Possible involvement of neuronal nitric oxide synthase enzyme in early-phase isoflurane-induced hypotension in rats

This study was conducted to demonstrate the involvement of nitric oxide synthase (NOS) in the early-phase isoflurane-induced hypotension and to ascertain whether this NOS is neuronal NOS (nNOS) or endothelial NOS (eNOS). Mean arterial pressures (MAPs) were directly measured from the femoral arteries of urethane-anesthetized rats. Isoflurane-induced changes in MAP were monitored in rats following pretreatment with vehicle or one of the following NOS inhibitors: L-N^G-monomethyl-L-arginine (L-NMMA), which is non-selective; L-N^G-nitro arginine (L-NOARG), which is more selective for nNOS and eNOS; and 7-nitroindazole (7-NI), which is selective for nNOS. Exposure to 2% isoflurane in oxygen produced a triphasic reduction in MAP, including an early phase in which mean arterial pressure (MAP) fell by 25-30% during the initial 2½ min. This early hypotensive response, but not subsequent phases, was abolished by i.v. pretreatment with either L-NMMA or L-NOARG. The early-phase hypotension was also significantly attenuated by i.p. pretreatment with 7-NI; however, the blockade was not as complete as with L-NMMA or L-NOARG. Cerebella and aorta were removed from vehicle- and 7-NI pretreated rats and assayed for NOS activity by determining the conversion of [¹⁴C]L-arginine to [¹⁴C]L-citrulline. The 7-NI pretreatment significantly reduced NOS activity in the cerebellum but not the aorta. These findings indicate that the early-phase isoflurane-induced hypotension may involve nNOS as well as eNOS. The nNOS may participate in regulation of isoflurane-induced neuronal release of endogenous opioid peptide, which produces a vasodilation that is dependent on NO derived from an action of eNOS.     

microRNA-124 attenuates isoflurane-induced neurological deficits in neonatal rats via binding to EGR1

Isoflurane anesthesia induces neuroapoptosis in the development of the brain. In this study, neonatal rats and hippocampal neurons were subjected to isoflurane exposure, in which the effect of miR-124 on the neurological deficits induced by isoflurane was evaluated. Isoflurane anesthesia models were induced in neonatal SD rats aged 7 days and then treated with miR-124 agomir, miR-124 antagomir, or LV-CMV-early growth response 1 (EGR1) plasmids. Then, the spatial learning and memory ability of rats were evaluated by Morris water maze. Furthermore, primary hippocampal neurons cultured 7 days were also exposed to isoflurane and transfected with miR-124 agomir, miR-124 antagomir, or LV-CMV-EGR1 plasmids. The targeting relationship of miR-124 and EGR1 was verified by the dual-luciferase reporter gene assay. To identify the effect of miR-124 on neuron activities, the viability and apoptosis of hippocampal neurons were assessed. In response to isoflurane exposure, miR-124 expression was reduced and EGR1 expression was increased in the hippocampal tissues and neurons. The isoflurane anesthesia damaged rats' spatial learning and memory ability, and reduced viability, and promoted apoptosis of hippocampal neurons. EGR1 was targeted and negatively regulated by miR-124. The treatment of miR-124 agomir improved rats' spatial learning and memory ability and notably increased hippocampal neuron viability and resistance to apoptosis, corresponding to an increased brain-derived neurotrophic factor (BDNF) expression, inhibited expression of proapoptotic factors (cleaved-Caspase-3 and Bax), and enhanced the expression of antiapoptotic factor (Bcl-2). Upregulated miR-124 inhibited the expression of EGR1, by which mechanism miR-124 reduced the neurological deficits induced by isoflurane in neonatal rats through inhibiting apoptosis of hippocampal neurons.     

Indomethacin attenuates post-suspension hypotension in Sprague-Dawley rats

Orthostatic hypotension is a serious condition that is sometimes manifested in astronauts during standing postflight. These observations may be related to impairment of autonomic function and/or excessive production of endothelium-dependent relaxing factors. To evaluate the role of the cyclooxygenase inhibitor indomethacin as a countermeasure against the post-suspension reduction in mean arterial pressure (MAP), we examined the cardiovascular responses to 7-day 30 degrees tail-suspension and a subsequent 6-hr post-suspension period in conscious male Sprague-Dawley rats. Indomethacin (2 mg/kg) or saline were administered intravenously prior to release from suspension and at 2 and 4 hrs post-suspension. Direct MAP and heart rate were determined prior to suspension, daily and every 2 hrs post-suspension. During suspension, MAP did not change, in contrast, during post-suspension; it decreased compared to parallel non-suspended, untreated animals. There were no significant changes in heart rate. The reduction in MAP post-suspension was associated with significant increases in plasma prostacyclin. Indomethacin attenuated the observed post-suspension reduction in MAP and reduced plasma prostacyclin levels. Also, the baroreflex sensitivity for heart rate was modified by indomethacin--the MAP threshold for baroreflex activation was raised and the effective MAP range expanded. Thus, the post suspension reduction in mean arterial pressure may be due to overproduction of vasodilatory prostaglandins and/or other endothelium-dependent relaxing factors and alteration in baroreflex activity.     

Velocity specificity in early-phase sprint training

A comparison of resistance running, normal sprint running, and supramaximal running was performed. Nineteen young, generally well-trained subjects were divided into 3 training groups: resistance, normal, and supramaximal groups. Resistance and supramaximal training was done using a towing device, providing extra resistance or propulsion forces, resulting in running speed differences of about 3.3% (supramaximal) and 8.5% (resistance), compared to normal sprinting. The training period was 6 weeks, with 3 training sessions per week (5 sprint-runs over 22 m). Running times were measured using photocells, and average step length and cadence were recorded by digital video. A small (0.5%) but significant (p < 0.05) overall pre-post difference was found in running velocity, but the 3 groups changed differently over the running conditions. All individual subjects improved sprinting velocity most on the trained form, at 1-2% (p < 0.001), and thus, the principle of velocity specificity in sprint training was supported. This indicates that to obtain short-distance sprinting improvement in a short period of time, one may prefer normal sprinting over other training forms.     

Hepatic venoconstriction is involved in anaphylactic hypotension in rats

We determined the roles of liver and splanchnic vascular bed in anaphylactic hypotension in anesthetized rats and the effects of anaphylaxis on hepatic vascular resistances and liver weight in isolated perfused rat livers. In anesthetized rats sensitized with ovalbumin (1 mg), an intravenous injection of 0.6 mg ovalbumin caused not only a decrease in systemic arterial pressure from 120 +/- 9 to 43 +/- 10 mmHg but also an increase in portal venous pressure that persisted for 20 min after the antigen injection (the portal hypertension phase). The elimination of the splanchnic vascular beds, by the occlusions of the celiac and mesenteric arteries, combined with total hepatectomy attenuated anaphylactic hypotension during the portal hypertension phase. For the isolated perfused rat liver experiment, the livers derived from sensitized rats were hemoperfused via the portal vein at a constant flow. Using the double-occlusion technique to estimate the hepatic sinusoidal pressure, presinusoidal (R(pre)) and postsinusoidal (R(post)) resistances were calculated. An injection of antigen (0.015 mg) caused venoconstriction characterized by an almost selective increase in R(pre) rather than R(post) and liver weight loss. Taken together, these results suggest that liver and splanchnic vascular beds are involved in anaphylactic hypotension presumably because of anaphylactic presinusoidal contraction-induced portal hypertension, which induced splanchnic congestion resulting in a decrease in circulating blood volume and thus systemic arterial hypotension.     

Phorbol ester suppression of opioid analgesia in rats

Protein kinase C (PKC) has been shown to be an important substrate in intracellular signal transduction. Very little is known concerning its possible role in mediating opiate-induced analgesia. In the present study, 12-O-tetradecanoylphorbol 13-acetate (TPA), a selective activator of PKC, was injected intrathecally (ith) to assess its influence on the analgesia induced by intrathecal injection of the mu opioid agonist PL017, the delta agonist DPDPE and the kappa agonist 66A-078. Radiant heat-induced tail flick latency (TFL) was taken as an index of nociception. TPA in the dose of 25-50 ng, which did not affect the baseline TFL, produced a marked suppression of opioid antinociception, with a higher potency in blocking mu and delta than the kappa effect. In addition, mu and delta agonists induced remarkable decreases in spinal cyclic AMP (cAMP) content whereas the kappa effect was weak. The results suggest a cross-talk between the PKC system and the signal transduction pathway subserving opioid analgesia.     

Stimulatory role for endogenous opioid peptides on postexercise insulin secretion in rats

Endogenous opioid peptides (EOP) and prior exercise may modulate the stimulatory effect of glucose on insulin secretion. To gain insights into these relationships, we studied male Wistar rats (187-245 g) during sustained hyperglycemia by use of the glucose clamp technique. Four groups of sedentary fed rats (n = 8/group) either ran (Ex) at 24 m/min, 0% grade, or rested (R) for 40 min. Thirty minutes after Ex or R, arterial blood glucose was elevated to and maintained at 11 mM for 2 h by a variable glucose infusion. At the start of Ex or R rats had saline (Sal) or naloxone (Nal, an opioid antagonist) intravenous infusions for 160 min (40 min Ex + 30 min R + 90 min of a 120-min glucose clamp). Steady-state glucose infusion rates (SSGIR) were approximately 55 mg.kg-1.min-1 at the start of the clamp and declined significantly over the 2nd h to approximately 45 mg.kg-1.min-1. No significant differences existed in SSGIR between groups. R-Sal and Ex-Sal groups did not differ in their insulin response to hyperglycemia. In contrast, when all groups were compared at the end of the Nal or Sal infusion, Ex-Nal had the lowest insulin concentration (749 +/- 174 pmol/l), whereas the R-Nal group had the highest (1,581 +/- 216 pmol/l, P less than 0.05). These data suggest a stimulatory role for EOP on insulin secretion that is expressed after a prior stress (Ex). Thus one function of exercise-induced activation of EOP may be to regulate insulin secretion in the immediate postexercise period.     

Compound 48/80 inhibits neurotensin-induced hypotension in rats

The intravenous injection of neurotensin (NT) (0.4 and 1.1 nmoles/kg) produced dose-dependent hypotensive effects in pentobarbital anesthetized rats. The acute or chronic administration of compound 48/80, a well known mast cell depletor, completely abolished the hypotensive effect of low to medium doses of NT and unmasked the previously unknown hypertensive effect of high doses (4.0 nmoles/kg) of NT. This hypertensive effect was significantly reduced by infusing the animals with [D-Trp¹¹]-NT a selective antagonist of NT. The hypotensive action of NT in control rats was also significantly reduced by pretreating the animals with disodium cromoglycate, an antiallergic drug which is believed to stabilize mast cells membranes, or with a mixture of azatadine and methysergide. The results suggest the participation of histamine, serotonin and possibly other endogenous vasoactive substances, to the hypotensive action of NT in rats. The possible origin of these mediators is discussed.     

An olfactory basis for maternal discrimination of sex of offspring in rats (rattus norvegicus)

Lactating Long-Evans rats (Rattus norvegicus) were presented with three-day-old male and female pups that were either untreated, coated with collodion in the anogenital region or on the neck, or perfumed; or with female pups odorized with either male or female pup urine. As measured by related t-tests of maternal anogenital licking, male and female pups were discriminated in the untreated condition, but not when masking stimuli were present. Female pups treated with male urine elicited more licking than female pups treated with female urine. Overall, maternal licking was decreased by olfactory masking agents and increased by pup urine. It was concluded that olfactory stimuli from pups both stimulate maternal licking and serve as a basis for discriminating male and female offspring.     

Ribonucleic-acid-biomarker candidates for early-phase group detection of common cancers

Cancer is considered as a challenging lethal agent around the world and its detection at early stages would help prevention of the high mortality. Among the widely used biomarkers in clinical diagnosis of cancer, extracellular non-coding RNAs as ribonucleic acid biomarkers serve as state-of-the-art candidates for molecular diagnosis. In that regard, microRNAs are of great priority mainly because of high variety and stability in body fluids. Accordingly, common miRNAs among most prevalent cancers could help us (pre)diagnose cancer with high accuracy in target samples. In this study, common lethal cancers to humans were investigated in case of miRNA profiles to determine the possible common correlation between miRNA up-regulation or down-regulation (as a ribonucleic acid biomarker) and developing the cancers. It was shown that among the investigated miRNAs, five typical extracellular miRNAs (miR-18a, miR-21, miR-155, miR-221, and miR-375) dysregulation are predominant in most cancer varieties comprising breast, colon, lung, prostate, pancreas, gastric, ovarian, esophagus and liver. This could serve as an appropriate target site for developing point-of-care approaches for cancer detection e.g. designing diagnostic biosensor-based microarrays or kits for both quantification and qualification of the biomarkers. Besides, the miRNA candidates could be efficiently applied to cancer therapeutic approaches.     

Serum opioid activity after physical exercise in rats.

In order to study the effect of exercise on the total serum opioid activity, female rats were trained for 3 weeks on a motor-driven treadmill and the experiment was ended by a final strenuous run until exhaustion. The serum samples were taken immediately after the final run and were analyzed by radioreceptor assay. Despite considerable interindividual variations, serum opioid activity, expressed in met-enkephalin equivalents (ME eq +/- S.D.), was significantly higher in the exercising group (74.5+/-50.5 pmol ME eq/ml) than in the control group (35.7+/-20.2 pmol ME eq/ml). Because of the much lower molar levels of beta endorphin and met-enkephalin, this result suggests that many other opioid peptides might be involved in that increase.     

Peripheral opioid receptors influencing heart rate in rats: evidence for endogenous tolerance

Opioid peptides injected into the circulation of rats evoke a vagally mediated bradycardia. The intravenous ED50 of morphine for producing a greater than or equal to 10% fall in heart rate was determined in urethane-anesthetized rats. Hypophysectomy, or adrenalectomy plus treatment with dexamethasone (0.5 microgram/h, s.c., 1 day), procedures that remove endogenous sources of opioid peptides, increased the sensitivity of the animal to morphine bradycardia by 6-10-fold. Conversely, stressing the animals by exposure to cold (4-6 degrees C for two days) elevated the ED50 for morphine sulfate and for beta h-endorphin by about 5-fold. Dexamethasone infusions prevented the cold-induced desensitization to morphine. Intravenous administration of rat corticotropin-releasing factor (CRF) also desensitized the animals to morphine. CRF alone produced a fall in blood pressure and heart rate. The bradycardia was prevented by pretreatment with naloxone. These results indicate that the sensitivity of vagal opioid chemoreceptors is influenced by endogenous sources of opioid peptides. This phenomenon can be called 'endogenous tolerance'.     

An osmoregulatory basis for shape oscillations in regenerating hydra

The freshwater polyp Hydra has considerable regeneration capabilities. A small fragment of tissue excised from an adult animal is sufficient to regenerate an entire Hydra in the course of a few days. During the initial stages of the regeneration process, the tissue forms a hollow sphere. Then the sphere exhibits shape oscillations in the form of repeated cycles of swelling and collapse. We propose a biophysical model for the swelling mechanism. Our model takes the osmotic pressure difference between Hydra's inner and outer media and the elastic forces of the Hydra shell into account. We validate the model by a comprehensive experimental study including variations in initial medium concentrations, Hydra sphere sizes and temperatures. Numerical simulations of the model provide values for the swelling rates that are in agreement with the ones measured experimentally. Based on our results we argue that the shape oscillations are a consequence of Hydra's osmoregulation.