Renal intracortical blood flow distribution,function and sodium excretion in response to saline loading of anesthetized and unanesthetized dogs

Summary In order to study the effect of anesthesia on the canine response to saline loading, experiments were performed on 10 dogs, first while awake and then during pentobarbital anesthesia. Individual kidney function and intrarenal blood flow response to saline loading (7.5% body weight) were measured in each condition and all data are reported as the average of a single kidney. C_IN is considerably reduced under anesthesia (24.7±3.2 vs. 43.2±3.9 ml/min,P<0.01). A directionally similar reduction of PAH clearance was noted (89±17 vs. 122±13 ml/min). The natriuretic response to saline loading of the dogs reached 290±61 Eq/min while awake, but only 70±27 Eq/min while anesthetized. No measurable increase of C_IN or C_PAH occurred in response to saline loading either in the anesthetized or unanesthetized state. The natriuresis was entirely due to a rise of C_NA/GFR in both circumstances. The change of C_NA/GFR in response to saline load was also appreciably larger while awake (1.24.7% vs. 0.71.8%). Although the fraction of blood flow to the outermost quarter of the kidney was initially the same (31±3 vs. 29±3%) awake or anesthetized, the changes with saline loading were in the opposite direction and the values reached were significantly different (37±3, awake, vs. 27±3%,P<0.05). We conclude that while increased outer cortical blood flow is not necessary for natriuresis, it may occur during sodium loading and may facilitate sodium excretion.Supported by VA Program 3385-01     

Effect of norethisterone-acetate on salt excretion and on the renin-aldosterone system in man

Summary The mechanism of a previously described rise in the excretion rate of aldosterone-18-glucuronide under the influence of norethisterone-acetate was further investigated in 10 male volunteers. Oral administration of 30 mg norethisterone-acetate daily for 1 week caused a significant natriuresis and a rise in the excretion rate of aldosterone-18-glucuronide. Aldosterone secretion rate rose slightly but insignificantly. Plasma aldosterone, renin activity, and angiotensin II remained unaltered while plasma renin substrate increased markedly. Norethisterone-acetate, or one of its metabolites, may directly stimulate aldosterone secretion and metabolism rendering plasma aldosterone levels unaltered. The rise in renin substrate is obviously due to estrogenic properties of the compound studied. The mechanism of natriuresis remains unexplained.Supported by the Deutsche Forschungsgemeinschaft     

Acute effects of lysine vasopressin injection (Single and continuous) on urinary composition in the conscious water diuretic rat

Summary ADH (synthetic lysine-vasopressin) was administered to conscious rats undergoing steady, sustained water diuresis. The magnitude and duration of the transient antidiuresis induced by single i. v. ADH injection (0.5–8 mU/100 g body weight) increased with the dose to a maximum urinary osmolality of 630 -osmole/g H₂O (returning towards control values within 1 hr).Both the magnitude of, and the time to attain, a stable antidiuretic effect with continuous i.v. ADH infusion (2.5–30 U/min/100 g body weight) varied with the dose. The maximal osmolality with 15 was almost as high as that with 30 U/min/100 g body weight (1815 and 1928 -osmole/g H₂O), but took longer to attain (4 and 2 hr, respectively).With both single and continuous ADH injection, a variable, inconsistent natriuresis and kaluresis occurred; the peak natriuresis preceded the time of maximal urinary osmolal and Na concentrations.The data are discussed in relation to (a) physiological rate of secretion of endogenous ADH and (b) the mechanisms responsible for the natriuresis.It is concluded that the natriuretic effect of ADH has little physiological significance in salt regulation.     

The carotid body of the harbour seal (Phoca vitulina richardsi)

Summary The bilateral distribution of carotid body type 1 and 11 cells was investigated in five harbour seals (Phoca vitulina richardsi), by serially sectioning the carotid bifurcation regions. The cells occurred bilaterally in the animals and were also present in one specimen from a sixth animal available for study. The type 1 and 11 cells were located in the space between the internal and external carotid arteries and had a varied relationship to the occipital and condyloid arteries. They lay within a division of connective tissue with irregular but defineable borders and this combination of connective tissue and type 1 and 11 cells constituted the principal mass of the carotid body. The carotid body occurred in a variety of forms: wedge-shaped, crescentic or horse-shoe shaped, or as a discrete oval structure. In some specimens the carotid body had a central neurovascular core of small blood vesels and nerves. The artery to the organ originated from either the external carotid, internal carotid or common carotid arteries. Using an interactive image analysis system in eight specimens, which had been perfusion-fixed at a normal arterial pressure, the mean volume of the carotid body was 1.666±0.45 (SD) mm³. Caudally and separate from the principal mass of the carotid body periadyentitial type 1 and 11 cells were noted in 4 out of 11 specimens in the connective tissues adjacent to the external carotid artery, origin of the occipital, and the rostral part of the common carotid artery and its bifurcation.     

Renal hemodynamics and natriuresis during water immersion in normal humans

The renal vascular and functional responses to acute central hypervolemia by water immersion to the neck were determined in six normal subjects. During isotonic-isooncotic expansion by water immersion there was a significant increase in urine flow from 1.1±0.1 to 6.9±1.0 ml/min (p<0.05) and sodium excretion from 99.1±8.8 to 300±28 Eq/min (p<0.05). Glomerular filtration rate did not change while renal blood flow significantly increased during water immersion. Deep intrarenal venous pressure (IRVP) increased from 18.2±1.4 to 32±1.7 mmHg (p<0.05) while mean arterial pressure was unchanged. This marked natriuresis seen during water immersion was associated with reduced renal vascular resistance and increased deep intrarenal venous pressure demonstrating that continued natriuresis could relate to increased capillary hydrostatic pressure.     

The volume of the carotid body and periadventitial type I and type II cells in the carotid bifurcation region of the fetal cat and kitten

Summary The bilateral distribution of carotid body type I cells was investigated in 6 fetuses (gestational age 95%) and 9 newborn kittens (aged 1 day to 4 days) by serially sectioning the carotid bifurcation regions. In most specimens type I cells occurred in close proximity to the wall of the occipital artery or one of its small proximal branches within a division of connective tissue with defineable but irregular borders. This combination of type I cells and connective tissue constituted the principal mass of the carotid body. Using an interacting image analysis system, the area of the carotid body in each serial section was measured by accurately contouring its perimeter. The volume of the carotid body was calculated by multiplying the sum of the areas of the serial sections by the thickness of the section. The volume of the carotid body was 0.052±0.018 mm³ in the fetuses and 0.025–0.117 mm³ in the 1–4 day old kittens. A degree of symmetry in the values for the volume of the right and left carotid body was found. Caudally, and separate from the principal mass of carotid body type I cells, isolated groups of periadventitial type I cells were noted in the connective tissues around the occipito-ascending pharyngeal trunk, origin of the occipital artery and rostral end of the common carotid artery in 7 out of 12 specimens from fetal cats and 11 out of 18 specimens in newborn kittens. The volumes of the periadventitial groups of cells ranged between 25–1,365 m³ in fetuses and 10–1,351 m³ in kittens.     

Renal and cardiovascular responses to water immersion in trained runners and swimmers

The purpose of this study was to determine if fluid-electrolyte, renal, hormonal, and cardiovascular responses during and after multi-hour water immersion were associated with aerobic training. Additionally, we compared these responses in those who trained in a hypogravic versus a 1-g environment. Seventeen men comprised three similarly aged groups: six long-distance runners, five competitive swimmers, and six untrained control subjects. Each subject underwent 5 h of immersion in water [mean (SE)] 36.0 (0.5)°C to the neck. Immediately before and at each hour of immersion, blood and urine samples were collected and analyzed for sodium (Na), potassium, osmolality, and creatinine (Cr). Plasma antidiuretic hormone and aldosterone were also measured. Hematocrits were used to calculate relative changes in plasma volume (%V _pl). Heart rate response to submaximal cycle ergometer exercise (35% peak oxygen uptake) was measured before and after water immersion. Water immersion induced significant increases in urine flow, Na clearance (C _Na), and a 3–5% decrease in V _pl. Urine flow during immersion was greater (P < 0.05) in runners [2.4 (0.4) ml · min^–1] compared to controls [1.3 (0.1) ml · min ^–1]. However, %A V _pl, C _Cr, C _Na and during immersion were not different (P > 0.05) between runners, swimmers, and controls. After 5 h of immersion, there was an increase (P < 0.05) in submaximal exercise heart rate of 9 (3) and 10 (3) beats · min^–1 in both runners and controls, respectively, but no change (P > 0.05) was observed in swimmers. Since swimmers did not experience elevated exercise tachycardia following water immersion compared to runners and sedentary controls, we conclude that exercise training in a hypogravic environment attenuates the acute cardiovascular adaption to microgravity. This effect of hypogravic aerobic training was not associated with the degree of hypovolemia and associated diuresis and natriuresis.     

Inhibition of Na-K-Cl cotransport fluxes and salidiuretic action by an urinary extract of salt-loaded rats

We previously found a potent inhibitor of the Na-K-Cl cotransport system in urines from salt-loaded rats (C.I.F. = cotransport inhibitory factor, ref. 1). Here we extracted an urinary fraction ( 1 urine dry weight), free from immunoreactive A.N.P. and digoxine activity, which: (i) potently inhibited cotransport fluxes in MDCK (Madin and Darby canine kidney] cells and in human erythrocytes, (ii) inhibited Na⁺-dependent chloride/bicarbonate exchange with 2–3 times less potency than cotransport and (iii) strongly increased natriuresis and diuresis after i.v. infusion in rats with no significant change in kaliuresis (salidiuretic action reduced by probenecid). Therefore, C.I.F. seems to be a new natriuretic factor with part, but not all the biological profile of loop diuretic drugs.     

Effects on renal sodium and potassium excretion of vasopressin and oxytocin in conscious dogs

Renal effects of arginine vasopressin and oxytocin were studied in conscious dogs, made water-diuretic by a waterload equivalent to 2% of body weight. Body water and content of sodium were maintained by separate servo-controlled infusions. Peptides were infused for 60 min at rates of 50 pg kg^-1 min^-1 (arginine vasopressin) or 1 ng kg^-1 min^-1 (oxytocin), either separately or combined. Infusions increased plasma arginine vasopressin to 1.9 ± 0.2 (arginine vasopressin alone) and 1.8 ± 0.3 pg kg^-1 (arginine vasopressin plus oxytocin and plasma oxytocin to 72 ± 5 (oxytocin alone) and 77 ± 8 pg ml^-1 (oxytocin plus arginine vasopressin). Arginine vasopressin or arginine vasopressin plus oxytocin increased urine osmolality similarly by a factor of 13, decreased urine flow to between 5 and 7% of control and decreased free water clearance. Oxytocin reduced urine flow and free water clearance and increased urine osmolality by a factor of 2. Oxytocin and arginine vasopressin separately increased excretion of sodium from 4 ± 2 to 15 ± 6 μmol min^-1 and from 7 ± 4 to 25 ± 13 μmol min^-1, respectively. Arginine vasopressin plus oxytocin led to a pronounced natriuresis (13 ± 4 to 101 ± 27 μmol min^-1). Arginine vasopressin and arginine vasopressin plus oxytocin increased the excretion of potassium by a factor of 2.5. Oxytocin and arginine vasopressin plus oxytocin increased urinary Na⁺/K⁺ ratio by a factor of 3.7. It is concluded, that oxytocin at plasma concentrations of 70–80 pg ml^-1 has modest antidiuretic and natriuretic effects and that the combined action of arginine vasopressin oxytocin may elicit supra-additive natriuretic effects.     

Control of renal function in isovolemic hemodilution or in vagotomized,infused rats

In male Sprague-Dawley rats cardiac output (CO) was increased 0.16 ml/min·g body weight and inulin clearance was increased 2.2 ml/min°g kidney weight either by isovolemic hemodilution with 6% albumin solution or by isohemic expansion to 133% of control blood volume. Despite similar changes in CO and glomerular filtration (GFR), hemodilution caused a much smaller rise in renal excretion at a much later time than did volume expansion. Therefore, in addition to simultaneous changes in CO and GFR an afferent factor indicating a state of expanded extracellular fluid volume was required for normal diuresis and natriuresis. This might have been mean central venous pressure . In further experiments, volume expansion in vagotomized or non-vagotomized rats led to nearly identical changes in water-, sodium- and potassium excretion in both groups. The only other measured parameter that showed identical behaviour in the two groups was . It was concluded that is an important contributor to body fluid control mechanisms even after vagotomy.     

Renovascular and tubular effects of neuropeptide Y are discriminated by PP56 (D-myo-inositol 1,2,6-triphosphate) in anaesthetized rats

 Systemic infusion of neuropeptide Y (NPY; 1 μg kg^–1 min^–1) for 120 min rapidly reduced renal blood flow and increased mean arterial pressure and renovascular resistance and, at later time points (> 30 min), enhanced diuresis, natriuresis and calciuresis in anaesthetized rats. Infusion of the reported NPY antagonist PP56 (D-myo-inositol 1,2,6-triphosphate, 333 mg kg^–1 min^–1) slightly but significantly enhanced renal blood flow and reduced renovascular resistance over the course of the infusion period. Infusion of PP56 together with NPY (starting 30 min prior to the NPY infusion) significantly inhibited NPY-induced alterations of mean arterial pressure, renal blood flow and renovascular resistance. Coinfusion of PP56 also attenuated the renovascular effects of bolus injections of NPY (0.1–10 μg/kg) but at the highest NPY dose the antagonistic effect of PP56 could partially be overcome. In contrast to the antagonism of the vascular NPY effects, infusion of PP56 did not significantly affect NPY-induced enhancements of diuresis, natriuresis and calciuresis. Thus, PP56 is a surmountable antagonist of vascular but not tubular NPY effects. We conclude that tubular NPY effects occur largely independently of alterations of renal haemodynamics. Received: 9 July 1996 / Received after revision: 9 December 1996/ Accepted: 7 January 1997     

DL-propranolol inhibits the vascular changes in the rat carotid body induced by long-term hypoxia

Summary Two groups of rats were exposed to hypoxia (10% O₂) for 1 and 3 weeks with or without daily injections of DL-propranolol (0.66 mg·kg^–1 ip). The structure of the carotid body was analyzed by light microscopical morphometry and the catecholamine content was assayed by high performance liquid chromatography. Exposure to hypoxia induced enlargement of the carotid body due to enhanced vascularity and hypertrophy of glomic and interstitial tissues. The dopamine and norepinephrine content were increased at both 1 and 3 weeks of hypoxia and reached levels 40–50 times those of the controls. The DL-propranolol treatment abolished the vasodilatory effect of hypoxia within the first week but did not prevent the other structural changes or the rise in catecholamine content. The data suggest that 1. the vasodilation elicited by long-term hypoxia may be controlled by-adrenoceptors and 2. the structural and biochemical events occurring in rat carotid body during long-term hypoxia do not influence each other and thus seem to be controlled by different mechanisms.     

A Simplified Murine Intimal Hyperplasia Model Founded on a Focal Carotid Stenosis

Murine models offer a powerful tool for unraveling the mechanisms of intimal hyperplasia and vascular remodeling, although their technical complexity increases experimental variability and limits widespread application. We describe a simple and clinically relevant mouse model of arterial intimal hyperplasia and remodeling. Focal left carotid artery (LCA) stenosis was created by placing 9-0 nylon suture around the artery using an external 35-gauge mandrel needle (middle or distal location), which was then removed. The effect of adjunctive diet-induced obesity was defined. Flowmetry, wall strain analyses, biomicroscopy, and histology were completed. LCA blood flow sharply decreased by ∼85%, followed by a responsive right carotid artery increase of ∼71%. Circumferential strain decreased by ∼2.1% proximal to the stenosis in both dietary groups. At 28 days, morphologic adaptations included proximal LCA intimal hyperplasia, which was exacerbated by diet-induced obesity. The proximal and distal LCA underwent outward and negative inward remodeling, respectively, in the mid-focal stenosis (remodeling indexes, 1.10 and 0.53). A simple, defined common carotid focal stenosis yields reproducible murine intimal hyperplasia and substantial differentials in arterial wall adaptations. This model offers a tool for investigating mechanisms of hemodynamically driven intimal hyperplasia and arterial wall remodeling.Arterial occlusive disease remains a major health issue in developed nations, affecting approximately 35% of the adult population in the United States.^1–3 Various open and endovascular procedures are currently used to treat occlusive lesions; however, postprocedure intimal hyperplasia and vascular wall maladaptation in treated arteries continue to plague these interventions in as many as 50% of patients, leading to recurrent end-organ ischemia.^4–6To understand the mechanisms of intimal hyperplasia and arterial wall remodeling, many animal models (eg, pig, rabbit, rat, and mouse) have been generated using chemical, mechanical, and electrical approaches to induce arterial injury. The mouse species holds great appeal because of advanced genetic knowledge. Murine common carotid artery (CCA) blood flow cessation via complete ligation and flow restriction via outflow branch ligation models have been popular approaches in the investigation of neointimal hyperplasia and vascular remodeling.^7–9 In the complete ligation model, blood flow in the left carotid artery (LCA) is disrupted by a ligature near the bifurcation; at 4 weeks, this manipulation results in blood flow cessation, substantial luminal area reduction, extensive smooth muscle cell–dominant intimal hyperplasia, and matrix deposition.⁷ Though technically simple, this model lacks direct clinical relevance. In contrast, the outflow branch ligation model requires advanced microsurgical skills and yields only limited intimal hyperplasia.⁹Combining the simplicity of complete carotid artery ligation with the hemodynamic principles of outflow branch ligation, we hypothesized that flow perturbation via a high-grade focal stenosis would yield arterial intimal hyperplasia and arterial wall remodeling. Herein, we detail the technical aspects and the physiologic and biological outcomes of this model.     

Ovary and ovulation: Interaction between oxytocin and prostaglandin F2{alpha} in human corpus luteum?

The effect of a single injection of oxytocin into the corpusluteum, with or without pretreatment with a prostaglandin synthetaseinhibitor, was studied in order to investigate possible localinteractions between prostaglandin (PG)F₂ and oxytocin in theregulation of the human corpus luteum. Oxytocin (4 IU) was injectedthrough the abdominal wall into the corpus luteum in women undergoinglaparoscopy for legal sterilization. In the control cases, salinewas injected into the corpus luteum, or oxytocin was injectedinto the contralateral ovary. Oxytocin injected into the corpusluteum caused a fall in serum progesterone and shortened theluteal phase. These effects were not seen following injectionof saline into the corpus luteum, or following injection ofoxytocin into the contralateral ovary. After the injection ofoxytocin into the corpus luteum a rise in 15-keto-dihydro-PGF₂,a PGF₂ metabolite, was seen. The changes in serum progesteronecaused by injection of oxytocin into the corpus luteum couldbe prevented if a PG synthetase inhibitor was given before theinjection. These findings suggest that local interaction betweenoxytocin and PGF₂ plays a role in the regulation of the humancorpus luteum.     

Influence of changes in the acid-base composition of the ventricular system on cerebral blood flow in cats

Summary In ventriculo-cisternal perfusion experiments performed in mechanically ventilated cats maintained under nitrous oxide anesthesia, the bicarbonate concentration of the ventricular perfusion fluid was decreased (from 21 to 4 mmol/l) or increased (from 21 to 84 mmol/l) during time intervals ranging from 45 to 120 min. The blood flow was measured in the caudate nucleus with two different methods: in a first series of experiments the temperature difference was continuously measured between a heated thermojunction and a reference junction, both devices being placed symmetrically in the right and left caudate nucleus (heat clearance method), while in a second series of experiments, the local blood flow was estimated from the rate of clearance of¹³³Xenon injected in micro-amounts (8–10 l) into the caudate nucleus. A decrease in the bicarbonate concentration of the ventricular perfusion fluid increased the blood flow in the caudate nucleus, estimated by both methods, while an increase in the bicarbonate concentration produced the opposite effect. The same alterations in the bicarbonate concentration of the ventricular perfusion fluid produced no detectable change in the hemispheric cerebral blood flow, measured by the clearance of¹³³Xenon injected into the carotid system.Finally, the bicarbonate concentration was independently altered in one of the lateral ventricles during bilateral ventricular perfusions, and changes in the blood flow distribution were studied in the caudate nuclei with a particle distribution method (⁸⁵Sr or¹⁴¹Ce labeled carbonized microspheres injected into the left heart ventricle). A ventricular perfusion, asymmetric with respect to the bicarbonate concentration induced an uneven distribution of the microspheres and hence of the local blood flow between both caudate nuclei. The results of the present experiments clearly argue in favour of a local influence of tissue pH on the blood flow in paraventricular gray matter.An abstract of this work was presented at the International Symposium on cerebral blood flow regulation, acid-base and energy metabolism in acute brain injuries held in Rome-Sienna, October 1971.     

Tityusγ toxin,a high affinity effector of the Na+ channel in muscle,with a selectivity for channels in the surface membrane

Toxin from the venom ofTityus serrulatus scorpion produces a partial block of the surface Na⁺ channel in frog muscle. This block occurs with no change in the voltage-dependence or in the kinetics of the remaining surface Na⁺ current. The partial blockade of Na⁺ channel activity occurs with no change in tubular Na⁺ currents nor in twitch tension. The maximum effect of the toxin is attained at concentrations as low as 3×10^–10 M. Hyperpolarization to potentials more negative than the resting potential (E=–90 mV) reduces or abolishes the effect of the toxin.Radioiodinated toxin binds to frog muscle membranes with a very high affinity corresponding to a dissociation constant of about 1×10^–11 M. Data obtained with both rabbit and frog muscle indicate that toxin is specific for Na⁺ channels in surface membranes. Toxin does not seem to bind to Na⁺ channels in T-tubule membranes. The biochemical data are in good agreement with electrophysiological studies and data on contraction. There is oneTityus toxin binding site per tetrodotoxin binding site in surface membranes. Competition experiments have confirmed thatTityus toxin binds to a new toxin receptor site on the Na⁺ channel structure. This site is the same that the toxin II fromCentruroides suffusus binding site, but this toxin has 100 times less affinity for the Na⁺ channel thanTityus toxin.     

Role of vasopressin V2 receptors in modulation of the renal cortico-papillary NaCl gradient

In order to examine if modulation by vasopressin of NaCl transport in Henle's loops (via V2 receptors) can significantly modify medullary ionic hypertonicity, the effects of stimulation or inhibition of these receptors were studied in anaesthetized Wistar rats. Total electrolyte concentration in the medullary interstitium was continuously measured as tissue admittance (reciprocal impedance), using needle electrodes recording from the inner and outer medulla of the in situ kidney. Deamino-[Cys¹,D-Arg⁸]vasopressin (dDAVP], a V2 agonist, infused i.v. at 7.5 ng · min^–1 · kg^–1, significantly increased admittance by 9% and 8% in the inner and outer medulla, respectively. A slightly pressor i.v. infusion of natural arginine vasopressin (AVP) induced pressure natriuresis and did not affect medullary electrolyte concentration. Inhibition of V2 receptors with [d(CH₂)⁵,D-Phe², Ile⁴]-AVP, infused i.v. at 133 g · h^–1 kg^–1 in indomethacin-treated rats, decreased admittance (significant in the inner medulla). Neither of the three agents used caused significant changes in the renal blood flow (RBF) or clearance of inulin (C _in). The demonstration that changing activity of V2 receptors affects the corticopapillary NaCl gradient indicates that, at least in rodents, stimulation of loop salt transport by AVP may represent an additional mechanism enhancing urine concentration.     

Computational Simulations of Magnetic Particle Capture in Arterial Flows

The aim of Magnetic Drug Targeting (MDT) is to concentrate drugs, attached to magnetic particles, in a specific part of the human body by applying a magnetic field. Computational simulations are performed of blood flow and magnetic particle motion in a left coronary artery and a carotid artery, using the properties of presently available magnetic carriers and strong superconducting magnets (up to B ≈ 2 T). For simple tube geometries it is deduced theoretically that the particle capture efficiency scales as \(\eta \sim \sqrt{{Mn}_{\rm p}}\), with Mn _p the characteristic ratio of the particle magnetization force and the drag force. This relation is found to hold quite well for the carotid artery. For the coronary artery, the presence of side branches and domain curvature causes deviations from this scaling rule, viz. η ～ Mn _p ^β , with β > 1/2. The simulations demonstrate that approximately a quarter of the inserted 4 μm particles can be captured from the bloodstream of the left coronary artery, when the magnet is placed at a distance of 4.25 cm. When the same magnet is placed at a distance of 1 cm from a carotid artery, almost all of the inserted 4 μm particles are captured. The performed simulations, therefore, reveal significant potential for the application of MDT to the treatment of atherosclerosis.