In vitro bronchial responsiveness in two highly inbred rat strains

Wang, C. G., J. J. Almirall, C. S. Dolman, R. J. Dandurand,and D. H. Eidelman. In vitro bronchial responsiveness in twohighly inbred rat strains. J. Appl.Physiol. 82(5): 1445-1452, 1997.We investigatedmethacholine (MCh)-induced bronchoconstriction in explanted airwaysfrom Fischer and Lewis rats. Lung explants, 0.5- to 1.0-mm thick, wereprepared from agarose-inflated lungs of anesthetized 8- to 12-wk-oldmale rats. After overnight culture, videomicroscopy was used to recordbaseline images of the individual airways. Dose-response curves to MChwere then constructed by repeated administration of MCh; airways werereimaged 10 min after each MCh administration. Airway internal luminalarea(A_i)was measured at successive MCh concentrations from10⁹ to10¹ M. Inaddition to the effective concentration leading to 50% of the achievedmaximal response, we also determined the effective concentrationleading to a 40% reduction inA_i.Both the effective concentration leading to 50% of the achievedmaximal response and the concentration leading to a 40% reduction inA_iwere significantly lower among Fischer rat airways(P < 0.05). Airway closure was morecommon among Fischer rat airways (17%) than among those of Lewis rats(7.5%). Responsiveness of Fischer rat airways was more heterogeneousthan among Lewis airways; a larger number of Fischer rat airwaysexhibited high sensitivity to MCh. There was no relationship betweenresponsiveness and baselineA_iin either strain. In a second experiment, we measured the rate ofcontraction of explanted airways from lungs inflated to 50, 75, and100% of total lung capacity. The average rate of contraction in thefirst 15 s was higher in Fischer rat airways at each inflation volume.These data indicate that the hyperresponsiveness of the Fischer rat reflects the responsiveness of individual airways throughout the airwaytree and are consistent with the notion that in this model hyperresponsiveness is an intrinsic property of airway smooth muscle.

     

Basal lung mechanics and airway and pulmonary vascular responsiveness in different inbred mouse strains.

Little is known about interstrain variations in baseline lung functions or smooth muscle contractility in murine lungs. We therefore examined basal lung mechanics and airway, as well as vascular reactivity to methacholine, thromboxane (using U-46619), and endothelin-1 (ET-1), A/J, AKR, BALB/c, C3H/HeN, C57BL/6, and SCID mice. All experiments were performed with isolated perfused mouse lungs. Except AKR mice (which were excluded from further analysis), all other strains showed stable pulmonary compliance, pulmonary resistance, and pulmonary arterial pressure within a control period of 45 min. Among these strains, C3H/HeN mice exhibited higher dynamic pulmonary compliance and lower pulmonary resistance, whereas SCID mice had higher baseline pulmonary resistance than the other strains. Concentration-response experiments with methacholine showed a lower airway reactivity for C57BL/6 mice compared with the other strains. Perfusion with 1 microM U-46619 or 100 nM ET-1 revealed a similar pattern: the agonist-inducible broncho- and vasoconstriction was lower in C57BL/6 mice than in all other strains, whereas it tended to be higher in SCID mice. The present study demonstrates a correlation between airway and vascular responsiveness in all tested strains. SCID mice are hyperreactive, whereas C57BL/6 mice are hyporeactive, to smooth muscle constrictors. Lung mechanics, as well as airway and vascular responsiveness, appear to be genetically controlled.     

Long-term stability of the human gut microbiota in two different rat strains

Human microbiota associated rats are frequently used as a model to study host microbe interactions. This study investigated the long-term stability of the bacterial community in such rats. Following the association of two strains of germ-free rats (12 male animals each) with fecal bacteria from a human donor the development of the microbiota was monitored for 12 months by PCR-denaturing gradient gel electrophoresis. During this time the Dice similarity coefficient (Cs) for the fecal microbial community of the rats associated with a human microbiota in comparison to the donor sample ranged between 73% +/- 8 and 74% +/- 3 for the Wistar and the Fischer 344 rats, respectively. After 12 months the similarity coefficients were 78% +/- 9 and 76% +/- 7, respectively, while the similarity coefficients for rat sample replicates ranged from 77% +/- 7 to 88% +/- 5; the similarity coefficient of the donor sample replicates was 78% +/- 9. DNA sequences of bands observed in the different denaturing gradient gel electrophoresis profiles exhibited the highest degree of identity to uncultured bacteria previously found in samples of human, mouse or pig intestinal origin. The results of this study suggest that the dominant human fecal microbiota can be maintained in the human microbiota associated rat model for at least one year.     

Mesenteric vascular responsiveness in a rat model of pregnancy-induced hypertension

Reduced perfusion to the placenta in early pregnancy is believed to be the initiating factor in the development of preeclampsia, triggering local ischemia and systemic vascular hyperresponsiveness. This sequence of events creates a predisposition to the development of altered vascular function and hypertension. This study was designed to determine the influence of placental insufficiency on the responsiveness of mesenteric resistance arteries in an animal model of preeclampsia. Placental insufficiency was induced by reduction in uteroplacental perfusion pressure (RUPP) in experimental Sprague-Dawley rat dams. The uterine branches of the ovarian arteries and the abdominal aortae of pregnant rats were surgically constricted on gestational Day 14. Dams in the control group underwent a sham procedure. Rats were euthanized on gestational Day 20, followed by removal of the small intestine and adjacent mesentery. First-order mesenteric resistance arteries were mounted on a small vessel wire myograph and challenged with incremental concentrations of vasoconstrictors and vasorelaxants. Mesenteric arteries in dams with placental insufficiency demonstrated an increased maximal tension to phenylephrine (7.15 +/- 0.15 vs. 5.4 +/- 0.27 mN/mm, P < 0.001); potassium chloride at 60 mM (3.43 +/- 0.11 vs. 2.77 +/- 0.14 mN/mm, P < 0.01) and 120 mM (3.92 +/- 0.18 vs. 2.97 +/- 0.16 mN/mm, P < 0.01); and angiotensin II (2.59 +/- 0.42 vs. 1.51 +/- 0.22 mN/mm, P < 0.05). Maximal relaxation to endothelium-dependent relaxants acetylcholine and calcium ionophore (A23187) was not significantly reduced. Data suggest that placental insufficiency leads to hyperresponsiveness to vasoconstrictor stimuli in mesenteric arteries.     

Actions and interactions of lipoxygenase and cyclo-oxygenase products in respiratory and vascular tissues

Actions of leukotrienes (LTs) B₄, C₄, D₄ and E₄ were found to be largely mediated via formationformitisn of cyclo-oxygenase products in guinea-pig isolated perfused lung and parenchymal strips. In contrast, LTs exerted a direct contractile effect on human isolated parenchymal and bronchial strips. An LT-like substance which had similar biological actions to LTD₄ was generated from porcine and guinea-pig vascular tissue. The highest concentration of this material was formed by coronary and pulmonary arteries and the surrounding adventitia, as well as from the lung parenchyma.     

Oocyte spontaneous activation in different rat strains

Oocyte spontaneous activation (OSA) has been reported to occur during in vitro culture of ovulated rat oocytes. The objective of this study was to compare the rate of oocyte spontaneous activation and the level of maturation promoting factor (MPF) activity in oocytes from different strains. Twelve strains were selected from two commercial sources. Females were superovulated and oocytes collected 17 h after hCG injection. Denuded oocytes were cultured in M16 medium under oil at 37 degrees C and 5% CO(2) in air. The proportion of activated oocytes was determined after 6 h of in vitro culture. Data were compared by analysis of variance (ANOVA), considering each animal as an experimental unit. MPF activity was determined in oocytes from the different strains at 0, 1.5, and 3 h after oocyte collection. The log ratio of the MPF activity at 1.5 and 3 h relative to 0 hours for each animal was analyzed by ANOVA. While significant (p < 0.01) differences were observed between strains in the rate of OSA, there were no differences between strains in the level of MPF during the time points measured (p > 0.3).     

Gastric mucus glycoprotein in different rat strains

The extent of gastric damage induced by aspirin was found to differ according to rat strain. The occurrence of ulcers varied, from high to low, in the following strain order: Donryu, Sprague-Dawley (SD) and Wistar. The content of corpus mucus glycoprotein was essentially the same in all the strains: about 6 mg as hexose of dry tissue. Antral mucus glycoprotein content increased in the order Wistar, SD and Donryu: 7.1, 8.3 and 9.1 mg, respectively. Gastric mucus glycoprotein carbohydrate composition was essentially the same in all three strains. The relatively low proportions of N-acetylglucosamine, galactose and sialic acid from the antrum was a characteristic feature in contrast to mucus glycoprotein from the corpus which contained a high proportion of these sugars.     

Aquaporins in complex tissues. II. Subcellular distribution in respiratory and glandular tissues of rat

The molecular pathways for fluid transport in pulmonary, oral,and nasal tissues are still unresolved. Here we use immunocytochemistry and immunoelectron microscopy to define the sites of expression of fouraquaporins in the respiratory tract and glandular epithelia, where theyreside in distinct, nonoverlapping sites. Aquaporin-1 (AQP1) is presentin apical and basolateral membranes of bronchial, tracheal, andnasopharyngeal vascular endothelium and fibroblasts. AQP5 is localizedto the apical plasma membrane of type I pneumocytes and the apicalplasma membranes of secretory epithelium in upper airway and salivaryglands. In contrast, AQP3 is present in basal cells of tracheal andnasopharyngeal epithelium and is abundant in basolateral membranes ofsurface epithelial cells of nasal conchus. AQP4 resides in basolateralmembranes of columnar cells of bronchial, tracheal, and nasopharyngealepithelium; in nasal conchus AQP4 is restricted to basolateralmembranes of a subset of intra- and subepithelial glands. These sitesof expression suggest that transalveolar water movement, modulation ofairway surface liquid, air humidification, and generation ofnasopharyngeal secretions involve a coordinated network of aquaporinwater channels.

     

Aquaporins in complex tissues. I.Developmental patterns in respiratory and glandular tissues of rat

Developmentalexpression of aquaporin water transport proteins is not well understoodin respiratory tract or secretory glands; here we define aquaporinprotein ontogeny in rat. Expression of aquaporin-3 (AQP3), AQP4, andAQP5 proteins occurs within 2 wk after birth, whereas AQP1 firstappears before birth. In most tissues, aquaporin protein expressionincreases progressively, although transient high-level expression isnoted in distal lung (AQP4 at postnatal day+2) and trachea (AQP5 at postnatalday +21 and AQP3 at postnatal day+42). In mature animals, AQP5 is abundant in distallung and salivary glands, AQP3 and AQP4 are present in trachea, andAQP1 is present in all of these tissues except salivary glands.Surprisingly, all four aquaporin proteins are highly abundant innasopharynx. Unlike AQP1, corticosteroids did not induce expression ofAQP3, AQP4, or AQP5 in lung. Our results seemingly implicate aquaporinsin proximal airway humidification, glandular secretion, and perinatalclearance of fluid from distal airways. However, the studies underscorea need for detailed immunohistochemical characterizations anddefinitive functional studies.

     

Changes in vascular responsiveness following chronic exposure to cold in the rat

The responsiveness of smooth muscle from rings of aortic tissue of cold-acclimated (CA, 6 degrees C, 5-15 wk) rats to both alpha- and beta-adrenergic agonists and KCl was tested and compared with that of warm-adapted (25 degrees C) controls. alpha-Adrenergic stimulation, induced by low doses (10(-8)-10(-7) M) of phenylephrine and norepinephrine in the presence and absence of the beta-adrenergic antagonist, propranolol, resulted in the development of less active tension by aortic smooth muscle from CA rats than from controls. Similar results were observed with the weakly alpha 1-adrenergic agonistic activities of tyramine, clonidine, and high concentrations of isoproterenol (10(-6)-10(-4) M). There was also a significant reduction in the tension developed by smooth muscles of the aortas from CA rats when depolarized with KCl in concentrations ranging from 8 to 20 mM. In contrast, aortic smooth muscle, contracted to 75% of maximum with KCl, showed an enhanced relaxation to the beta-adrenergic agonist, isoproterenol, in CA rats. These studies suggest that acclimation of rats to cold results in both a decrease in alpha-adrenergic responsiveness and an increase in beta-adrenergic responsiveness in vascular smooth muscle as well as a change in the biochemical events that couple activation of adrenergic receptors to changes in vasomotor tone.     

Cholinergic responsiveness of intestinal muscle in the pregnant guinea pig

Clinical observations and limited animal experiments have suggested that gastrointestinal motility is suppressed during pregnancy. We therefore compared isometric contractions of colon and ileal circular muscle in response to carbachol (10(-8) to 10(-4) M). Data was analyzed by comparing mean maximal tension, dose-response curves, and EC50 values for tissue from the two groups of animals. Circular muscle from proximal colon, distal colon, and ileum in pregnant animals developed less tension in response to carbachol than did tissue from non-pregnant controls. Dose-response curves in the pregnant groups were depressed, when compared with non-pregnant groups, at concentrations of 10(-6) M and greater. Sensitivity of the muscle to cholinergic stimulation, as measured by EC50 values, was similar in the ileum and proximal colon but increased slightly (p less than 0.05), by a factor of approximately 2, for distal colonic muscle from pregnant animals. Assuming that circular muscle contractions are primarily responsible for mixing and propulsion in the gut, this reduction in responsiveness to excitatory cholinergic stimulation is consistent with the concept of pregnancy-related suppression of gastrointestinal motility.     

Cholinergic stimulation of vascular prostacyclin synthesis

The production of prostacyclin by rings of rabbit aorta was assessed by the radioimmunoassay of 6-K-PGF_1α. In steady-state conditions, the rings released 11 ng 6-K-PGF_1α per 100 mg tissue in 30 min. Acetylcholine increased this output: a significant effect was detected at 1 μM and at 10 μM the amplitude of stimulation was 10-fold. The production of PGE₂ and PGF_2α was also increased, but to a lesser extent. The stimulatory action of acetylcholine was mimicked by carbamylcholine and inhibited by atropine; it was abolished in a calcium-free medium. Dog and rat aorta also produced more 6-K-PGF_1α in response to cholinergic agonists. A short rubbing of the intimal surface of the aorta removed the layer of endothelial cells and completely abolished the cholinergic effect. It is concluded that in the aorta, cholinergic agonists, acting on a muscarinic receptor, stimulate the production of prostacyclin by endothelial cells.     

Determination of reference genes for circadian studies in different tissues and mouse strains

Background  

Circadian rhythms have a profound effect on human health. Their disruption can lead to serious pathologies, such as cancer and obesity. Gene expression studies in these pathologies are often studied in different mouse strains by quantitative real time polymerase chain reaction (qPCR). Selection of reference genes is a crucial step of qPCR experiments. Recent studies show that reference gene stability can vary between species and tissues, but none has taken circadian experiments into consideration.     

Findings of somatosensory evoked potential to stimulation of the sciatic nerve in two different rat strains.

No comparative study about somatosensory evoked potentials (SEP) on different rat strains has been done yet. It is evident that comparative SEP studies are important since different rat strains have different physiological properties. We aimed to compare early latency SEP values from stimulation of sciatic nerve in Wistar (Wr) and Sprague-Dawley (SDr) rats which are frequently used rat strains in experimental studies. In Wr group, the mean of first far field potential (Ff1) latency was shorter and the mean Ff1 amplitude was lower than that of Sprague-Dawley rat group. Mean cortical potential latency in Wr group was longer than that of SDr group while amplitude was not different. Central conduction time (CCT) in Wistar rat group was found to be longer than that of SDr group. Shorter Ff1 latency in Wr group implies that afferent volley reaches cervical posterior fasciculus from sciatic nerve earlier than SDr group while longer CP latency implies that afferent volley reaches cortex later than SDr group. Similarity between the latencies of lumbar potentials implies that peripheral conduction velocity has no effect on the difference of Ff1 latencies.