rectal structures. This unique exploitation of atmospheric water depends on adequate areas for condensing water vapor and the capacity for considerable "uphill" water transport. All known uptake mechanisms depend on producing fluids of sufficiently low water activity to bring about condensation from a range of environmental humidities. In the best-understood examples (mealworms and their relatives) active KCl transport by the Malpighian tubules generates osmotic pressures sufficient to extract water from activities down to 0.88. A standing gradient model seems to describe the coupling in the tubular lumen between water flows and ion transport. Low water permeabilities and ion transport modulated with flow rate are unusual features of this coupling.
Central injection of angiotensin II alters catecholamine activity in rat brain
Authors: Sumners C. , Phillips M. I.
Published: December 2017

Centrally injected angiotensin II (ANG II) produces a pressor response. The effect of ANG II injected intracerebroventricularly on catecholamine utilization in specific rat brain regions was examined. A pressor dose of ANG II stimulated an increase in norepinephrine (NE) utilization in the locus coeruleus, raphe magnus and AI regions of the brain stem, and in the hypothalamus. These increases in NE utilization were selective, and dopamine utilization was not altered in the same regions. Also, the changes in NE utilization were direct and not due to the rise in blood pressure caused by ANG II, since a similar pressor effect caused by intravenously injected hypertonic saline did not alter NE utilization in any of the above regions. Areas such as the subfornical organ and organum vasculosum of the lamina terminalis that contain both catecholamines and ANG II receptors did not show a substantial change in catecholamine utilization after intracerebroventricularly injected ANG II. This study demonstrates that specific brain NE rich regions are activated by intracerebroventricular injection of ANG II. Some of these regions correlate with known blood pressure control centers and the data points to brain catecholaminergic regions which are involved in the central ANG II pressor response.
Effects of spaceflight on trabecular bone in rats
Authors: Jee W. S. , Wronski T. J. , Morey E. R. , Kimmel D. B.
Published: December 2017

Alterations in trabecular bone were observed in growing male Wistar rats after 18.5 days of orbital flight on the COSMOS 1129 biosatellite. Spaceflight induced a decreased mass of mineralized tissue and an increased fat content of the bone marrow in the proximal tibial and humeral metaphyses. The osteoblast population appeared to decline immediately adjacent to the growth cartilage-metaphyseal junction, but osteoclast numbers were unchanged. These results suggested that bone formation may have been inhibited during spaceflight, but resorption remained constant. With the exception of trabecular bone mass in the proximal tibia, the observed skeletal changes returned to normal during a 29-day postflight period.
Pulmonary mechanoreceptors in the dipnoi lungfish Protopterus and Lepidosiren
Authors: DeLaney R. G. , Laurent P. , Galante R. , Pack A. I. , Fishman A. P.
Published: December 2017

Pulmonary mechanoreceptors in the dipnoi lungfish Protopterus aethiopicus and Lepidosiren paradoxa were identified and characterized both in vivo and in vitro. Both slowly adapting receptors (SAR) and rapidly adapting receptors (RAR) were found, with the majority of receptors being of the slowly adapting type. The SAR discharged during inflation once their threshold volume was exceeded, and this activity persisted during prolonged lung inflation. For most of the SAR, interaction between the rate of inflation and lung volume was involved in setting the firing rate of the receptor. Increase in intrapulmonary carbon dioxide partial pressure decreased the activity of the SAR during sustained inflation at a constant intrapulmonary pressure. The RAR also discharged during inflation once the threshold volume was exceeded. However, in contrast to the SAR, the RAR became silent within 1.5 – 15 s after the end of inflation. The activity of these receptors during inflation was influenced predominantly by the rate and influenced little by the volume of inflation. According to these observations, the behavior of lungfish pulmonary mechanoreceptors closely resembles that of pulmonary mechanoreceptors in amphibians but differs from that of mechanoreceptors in the swim bladder of teleosts.
Suprachiasmatic nuclei influence circannual and circadian rhythms of ground squirrels
Authors: Zucker I. , Boshes M. , Dark J.
Published: December 2017

Golden-mantled ground squirrels, maintained under constant conditions of photoperiod and temperature sustained lesions of the suprachiasmatic nuclei (SCN) or of the medial basal hypothalamus. Destruction of the SCN eliminated or disrupted circadian activity rhythms and shortened the period of the circannual reproductive cycle. Circannual body weight cycles were eliminated or disrupted in several SCN-lesioned animals and one squirrel had a 3- to 5-mo body weight rhythm; however, most SCN-lesioned squirrels with disrupted circadian activity cycles manifested normal circannual body weight rhythms. The SCN are important for circadian organization of locomotor activity of this diurnal rodent, but the generation and expression of circannual body weight and reproductive rhythms can proceed in the absence of coherent circadian organization. The SCN are less essential for the generation and expression of circannual than of circadian cycles
Effects of area postrema/caudal medial nucleus of solitary tract lesions on food intake and body weight
Authors: Hyde T. M. , Miselis R. R.
Published: December 2017

Lesions of the area postrema/caudal medial nucleus of the solitary tract (AP/cmNTS), located on the surface of the dorsal medulla of the rat, cause a transient syndrome of hypophagia and body weight loss, with the establishment of a new growth curve at a lower body weight set point. The regulatory responses to prolonged food deprivation, glucoprivic stimulation, and chronic access to a palatable diet are left largely intact. However, there is an overconsumption of highly palatable foods during acute exposure to supermarket and high-fat diets. Intestinal transit and gastric retention are unaffected by the lesion, indicating normal motor function within the gastrointestinal system. The hypophagia and chronic depression of body weight by the AP/cmNTS lesion demonstrate that this area is an important part of the larger neurocircuitry subserving feeding behavior and energy balance.
Neural control of insulin secretion: interaction of norepinephrine and acetylcholine
Authors: Campfield L. A. , Smith F. J.
Published: December 2017

We have quantitatively characterized the interaction of several concentrations of norepinephrine and acetylcholine applied simultaneously on insulin secretion in response to an intermediate glucose concentration (10 mM) from statically incubated pancreatic islets isolated from normal rats. When either norepinephrine or acetylcholine were applied alone, insulin secretion was respectively inhibited or enhanced in a dose-dependent manner. When combinations of norepinephrine and acetylcholine were applied simultaneously to the islet, insulin secretion was enhanced, inhibited, or not affected. The net effects of the interaction of norepinephrine and acetylcholine on insulin secretion were not only a function of the concentration of each neurotransmitter but also the relative concentrations of both neurotransmitters. Analysis of these interaction data suggests that 1) insulin secretion is the result of a complex interaction between sympathetic and parasympathetic neural and metabolic inputs; 2) norepinephrine and acetylcholine modulate insulin secretion primarily by direct action on the beta-cell membrane; 3) insulin secretion is more sensitive to perturbations in norepinephrine concentration than acetylcholine concentrations under these experimental conditions; and 4) the autonomic nervous system has the potential to play a major role in the control of insulin secretion in response to glucose.
Calorigenic effect of glucagon and catecholamines in king penguin chicks
Authors: Barre H. , Rouanet J. L.
Published: December 2017

The calorigenic action of glucagon and catecholamine infusion was evaluated in winter-acclimatized king penguin chicks at 20 and 0 degrees C ambient temperature (Ta). At Ta = 20 degrees C the mean increase in metabolic rate was 0.73 W . kg-1 for epinephrine (80 micrograms . kg-1), 0.42 W . kg-1 for norepinephrine (150 micrograms . kg-1), and 1.16 W . kg-1 for glucagon (0.75 micrograms . kg-1); i.e., respectively 30, 17, and 47% of the control value. The maximum response to glucagon reached 89% over control. At Ta = 0 degrees C, for the same glucagon infusion, the mean increase in specific metabolic rate was 0.84 W . kg-1, 27% of control rate. In the cold, glucagon infusion inhibited shivering and substituted its calorigenic action, resulting in a less apparent effect. In contrast with the negligible effect of catecholamines, glucagon infused at low doses exerted a powerful calorigenic action in young king penguins and could be considered as a possible nonshivering thermogenesis mediator.
Energy metabolism rate equation for fasting and postabsorptive subjects
Authors: Ben-Porat M. , Sideman S. , Bursztein S.
Published: December 2017

The energy metabolism rate, an important parameter in severe clinical polytrauma and burns, is evaluated here using mass conservation law and simple thermodynamic considerations. The expressions for the energy and fat metabolism rates are evaluated utilizing easily measurable quantities: oxygen consumption, CO2 production, and nitrogen excretion rates. The derived equations are identical for the fasting and postabsorptive states, independent of feed composition. A new criteria for distinguishing between the fasting and postabsorptive states is suggested. These equations should help in evaluating energy metabolism rate for patients receiving continuous parenteral nutrition.
Reflex interactions between aerial and aquatic gas exchange organs in larval bullfrogs
Authors: West N. H. , Burggren W. W.
Published: December 2017

The interaction between lung and gill ventilation was investigated in unanesthetized Rana catesbeiana larvae (stage XVII-XIX) in hypoxic (PO2 = 80 +/- 1 Torr), normoxic (PO2 = 142 +/- 1 Torr), and hyperoxic (PO2 = 580 +/- 23 Torr) water. Lung inflation with N2, air, or O2 initially reduced the frequency (fG) and buccal pressure amplitude (PBC) of the following gill ventilation cycles. However, 65 s after lung inflation fG was significantly greater for N2 inflation than for air inflation, whereas fG after O2 inflation was significantly lower. In further experiments, the effects of lung inflation and gaseous PO2 on gill ventilation were dissociated. Flow of N2, air, or O2 was established through the lungs of tadpoles in hypoxic water. Flow of N2 produced a significant rise in fG and flow of O2 a significant fall compared with airflow. Regardless of the PO2 of the gas, subsequent lung inflation produced by occlusion of the outflow cannula caused a fall in fG and PBC from the preestablished flow value. We conclude that lung inflation per se and the resulting increase in PO2 both contribute to the suppression of gill ventilation following spontaneous air breathing, which serves to limit O2 loss of the gills in aquatic hypoxia.
Simultaneous determination of net uptake of 16 amino acids by a marine bivalve
Authors: Manahan D. T. , Wright S. H. , Stephens G. C.
Published: December 2017

High-performance liquid chromatography was used to measure the simultaneous transport of 16 amino acids from seawater into the mussel Mytilus edulis. All the substrates, including representative neutral, basic, and acidic amino acids, were accumulated from ambient concentrations as low as 5 nM. Influx of four radioactively labeled amino acids was compared with their net flux. In each case the influx of the 14C-labeled substrate, determined from the removal of isotope from test solutions, accurately represented the net flux of that substrate as measured by direct chemical analysis. Ammonia was the only compound observed to be routinely lost from these animals. Rates of uptake of individual amino acids, each at concentrations of 10 nM, ranged from 2.4 to 7.0 nmol . g dry flesh wt-1 . min-1. The studies show that M. edulis is capable of a net uptake of dissolved amino acid from the very low concentrations characteristic of seawater. Moreover, net accumulation can occur against chemical gradients calculated to be in excess of one million to one. The rates of amino acid uptake may contribute significantly to the animals' energy requirements.
Post-cough heart rate response: influence of age, sex, and basal blood pressure
Authors: Wei J. Y. , Rowe J. W. , Kestenbaum A. D. , Ben-Haim S.
Published: December 2017

Although the chronotropic response to cough may provide an index of the capacity for cardioacceleration, how the heart rate change may be influenced by age is not established. In 213 healthy men and women aged 20-90 yr we measured the heart rate response following three forceful coughs performed over a 3-s period. Resting heart rate was not age related. Increasing age was associated with a linear reduction in cough-induced maximum rise in heart rate (r = -0.58, P less than 0.0001) and a prolongation of the time to peak heart rate (P less than 0.001). The responses were not different between women and men. Multiple regression analysis performed on age and systolic, diastolic, and mean basal arterial pressure measurements revealed that age was the sole variable that correlated significantly with peak heart rate response. Thus advancing age is associated with a decline in the amplitude and rapidity of the chronotropic response to cough. These age-related changes are independent of the basal arterial pressure and may contribute to the decreased cardiovascular homeostatic response to stress, such as upright posture or volume depletion, which is commonly observed in the elderly.
Electrolytes in slow and fast muscle fibers of humans at rest and with dynamic exercise
Authors: Sjogaard G.
Published: December 2017

Sodium, potassium, and magnesium were analyzed in human slow-twitch (ST) and fast-twitch (FT) skeletal muscles. In contrast to other species, no relation was found between fiber composition and electrolyte distribution. In soleus (S), vastus lateralis (VL), and triceps brachii (TB) the overall mean values for 6 men and 6 women were 44 mmol K/100 g dry wt and 11 mmol Na/100 g dry wt; the intracellular concentrations were 161 mmol K/l and 26 mmol Na/l with no differences between the muscles. Analysis of fragments of single ST and FT fibers from each of the muscles also showed no difference between the fiber types in Na and K content. Small differences were seen between the muscles with regard to Mg, but these were not related to fiber composition compared with other species. During exercise to exhaustion (3 bouts of bicycling for 3 min at 325-395 W, 6 men) the extracellular electrolyte concentrations for Na, K, and Mg increased from 134 to 140, 4.5 to 5.8, and 0.75 to 0.87 mmol/l, respectively (P less than 0.05). In VL Na content increased from 9.8 to 16.5 mmol/100 g dry wt, while intracellular [Na] remained constant. In contrast, intracellular [K] decreased from 161 to 141 mmol/l (P less than 0.05). No such changes occurred in TB. In concert with other studies the present changes in electrolytes in the working muscles indicate that muscle fatigue may be related to changes at the muscle fiber membrane.
Gastric distension and short-term satiety in the rhesus monkey
Authors: Wirth J. B. , McHugh P. R.
Published: December 2017

Fasted rhesus monkeys given access to a solution of glucose (0.5 kcal/ml) would, within 15 min, consume it to satiety. If, after such a 15-min bout of consumption, the contents of the stomach were removed via an indwelling cannula, the monkeys would again consume glucose in a following 15-min bout. With experiments paired such that gastric contents were either removed or left in place, the total glucose consumption over four successive bouts when the stomach was emptied between bouts was twice that when the contents were undisturbed. Despite this large difference in consumption, the amount of glucose passing through the pylorus to the intestine was not different in the two conditions. Similar results were demonstrated in a nine-bout series of the same design, in a two-bout series in which gastric contents remaining after the first bout were replaced with equivolumetric amounts of 0.15 M NaCl, and in a one-bout experiment in which consumption of glucose followed a 0.15-M NaCl preload equal in volume to the glucose intake in a single bout the preceding day. Since in the stomach-empty and the stomach-distended conditions of each experiment the postpyloric compartments (small intestine, portal, and systemic circulations) were exposed to identical and physiological amounts of glucose, the difference in consumption must be ascribed to the distension of the stomach.
Distributed model for drug delivery to CSF and brain tissue
Authors: Collins J. M. , Dedrick R. L.
Published: December 2017

Measurements of drug concentration in cerebrospinal fluid (CSF) provide the most accessible index of drug delivery to the brain. Our perception of the blood-brain barrier has been largely shaped by these measurements. A crucial question for the interpretation of these data is the nature of the relationships between drug concentration in CSF and the drug concentration profile in brain tissue. A distributed model for the delivery of drugs via plasma to brain tissue and CSF is presented, and the relationships between capillary exchange, tissue diffusion, and CSF turnover rate are explored. The effects of blood-brain barrier disruption on tissue and CSF concentrations are also simulated.
Vasopressin in blood and third ventricle CSF during dehydration, thirst, and hemorrhage
Authors: Szczepanska-Sadowska E. , Gray D. , Simon-Oppermann C.
Published: December 2017

Samples of cerebrospinal fluid (CSF) were collected from the anterior part of the third cerebral ventricle of mongrel dogs with a chronically implanted device. Repeated experiments with simultaneous sampling of CSF and venous blood in 60- to 90-min intervals were performed in conscious dogs after 24-h water deprivation and during subsequent rehydration by drinking, during thirst stimulation by intravenous infusion of 5% saline, and during blood removal (12 ml X kg body wt-1). The CSF and plasma samples were analyzed for osmolality and arginine vasopressin (AVP) with a radioimmunoassay. Compared with normally hydrated dogs, 24-h water deprivation caused plasma AVP to rise significantly from 2.5 to 7.7 pg X ml-1 and CSF AVP from 24.2 to 31.3 pg X ml-1. Subsequent drinking significantly reduced plasma and CSF AVP. Thirst stimulation by hypertonic infusions was associated with rises of plasma and CSF AVP. Modest reduction of blood volume also increased both plasma and CSF AVP. Plasma AVP in each of the described physiological disturbances of salt or fluid balance was positively correlated with CSF AVP.
Renal ammonia excretion and production in goldfish, Carassius auratus, at low environmental pH
Authors: King P. A. , Goldstein L.
Published: December 2017

Renal ammonia excretion and production were investigated in normal and acidotic goldfish (Carassius auratus). Goldfish were made acidotic by exposure to a low pH environment (pH 4.0), which caused a lowering of blood pH from 7.88 to 7.61. Environmental acidification resulted in an increase in total renal ammonia excretion (from 0.43 to 1.00 mueq X 100 g-1 X h-1) and urinary concentration (from 0.58 to 0.76 mM), as well as a rise in renal titratable acid output (from -0.57 to +0.62 mueq X 100 g-1 X h-1). The acidotic fish showed a rise in urine flow that was due to an increased glomerular filtration rate. In vitro studies demonstrated the capacity for renal ammonia formation from aspartate, alanine, glutamine, glutamate, and glycine. The relatively high level of glutamate in the renal tissue suggested that the generation of ammonia from these amino acids occurs via the formation of glutamate, either by deamidation of glutamine or transdeamination of aspartate and alanine. Both ammonia production by isolated renal tubules and individual enzyme assays in kidney homogenates indicated that aspartate has the greatest potential as a renal ammonia precursor in vitro. The purine nucleotide cycle, investigated with the use of the inhibitor coformycin, does not appear to contribute to ammonia production in the kidney of this species.
Stimulation of pancreatic afferents reflexly activates the cardiovascular system in cats
Authors: Ordway G. A. , Longhurst J. C. , Mitchell J. H.
Published: December 2017

Chemical stimulation of afferents from the stomach and gallbladder has been shown reflexly to activate the cardiovascular system. It is not known, however, whether stimulating afferents from the pancreas evoke similar reflex activity. Therefore we recorded the cardiovascular responses in cats anesthetized with methoxyflurane, while we applied capsaicin (200 micrograms/ml) and bradykinin (0.001-1,000 micrograms/ml) to the surface of the pancreas. Topically applying these algesic substances evoked cardiovascular responses that included increases in systemic arterial pressure, heart rate, left ventricular dP/dt at 40-mmHg developed pressure and systemic vascular resistance. Bilateral vagotomy at the level of the diaphragm did not diminish the cardiovascular responses evoked by capsaicin or bradykinin. In contrast, removal of the celiac and superior mesenteric ganglia abolished the cardiovascular responses demonstrated previously when capsaicin or bradykinin was applied to the pancreas. We conclude that afferent endings in the pancreas can be stimulated reflexly to increase cardiovascular function in cats. This reflex activation represents a potential mechanism for eliciting the cardiovascular changes observed during acute pancreatitis, particularly the marked vasoconstriction that may lead to renal failure.
Relative peripheral and central chemosensory responses to metabolic alkalosis
Authors: Pokorski M. , Lahiri S.
Published: December 2017

We investigated the relative contribution of peripheral and central chemosensory mechanisms to ventilatory responses to metabolic alkalosis in anesthetized cats by simultaneously measuring steady-state carotid body chemosensory activity and ventilation. The effects of graded steady-state levels of metabolic alkalosis at constant levels of arterial O2 and CO2 partial pressure (PaO2 and PaCO2, respectively) were studied first. Then the responses to isocapnic hypoxia and hyperoxic hypercapnia before and after the induction of a given level of metabolic alkalosis were studied. From the relationship between the carotid chemosensory activity and ventilation, the contribution of the two chemosensory mechanisms was estimated. The depression of ventilation that could not be accounted for by a decrease in the carotid chemosensory activity is attributed to the central effect. We found that metabolic alkalosis decreased both carotid chemosensory activity and ventilation at all levels of PaO2 or PaCO2. The ventilatory effect of alkalosis increased during hypoxia due to suppression of both peripheral chemosensory input and its interaction with the central CO2-H+ drive. During hyperoxia the central effect of alkalosis was predominant, although the peripheral effect increased with hypercapnia. We conclude that acute metabolic alkalosis suppresses both peripheral and central chemosensory drives, and its ventilatory effect grows larger with decreasing PaO2.
Regulation of ovarian follicular growth and steroidogenesis by low-amplitude LH pulses
Authors: Peluso J. J. , Gruenberg M. L. , Steger R. W.
Published: December 2017

A perifusion culture system controls the delivery of regulatory agents such that their concentration in the culture chamber is known at each and every point in time. The concentration in the culture chamber is predicted by the following equation: C(t) = Cf + (Ci - Cf)e(-R.t)/V, where C(t) is concentration in culture chamber (CC) at time t, Cf is concentration in holding flask (HF) (final CC concentration at t = infinity), Ci is initial CC concentration (t = 0), R is rate of media delivery from HF to CC (ml/h), V is volume of medium in CC (ml), and t is time (h). With this perifusion culture system, metestrous rat ovaries were exposed to tonic levels of follicle-stimulating hormone (FSH) and either tonic levels or hourly pulses of luteinizing hormone (LH). Both groups, however, received the same amount of FSH and LH. Compared with tonic levels, hourly pulses of LH increased estradiol-17 beta and suppressed testosterone secretion. In addition, pulsatile LH caused 1) a reduction in the atresia of small and midsized antral follicles, 2) an increase in atretic large follicles, and 3) an increase in the percent of growing midsized follicles. These results clearly demonstrate that ovarian responses depend on the pattern of LH stimulation. Since the LH pulses used in this study mimic in vivo metestrous levels, the LH pulses may be important in controlling ovarian function in vivo. The mechanism by which the ovary can distinguish between tonic and pulsatile stimuli remains to be determined.
Discontinuities in phase-resetting experiments
Authors: Glass L. , Winfree A. T.
Published: December 2017

The effects of perturbing an on-going biological oscillation with a single brief stimulus are considered. If the time from some observable event before the stimulus to the next event after the stimulus is plotted as a function of the phase of the stimulus, then there may be discontinuities in this plot. The discontinuities reflect the size of the stimulus and the topological properties of the biological oscillation. The implications for experiments are discussed.
Blood-brain interfaces in vertebrates: a comparative approach
Authors: Cserr H. F. , Bundgaard M.
Published: December 2017

The neuronal microenvironment in the vertebrate brain is isolated from plasma by a series of selective membranes, including the blood-brain barrier, the choroid plexus, and the meningeal barrier. This review deals with the structure and function of these selective membranes in the different vertebrate classes. Present knowledge indicates that all vertebrates have brain barrier membranes and, further, that functional characteristics of these membranes are basically similar in all the vertebrate classes. The blood-brain barrier (or capillary-glial complex) and the meningeal barrier have many of the properties of a tight epithelium, including the presence of tight junctions and specific transport mechanisms. The choroidal epithelium is a typical secretory epithelium. The functional significance of the specialized membranes located at the blood-brain interface is considered, and we suggest that the phylogenetic development of a blood-brain barrier provided neurons of the vertebrate brain with a unique extracellular milieu optimal both for synaptic communication and for nonsynaptic communication via the entire extracellular space.
Circadian rhythm in sweating and cutaneous blood flow
Authors: Stephenson L. A. , Wenger C. B. , O'Donovan B. H. , Nadel E. R.
Published: December 2017

To characterize the changes in the control of the heat loss responses associated with the circadian variation in body temperature, we studied five men during 20 min of exercise in 25 degrees C on 6 separate days. Experiments were conducted at six times, equally spaced over the 24-h day. Esophageal temperature (Tes) and chest sweat rate (msw) were measured continuously, and forearm blood flow (FBF) was measured one to two times per minute. The thresholds for sweating and forearm vasodilation were significantly higher at 1600 and 2000 than at 2400 and 0400, averaging 0.57 and 0.65 degrees C higher, respectively, at 1600 than at 0400. Resting Tes and the Tes thresholds for cutaneous vasodilation and sweating during exercise all showed a similar circadian rhythm. The level at which core temperature is regulated therefore varies over the 24-h day with the zenith occurring around 1600 and the nadir at 0400. However, whereas the slope of the msw-to-Tes relation did not change over the 24-h day, the slope of the FBF-to-Tes relation tended to increase between 0400 and 2400, implying that the circadian rhythm may be more complex than just a shift in the central reference temperature.
Why bluefin tuna have warm tummies: temperature effect on trypsin and chymotrypsin
Authors: Stevens E. D. , McLeese J. M.
Published: December 2017

Giant bluefin tuna warm their viscera during and after a meal. The cecum of a 500-kg bluefin weighs about 9 kg and contains about 20,000 pyloric ceca, each about 10 cm long and 1.5 mm diam. Trypsin was assayed with alpha-benzoyl-DL-arginine-p-nitroanilide HCl and chymotrypsin with glutaryl-L-phenylalanine-p-nitroaniline. The effects of pH on specific activity over the range 7.5–9.5 were negligible relative to temperature effects. Specific activity and maximal reaction velocity extrapolated from a Lineweaver-Burke plot (Vmax) increased with an increase in temperature in a similar fashion (Q10 ca. 2 over temperature range of physiological significance), whereas Km was constant over the same temperature range. The advantage of the warm cecum is that protein is digested in about one-third the time, so that these tuna can process about three times as much food per day.
A mechanistic model of ACTH-stimulated cortisol secretion
Authors: Dempsher D. P. , Gann D. S. , Phair R. D.
Published: December 2017

Adrenal secretory rates of cortisol and arterial concentrations of adrenocorticotropin (ACTH) were measured in conscious trained dogs subjected to intravenous infusion of ACTH. To investigate the causal relation of ACTH to the secretion of cortisol, a mechanistic mathematical model based on current hypotheses of adrenocortical function was constructed and tested. It is widely believed that ACTH stimulates cortisol secretion through adenosine 3',5'-cyclic monophosphate (cAMP), which provides substrate cholesterol by activating cholesterol ester hydrolase and facilitating transport of cholesterol to the side-chain cleavage enzyme. In addition, cholesterol modulates its own synthesis by inhibiting beta-hydroxy-beta-methylglutaryl (HMG)-CoA reductase in the adrenocortical cell. These and other steps in the biosynthetic reaction sequence were described using differential equations subject to the additional constraints imposed by available measurements of intracellular quantities. The resulting model is consistent with many of the known characteristics of the canine adrenal response to ACTH. In this model, steady-state nonlinearities arise from cooperative binding of cAMP to its receptor protein and saturation of mitochondrial pregnenolone transport. The transient response is dominated by a depletable pool of intracellular free cholesterol. Other inferences based on the model are presented, and a quantifiable cellular basis for increased adrenal sensitivity to ACTH is proposed.
Renal response of fowl to hypertonic saline infusion into the renal portal system
Authors: Bailey J. R. , Nishimura H.
Published: December 2017

The avian kidney has a dual blood supply: one arising from the renal arteries and the other from the renal portal system. In anesthetized pullets (Gallus gallus) two major shunt pathways bypassing the kidney were occluded to ensure the venous blood returning from the leg suffuses the peritubular sites before it enters the systemic circulation. Urine was collected from the ureteral orifices. When 5% NaCl (2.0 ml X kg-1 X h-1) was infused for 20 min into the renal portal system, urine flow and urinary NaCl concentrations and excretion rates increased immediately in the infused side. Infusion of 5% NaCl into the systemic circulation produced no natriuresis. Infusion of 10% NaCl (4.0 ml X kg-1 X h-1), into either the systemic or renal portal route, caused a prolonged antidiuresis. Plasma renin activity (PRA) decreased after portal infusion of 5% NaCl and after both portal and systemic infusion of 10% NaCl. These results suggest that 1) infusion of hypertonic saline into the renal portal system produces local renal effects and 2) increases in tubular or peritubular NaCl levels may suppress PRA.
Extremely high pH in biological systems: a model for carbonate transport
Authors: Dow J. A.
Published: December 2017

The pH profiles along the midgut of several lepidopteran species are described in detail. The peak pH recorded (12.0) is the highest observed in a living system and is too high to be achieved by conventional bicarbonate transport. By calculating the rate of net alkali transport in vivo, it is shown that the midgut transports equal amounts of potassium and alkali from blood to gut lumen. It is suggested that the specialized goblet cavities in lepidopteran midgut allow coupling of electrogenic transport of potassium with the electrostatic removal of protons from transported bicarbonate, producing a unique potassium carbonate secretion system.
Calcium homeostasis in cows, with special reference to parturient hypocalcemia
Authors: Ramberg C. F. , Johnson E. K. , Fargo R. D. , Kronfeld D. S.
Published: December 2017

Calcium homeostasis is described in terms of controlled, disturbing, and controlling signals. Plasma calcium concentration [( Ca]p) and bone calcium mass (Mb) are the two main controlled signals. Disturbing signals include calcium intake (Vi) and clearance of plasma calcium to feces ( Clf ), bone (Clo+), placenta (Clp), and milk ( Clm ). Clo+ is a disturbing signal for [Ca]p and a controlling signal for Mb. Homeostasis is maintained by input control. Fractional renal calcium reabsorption (alpha r) decreases when calcium entry into plasma is excessive, but usually calcium entry rate (VT) responds effectively to small changes in [Ca]p associated with changes in disturbing signals. With increases in Vi, both fractional calcium absorption (alpha d) and fraction of bone calcium removed (lambda b) decrease to maintain VT at an appropriate level. As Clo+ declines with advancing age, [Ca]p rises slightly but VT decreases: a 1% change in [Ca]p would lead to a 13% change in VT. In heavily lactating cows, this response of VT may be enhanced. Parturient hypocalcemia may be the result of delayed negative feedback responses of lambda b (1 wk) and alpha d (1 day). Positive feedback between [Ca]p and gut motility may lead to transient suppression of VT during hypocalcemia, despite high plasma parathyroid hormone and 1,25-dihydroxyvitamin D3 concentrations. Parturient paresis is an example of a disordered accelerative response in a complex control system amenable to a variety of physiologically rational management procedures.
Sleep-promoting effects of endogenous pyrogen (interleukin-1)
Authors: Krueger J. M. , Walter J. , Dinarello C. A. , Wolff S. M. , Chedid L.
Published: December 2017

When infused into the lateral cerebral ventricles of rabbits, human endogenous pyrogen (EP) preparations induced dose-dependent increases in slow-wave sleep concomitant with increasing body temperature. Heating EP to 70 degrees C destroyed its sleep-promoting and pyrogenic activity. Anisomycin (an antipyretic) prevented EP from increasing body temperature without affecting its sleep-promoting activity. Intravenous injection of EP induced fever and transient increases in slow-wave sleep but failed to induce prolonged increases in slow-wave sleep. We conclude that the somnogenic activity of EP is not secondary to its pyrogenic activity.
Effect of iron-deficiency anemia on hormone levels and thermoregulation during cold exposure
Authors: Beard J. , Green W. , Miller L. , Finch C.
Published: December 2017

When exposed to an ambient temperature of 4 degrees C, iron-deficient anemic rats become hypothermic. This lesion is related more to anemia than to tissue iron deficiency, since exchange transfusion to hematocrits over 25 restored normal thermoregulatory performance. Likewise poor cold responses were induced in control rats by transfusion to low hematocrits. Cold sensitivity in all anemic animals was paralleled by poor thyroid responses: there was a significant positive correlation between hematocrit and percent rise in triiodothyronine (r = 0.63) and thyroxine (r = 0.53) during 6 h at 4 degrees C. Basal levels of thyroid-stimulating hormone (TSH) were similar in control and iron-deficient animals: after cold exposure, TSH rose to higher levels in those animals with hematocrits over 25 than in those with lower hematocrits. Diminished O2 delivery to tissues responsible for heat production is probably a major component of the cold sensitivity of anemic rats. The novel finding that thyroid hormone responses are compromised by anemia implies effects on hormonal regulation that may also contribute to this functional lesion.
Allometry of water vapor absorption in two species of tenebrionid beetle larvae
Authors: Coutchie P. A. , Machin J.
Published: December 2017

Water vapor absorption is compared in the two tenebrionid larvae Tenebrio molitor and Onymacris marginipennis. Thresholds for absorption and "absorption capacity," which depend on ion transport by Malpighian tubules, are consistently different over the entire size range of the two species. Because of lower thresholds, uptake rates of Onymacris are over double those of Tenebrio in larvae of the same size at identical ambient water activities. By contrast, passive determinants of uptake, rectal conductance, and morphometry are similarly scaled with size in the two species. A ventilatory mechanism of vapor entry into the rectum is proposed for both species, since the anal canal is too long and narrow for exclusively diffusional entry. Vapor uptake in relation to larval mass was described by a simple diffusion model through rectal tissue, where flux varied directly with surface area and inversely with the distance between the lumen and Malpighian tubules. Failure of rectal conductance to increase proportionally with body mass means that size-specific vapor uptake declines with larval size in both species.
Epidermal taurine transport in marine mussels
Authors: Wright S. H. , Secomb T. W.
Published: December 2017

We examined the structural specificity and kinetic characteristics of epidermal taurine transport in the marine mussels Mytilus edulis and M. californianus. The gill was the primary site of taurine uptake in both species, responsible for 70% of the accumulation of radioactively labeled substrate. Taurine transport was inhibited by short-chain beta-amino acids, including beta-alanine and beta-aminobutyric acid (beta-ABA), and by gamma-ABA; alpha-neutral, acidic, and basic amino acids had no effect on this transport. The uptake process was clearly a saturable phenomenon and was adequately described by Michaelis-Menten-type kinetics in both intact animals and isolated preparations of gill. The maximal rates of taurine uptake, expressed per gram of gill tissue, were 8.4 and 3.2 mumol X g-1 X h-1 for M. edulis and M. californianus, respectively. In intact mussels the half-saturation constant for both species ranged from 5 to 8 microM. A mathematical model was developed that describes the epidermal transport of taurine in the gill of the actively pumping mussel. The model takes into account the geometry and pattern of water flow in the gill. Calculations based on this model indicate that because of the convective movement of water through the gill, the actual Michaelis constant of the taurine transporter must be much lower (i.e., 0.5-2.5 microM) than the half-saturation constants determined with intact animals and isolated gills. The model also predicts that the presence of the transporter in the gill can result in a significant reaccumulation of taurine lost from the gill by passive diffusion. We suggest that epidermal taurine transport is involved with maintenance of the high concentrations of this compound commonly associated with gill tissue in mussels.
Effect of hypokinesia and hypodynamia on protein, RNA, and DNA in rat hindlimb muscles
Authors: Steffen J. M. , Musacchia X. J.
Published: December 2017

Weightlessness is associated with a differential atrophic effect on skeletal muscle that has been attributed to both hypokinesia and hypodynamia. A suspension technique was developed to simulate this atrophic effect by inducing hypokinesia/hypodynamia (H/H) in the rat hindlimb. The purpose of the present studies was to assess the effects of H/H on protein, RNA, and DNA contents in hindlimb skeletal muscles. Suspended animals exhibited a differential reduction in absolute muscle protein content with some alterations in protein concentration. Absolute DNA levels did not change in atrophic muscles. There were pronounced effects of suspension on DNA concentration and on protein/DNA, which suggests that muscle atrophy was accompanied by a reduction in muscle cell size. Hindlimb H/H was associated with a decreased absolute content of RNA in atrophic muscles as well as reductions in RNA/DNA. RNA concentration was reduced 16–21% in atrophic muscles. These findings document a pronounced and differential effect of suspension on hindlimb muscle protein and suggest the potential for effects on the capacity for protein synthesis in muscles from suspended animals.
Fetal whole-body interstitial compliance, vascular compliance, and capillary filtration coefficient
Authors: Brace R. A. , Gold P. S.
Published: December 2017

Fluid movements across the capillary wall were studied in chronically catheterized, near-term fetal sheep. We hemorrhaged 15 fetuses and infused isotonic saline in seven fetuses. The average experimental changes in arterial pressure, venous pressure, and blood volume were then analyzed by using mathematical modeling and parameter optimization techniques to estimate mean values for the average whole-body interstitial and vascular compliances of the fetus and for the average whole-body fetal capillary filtration coefficient. After fetal hemorrhage, interstitial compliance averaged 45 ml X mmHg-1 X kg-1 of fetal weight and vascular compliance averaged 3.0 ml X mmHg-1 X kg-1, whereas the capillary filtration coefficient averaged 0.4 ml X min-1 X mmHg-1 X kg-1. For intravenous saline infusions, interstitial compliance averaged 45 ml X mmHg-1 X kg-1, and vascular compliance averaged 3.5 ml X mmHg-1 X kg-1, whereas the capillary filtration coefficient averaged 0.8 ml X min-1 X mmHg-1 X kg-1. These data suggest that the fetus has a high whole-body interstitial compliance and a high capillary filtration coefficient compared with the adult. In addition, it appears that the fetus has the ability to decrease its vascular compliance and capillary surface area after a fetal hemorrhage.
Physiological correlates of locomotory performance in a lizard: an allometric approach
Authors: Garland T.
Published: December 2017

Three measures of locomotory performance and a series of variables thought to affect performance were measured in the iguanid lizard Ctenosaura similis. Burst speed is mass independent; however, endurance time at 1 km/h (EN-DUR) and maximal distance run (MAX DIS) scale as M0.3. Standard and maximal rates of O2 consumption (VO2max) scale as M0.9; VO2max averages 10-fold greater than standard metabolic rate (SMR). Three of ten enzyme activities measured exhibit significant scaling. After statistically removing the effects of body mass, multiple-regression analysis indicates that 1) 89% of the residual variation in ENDUR is correlated with variation among individuals in thigh muscle mass, VO2max, heart mass, and liver citrate synthase (CS) activity; 2) maximal CO2 consumption (VCO2max) and thigh pyruvate kinase activity statistically explain 64% of the variation in MAX DIS; 3) heart and liver masses together predict 35% of the variation in SMR; 4) thigh and liver CS activity, heart lactate dehydrogenase (LDH) activity, and hematocrit account for 67% of the variation in VO2max;5) 97% of the variation in VCO2max is statistically related to variation in liver CS activity, thigh and heart masses, and heart LDH activity.
Pentobarbital anesthesia suppresses basal and 2-deoxy-D-glucose-stimulated plasma catecholamines
Authors: Taborsky G. J. , Halter J. B. , Baum D. , Best J. D. , Porte D.
Published: December 2017

Since pentobarbital anesthesia is known to attenuate certain autonomic reflexes, we tested whether pentobarbital would suppress both basal and stimulated levels of plasma catecholamines and whether a large stimulus might counterbalance this suspected suppression. In untrained dogs, sampled by venipuncture, pentobarbital (30 mg/kg iv) decreased the plasma concentration of epinephrine (E) from 146 +/- 9 to 38 +/- 8 (SE) pg/ml (n = 46) and norepinephrine (NE) from 276 +/- 13 to 91 +/- 10 pg/ml (both P less than 0.0005), suggesting that barbiturate anesthesia suppresses sympathetic outflow in these mildly stressed animals. Pentobarbital also had a marked suppressive effect on the lower baseline catecholamines (E, 84 +/- 14 pg/ml; NE, 118 +/- 10 pg/ml; n = 6) of trained, chronically catheterized dogs, suggesting that it was capable of suppressing resting sympathetic outflow as well. To determine whether pentobarbital anesthesia also suppressed reflex activation of the sympathetic nervous system, the plasma catecholamine response to the neuroglucopenic agent, 2-deoxy-D-glucose (2-DG), was measured in conscious and in pentobarbital-anesthetized dogs. In conscious dogs, the administration of 2-DG (100 mg/kg iv) doubled the base-line plasma concentration of E and NE 30 min after the 2-DG injection. In contrast, the administration of 2-DG (100 mg/kg iv) to pentobarbital-anesthetized dogs produced no significant increase of either plasma catecholamine, suggesting marked suppression of this sympathetic reflex.(ABSTRACT TRUNCATED AT 250 WORDS)
A neural theory of circadian rhythms: Aschoff's rule in diurnal and nocturnal mammals
Authors: Carpenter G. A. , Grossberg S.
Published: December 2017

A neural model of the suprachiasmatic nuclei suggests how behavioral activity, rest, and circadian period depend on light intensity in diurnal and nocturnal mammals. These properties are traced to the action of light input (external zeitgeber) and an activity-mediated fatigue signal (internal zeitgeber) on the circadian pacemaker. Light enhances activity of the diurnal model and suppresses activity of the nocturnal model. Fatigue suppresses activity in both diurnal and nocturnal models. The asymmetrical action of light and fatigue in diurnal vs. nocturnal models explains the more consistent adherence of nocturnal mammals to Aschoff's rule, the consistent adherence of both diurnal and nocturnal mammals to the circadian rule, and the tendency of nocturnal mammals to lose circadian rhythmicity at lower light levels than diurnal mammals. The fatigue signal is related to the sleep process S of Borbely (Hum. Neurobiol. 1: 195–204, 1982.) and contributes to the stability of circadian period. Two predictions follow: diurnal mammals obey Aschoff's rule less consistently during a self-selected light-dark cycle than in constant light, and if light level is increased enough during sleep in diurnal mammals to compensate for eye closure, then Aschoff's rule will hold more consistently. The results are compared with those of Enright's model.