Basal Physiological Conditions Research Articles

Neonate Antigen Presenting Cells within Murine Intestinal Muscular Layer

The intestinal mucosa is exposed to a vast antigenic contact. Several antigen presenting cell (APCs) have been described within the gut associated lymphoid tissue (GALT) (Peyer’s patches, lamina propria, mesenteric lymph nodes, muscular layer); however, this has been done almost exclusively in adult organisms. As there is no characterization of intestinal muscular layer’s APCs during early neonate development we adapted the conventional technique used in adults, to the neonate intestine. We obtained the intestinal muscular layer from early neonates (days 0–3 upon birth) and from young mice (2 and 3 weeks after birth). A planar network of CD45+, MHC-II+, DEC-205+ cells with irregular, some with prominent dendritic morphology was found at birth under basal physiological conditions, whereas Langerin+ DCs appeared after two weeks. The variations seen in CD45+, MHC-II+ and DEC-205+ cells along the early neonatal development, could be related to the new challenges by intestinal antigen exposure from the newborn diet (breast milk, solid food), and to important environmental changes (start walking, exploring the surroundings, etc). Our study reveals the presence of APCs in intestinal muscular layer at birth, and their subsequent changes in physiological, non-induced conditions, contributing basic information about these cells in the neonate intestinal immune system.

In Vivo Clonal Analysis Reveals Self-Renewing and Multipotent Adult Neural Stem Cell Characteristics

Neurogenesis and gliogenesis continue in discrete regions of the adult mammalian brain. A fundamental question remains whether cell genesis occurs from distinct lineage-restricted progenitors or from self-renewing and multipotent neural stem cells in the adult brain. Here, we developed a genetic marking strategy for lineage tracing of individual, quiescent, and nestin-expressing radial glia-like (RGL) precursors in the adult mouse dentate gyrus. Clonal analysis identified multiple modes of RGL activation, including asymmetric and symmetric self-renewal. Long-term lineage tracing invivo revealed a significant percentage of clones that contained RGL(s), neurons, and astrocytes, indicating capacity of individual RGLs for both self-renewal and multilineage differentiation. Furthermore, conditional Pten deletion in RGLs initially promotes their activation and symmetric self-renewal but ultimately leads to terminal astrocytic differentiation and RGL depletion in the adult hippocampus. Our study identifies RGLs as self-renewing and multipotent neural stem cells and provides novel insights into invivo properties of adult neural stem cells.

El Gasto Energético del Venado Cola Blanca (Odocoileus Virginianus Texanus) en Relación a La Precipitación en una Zona Semiárida de México

The energetic requirements of animals are dependent upon their basal metabolism, behavior and physiological conditions. Every activity of the animal represents an energetic cost. It is unknown how deer deal with the thermal conditions in arid and semiarid areas where the air temperature is higher than 40°C and the precipitation is lower than 400 mm annually. Therefore, it is important to understand the energetic cost between sexes under different physiological conditions and in different years. This can also help us understand the response of individuals to annual variation in environmental changes such as the amount of precipitation that influences food availability and amount of protective cover. This research was carried out in Rancho San Francisco and Rancho Penitas, in the Municipality of Lampazos, Nuevo Leon and Progreso, Coahuila, Mexico. From 1995 to 1998, 10 bucks and 14 does with radiocollars (with activity sensor) were tracked. We were able to record three main activities: feeding, walking and resting. We found significant differences in each of the three activity patterns and found that the greatest energy expenditure occurs while the animal is resting. The energy expenditure of the white tailed deer in arid zones differs between sexes because males spent more energy (1726 ± 38 kcal/day/individual) than females (1556 ± 35 kcal/day/individual). We found significant differences between season-year interactions in the three activity patterns. However, the only difference we found between sexes was the energy expenditure while feeding. Deer in arid zones had less energetic expenditure in years with severe drought, when food was scarce, suggesting that they are capable of modifying their behavioral strategies in order to save energy when environmental conditions are unfavorable. Key words: energetic, physiological condition, metabolism, activity pattern, radiotracking, Mexico.

Functional Characterization of a ClC-2-Like Cl− Conductance in Surface Epithelial Cells of Rat Rectal Colon

ClC-2, a member of the voltage-gated Cl(-) channel family, is expressed in the distal colonic surface epithelial cells of various species, but its functional significance remains unclear. Here, by means of electrophysiological and molecular biological techniques, we have identified and characterized a ClC-2-like conductance naturally expressed by surface epithelial cells acutely dissociated from rectal colon of rats fed a standard diet. Whole-cell patch-clamp experiments showed that the surface cells, whether an amiloride-sensitive Na(+) conductance was present or not, displayed a strong hyperpolarization-activated, inwardly rectifying Cl(-) current. Analysis both by in situ hybridization and immunohistochemistry confirmed the expression of ClC-2 in the rectal surface epithelium. The native Cl(-) current shared common electrophysiological properties including voltage-dependent activation, anion selectivity sequence, and Zn(2+) sensitivity with that recorded from HEK293 cells transfected with ClC-2 cloned from rat rectal colon (rClC-2). Cell-attached patch recordings on the surface cells revealed that native ClC-2-like currents activated only at potentials at least 40 mV more negative than resting membrane potentials. In Ussing chamber experiments with rat rectal mucosa, either basolateral or apical application of Zn(2+) (0.1 mM), which inhibited both native ClC-2-like currents and recombinant rClC-2 currents, had little, if any, effects on basal amiloride-sensitive short-circuit current. Collectively, these results not only demonstrate that a functional ClC-2-type Cl(-) channel is expressed in rat rectal surface epithelium, but also suggest that the channel activity may be negligible and thus nonessential for controlling electrogenic Na(+) transport in this surface epithelium under basal physiological conditions.

Regulation of activity-dependent neuroprotective protein (ADNP) by the NO-cGMP pathway in the hippocampus during kainic acid-induced seizure

Activity-dependent neuroprotective protein (ADNP) is widely distributed in the cytoplasm of neurons and astrocytes of the hippocampus. Kainic acid (KA)-induced seizures increases neuronal nitric oxide synthase (nNOS) in neurons and inducible NOS (iNOS) in glia cells which coincides with a reduction in ADNP in the hippocampus. Inhibitors of NOS or soluble guanylyl cyclase (sGC) activity reduce ADNP under basal conditions in the absence of seizures. Treating animals with these inhibitors prior to KA-induced seizure, in particular, L-NAME (NG-nitro-l-arginine methyl ester), advances the onset of the first seizure but reverses the loss of ADNP by 3 days after the first seizure. This suggests that the NO-cGMP pathway has a role in regulating ADNP under both basal physiological conditions and in the pathophysiological changes produced during epileptogenesis.

Novel cyclooxygenase‐catalyzed bioactive prostaglandin F2α from physiology to new principles in inflammation

Prostaglandin F2alpha (PGF2alpha), a foremost stable vasoactive cyclooxygenase (COX)-catalyzed prostaglandin, regulates a number of key physiological functions such as luteolysis, ovarian function, luteal maintenance of pregnancy, and parturition as a constitutive part of ongoing reproductive processes of the body. It has recently been implicated in the regulation of intricate pathophysiological processes, such as acute and chronic inflammation, cardiovascular and rheumatic diseases. Since the discovery of a second isoform of COXs, it has been shown that PGF2alpha can be formed in vivo from arachidonic acid through both isoforms of COXs, namely cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). Being synthesized in various parts of the body, it metabolizes instantly to a number of rather inactive metabolites mainly in the lungs, liver, kidney, and efficiently excretes into the urine. 15-Keto-dihydro-PGF2alpha, a major stable metabolite of PGF2alpha that reflects in vivo PGF2alpha biosynthesis, is found in larger quantities than its parent compound in the circulation and urine in basal physiological conditions, with short-lived pulses during luteolysis, induced termination of pregnancy and parturition, and is increased in tissues and various body fluids during acute, sub-chronic, and severe chronic inflammation. Further, the close relationship of PGF2alpha with a number of risk factors for atherosclerosis indicates its major role in inflammation pathology. This review addresses multiple aspects of PGF2alpha in addition to its emerging role in physiology to inflammation.

Disruption of Rho signaling results in progressive atrioventricular conduction defects while ventricular function remains preserved.

Recent studies suggest that RhoA and Rac1 mediate hypertrophic signals in cardiac myocyte hypertrophy. However, effects on cardiac function caused by inhibition of their activity in the heart have yet to be evaluated. Cardiac-specific inhibition of Rho family protein activities was achieved by expressing Rho GDIalpha, an endogenous specific GDP dissociation inhibitor for Rho family proteins, using the alpha-myosin heavy-chain promoter. Increased expression of Rho GDIalpha led to atrial arrhythmias and mild ventricular hypertrophy in adult mice (4-7 months). However, left ventricular systolic and diastolic function was largely preserved before and after the development of cardiac hypertrophy, indicating that Rho GTPases are not required to maintain ventricular contractile function under basal physiological condition. Electrocardiography and intracardiac electrophysiological studies revealed first-degree atrioventricular (AV) block in the transgenic heart at 1 week of age, which further progressed into second-degree AV block at 4 weeks of age before the development of cardiac hypertrophy. Expression of connexin 40 dramatically decreased from 1 week to 4 weeks of age in the transgenic heart, which may contribute in part to the conduction defects in the transgenic mice. This study provides novel evidence for an important role of Rho GTPases in regulating AV conduction.

Interaction of nitrogen monoxide with hemoglobin and the artefactual production of S-nitroso-hemoglobin

Hemoglobin (Hb) is probably the most thoroughly studied protein in the human body. However, it has recently been proposed that in addition to the well known function of dioxygen and carbon dioxide transporter, one of the main roles of hemoglobin is to store and transport nitrogen monoxide. This hypothesis is highly disputed and is in contrast to the proposal that hemoglobin serves as an NO • scavenger in the blood. In this short review, I have presented the current status of research on the much-debated mechanism of the reaction between circulating hemoglobin and NO •. Despite the fact that oxyHb is extremely rapidly oxidized by NO •, under basal physiological conditions the biological activity of NO • in the blood vessels is not completely lost. It has been shown that three factors reduce the efficiency of hemoglobin to scavenge NO •: a so-called red blood cell-free zone created close to the vessel wall by intravascular flow, an undisturbed layer around the red blood cells – where the NO • concentration is much smaller than the bulk concentration – and/or the red blood cell membrane. Alternatively, it has been proposed that NO • binds to Cys β93 of oxyHb, is liberated after deoxygenation of Hb, and consequently allows for a more effective delivery of O 2 to peripheral tissues. However, because of the extremely fast rate of the reaction between NO • and oxyHb, experiments in vitro lead to artefactual production of large amounts of S-nitroso-hemoglobin. These results, together with other data, which challenge most steps of the NO •-transporter hypothesis, are discussed. To cite this article: S. Herold, C. R. Biologies 326 (2003).

Modulation of catecholamine release by endogenous adenosine in the rat adrenal medulla.

Adenosine was shown to inhibit norepinephrine (NE) release from sympathetic nerve endings. The purpose of this study was to examine whether endogenous adenosine restrains NE and epinephrine release from the adrenal medulla. The effects of an adenosine receptor antagonist, 1,3-dipropyl-8-(p-sulfophenyl) xanthine (DPSPX), on epinephrine and NE release induced by intravenous administration of insulin in conscious rats were examined. Plasma catecholamines were measured by HPLC with an electrochemical detector. DPSPX significantly increased plasma catecholamine in both control rats and rats treated with insulin. The effect of DPSPX on plasma catecholamine was significantly greater in rats treated with insulin. Additional experiments were performed in adrenalectomized rats to investigate the contribution of the adrenal medulla to the effect of DPSPX on plasma catecholamine. The effect of DPSPX and insulin on epinephrine in adrenalectomized rats was significantly reduced compared with that of the controls. Finally, we tested whether endogenous adenosine restrains catecholamine secretion partially through inhibiting the renin-angiotensin system. The effect of DPSPX on plasma catecholamine in rats pretreated with captopril (an angiotensin-converting enzyme inhibitor) was reduced. These results demonstrate that under basal physiological conditions, endogenous adenosine tonically inhibits catecholamine secretion from the adrenal medulla, and this effect is augmented when the sympathetic system is stimulated. The effect of endogenous adenosine on catecholamine secretion from the adrenal medulla is achieved partially through the inhibitory effect of adenosine on the renin-angiotensin system.

Modulation of Catecholamine Release by Endogenous Adenosine in the Rat Adrenal Medulla

Adenosine was shown to inhibit norepinephrine (NE) release from sympathetic nerve endings. The purpose of this study was to examine whether endogenous adenosine restrains NE and epinephrine release from the adrenal medulla. The effects of an adenosine receptor antagonist, 1,3-dipropyl-8-(p-sulfophenyl) xanthine (DPSPX), on epinephrine and NE release induced by intravenous administration of insulin in conscious rats were examined. Plasma catecholamines were measured by HPLC with an electrochemical detector. DPSPX significantly increased plasma catecholamine in both control rats and rats treated with insulin. The effect of DPSPX on plasma catecholamine was significantly greater in rats treated with insulin. Additional experiments were performed in adrenalectomized rats to investigate the contribution of the adrenal medulla to the effect of DPSPX on plasma catecholamine. The effect of DPSPX and insulin on epinephrine in adrenalectomized rats was significantly reduced compared with that of the controls. Finally, we tested whether endogenous adenosine restrains catecholamine secretion partially through inhibiting the renin-angiotensin system. The effect of DPSPX on plasma catecholamine in rats pretreated with captopril (an angiotensin-converting enzyme inhibitor) was reduced. These results demonstrate that under basal physiological conditions, endogenous adenosine tonically inhibits catecholamine secretion from the adrenal medulla, and this effect is augmented when the sympathetic system is stimulated. The effect of endogenous adenosine on catecholamine secretion from the adrenal medulla is achieved partially through the inhibitory effect of adenosine on the renin-angiotensin system.

Cerebral energetics and the glycogen shunt: neurochemical basis of functional imaging.

Positron-emission tomography and functional MRS imaging signals can be analyzed to derive neurophysiological values of cerebral blood flow or volume and cerebral metabolic consumption rates of glucose (CMR(Glc)) or oxygen (CMR(O(2))). Under basal physiological conditions in the adult mammalian brain, glucose oxidation is nearly complete so that the oxygen-to-glucose index (OGI), given by the ratio of CMR(O(2))/CMR(Glc), is close to the stoichiometric value of 6. However, a survey of functional imaging data suggests that the OGI is activity dependent, moving further below the oxidative value of 6 as activity is increased. Brain lactate concentrations also increase with stimulation. These results had led to the concept that brain activation is supported by anaerobic glucose metabolism, which was inconsistent with basal glucose oxidation. These differences are resolved here by a proposed model of glucose energetics, in which a fraction of glucose is cycled through the cerebral glycogen pool, a fraction that increases with degree of brain activation. The "glycogen shunt," although energetically less efficient than glycolysis, is followed because of its ability to supply glial energy in milliseconds for rapid neurotransmitter clearance, as a consequence of which OGI is lowered and lactate is increased. The value of OGI observed is consistent with passive lactate efflux, driven by the observed lactate concentration, for the few experiments with complete data. Although the OGI changes during activation, the energies required per neurotransmitter release (neuronal) and clearance (glial) are constant over a wide range of brain activity.

Adenosine receptor signaling in vitro and in vivo

AbstractThis overview will focus on recent data from our laboratory. The four cloned human adenosine receptors stably transfected into Chinese hamster ovary cells were studied with respect to signaling via cyclic AMP and mitogen‐activated protein (MAP) kinases. Adenosine acted as a full agonist at all the adenosine receptors when increases (A2A or A2B receptors) or decreases (A1 and A3 receptors) in cyclic AMP accumulation were studied. Adenosine was approximately equipotent at A1, A2A, and A3 receptors, but approximately 50 times higher concentrations were needed at A2B receptors. The potency of adenosine was such that levels encountered under basal physiological conditions (30–300 nM) were sufficient to activate all but the A2B receptors. Inosine was a low‐efficacy agonist at A1 and A3 receptors but was inactive at A2A and A2B receptors. Thus, adenosine is the most important agonist and the only one at A2A and A2B receptors. When MAP kinase signaling was examined, adenosine was equipotent at all the four receptors, and significant activation was noted at 100 nM adenosine. The potency of adenosine is dependent not only on the type of receptor but also on receptor number. Thus, high potency of adenosine is seen only where the receptor is expressed abundantly. These and other results are reviewed and discussed in relation to agonist and antagonist effects in vivo. In particular, we summarize recent data that show that adenosine tonically activates A2A receptors in the basal ganglia. Some aspects of the use of adenosine A2A receptor antagonists in the treatment of Parkinson disease also are highlighted. Drug Dev. Res. 52:274–282, 2001. © 2001 Wiley‐Liss, Inc.

Elevation of blood pressure by genetic and pharmacological disruption of the ETB receptor in mice.

Exogenously administered endothelin (ET) elicits both pressor and depressor responses through the ETA and/or the ETB receptor on vascular smooth muscle cells and ETB on endothelial cells. To test whether ETB has pressor or depressor effects under basal physiological conditions, we determined arterial blood pressure (BP) in ETB-deficient mice obtained by crossing inbred mice heterozygous for targeted disruption of the ETB gene with mice homozygous for the piebald (s) mutation of the ETB gene (ETBs/s). F1 ETB-/s and ETB+/s progeny share an identical genetic background but have ETB levels that are approximately (1)/(8) and (5)/(8), respectively, of wild-type mice (ETB+/+). BP in ETB-/s mice was significantly higher, by approximately 20 mmHg, than that in ETB+/s or ETB+/+ mice. Immunoreactive ET-1 concentration in plasma as well as respiratory parameters was not different between ETB-/s and ETB+/s mice. A selective ETB antagonist, BQ-788, increased BP in ETB+/s and ETB+/+ but not in ETB-/s mice. Pretreatment with indomethacin, but not with NG-monomethyl-L-arginine, can attenuate the observed pressor response to BQ-788. The selective ETA antagonist BQ-123 did not ameliorate the increased BP in ETB-/s mice. Moreover, BP in mice heterozygous for targeted disruption of the ETA gene was not different from that in wild-type controls. These results suggest that endogenous ET elicits a depressor effect through ETB under basal conditions, in part through tonic production of prostaglandins, and not through secondary mechanisms involving respiratory control or clearance of circulating ET.

The role of alcohol in the oxidant antioxidant balance in heart.

The myocardium, like other tissues, has enzyme and non-enzyme systems to neutralize free radicals. The enzymes superoxide dismutase, catalase and glutathione peroxidase and glutathione reductase as well as the non-enzyme antioxidants vitamin E and ascorbic acid are the main antioxidants. Oxidants are produced by the mitochondria under normal conditions and by other sources under pathologic conditions. The quantity of antioxidants present in the myocardium is matched to the production of oxygen free radicals that may be produced under basal physiological conditions. However, the myocardium can be exposed to increased levels of oxygen free radicals under conditions in which myocardial metabolism, i.e. mitochondrial oxidative phosphorylation, is accelerated to match the adenosine triphosphate utilized to support the increased work load on the heart or can be exposed to oxygen free radicals under pathologic conditions such as ischemia and reperfusion, inflammation, and cardiotoxic drugs such as anti-cancer agents. Under such circumstances the normal heart has been shown to increase its antioxidant production and to be, with time, protected from further sources of oxygen free radicals. In particular, hearts previously exposed to a stimulus to produce greater antioxidant levels show less damage during ischemia reperfusion injury presumably because of neutralization of oxygen free radicals. This review will present several situations in which the myocardium increases its tolerance to ischemia reperfusion injury as a result of an initial oxidative stress.

Activated protein C correlates inversely with thrombin levels in resting healthy individuals.

To study whether the circulating anticoagulant, activated protein C (APC), could be a regulator of thrombin activity in basal physiological conditions, fibrinopeptide A and activated protein C levels were determined in samples from 40 healthy individuals. There was a significant inverse correlation between the fibrinopeptide A and APC levels (Spearman rank correlation R = -0.487; P = 0.0023). Because of well-known mechanisms by which decreasing APC levels could cause increased thrombin formation, we suggest that APC may downregulate thrombin activity in subjects with normal protein C levels. Regulation of thrombin formation in health is likely significant for maintaining vascular patency but its molecular mechanisms are poorly understood. The current data suggest that a single physiological anticoagulant, namely APC, may be a significant regulator of procoagulant thrombin activity.

Adenosine A 1 and A 2A receptors and nitrobenzylthioinosine-sensitive transporters in gerbil brain: No changes following long-term treatment with the adenosine transport inhibitor propentofylline

There is evidence that adenosine is an endogenous neuroprotective substance in the gerbil and that propentofylline, a novel xanthine derivative that acts as a transport inhibitor, exerts part of its neuroprotective activity in this species by enhancing adenosine actions. Using autoradiography we have examined the distribution of adenosine A 1 and A 2A receptors and of equilibrative adenosine transporters in gerbil brain as well as the possible changes induced by repeated treatment with propentofylline. Nucleoside transporters, studied by [ 3H]NBMPR binding, were found to be widely distributed in the gerbil brain, with no clear relationship to the distribution of adenosine receptors. Adenosine A 2A receptors, studied by [ 3H]CGS 21680 binding and by in situ hybridization, were found to be present in intrinsic neurons in the caudate putamen, nucleus accumbens and tuberculum olfactorium. Adenosine A 1 receptors were studied by examining the binding of [ 3H]CHA, an agonist, and [ 3H]DPCPX, an antagonist. There was an overall similarity in the distribution of binding sites for these two ligands, and a similarity with the distribution in the rat. However, the antagonist was found to label certain structures, especially white matter structures, more than the agonist. It is argued that these binding sites for antagonists represent receptors that are in transit from the site of synthesis in the perikaryon to the destination in the nerve terminal, and are not coupled to G proteins. There were no differences in the binding of any of these ligands or in A 2A mRNA following 2 weeks' treatment with propentofylline, indicating that the drug has minimal effects on adenosine mechanisms under basal physiological conditions. This also suggests that tolerance to adenosine-related effects of the drug is less likely to occur.

Interaction of protein kinase C isozymes with phosphatidylinositol 4,5-bisphosphate

Interaction of protein kinase C (PKC) isozymes with phosphatidylinositol 4,5-bisphosphate (PIP2) was investigated by monitoring the changes in the intrinsic fluorescence of the enzyme, the kinase activity, and phorbol ester binding. Incubation of PKC I, II, and III with PIP2 resulted in different rates of quenching of PKC fluorescence and different degrees of inactivation of these enzymes. Other inositol-containing phospholipids such as phosphatidylinositol and phosphatidylinositol 4-phosphate also caused differential rates of quenching of the intrinsic fluorescence of these enzymes. These latter two phospholipids were, however, less potent in the inactivation of PKCs than PIP2. The IC50 of PIP2 were 2, 4, and 11 microM for PKC I, II, and III, respectively. Inactivation of PKCs by PIP2 cannot be reversed by extensive dilution of PIP2 with Nonidet P-40 nor by digestion of PIP2 with phospholipase C. Interaction of PIP2 with the various PKC isozymes was greatly facilitated in the presence of Mg2+ or Ca2+ as evidenced by the accelerated quenching of the PKC fluorescence, however, these divalent metal ions protected PKC from the PIP2-induced inactivation. Binding of PIP2 to PKC in the absence of divalent metal ion also caused a reduction of [3H]phorbol 12,13-dibutyrate binding as a result of reducing the affinity of the enzyme for phorbol ester. Based on gel filtration chromatography, it was estimated that one molecule of PKC interacted with one PIP2 micelle with an aggregation number of 80-90. The PIP2-bound PKC could further interact with phosphatidylserine in the presence of Ca2+ to form a larger complex. Binding of PKC to both PIP2 and phosphatidylserine in the presence of Ca2+ was also evident by changes in the intrinsic fluorescence of PKC. As the interaction of PKC with PIP2, but not with phosphatidylserine, could be enhanced by millimolar concentrations of Mg2+, we propose that PIP2 may be a component of the membrane anchor for PKC under basal physiological conditions when [Ca2+]i is low and Mg2+ is plentiful. Under the in vitro assay conditions, PIP2 could stimulate PKC activity to a level approximately 10-20% of that by diacylglycerol. The stimulatory effect of PIP2 on PKC apparently is not due to binding to the same site recognized by diacylglycerol or phorbol ester, because PIP2 cannot effectively compete with phorbol 12,13-dibutyrate in the binding assay.

Endogenous adenosine restrains renin release in conscious rats.

The purpose of this study was to test the hypothesis that endogenous adenosine functions to restrain the renin release response to pharmacological and pathophysiological stimuli. To achieve this objective, we examined the effects of an adenosine receptor antagonist, 1,3-dipropyl-8-(p-sulfophenyl)xanthine (DPSPX), on the renin release response induced by acute administration of hydralazine or by chronic clipping of the left renal artery (renovascular hypertensive rats). In conscious, unrestrained rats, DPSPX significantly increased plasma renin activity (PRA) in control rats, in rats treated with hydralazine, and in renovascular hypertensive rats. The effect of DPSPX on PRA was significantly greater in rats treated with hydralazine or in renovascular hypertensive rats compared with control rats. DPSPX did not influence arterial blood pressure in any group, did not affect the measurement of PRA, and did not alter the elimination of renin activity from the circulation. Additional experiments were performed in the in situ autoperfused kidney so that the effects of DPSPX on renal hemodynamics and renal excretory function could be assessed. In this experimental model, DPSPX also increased PRA in hydralazine-treated rats and in renovascular hypertensive rats without affecting arterial pressure, renal blood flow, or sodium excretion. In a final set of studies in conscious, unrestrained rats, adenosine deaminase increased PRA in a dose-dependent manner in hydralazine-treated rats and significantly increased the slope of the relation between PRA and the depressor response to hydralazine. We conclude: 1) Although the kidney has both A1 and A2 adenosine receptors mediating inhibitory and stimulatory actions, respectively, on renin release, the dominant effect of endogenous adenosine on renin release is inhibitory. 2) Even under basal physiological conditions, endogenous adenosine tonically inhibits renin release. 3) This inhibitory effect is augmented whenever the renin-angiotensin system is stimulated regardless of the approach used to activate renin release. 4) Endogenous adenosine negatively modulates renin release by a direct effect on juxtaglomerular cells.

Shunting in renal microvasculature of the rat: a scanning electron microscopic study of corrosion casts.

We reinvestigated the still controversial existence of arterial pathways by-passing glomeruli within kidneys of rats from weaning to more than 12 months old (i.e., body weight ranging from 39 g to 643 g). For this purpose, the arterial injection of microspheres 7.5 micrometer to 17 micrometer in diameter was combined to corrosion-replication of the arterial bed of a vasodilated perfused kidney preparation. This procedure allowed easy detection of arterial by-passes with light microscope and detailed observation with scanning electron microscope. Our results clearly demonstrate the existence of various categories of arterial by-passes throughout renal cortex regardless of age. Some of them had never been described before. These vascular by-passes were found with increased frequency from superficial to juxtamedullary cortex. In the latter area, frequency was not age-dependent, and approximately 10% (range 4-22%) of juxtamedullary glomeruli were involved. Data derived from previous microsphere studies would suggest that these structures are (partially) nonfunctioning in basal physiological conditions, but more information is needed to assess their possible functional role in the rat.

The effects of lethal procedures on the histochemical localization of acid hydrolases.

The distribution and activities, as revealed by histochemical techniques, of acid phosphatase, β-glucuronidase, arylsulphatase and β-galactosidase in the kidney, liver and skeletal muscle of rats and dystrophic hamsters killed by each of the following methods were studied: overdose of ether, chloroform and nembutal anaesthesia, immersion in liquid air, stunning followed by decapitation, and carbon dioxide asphyxiation. In rats killed with overdoses of ether or chloroform, the activity of acid phosphatase in sections of formaldehyde-fixed kidney was, it was found, less than that in decapitated ones. Sometimes the activity was abolished completely. The intensity of colour, the particulate granularity and the distribution of final reaction product normally obtained for other acid hydrolases and tissues were also affected, e.g. the distribution was more diffuse. Often the minimum time of incubation for the final reaction product to appear was shortened. One example where this happened was the activity of arylsulphatase against 6-benzoyl-2-naphthyl sulphate. The activities of the three other enzymes studied were affected in the same way but to a different degree. However, killing animals with nembutal or liquid air or by decapitation seemed to have little effect on the activities of any of lysosomal enzymes investigated. In order to obtain a reproduceable localization of strong acid hydrolase activity in a particulate form (presumably indicative of lysosomes), it is necessary to bring experimental animals to a basal physiological condition by isolating them overnight away from other animals before killing them (with nembutal or by stunning and decapitation) after a substantial period of rest.