NaCl Injection Research Articles

Corticotropin-releasing hormone causes antidiuresis and antinatriuresis by stimulating vasopressin and inhibiting atrial natriuretic peptide release in male rats.

In both normally hydrated and volume-expanded rats, there was a biphasic effect of corticotropin-releasing hormone (CRH) (1-10 microgram, i.v.) on renal function. Within the first hour, CRH caused antidiuresis, antinatriuresis, and antikaliuresis together with reduction in urinary cGMP output that, in the fourth hour, were replaced by diuresis, natriuresis, and kaliuresis accompanied by increased cGMP output. Plasma arginine vasopressin (AVP) concentrations increased significantly within 5 min, reached a peak at 15 min, and declined by 30 min to still-elevated values maintained for 180 min. Changes in plasma atrial natriuretic peptide (ANP) were the mirror image of those of AVP. Plasma ANP levels were correlated with decreased ANP in the left ventricle at 30 min and increased ANP mRNA in the right atrium at 180 min. All urinary changes were reversed by a potent AVP type 2 receptor (V(2)R) antagonist. Control 0.9% NaCl injections evoked an immediate increase in blood pressure and heart rate measured by telemetry within 3-5 min. This elevation of blood pressure was markedly inhibited by CRH (5 microgram). We hypothesize that the effects are mediated by rapid, direct vasodilation induced by CRH that decreases baroreceptor input to the brain stem, leading to a rapid release of AVP that induces the antidiuresis by direct action on the V(2)Rs in the kidney. Simultaneously, acting on V(2)Rs in the heart, AVP inhibits ANP release and synthesis, resulting in a decrease in renal cGMP output that is responsible for the antinatriuretic and antikaliuretic effects.

Assessment of the Myotoxicity of Pharmaceutical Buffers Using an In Vitro Muscle Model: Effect of pH, Capacity, Tonicity, and Buffer Type

The purpose of the present study was to investigate the myotoxicity of three buffers containing carboxylic acid groups (i.e., acetate, succinate, and citrate) as a function of their pH, capacity, and tonicity. The myotoxicity of these buffers in the range of pH 2–6 and 0.001–0.1 M buffer capacity was assessed using cumulative creatine kinase (CK) release from an isolated rodent muscle model following injection. Phenytoin and 0.9% NaCl injection were used as positive and negative controls, respectively. Buffer solutions were prepared. A lower pH and higher buffer capacity was linked to increased myotoxicity for the acetate buffers. However, for succinate and citrate buffers, pH appeared to influence the extent of myotoxicity, whereas buffer capacity did not seem to have an effect. When either NaCl or trehalose was used as a tonicity-adjusting agent at pH 6, isotonic 0.01 M buffer solutions dramatically lowered the cumulative CK release compared to those that were not isotonic. Isotonic succinate buffers displayed the lowest myotoxicity, whereas citrate buffers displayed the highest values. Citrate buffers containing three carboxylic acid groups showed higher myotoxicity than succinate buffers and acetate buffers at 0.001 and 0.01 M buffer capacities, whereas acetate buffer produced higher cumulative CK release than citrate and succinate buffers at 0.1 M buffer capacity. The myotoxicity of pharmaceutical buffers containing carboxylic acid groups appears to be directly affected by lowering the pH of the solution.

Repeated injections of lipopolysaccharide attenuate the satiety effects of cholecystokinin.

The present study examined the effects of repeated injections of lipopolysaccharide (LPS) and cholecystokinin (CCK) on both sucrose palatability and body weight. Rats received repeated injections of LPS (200 microg/kg), CCK (8 microg/kg) and/or NaCl on days 1, 4, 7 and 10. Body weight was monitored on each test day and sucrose palatability was assessed using the taste reactivity test (TRT) on days 7 and 10. Rats treated with LPS developed a rapid tolerance to the reductions in body weight; however, this tolerance did not affect sucrose palatability. Furthermore it was found that repeated exposures to LPS and CCK attenuated the typical satiety related behaviors produced in the TRT by administration of CCK. This desensitization to CCK with repeated exposures to LPS may be one of the mechanisms that could account for the rapid development of tolerance to LPS-induced hypophagia.

Comparison of intra-articular injection of 2 ml of 0.9% NaCl solution with rest alone for treatment of horses with traumatic arthritis

Abstract Objective To compare effects of intra-articular injection of 2 ml of 0.9% NaCl solution with rest alone for treatment of horses with traumatic arthritis. Animals 38 Standardbred horses with moderate to severe lameness that resulted from traumatic arthritis. Procedure Horses were stratified on the basis of number of affected joints. In each stratum, horses were allocated randomly to treatment groups (intra-articular injection of 2 ml of 0.9% NaCl solution vs rest only). Treatment was for a period of 3 weeks. Horses were inspected weekly with a final examination 2 to 4 weeks after completion of treatment. Results Mean lameness index was significantly lower during the 3-week treatment period and the entire study period for the NaCl-injected group. A significant decrease in the lameness index during the first 3-week treatment period also was detected for the rest-only group; however, the lameness index increased significantly for this group during the follow-up period, and an overall significant decrease was not detected. Comparison of the lameness index curve indicated a difference in favor of NaCl injection, with a significant difference between the 2 groups at final examination. Nine horses became sound during treatment with rest only, but 6 relapsed before final examination. In the NaCl-injected group, 5 of 10 sound horses relapsed. Conclusions and Clinical Relevance Intra-articular injection of 2 ml of 0.9% NaCl solution was beneficial in horses with traumatic arthritis. Use of rest alone for a limited period was inadequate for treatment of young Standardbred horses with traumatic arthritis. (Am J Vet Res 1999;60:1117–1121)

Differential effects of lipopolysaccharide and cholecystokinin on sucrose intake and palatability.

The differential effects of CCK and lipopolysaccharide (LPS) on sucrose intake and palatability were examined. Rats were injected with LPS (200 microg/kg ip) or NaCl (0.9%, vehicle) and 2 h later received a second injection of either CCK (8 microg/kg ip) or NaCl. In experiment 1, sucrose (0.3 M) intake was monitored for 1 h on three different test days 72 h apart, while in experiment 2, palatability was assessed by means of the taste reactivity test (TRT) on two separate days (72 h apart). In the TRT, orofacial and somatic responses to brief (30 s) intraoral infusions of sucrose were recorded and analyzed for response frequency. Singly, LPS and CCK reduced sucrose intake, with a more pronounced effect from combined LPS and CCK. LPS by itself did not alter sucrose palatability, as evidenced by continuous high levels of ingestive responding. In contrast, CCK-treated rats displayed a pattern of responding indicative of satiety, as did the combined LPS-CCK-treated rats. These results suggest that LPS does not induce hypophagia by altering palatability.

Elevated plasma osmotic concentration stimulates water absorption response in a toad

The water-seeking behavior (WR) of toads (Bufo viridis) was investigated. Fully hydrated toads that are allowed free choice of wet or dry filter paper voluntarily and spontaneously select to sit on water-soaked paper at a regular frequency during trials. Dehydration of bladder-emptied toads by 14% elicits WR in all animals. Injection of aldosterone or angiotensin-I reduced the dehydration threshold to 7% weight loss. WR frequency increased when plasma osmolality was elevated by injection of NaCl or other solutes (both ionic and non-ionic). Only urea, to which cell membranes are highly permeable, was the exception that did not produce this response. The increase in WR frequency induced by elevated plasma osmolality was augmented by injection of aldosterone or angiotensin-I. In vivo water uptake, measured in a water bath, was increased by an NaCl or oxytocin injection, but not by aldosterone. It is concluded that elevated plasma osmolality induces an increase in WR frequency that is separate and prior to the water uptake process. Different hormones are involved in each step. J. Exp. Zool. 284:168–173, 1999. © 1999 Wiley-Liss, Inc.

Elevated plasma osmotic concentration stimulates water absorption response in a toad.

The water-seeking behavior (WR) of toads (Bufo viridis) was investigated. Fully hydrated toads that are allowed free choice of wet or dry filter paper voluntarily and spontaneously select to sit on water-soaked paper at a regular frequency during trials. Dehydration of bladder-emptied toads by 14% elicits WR in all animals. Injection of aldosterone or angiotensin-I reduced the dehydration threshold to 7% weight loss. WR frequency increased when plasma osmolality was elevated by injection of NaCl or other solutes (both ionic and non-ionic). Only urea, to which cell membranes are highly permeable, was the exception that did not produce this response. The increase in WR frequency induced by elevated plasma osmolality was augmented by injection of aldosterone or angiotensin-I. In vivo water uptake, measured in a water bath, was increased by an NaCl or oxytocin injection, but not by aldosterone. It is concluded that elevated plasma osmolality induces an increase in WR frequency that is separate and prior to the water uptake process. Different hormones are involved in each step.

Consequences of treatment with dexamethasone in rats on the susceptibility of total plasma and isolated lipoprotein fractions to copper oxidation.

According to the oxidative hypothesis of atherosclerosis, a hyperoxidizability of lipoproteins could favor the development of the atherosclerotic process. Besides, it has been recently reported that models of elevated very-low-density-lipoprotein (VLDL) levels in rats resulted in an increased susceptibility of these VLDL to oxidation. Treatment with dexamethasone classically induces an increase in plasma VLDL concentration. The aim of our study was thus to assess the effects of a treatment with dexamethasone in rats on the susceptibility to copper oxidation, both on total plasma and on isolated lipoproteins. Male Sprague-Dawley rats aged three months were treated with a daily intraperitoneal injection of dexamethasone (1.5 mg per kg) for five days (DEX group), whereas control rats were fed ad libitum (AL group). In order to take into account the decrease of food intake induced by dexamethasone treatment, a group of pair-fed rats was constituted (PF group). These rats had the same food intake as rats of the DEX group and were treated with a daily isovolumic intraperitoneal injection of NaCl for 5 d. After 5 d treatment, rats were fasted overnight, then killed, and blood was collected on EDTA. Low-density lipoproteins (VLDL + LDL) and high-density lipoproteins (HDL) were isolated by ultracentrifugation. A copper oxidation was conducted both on total plasma and on isolated lipoproteins. As expected, after treatment with dexamethasone, plasma exhibited increased triglyceride and glucose levels. Similarly, VLDL + LDL of rats from the DEX group were enriched with triglycerides, when compared with VLDL + LDL of the other two groups of rats. Our major finding was a marked increase in the susceptibility of total plasma of the DEX group to copper oxidation, in comparison with the other two groups of rats. This oxidizability was assessed by the maximal level of oxidation products absorbing at 234 nm and classically considered to be conjugated dienes (7.46+/-0.70 micromol L(-1) in the DEX group vs. 3.36+/-0.40 and 2.05+/-0.60 micromol L(-1) in the AL and PF groups, respectively). Nevertheless, this higher oxidizability was not observed in the isolated lipoprotein fractions, as shown by the formation of lipid peroxidation products such as conjugated dienes, thiobarbituric-acid reactive substances, hydroperoxides, 7-ketocholesterol, and dienals. This is not in agreement with other models of hypertriglyceridemia that have been reported to induce a hyperoxidizability of lipoproteins in rats. Our results led us to hypothesize that other plasma components such as proteins could be involved in this susceptibility to oxidation. Indeed, the severe protein catabolism induced by dexamethasone treatment could support this hypothesis, by forming protein components that are more susceptible to oxidation, as shown by an increased carbonyl formation upon plasma copper oxidation.

The potentiation of amphetamine-induced hyperlocomotion by fimbria-fornix lesions in rats is abolished by intrahippocampal grafts rich in serotonergic neurons

Three-month old Long-Evans female rats were submitted to aspirative lesions of the fimbria-fornix and intrahippocampal grafts of a cell suspension prepared from a region of the fetal brain including the septum and the diagonal band of Broca (rich in cholinergic neurons) or the raphe (rich in serotonergic neurons). A group of lesioned rats was grafted with both suspensions mixed. Lesion-only and sham-operated rats served as controls. Four months after the lesions, all rats were tested daily for locomotor activity in their home cage, 1 day without being injected, 2 days with an injection of NaCl and 5 days with an injection of 1 mg/kg (i.p.) d-amphetamine. The effects of the lesions and grafts were assessed by measuring the accumulation of [3H]-choline or [3H]-5-hydroxytryptamine (5-HT) by hippocampal slices, and the electrically-evoked release of tritium. Amphetamine injections produced hyperlocomotion which was potentiated by the lesion. This lesion-induced potentiation was also found in rats with septal grafts, but not in those with raphe or co-grafts. The uptake and electrically-evoked release of [3H]-acetylcholine or [3H]-5-HT were reduced in hippocampal slices from lesion-only rats. In rats which received grafts of septal cells or co-grafts, but not in those with raphe grafts, uptake and release of [3H]-acetylcholine were close to normal. Uptake and release of [3H]-5-HT were close to normal in rats with raphe grafts or with co-grafts, but not in those with septal grafts. Altogether, these data suggest that damage to the serotonergic afferents of the hippocampus might play some role in the potentiation of amphetamine-induced hyperlocomotion associated with fimbria-fornix lesions.

Cimetidine inhibits nitric oxide associated nitrate production in a soft-tissue inflammation model in the horse.

Cimetidine (CIM) is an H2-receptor antagonist that has been used in racehorses in an attempt to reduce the occurrence of stress-related gastric ulceration. It has also been shown to produce several useful effects other than its gastric acid suppression properties. Further, it is a well documented antagonist of cytochrome P-450 (CYP) mediated oxygenation reactions. Nitric oxide (NO), a recently discovered mediator or modifier of numerous physiological functions, is generated by several forms of nitric oxide synthase (NOS), one of which is inducible (iNOS). Inducible NOS, expressed in neutrophils and macrophages as part of the inflammatory response to noxious stimuli, contains both a CYP and a CYP reductase domain. Because of the similarity of structure of iNOS and CYP, it was decided to determine whether CIM could reduce NO production, using a carrageenan inflammation model in the horse. Two experiments were conducted. In Trial 1, six female Thoroughbred horses each had three tissue chambers inserted subcutaneously on the sides of the neck. The study was divided into three treatments: 0.9% NaCl (NaCI), CIM (3 mg/kg), and aminoguanidine (AG; 25 mg/kg), an inhibitor of iNOS. Each mare received three i.v. injections 12 h apart prior to instillation of 1 mL of carrageenan into the test chamber. Blood and tissue chamber fluid (TCF) were collected serially. Concentrations of NO3- (the major metabolite of NO), albumin, total protein, CIM and AG were measured and complete cell counts and differentials were conducted. Trial 2 also used six female Thoroughbred horses implanted with at least two tissue chambers inserted subcutaneously on the sides of the neck. The study was divided into two treatments: NaCl (0.9%) and CIM (6 mg/kg). Each mare received seven i.v. injections of either NaCl or CIM 8 h apart prior to instillation of 1 mL of carrageenan into the test chamber. Blood and TCF were collected serially as before, and analysed for NO3- and CIM content. Areas under the curve (AUC) of the different parameters were calculated for the periods of -1-1, -1-3 and -1-7 days (Trial 1) and -2-1 for Trial 2. Absolute values were also compared at 4, 8 and 12 h postcarrageenan. Saline treatment did not reduce the elevated concentrations of NO3- in either plasma or TCF. Plasma, test chamber and control chamber NO3-concentrations rose from 0 to 12 h, and were very similar in all three sampled fluids. Cimetidine significantly (P< or =0.05) decreased NO3- production in plasma over the periods of -1-1, -1-3, and -1-7 days post inflammation when compared to NaCl treatment in Trial 1. Aminoguanidine and CIM decreased NO3-production in TCF for the periods -1-1, 1-3, and -1-7 days post inflammation in Trial 1 and -2-1 for Trial 2. Both CIM and AG also significantly reduced NO3-concentrations in plasma and TCF at 12 h postinitiation (Trials 1 and 2). Thus CIM, at the doses studied, was capable of reducing NO3- concentrations in this model as effectively as AG, a relatively specific inhibitor of iNOS activity.

Functional evidence for involvement of bumetanide-sensitive Na +K +2Cl − cotransport in the hepatoportal Na + receptor of the Sprague–Dawley rat

To investigate mechanisms involved in hepatoportal Na + sensing, responses of hepatic afferent nerve activity (HANA) to intraportal hypertonic NaCl injection were measured before, and after, intraportal infusion of inhibitors of Na + transport systems. HANA increased in response to the intraportal injection of 0.75 M NaCl in a dose-dependent manner. The HANA response was not affected by amiloride or 4-acetamido-4′-isothiocyanato-stilbene-2,2′-disulfonic acid (SITS), but was suppressed in a dose-dependent manner by intraportal infusion of ouabain, furosemide, or bumetanide. These results indicate that the hepatoportal Na + receptor senses the Na + concentration via the bumetanide-sensitive Na +K +2Cl − cotransporter.

Postinjury magnesium sulfate treatment is not markedly neuroprotective for striatal medium spiny neurons after perinatal hypoxia/ischemia in the rat.

Hypoxic/ischemic (H/I) brain injury is thought to be mediated via the N-methyl-D-aspartate receptor complex, which can be blocked by the magnesium ion. Striatal medium spiny neurons abundantly express N-methyl-D-aspartate receptors and are known to be injured after H/I. Thus, the aim of this study was to investigate the effect of postinjury magnesium treatment on the total number of medium spiny neurons in the striatum after perinatal H/I injury in the rat. Anesthetized postnatal day (PN) 7 rats underwent common carotid artery ligation followed 2 h later by exposure to hypoxia for 1.5 h. Contralateral hemispheres served as controls as did animals exposed to normoxia. Immediately after hypoxia or normoxia, the magnesium groups received s.c. injections of 300 mg/kg MgSO4. Control, hypoxic or normoxic animals received NaCl injections. This continued daily until PN13. Eleven matched-for-weight H/I pups were injected in total. A power calculation showed that 11 pups per treatment group would permit detection of a treatment difference of 32% or more. Animals were killed on PN18, and 40-micron serial sections were cut through each entire striatum. The total number of the predominant medium spiny neurons within each striatum was stereologically determined via the use of an unbiased optical dissector/Cavalieri combination. It was found that postinjury magnesium treatment did not improve neuronal survival by 32% or more in the striatum. The results suggest that magnesium treatment after perinatal H/I damage in the rat is not markedly neuroprotective for striatal medium spiny neurons.

Acute in Vivotoxicity of Heat-Sterilized Glucose Peritoneal Dialysis Fluids to Rat Peritoneal Macrophages

To evaluate the in vivo effects of heat-sterilized peritoneal dialysis (PD) fluids on the respiratory burst response of rat peritoneal leukocytes. Rats were exposed to intraperitoneal injections of a laboratory-made PD fluid that was either heat-sterilized (H-PD) or filtered (F-PD). Control groups of animals were given Hank's buffer (HBSS) or saline (NaCl). Leukocytes were harvested by intraperitoneal lavage at different times in different animals and analyzed with respect to cell numbers, differential counts, and production of superoxide (chemiluminescence) in response to opsonized zymosan. The chemiluminescence responses of the macrophage and the neutrophil populations, respectively, were obtained by curve-fitting techniques from the responses of the mixed populations. All fluids induced a recruitment of neutrophils, the PD fluids causing a cell number increase that was more transient than that caused by NaCl and HBSS. Macrophage numbers were only slightly influenced, but were generally higher after NaCl and HBSS injections than after PD fluid injections. The H-PD exposure induced a significant inhibition of the macrophage chemiluminescence response after 2 and 12 hours, compared with the exposure to F-PD. The neutrophil chemiluminescence response was not significantly affected. The toxins produced by heat-sterilization of glucose-containing PD fluids inhibit in vivo the respiratory burst response of peritoneal macrophages.

Maternal plasma hypo-osmolality: Effects on spontaneous and stimulated ovine fetal swallowing

Fetal swallowing is a major route of amniotic fluid resorption, and thus swallowing activity may alter amniotic fluid volume. Near-term ovine fetal swallowing increases in response to plasma and/or cerebrospinal fluid hypertonicity. As maternal hydration status alters amniotic fluid volume, we hypothesized that maternal plasma hypotonicity may alter fetal swallowing activity. Pregnant ewes (130 +/- 1 d; n = 6) were chronically prepared with maternal and fetal vascular catheters, a fetal esophageal flow probe, and fetal thyrohyoid and nuchal and thoracic esophagus electromyogram electrodes. Spontaneous fetal swallowing and hypertonic saline thresholds for stimulated swallowing were determined prior to and following maternal hypotonicity induced with water loading and intravenous DDAVP (arginine vasopressin V2 agonist). Fetal swallowing thresholds were determined with intracarotid injections (0.15 ml/kg) of increasing sodium chloride concentrations (0.15-1.2 M) at 2-min intervals. Maternal DDAVP infusion significantly decreased mean (+/-SEM) maternal and fetal plasma osmolalities (298 +/- 2-284 +/- 3; 295 +/- 2-278 +/- 3 mOsm/kg, respectively) and sodium concentrations (147.3 +/- 0.4-137.5 +/- 0.9; 142.7 +/- 0.8-133.5 +/- 1.0 mEq/l, respectively), suppressed spontaneous swallowing activity and volume (1.1 +/- 0.2-0.6 +/- 0.1 swallows/min; 0.7 +/- 0.2-0.5 +/- 0.1 ml/min, respectively) and significantly increased the osmotic threshold for swallowing stimulation (0.77 +/- 0.08-1.03 +/- 0.09 M NaCl). We conclude that: (1) maternal, and thus fetal, plasma hypotonicity results in suppression of spontaneous fetal swallowing activity and a decrease in volume swallowed, suggesting that spontaneous fetal ingestive behavior results, in part, from tonic dipsogenic stimulation, and (2) under hypotonic conditions, the intracarotid NaCl injection concentration for swallowing stimulation increases. These results suggest that the reset (lower) maternal plasma osmolality during human pregnancy may serve to minimize fetal ingestive and perhaps arginine vasopressin-mediated antidiuretic responses to acute maternal hypertonicity.

Syndrome X-like alterations in adult female rats due to neonatal insulin treatment

Hypothalamic structures are decisively involved in the regulation of body weight and metabolism. In syndrome X, complex metabolic alterations are present, which in women are found to be associated with disturbances of reproductive function and altered androgen levels. In previous experiments in rats, it was shown that a temporary intrahypothalamic hyperinsulinism during early life predisposes to overweight and diabetogenic disturbances later in life, associated with disorganization of hypothalamic regulatory centers. To investigate the possible long-term consequences of elevated peripheral insulin levels during ontogenesis, the following experiment was performed. Newborn female Wistar rats were treated during neonatal life with daily subcutaneous injections of long-acting insulin ([IRI group] 0.3 IU on days 8 and 9 of life and 0.1 IU on days 10 and 11 of life), whereas control animals (CO) received daily NaCl injections. This temporary exposure to increased insulin levels during a critical developmental period resulted in an increased body weight gain including juvenile life and adulthood ( P < .01), accompanied by hyperinsulinemia ( P < .01), impaired glucose tolerance ( P < .05), and increased systolic blood pressure in adulthood ( P < .025). No significant alterations were detected either in cyclicity and fertility or in the levels of testosterone, androstenedione, or dehydroepiandrosterone (DHEA) in IRI rats. Morphometric evaluation of hypothalamic nuclei showed a reduced numerical density of neurons ( P < .025) and a decreased neuronal volume density ( P < .025) within the ventromedial hypothalamic nucleus (VMN) of the IRI rats, whereas the antagonistic lateral hypothalamic area (LHA) was morphometrically unchanged. Newborn offspring of IRI rats (F1 generation) were overweight ( P < .05) and had an increased pancreatic insulin concentration ( P < .02). In conclusion, perinatal hyperinsulinism seems to predispose to the later development of syndrome X—like changes in female rats, possibly due to impaired organization of hypothalamic regulators of body weight and metabolism.

Central c-Fos expression in neonatal and adult rats after subcutaneous injection of hypertonic saline

Centrally-mediated responses to plasma hyperosmolality include compensatory drinking and pituitary secretion of vasopressin and oxytocin in both adult and neonatal rats. However, the anorexia that is produced by plasma hyperosmolality in adult rats is not evident in neonates, perhaps due to functional immaturity of osmoresponsive hindbrain circuits. To examine this possibility, the present study compared treatment-induced brain expression of the immediate-early gene product c-Fos as a marker of neural activation in adult and two-day-old rats after subcutaneous injection of 2 M NaCl (0.1 ml/10 g body weight). This treatment produced marked hypernatremia in adult and two-day-old rats without altering plasma volume. Several brain regions (including components of the lamina terminalis, the paraventricular and supraoptic nuclei of the hypothalamus, and the area postrema) were activated to express c-Fos similarly in adult and two-day-old rats after 2 M NaCl injection, consistent with previous reports implicating a subset of these regions in osmotically-stimulated drinking and neurohypophyseal secretion. In contrast, other areas of the brain that were activated to express c-Fos in adult rats after 2 M NaCl injection were not activated in neonates; these areas included the central nucleus of the amygdala, the parabrachial nucleus and catecholamine cell groups within the caudal medulla. This study demonstrates that certain brain regions that are osmoresponsive in adult rats (as defined by induced c-Fos expression) are not osmoresponsive in two-day-old rats. When considered in the context of known differences between the osmoregulatory capacities of adult and neonatal rats, our results are consistent with the idea that osmoresponsive forebrain centres are primarily involved in osmotically-stimulated compensatory drinking and neurohypophyseal secretion, whereas osmoresponsive regions of the hindbrain are important for concomitant inhibition of feeding and gastric emptying.

Cholestatic effects of cyclosporine in the rat.

Previous studies of cyclosporine-induced cholestasis were flawed by confounders encountered in human studies and discrepancies in acute animal experiments. Even the cyclosporine vehicle, polyoxyethylated castor oil (Cremophor EL), had been implicated in cholestasis. The purpose of this study was to investigate how cyclosporine affects bile salt kinetics and biliary lipid secretion in a rat model under steady state conditions. Three groups of male Lewis rats (n=10) were given daily subcutaneous injections of either cyclosporine (CsA; 10 mg/kg body weight), Cremophor, or NaCl (control) for 1 week. Twenty-four-hour bile collection was performed 18 hr after the last injection. The first hour's output measured bile flow and organic bile solute secretion rates. Bile salt pool size and basal synthesis were determined with the washout technique. CsA significantly reduced basal bile flow and bile salt secretion by 25%. Bile salt synthesis was suppressed 45% (CsA: 3.50+/-0.8 micromol/g liver/24 hr vs. control: 6.31+/-1.17 micromol/g liver/24 hr; P<0.05), which resulted in a 28% reduction in the bile salt pool size (CsA: 16.9+/-1.9 micromol/g liver vs. control: 23.6+/-2.0 micromol/g liver; P<0.05). Bile salt-independent flow was significantly suppressed (29%), whereas bile salt-dependent flow was only modestly reduced. Biliary phospholipid output decreased 23% (CsA: 11.7+/-0.8 nmol/min/g liver vs. control 15.2+/-1.1 nmol/min/g liver; P<0.05), but cholesterol secretion was unaltered, resulting in a 29% increase in the cholesterol saturation index (CsA: 0.40+/-0.03 vs. control 0.31+/-0.02; P<0.05). Cremophor had no significant effects on bile secretion or bile salt kinetics. CsA induces cholestasis by decreasing both bile flow and bile salt secretion. Its suppression of bile salt synthesis reduces the bile salt pool size. The drug inhibits bile salt and phospholipid secretion without a corresponding change in cholesterol secretion and thus elevates cholesterol saturation in bile, a potential risk for gallstone formation.

Angiogenesis and osteogenesis in an orthopedically expanded suture

The purpose of this study was to examine the angiogenic and the subsequent osteogenic responses during a 96-hour time-course after sutural expansion. Fifty rats were divided into: (1) a control group that received only angiogenic induction through injection of 5 ng/gm recombinant human endothelial cell growth factor (rhECGF); (2) an experimental group that received orthopedic expansion and rhECGF; (3) a sham group that received expansion and sodium chloride (NaCl) injection; and (4) a baseline group that received no expansion or injection. All rats were injected with 3H-thymidine (1.0 microCi/gm) 1 hour before death to label the DNA of S-phase cells. Demineralized sections (4 microm thick) were stained with hematoxylin and eosin. Angiogenesis and cell migration were analyzed with a previously established cell kinetics model. Analysis of variance was used to test the hypothesis that enhancement of angiogenesis stimulates reestablishment of osteogenic capability. Blood vessel number, area, and endothelial cell-labeled index significantly increased in experimental groups, but no difference was found between control and baseline groups. Labeled-pericyte index and activated pericyte numbers in the experimental group were also higher than in the sham groups. These results show that supplemental rhECGF enhances angiogenesis in expanded sutures but not in nonexpanded sutures. Data also suggest that pericytes are the source of osteoblasts in an orthopedically expanded suture.

Tenderizing spent fowl meat with calcium chloride. 4. Improved oxidative stability and the effects of additional aging

The goal of these experiments was to determine the effects of CaCl2 and NaCl injections on spent fowl meat tenderness and oxidative stability. Two hundred spent Leghorn hens were used in this two-part study. In the first experiment, breast fillets from 160 spent Leghorn hens were harvested immediately after death, injected with 0.3 M CaCl2 or H2O, vacuum tumbled, and either cooked immediately after tumbling or aged at 1 C for 23 h prior to cooking. Although the CaCl2 injection reduced shear values without aging, additional tenderization occurred during the aging period. In the second experiment, breast fillets from 40 spent Leghorn hens were harvested immediately after death, injected with 0.3 M CaCl2, 0.6 M NaCl, 0.15 M CaCl2 + 0.3 M NaCl, or H2O, vacuum tumbled, and then aged at 1 C for 23 h before cooking. The three salt injection treatments reduced shear values to a similar extent, but the sarcomeres were significantly longer for the NaCl treatment than the CaCl2 or combination treatments. Panelists preferred the CaCl2 + NaCl fillets over the CaCl2 fillets. Replacing some of the CaCl2 with NaCl maintained the tenderizing effect, and panelist comments indicated that the slight aftertaste of the 0.3 M CaCl2 treatment was reduced. The sodium contribution of the 0.6 M NaCl treatment would also be reduced by the CaCl2 + NaCl treatment.

Baroreceptor input regulates osmotic control of central vasopressin secretion.

Sinoaortic baroreceptor denervation (SAD) results in increased osmotically induced secretion of vasopressin (VP) and oxytocin (OT) and increased cardiovascular responses to many centrally acting pressor agents. Studies were conducted to determine whether SAD increases the cardiovascular and endocrine responses to direct and peripheral osmotic stimulation of the supraoptic nucleus (SON). SON microdialysis was performed in urethane-anesthetized male rats with measurement of dialysate peptides, mean arterial pressure (MAP) and heart rate. Experiment 1 tested the effect of direct stimulation of the SON with hypertonic NaCl in SAD, sham-operated (control) and intake-matched (matched) rats. Osmotically induced VP release into the SON was significantly greater in SAD than in control or matched groups. VP release peaked at 36 +/- 13 and 15 +/- 7 pg in SAD and controls, respectively, with no increase observed in the matched group. Plasma VP was significantly elevated after SON osmotic stimulation with no differences observed among the groups. The pressor response to osmotic stimulation was greater in SAD (29 +/- 4 mm Hg) than in control (20 +/- 3 mm Hg) and matched animals (15 +/- 3 mm Hg). Experiment 2 tested the effect of intraperitoneal injection of hypertonic NaCl on SON VP and OT release. SAD rats showed an increased central VP response to peripheral osmotic stimulation, a 64-fold increase in SAD as compared to a 4-fold one in controls. Central OT release was not significantly altered (peak of 22 +/- 6 vs. 11 +/- 4 pg, SAD vs. control). A direct SON osmotic challenge given 3.5 h after the intraperitoneal test confirmed an increased VP responsiveness in the SAD group. Plasma VP and OT were significantly increased after intraperitoneal hypertonic saline with no difference observed between groups. The MAP response to intraperitoneal hypertonic saline was greater in the SAD group with an elevation of 37 +/- 4 versus 18 +/- 3 mm Hg observed in SAD versus control subjects. These results demonstrate that baroreceptor denervation produces a state of heightened osmotic sensitivity for VP neurons, with evidence for increased central VP release to both direct and peripheral hypertonic NaCl stimulation.