Effects of Δ9-Tetrahydrocannabinol and the Aminoalkylindole K2/Spice Constituent JWH-073 on Cardiac Tissue and Mesenteric Vascular Reactivity

Background: Although use of Cannabis sativa is not associated with serious adverse effects, recreational use of aminoalkylindole (AAI) cannabinoid receptor agonists found in K2/Spice herbal blends has been reported to cause adverse cardiovascular events, including angina, arrhythmia, changes in blood pressure, ischemic stroke, and myocardial infarction. Δ9-Tetrahydrocannabinol (Δ9-THC) is the primary CB1 agonist found in cannabis and JWH-073 is one of the AAI CB1 agonists found in K2/Spice brands sold to the public. Methods: This study used in vitro, in vivo, and ex vivo approaches to investigate potential differences on cardiac tissue and vascular effects betweenJWH-073 and Δ9-THC. Male C57BL/6 mice were treated with JWH-073 or Δ9-THC and cardiac injury was assessed by histology. Effects of JWH-073 and Δ9-THC on H9C2 cell viability and ex vivo mesenteric vascular reactivity were also determined. Results: JWH-073 or Δ9-THC induced typical cannabinoid effects of antinociception and hypothermia but did not promote death of cardiac myocytes. No differences in cell viability were observed in cultured H9C2 cardiac myocytes after 24 h of treatment. In isolated mesenteric arteries from drug-naive animals, JWH-073 produced significantly greater maximal relaxation (96%±2% vs. 73%±5%, p<0.05) and significantly greater inhibition of phenylephrine-mediated maximal contraction (Control 174%±11%KMAX) compared with Δ9-THC (50%±17% vs. 119%±16%KMAX, p<0.05). Discussion: These findings suggest that neither cannabinoid at the concentrations/dose studied caused cardiac cell death, but JWH-073 has the potential for greater vascular adverse events than Δ9-THC through an increased vasodilatory effect.

Molecular Modeling and Potential Ca2+ Channel Blocker Activity of Diphenylmethoxypiperidine Derivatives

Molecular interactions of 4-diphenylmethoxy-1-methylpiperidine derivatives with the calcium channel CaV1.1 (pdb:6JP5) are described. All the compounds tested, previously shown to inhibit adrenergic vascular contractions, display similar binding energetics and interactions with the trans-membrane domain of 6JP5 on the opposite side relative to the channel pore, where nifedipine, a known dihydropyridine Ca2+ channel blocker binds. Additionally, the compounds tested inhibit Ca2+-dependent contractions in isolated mouse mesenteric arteries. Thus, diphenylpyraline analogs may exert their anticontractile effects, at least partially, by blocking vascular Ca2+ channels.

Revealing coastal upwelling impact on the muscle growth of an intertidal fish

Upwelling oceanographic phenomenon is associated with increased food availability, low seawater temperature and pH. These conditions could significantly affect food quality and, in consequence, the growth of marine species. One of the most important organismal traits is somatic growth, which is highly related to skeletal muscle. In fish, skeletal muscle growth is highly influenced by environmental factors (i.e. temperature and nutrient availability) that showed differences between upwelling and downwelling zones. Nevertheless, there are no available field studies regarding the impact of those conditions on fish muscle physiology. This work aimed to evaluate the muscle fibers size, protein content, gene expression of growth and atrophy-related genes in fish sampled from upwelling and downwelling zones. Seawater and fish food items (seaweeds) samples were collected from upwelling and downwelling zones to determine the habitat's physical-chemical variations and the abundance of biomolecules in seaweed tissue. In addition, white skeletal muscle samples were collected from an intertidal fish to analyze muscular histology, the growth pathways of protein kinase B and the extracellular signal-regulated kinase; and the gene expression of growth- (insulin-like growth factor 1 and myosin heavy-chain) and atrophy-related genes (F-box only protein 32 and muscle RING-finger protein-1). Upwelling zones revealed higher nutrients in seawater and higher protein content in seaweed than samples from downwelling zones. Moreover, fish from upwelling zones presented a greater size of muscle fibers and protein content compared to downwelling fish, associated with lower protein ubiquitination and gene expression of F-box only protein 32. Our data indicate an attenuated use of proteins as energy source in upwelling conditions favoring protein synthesis and muscle growth. This report shed lights of how oceanographic conditions may modulate food quality and fish muscle physiology in an integrated way, with high implications for marine conservation and sustainable fisheries management.

WIN55212-2 Modulates Intracellular Calcium via CB1 Receptor-Dependent and Independent Mechanisms in Neuroblastoma Cells

The CB1 cannabinoid receptor (CB1R) and extracellular calcium (eCa2+)-stimulated Calcium Sensing receptor (CaSR) can exert cellular signaling by modulating levels of intracellular calcium ([Ca2+]i). We investigated the mechanisms involved in the ([Ca2+]i) increase in N18TG2 neuroblastoma cells, which endogenously express both receptors. Changes in [Ca2+]i were measured in cells exposed to 0.25 or 2.5 mM eCa2+ by a ratiometric method (Fura-2 fluorescence) and expressed as the difference between baseline and peak responses (ΔF340/380). The increased ([Ca2+]i) in cells exposed to 2.5 mM eCa2+ was blocked by the CaSR antagonist, NPS2143, this inhibition was abrogated upon stimulation with WIN55212-2. WIN55212-2 increased [Ca2+]i at 0.25 and 2.5 mM eCa2+ by 700% and 350%, respectively, but this increase was not replicated by CP55940 or methyl-anandamide. The store-operated calcium entry (SOCE) blocker, MRS1845, attenuated the WIN55212-2-stimulated increase in [Ca2+]i at both levels of eCa2+. Simultaneous perfusion with the CB1 antagonist, SR141716 or NPS2143 decreased the response to WIN55212-2 at 0.25 mM but not 2.5 mM eCa2+. Co-perfusion with the non-CB1/CB2 antagonist O-1918 attenuated the WIN55212-2-stimulated [Ca2+]i increase at both eCa2+ levels. These results are consistent with WIN55212-2-mediated intracellular Ca2+ mobilization from store-operated calcium channel-filled sources that could occur via either the CB1R or an O-1918-sensitive non-CB1R in coordination with the CaSR. Intracellular pathway crosstalk or signaling protein complexes may explain the observed effects.

Angiotensinogen uptake and stimulation of oxidative stress in human pigment retinal epithelial cells

We previously reported that isolated proximal tubules (PT) internalize the precursor protein angiotensinogen and that the ¹²⁵Iodine-labeled protein accumulated in the nuclear and mitochondrial fractions of the PT cells; however, whether internalization of angiotensinogen occurs in non-renal epithelial cells is unknown. Therefore, the present study assessed the cellular uptake of ¹²⁵I-angiotensinogen in human retinal pigment ARPE-19 epithelial cells, a widely utilized cell model for the assessment of retinal injury, inflammation and oxidative stress. ARPE-19 cells, maintained in serum-free media to remove extracellular sources of bovine serum angiotensinogen and renin, were incubated with ¹²⁵Iodine-angiotensinogen at 37 °C and revealed the time-dependent uptake of angiotensinogen over 24 h. In contrast, incubation with labelled Ang II, Ang-(1-7) or Ang I revealed minimal cellular uptake. Subcellular fractionation following a 4-hour uptake of ¹²⁵I-angiotensinogen revealed that the majority of the labeled protein localized to the nuclear fraction with lower accumulation in the mitochondrial and cytosolic fractions. Finally, we show that addition of angiotensinogen (2 nM) to the ARPE-19 cells increased oxidative stress as assessed by DCF fluorescence that was blocked by pretreatment of the cells with either the NADPH oxidase 1/4 inhibitor GKT137831, apocynin or atorvastatin, but not the AT₁ receptor antagonist losartan. In contrast, treatment of the cells with Angiotensin II at an equivalent dose to angiotensinogen failed to stimulate oxidative stress. We conclude that human retinal pigment cells internalize angiotensinogen to elicit an increase in oxidative stress through a pathway that appears distinct from the Ang II-AT₁ receptor axis.

Abstract P277: β-arrestin-2-mediated Vasodilatation In Mouse Mesenteric Arteries

As part of GPCRs-dependent signaling, β -arrestin-2 has been shown to stimulate eNOS activity and thus has the potential to modulate vascular function. We hypothesized that the absence of β -arrestin-2 would alter vascular dilatation and contraction in resistance arteries. We tested acetylcholine (ACh)-dependent relaxation and phenylephrine (PE)-dependent contraction in mouse mesenteric arteries isolated from 3-mo old male C57Bl6 (WT, n=5) and β -arrestin-2 KO ( βarr2 -/- , n=5) mice. Segments were mounted in a Wire Myograph (DMT) for determination of isometric force; vessels studied included intact, without endothelium, or pre-incubated with L-NAME (10 -4 M). Dose-response curves were performed for ACh (10 -10 -10 -4.5 M) and PE (10 -10 -10 -4.5 M). Data were acquired using a PowerLab (ADInstruments) system. Maximal response to ACh (ACh MAX ) was expressed as maximal relaxation after pre-constriction, maximal response to PE (PE MAX ) as % of contraction to 75mM KCl (%K MAX ), and sensitivity as pD 2 (-Log[EC 50 ]). Data were analyzed using Prism (GraphPad). After pre-constriction (PE, 3x10 -6 M), arteries from βarr2 -/- mice presented similar ACh MAX (79±6 vs. 82±6, p>0.05) and lower sensitivity to ACh compared to WT (6.66±0.2 vs. 7.12±0.1, p<0.05). The sensitivity of the contraction to PE was increased in βarr2 -/- arteries (6.4±0.2 vs. 6.04±0.1, p<0.05), with no changes in PE MAX . Differences in vasodilation and contraction were abolished in arteries without endothelium and in arteries pre-incubated with L-NAME. We conclude that the absence of β -arrestin-2 induces a pro-contractile phenotype in an endothelium- and nitric oxide-dependent manner in mouse resistance arteries.

Abstract P078: Sex Differences In Aortic Stiffness Following Simulated Microgravity In Middle Aged Rats

Men and women have different cardiovascular responses to spaceflight. We determined sex differences in arterial stiffness, an independent risk factor for cardiovascular dysfunction, in rats after the exposure to 14-days of simulated weightlessness via hindlimb unloading (HLU). Male and female Sprague-Dawley rats at 20 weeks of age were either tail suspended via HLU or remained full-weight bearing in similar cages. Female control rats had lower body weight compared with males. There was no significant effect of HLU on body weight in either male or female rats. Our data demonstrate that HLU increased aortic pulse wave velocity, an index of arterial stiffness, in female rats (2.7 fold vs. control female- adjusted for body weight, n=5-6), but not in males. HLU had no effect on the levels of structural proteins (alpha smooth muscle actin or myosin) in either female or male rats. The levels of G-protein-coupled estrogen receptor 1 (GPER) were lower in the thoracic aorta of female rats exposed to HLU compared with female controls (0.3±0.02 vs. 0.39±0.01 relative density, p<0.05, n=6-7); lower aortic GPER levels were associated with greater aortic media thickness (110.5±4.2 vs. 97.1±3.1 μm, p<0.05, n=5) and lower COX-2 protein levels (0.47±0.04 vs. 0.61±0.02 relative density, p<0.05, n=3-4). However, no differences in GPER, aortic media thickness, or COX-2 were observed in the aortas of male rats after HLU versus male controls. The administration of GPER agonist, G1 (400 ug/kg/day) prevented the increase in aortic pulse wave velocity in the intact females following HLU (2.2±0.2 vs. 9.7±1.8, p<0.05, n=4). Our data demonstrate sex differences in aortic stiffness in response to simulated microgravity. Since GPER has many protective actions in the cardiovascular system, a dysregulation of estrogen signaling may attenuate the protection of females from cardiovascular dysfunction following the exposure to spaceflight stressors.

Sex differences in vascular reactivity in mesenteric arteries from a mouse model of acute intermittent porphyria

BACKGROUND AND AIMS

Acute intermittent porphyria (AIP) results from a partial deficiency of porphobilinogen deaminase (PBGD). Symptomatic AIP patients, most of whom are women, experience acute attacks characterized by severe abdominal pain and abrupt increases in blood pressure. Here, we characterized the reactivity of mesenteric arteries from male and female AIP mice with ~30% of normal PBGD activity and wild type C57BL/6 mice.

METHODS

An acute porphyric attack was induced in AIP mice by treatment with phenobarbital. Vascular responses to K⁺, phenylephrine (PE), acetylcholine (ACh), and hemin were determined (Wire Multi Myograph).

RESULTS

Maximal contraction to PE was increased in arteries from male and female AIP mice (p < .05) during an induced attack of acute porphyria. Female AIP arteries had increased sensitivity to PE (p < .05) even after nitric oxide (NO) blockade with N_ω-nitro-L-arginine methyl ester (L-NAME) (p < .05). Maximal relaxation to ACh was similar in males and females with lower sensitivity in female AIP arteries (p < .05). Hemin induced greater relaxation in AIP arteries in both males and females (p < .05).

SUMMARY/CONCLUSIONS

Sex differences in this AIP mouse model include a pro-contractile response in females. These alterations may contribute to the increased blood pressure during an acute attack and provide a novel mechanism of action whereby heme ameliorates the attacks.

Transcytosis to Cross the Blood Brain Barrier, New Advancements and Challenges

The blood brain barrier (BBB) presents a formidable challenge to the delivery of drugs into the brain. Several strategies aim to overcome this obstacle and promote efficient and specific crossing through BBB of therapeutically relevant agents. One of those strategies uses the physiological process of receptor-mediated transcytosis (RMT) to transport cargo through the brain endothelial cells toward brain parenchyma. Recent developments in our understanding of intracellular trafficking and receptor binding as well as in protein engineering and nanotechnology have potentiated the opportunities for treatment of CNS diseases using RMT. In this mini-review, the current understanding of BBB structure is discussed, and recent findings exemplifying critical advances in RMT-mediated brain drug delivery are briefly presented.

Abstract P428: Internalization of Angiotensinogen is Coupled to Oxidative Stress in Human Retinal Epithelial Cells

We previously reported that isolated proximal tubules internalize angiotensinogen (Aogen); labeled Aogen accumulated in the nuclear and mitochondrial fractions and was associated with increased oxidative stress. Aogen internalization in non-renal epithelial cell types is unknown, thus, we assessed Aogen uptake in human retinal ARP-19 cells. Cells, maintained in serum-free media to remove extracellular sources of Aogen and renin were exposed to 125I-Aogen at 37°C and washed in HCl-glycine to dissociate any membrane-bound label. Subcellular fractionation revealed that the majority of the labeled Aogen localized to the nucleus with a lower accumulation in the mitochondrial and cytosolic fractions [42.0 ± 0.2% vs. 12.0 ± 0.2% and 5.2 ± 0.2%, respectively, p<0.01; n=3]. The rate of Aogen internalization in the retinal cells was 244 ± 15 fmol/hr/mg [n=3]; however, the cellular uptake of 125I-labeled Ang II, Ang I or Ang 7 was not evident [< 1 fmol/hr/mg]. Cells were then exposed to a low concentration of Aogen [200 pM] for 60 mins and oxidative stress assessed. As shown in the figure, Aogen elicited a marked increase in oxidative stress [*P<0.01 vs. control(CON); n=4-5 all groups] that was abolished by Apocynin (APO). Atorvastatin (ATV) also blocked the Aogen response, but did not attenuate Aogen uptake. Ang II (AII, 200 pM) had no effect and the AT1R antagonist losartan (LOS, 10 μM) failed to block Aogen uptake or its response. Finally, the dynamin inhibitor dynasore (DYN) blocked internalization and abolished the Aogen response. We conclude that human retinal cells internalize Aogen through a pathway distinct from the Ang II-AT1R axis to elicit an acute increase in oxidative stress.

Antenatal betamethasone attenuates the angiotensin-(1-7)-Mas receptor-nitric oxide axis in isolated proximal tubule cells

We previously reported a sex-specific effect of antenatal treatment with betamethasone (Beta) on sodium (Na⁺) excretion in adult sheep whereby treated males but not females had an attenuated natriuretic response to angiotensin-(1-7) [Ang-(1-7)]. The present study determined the Na⁺ uptake and nitric oxide (NO) response to low-dose Ang-(1-7) (1 pM) in renal proximal tubule cells (RPTC) from adult male and female sheep antenatally exposed to Beta or vehicle. Data were expressed as percentage of basal uptake or area under the curve for Na⁺ or percentage of control for NO. Male Beta RPTC exhibited greater Na⁺ uptake than male vehicle cells (433 ± 28 vs. 330 ± 26%; P < 0.05); however, Beta exposure had no effect on Na⁺ uptake in the female cells (255 ± 16 vs. 255 ± 14%; P > 0.05). Ang-(1-7) significantly inhibited Na⁺ uptake in RPTC from vehicle male (214 ± 11%) and from both vehicle (190 ± 14%) and Beta (209 ± 11%) females but failed to attenuate Na⁺ uptake in Beta male cells. Beta exposure also abolished stimulation of NO by Ang-(1-7) in male but not female RPTC. Both the Na⁺ and NO responses to Ang-(1-7) were blocked by Mas receptor antagonist d-Ala⁷-Ang-(1-7). We conclude that the tubular Ang-(1-7)-Mas-NO pathway is attenuated in males and not females by antenatal Beta exposure. Moreover, since primary cultures of RPTC retain both the sex and Beta-induced phenotype of the adult kidney in vivo they appear to be an appropriate cell model to examine the effects of fetal programming on Na⁺ handling by the renal tubules.

UV radiation impacts body weight, oxygen consumption, and shelter selection in the intertidal vertebrate Girella laevifrons

The amount of ultraviolet (UV) radiation reaching the earth's surface has increased due to ozone layer depletion, and this fact represents an opportunity to evaluate the physiological and behavioral responses of animals to this global-scale stressor. The transitory fish Girella laevifrons inhabits pools in the upper intertidal zone, which is characterized by exposure to a wide range of stressors, including UV radiation. We documented the field magnitude and the impact of UV radiation on oxygen consumption, body mass variations, and shelter (rocky and algae) selection by G. laevifrons. UV-exposed animals showed increased oxygen consumption, slower body weight increase, and active rocky shelter selection. Control fish showed increased body weight and no evident shelter selection. The results indicated that UV exposure affects fish energetic balance and habitat selection to favor greater protection against radiation. Increased UV exposure in transitory intertidal animals at levels observed in upper intertidal pools may alter the residency time of fish before leaving for the subtidal zone. Therefore, UV-induced energetic changes may determine animal performance and ontogenetic physiological itineraries, whereas shelter quality might determine habitat use.

Local intra-uterine Ang-(1-7) infusion attenuates PGE2 and 6-keto PGF1α in decidualized uterus of pseudopregnant rats

BACKGROUND

Cyclooxygenase (COX)-derived prostanoids (PGE_2, PGI₂) are important contributors to the process of decidualization. Previous studies showed the presence of Ang-(1-7) in the primary and secondary decidualized zones of the implantation site at early pregnancy. Decreased concentrations of Ang-(1-7) were found in the decidualized uterus compared to the non-decidualized uterus of pseudopregnant rats, suggesting that low levels of Ang-(1-7) are required for successful decidualization at early pregnancy.

METHODS

To understand the role of Ang-(1-7) in prostaglandin production in a decidualized uterus, induced by a bolus injection of sesame oil, Ang-(1-7) (24 μg/kg/h) or vehicle was then infused directly into the decidualized uterine horn using an osmotic minipump. The right horns were not injected or infused and served as non-decidualized uterine horns in both groups of animals.

RESULTS

Decidualization increased PGE₂ concentration in the uterus (0.53 ± 0.05 vs. 12.0 ± 3.2 pmol/mg protein, p < 0.001, non-decidualized vs. decidualized horns); Ang-(1-7) infusion attenuated the increase of PGE₂ (12.0 ± 3.2 vs. 5.1 ± 1.3 pmol/mg protein, p < 0.01 control vs. Ang-(1-7) treated decidualized horns). The stable metabolite of PGI₂ (6-keto PGF_1α) was increased with decidualization (0.79 ± 0.17 vs. 3.5 ± 0.82 pmol/mg protein, p < 0.001, non-decidualized vs. decidualized horns). Ang-(1-7) infusion attenuated the increase in 6-keto PGF_1α in the decidualized horn (3.5 ± 0.82 vs 1.8 ± 0.37 pmol/mg protein, p < 0.05 control vs. Ang-(1-7) treated decidualized horns). The circulating levels of 6-keto-PGF_1a and TXB₂ were decreased by Ang-(1-7) infusion, while no difference was observed in circulating PGE₂. Although the global assessment of cleaved caspase 3 immunostaining, a marker of apoptosis, was unchanged within the Ang-(1-7) decidualized horn, there were localized decreases in cleaved caspase 3 staining in the luminal region in the decidualized uterus of Ang-(1-7)-treated rats.

CONCLUSIONS

These studies show that increased local uterine Ang-(1-7) alters the uterine prostaglandin environment, possibly leading to disruptions of early events of decidualization.

Abstract P273: Increased Inhibition of Potassium Channel Currents by Angiotensin II in Sympathetic Neurons may Contribute to a Sustained Blood Pressure Elevation in (mRen2)27 Rats

It is well established that the increased sympathetic tone may contribute to initiation and progression of various forms of hypertension. Several lines of evidence suggest a link between the renin-angiotensin system and sympathetic nerve activity in hypertension, and the previous studies in animal models demonstrated increased sympathetic output in the presence of Angiotensin II (AngII). To elucidate potential underlying molecular mechanisms of such phenomenon, we compared the effect of AngII on the whole-cell potassium channel currents in superior cervical ganglia (SCG) neurons isolated from hypertensive (mRen2)27 rats with overexpression of renin gene, and control Sprague Dawley® (SD) rats. In both groups, the whole-cell potassium channel currents were identified as rapidly-activating, 4-Aminopyridine-sensitive transient A-type currents, as well as slowly-activating tetraethylammonium-sensitive delayed rectifier currents. When the cell membrane was depolarized to -40, -30 and -20 mV from a holding potential of -80 mV, AngII (100 nM) profoundly inhibited A-type current, but the magnitude of such inhibition was not significantly different between neurons isolated from (mRen2)27 (38.1±6.2%, 47.8±5.7% and 52.1±5.7%; n=11) and SD rats (37.2±4.6%, 44.±4.5% and 46.1±4.8%; n = 13). Delayed rectifier potassium channel currents were isolated by holding cells at -40 mV, which resulted in complete elimination of the transient A-type current. In contrast to transient current, inhibition of the delayed rectifier current by AngII in the range of membrane potentials between +20 and +80 mV was significantly greater (p<0.05) in neurons obtained from (mRen2)27 rats (11.0±3.2% to 25.0±2.9%, n=12) when compared to SD rats (4.7±1.5% to 16.3±2.7%, n = 12). In both groups, inhibition of both channel types was completely abolished by 10 uM Losartan, indicating involvement of AT1 receptors. Our results suggest that in (mRen2)27 hypertensive rats, the increased inhibitory effect of AngII on delayed rectifier potassium channel currents could possibly lead to lowering spike threshold, which, in turn, could elevate sympathetic outflow and lead to sustained blood pressure elevation.

Abstract P344: Increased Expression and Function of Endothelin Receptors in Aorta of (mRen2)27 Hypertensive Rats

Endothelin-1 (ET-1) contributes to various cardiovascular diseases including hypertension. ET-1 is produced in the endothelium and acts via ET A receptors, located in smooth muscle cells, and via ET B receptors, located in both endothelium and smooth muscle cells. Activation of ET A produces vasoconstriction, whereas endothelial ET B activation mediates vasodilation, with previous studies showing that ET-1-mediated vasoconstriction is enhanced in hypertension. We hypothesized that increased ETA-mediated function is present in vasculature of the (mRen2)27 hypertensive rat. Western blotting of total protein extracts from thoracic aorta was used to determine expression of ET A and ET B from Sprague-Dawley (SD n=4) and (mRen2)27 hypertensive (n=5) rats. Specificity of western blot signals for ET A and ET B was assessed by using pre-absorption of primary antibody with the corresponding antigenic peptide and intensity of signals was measured by densitometry (NIH-J Image). Contractile responses to ET-1 (10 -11 -10 -7 M) in intact and denuded aorta were determined by wire myography (Multi Myograph, DMT-USA) in the presence of the ET A blocker BQ123 (10 -6 M) or the ET B blocker BQ788 (10 -6 M). Contraction to ET-1 was expressed as maximal response (ET MAX as %K MAX ) and sensitivity (pD 2 =-Log [EC 50 ]). In aortae from (mRen2)27 rats ET A and ET B receptor expression (48 and 31 kDa bands) was greater relative to aortae of SD rats (p<0.05). ET-1 contraction showed increased sensitivity in (mRen2)27 vs SD aortae (pD 2 , 8.17±0.15 vs 7.76±0.12, p<0.05) with similar ET MAX (157±16 vs 145±6 %K MAX , p>0.05). In intact arteries, blockade of ET B increased ET-1 sensitivity (pD 2 8.4±0.3, p<0.05) in SD without effect on intact arteries from (mRen2)27 rats. In denuded arteries, ETB blockade increased ET MAX only in aortae from (mRen2)27 (205±12 vs 152±5, p<0.05). Thus, increased ET A expression mediates greater ET-1-dependent contraction in vasculature of (mRen2)27 rats. In (mRen2)27 rats, loss of endothelial ET B receptor function in intact arteries may contribute to enhanced constrictor responses to ET-1, whereas increased ET B receptors in smooth muscle cells provide a counterbalancing vasodilation to offset maximal contractile effects of ET-1 in this model of hypertension.

Prolonged Mild Hypoxia Alters Fetal Sheep Electrocorticogram Activity

OBJECTIVE

To assess the effects of prolonged mild hypoxemia on fetal brain electrocorticogram (ECoG) in late gestation.

STUDY DESIGN

Fetal and maternal catheters were placed under general anesthesia and animals allocated at random to receive intratracheal maternal administration of either nitrogen (n = 8) or compressed air (n = 8). Five days after surgery (125 days' gestational age), nitrogen infusion was adjusted to reduce fetal brachial artery PO2 by 25%. The targeted decrease in fetal oxygenation was maintained for 5 days while fetal ECoG activity and fetal and maternal cardiovascular variables were continuously recorded. Data are presented as mean +/- SEM and were analyzed by two-way analysis of variance (ANOVA) or two-sample t test.

RESULTS

Nitrogen infusion decreased fetal Po2 by 26% (20.5 +/- 1.7 versus 14.3 +/- 0.8) without changing fetal PCO2 or pH. Mild fetal hypoxemia was associated with fetal tachycardia and increased fetal blood pressure (P < .05). Fetal ECoG in hypoxic fetuses showed a significant decrease in the time spent in high voltage (HV) (P < .05) and an increase in the time spent in low voltage (LV) and in the number of low voltage events (P < .05). Also, a significant decrease in the proportion of 1-4 Hz and an increase in the proportion of 13-20 Hz frequencies was observed in LV events without a significant change in the frequency profile of HV events (P < .05).

CONCLUSION

Prolonged mild hypoxemia significantly altered fetal homeostasis as reflected by the sustained tachycardia and increased blood pressure. Fetal ECoG activity was affected significantly in a qualitatively and quantitative manner by mild prolonged hypoxemia.

Functional changes in the uterine artery precede the hypertensive phenotype in a transgenic model of hypertensive pregnancy

The pregnant female human angiotensinogen (hAGN) transgenic rat mated with the male human renin (hREN) transgenic rat is a model of preeclampsia (TgA) with increased blood pressure, proteinuria, and placenta alterations of edema and necrosis at late gestation. We studied vascular responses and the role of COX-derived prostanoids in the uterine artery (UA) at early gestation in this model. TgA UA showed lower stretch response, similar smooth muscle α-actin content, and lower collagen content compared with Sprague-Dawley (SD) UA. Vasodilation to acetylcholine was similar in SD and TgA UA (64 ± 8 vs. 75 ± 6% of relaxation, P > 0.05), with an acetylcholine-induced contraction in TgA UA that was abolished by preincubation with indomethacin (78 ± 6 vs. 83 ± 11%, P > 0.05). No differences in the contraction to phenylephrine were observed (159 ± 11 vs. 134 ± 12 %KMAX, P > 0.05), although in TgA UA this response was greatly affected by preincubation with indomethacin (179 ± 16 vs. 134 ± 9 %KMAX, P < 0.05, pD2 5.92 ± 0.08 vs. 5.85 ± 0.03, P < 0.05). Endothelium-independent vasodilation was lower in TgA UA (92 ± 2 vs. 74 ± 5% preconstricted tone, P < 0.05), and preincubation with indomethacin restored the response to normal values (90 ± 3 vs. 84 ± 3%). Immunostaining showed similar signals for α-actin, COX-2, and eNOS between groups (P > 0.05). Plasma thromboxane levels were similar between groups. In summary, TgA UA displays functional alterations at early gestation before the preeclamptic phenotype is established. Inhibition of COX enzymes normalizes some of the functional defects in the TgA UA. An increased role for COX-derived prostanoids in this model of preeclampsia may contribute to the development of a hypertensive pregnancy.

Abstract P169: Antenatal Betamethasone Attenuates the Angiotensin-(1-7)/Nitric Oxide Axis in Adult Male but not Female Renal Proximal Tubule Cells

Our studies have revealed a sex-specific effect of fetal programming on sodium (Na+) excretion in adult sheep whereby the males exhibit reduced Na+ excretion and an attenuated natriuretic response to Ang-(1-7) as compared to the females. We hypothesize that the renal proximal tubules are a key target for the early programming effects of glucocorticoids exposure to regulate Na+ handling in the adult males. Therefore, we isolated and cultured cortical proximal tubule cells (RPTC) from adult male and female sheep antenatally exposed to betamethasone (Beta) or vehicle. Na+ uptake and nitric oxide (NO) were assessed with Sodium Green and DAF fluorescence prior to and following a low dose of Ang-(1-7) (1x10-11 M) in isolated RPTC from sheep at ~1.5 years of age. Data are expressed as % of basal uptake or area under the curve (AUC) for Na+ or % of control for NO. Male Beta RPTC exhibit greater Na+ uptake than male vehicle cells (427±32%, n=13, vs. 315±28%, n=14, p<0.05; however, Beta had no effect on Na+ uptake in the female cells (242±18%, n=9, vs. 250±15%, n=10, p>0.05). Ang-(1-7) inhibited Na+ uptake in RPTC from vehicle male (255±40%) and from both vehicle (191±14%) and Beta (209±11%) females (Figure 1B), but failed to attenuate Na+ uptake in Beta male cells (Figure 1A). Beta exposure also abolished NO stimulation by Ang-(1-7) in male but not female RPTC (Figure 1C). We conclude that an Ang-(1-7)-NO-dependent pathway contributes to the sex-dependent consequences of programming on Na+ regulation in the proximal tubules of the kidney. Moreover, the RPTC retain both the sex and Beta-induced phenotype of the adult and may reflect an appropriate cell model of fetal programming.

Uterine artery dysfunction in pregnant ACE2 knockout mice is associated with placental hypoxia and reduced umbilical blood flow velocity

Angiotensin-converting enzyme 2 (ACE2) knockout is associated with reduced fetal weight at late gestation; however, whether uteroplacental vascular and/or hemodynamic disturbances underlie this growth-restricted phenotype is unknown. Uterine artery reactivity and flow velocities, umbilical flow velocities, trophoblast invasion, and placental hypoxia were determined in ACE2 knockout (KO) and C57Bl/6 wild-type (WT) mice at day 14 of gestation. Although systolic blood pressure was higher in pregnant ACE2 KO vs. WT mice (102.3 ± 5.1 vs. 85.1 ± 1.9 mmHg, n = 5-6), the magnitude of difference was similar to that observed in nonpregnant ACE2 KO vs. WT mice. Maternal urinary protein excretion, serum creatinine, and kidney or heart weights were not different in ACE2 KO vs. WT. Fetal weight and pup-to-placental weight ratio were lower in ACE2 KO vs. WT mice. A higher sensitivity to Ang II [pD2 8.64 ± 0.04 vs. 8.5 ± 0.03 (-log EC50)] and greater maximal contraction to phenylephrine (169.0 ± 9.0 vs. 139.0 ± 7.0% KMAX), were associated with lower immunostaining for Ang II receptor 2 and fibrinoid content of the uterine artery in ACE2 KO mice. Uterine artery flow velocities and trophoblast invasion were similar between study groups. In contrast, umbilical artery peak systolic velocities (60.2 ± 4.5 vs. 75.1 ± 4.5 mm/s) and the resistance index measured using VEVO 2100 ultrasound were lower in the ACE2 KO vs. WT mice. Immunostaining for pimonidazole, a marker of hypoxia, and hypoxia-inducible factor-2α were higher in the trophospongium and placental labyrinth of the ACE2 KO vs. WT. In summary, placental hypoxia and uterine artery dysfunction develop before major growth of the fetus occurs and may explain the fetal growth restricted phenotype.

Antenatal glucocorticoid treatment alters Na+ uptake in renal proximal tubule cells from adult offspring in a sex-specific manner

We have shown a sex-specific effect of fetal programming on Na(+) excretion in adult sheep. The site of this effect in the kidney is unknown. Therefore, we tested the hypothesis that renal proximal tubule cells (RPTCs) from adult male sheep exposed to betamethasone (Beta) before birth have greater Na(+) uptake than do RPTCs from vehicle-exposed male sheep and that RPTCs from female sheep similarly exposed are not influenced by antenatal Beta. In isolated RPTCs from 1- to 1.5-yr-old male and female sheep, we measured Na(+) uptake under basal conditions and after stimulation with ANG II. To gain insight into the mechanisms involved, we also measured nitric oxide (NO) levels, ANG II receptor mRNA levels, and expression of Na(+)/H(+) exchanger 3. Basal Na(+) uptake increased more in cells from Beta-exposed male sheep than in cells from vehicle-exposed male sheep (400% vs. 300%, P < 0.00001). ANG II-stimulated Na(+) uptake was also greater in cells from Beta-exposed males. Beta exposure did not increase Na(+) uptake by RPTCs from female sheep. NO production was suppressed more by ANG II in RPTCs from Beta-exposed males than in RPTCs from either vehicle-exposed male or female sheep. Our data suggest that one site of the sex-specific effect of Beta-induced fetal programming in the kidney is the RPTC and that the enhanced Na(+) uptake induced by antenatal Beta in male RPTCs may be related to the suppression of NO in these cells.

Effect of UV radiation on habitat selection by Girella laevifrons and Graus nigra (Kyphosidae)

The effect of UV radiation on habitat use of two species of intertidal fishes that inhabit the same pools but exhibit different activity levels and diets was measured: the highly active omnivorous Girella laevifrons and the cryptic carnivorous Graus nigra. Individuals of each species were acclimated to a tank divided in three sections with different illumination; no light (NL), ultraviolet light (UV) and white light (WL), and the time spent and number of visits to each section were recorded. Although both species preferred the NL section, G. laevifrons spent more time in UV and less time in WL compared with G. nigra; G. laevifrons also displayed higher number of visits to UV, suggesting a different tendency in space use in response to UV exposure in intertidal fishes.

Local uterine Ang-(1-7) infusion augments the expression of cannabinoid receptors and differentially alters endocannabinoid metabolizing enzymes in the decidualized uterus of pseudopregnant rats

BACKGROUND

Endocannabinoids (ECs) are important contributors to implantation and decidualization and are suppressed in early pregnancy. Elevated levels of anandamide (AEA), the endogenous ligand for the CB1 and CB2 receptors (R), interfere with receptivity of the blastocyst. Ang-(1-7) is down-regulated in the implantation site (IS) in normal pregnancy at day 7 of gestation. We determined the effects of intra-uterine angiotensin-(1-7) [Ang-(1-7)] (24 microg/kg/h) or vehicle given into the left uterine horn on the ECs in the decidualized uterus.

METHODS

Ovariectomized rats were sensitized for the decidual cell reaction by steroid treatment and decidualization was induced by a bolus of oil injected into the left horn; the right horn served as a control.

RESULTS

Decidualization increased endometrial permeability (3.1+/-0.2 vs. 7.1+/-0.5 uterus/muscle of cpm of (125)I-BSA, p < 0.0001). VEGF mRNA was increased by the decidualization (1.4-fold, p < 0.05) and by Ang-(1-7) (2.0-fold, p < 0.001). CB1R mRNA was reduced by decidualization (2.7-fold, p < 0.001), but increased by Ang-(1-7) (1.9-fold, p < 0.05). CB2R mRNA was increased by decidualization (4-fold, p < 0.05) and by Ang-(1-7) (2.4-fold, p < 0.001). The enzyme metabolizing AEA, fatty acid amide hydrolase (FAAH), was reduced by decidualization (7.8 fold, p < 0.001) and unchanged by Ang-(1-7) (p > 0.05), whereas the enzyme metabolizing 2-arachidonoylglycerol, monoacyl glycerol lipase (MAGL), was unchanged by decidualization (p > 0.05) and increased by Ang-(1-7) (1.7 fold, p < 0.001).

CONCLUSIONS

These findings report for the first time that Ang-(1-7) augments the expression of CB1R, CB2R and MAGL in the decidualized uterus and thus may interfere with the early events of decidualization.

Acclimatization to chronic intermittent hypoxia in mine workers: a challenge to mountain medicine in Chile

In the past two decades, Chile has developed intense mining activity in the Andes mountain range, whose altitude is over 4,000 meters above sea level. It is estimated that a workforce population of over 55,000 is exposed to high altitude hypobaric hypoxia. The miners work under shift systems which vary from 4 to 20 days at the worksite followed by rest days at sea level, in a cycle repeated for several years. This Chronic Intermittent Hypoxia (CIH) constitutes an unusual condition for workers involving a series of changes at the physiological, cellular and molecular levels attempting to compensate for the decrease in the environmental partial pressure of oxygen (PO₂). The mine worker must become acclimatized to CIH, and consequently undergoes an acute acclimatization process when he reaches the worksite and an acute reverse process when he reaches sea level. We have observed that after a period of 3 to 8 years of CIH exposure workers acclimatize well, and evidence from our studies and those of others indicates that CIH induces acute and chronic multisystem adjustments which are effective in offsetting the reduced availability of oxygen at high altitudes. The aims of this review are to summarize findings of the physiological responses to CIH exposure, highlighting outstanding issues in the field.

Abstract 577: Increased Uterine Interimplantation Levels of Ang II, AT 1 R, and CB 1 R are Associated with Reduced Uterine Permeability at Early Pregnancy in a Transgenic Model of Preeclampsia

Both the renin-angiotensin (RAS) and endocannabinoid (ECS) systems are down-regulated at the early stages of normal pregnancy. The striking similarity of the pattern of distribution of the two systems and their required down-regulation in early events of pregnancy make a compelling argument to compare their regulation in the early events of pregnancy in an animal that has placental activation of the RAS at l ate gestation. Female transgenic rats with overexpression of human (h) angiotensinogen were mated with male rats with h renin [Preeclamptic model (PRE)]. At day 7 of gestation, normal pregnant Sprague Dawley (SD) and PRE animals were anesthetized and bovine serum albumin (BSA) conjugated to Alexa Fluor 488 was injected systemically to assess uterine permeability in the implantation (IS) and interimplantation (IIS) uterine sites. Mean blood pressures were not different between SD and PRE animals (98.8±2 vs 97±3 mmHg, p>0.05). Uterine permeability measured as the IS/IIS ratio of fluorescent BSA signal was decreased in PRE vs. SD (1.36±0.2 vs 0.68±0.1, p<0.05). The levels of Ang II and AT 1 R mRNA were increased in the IIS of PRE vs IS of PRE and IIS of SD ( FIGURE ). CB 1 R mRNA was increased in the IIS vs. IS of PRE rats, and this was associated with a significant increase in the levels of total 1+2-arachidonoylglycerol (24.9±4.1 vs 12.2±3.5 ng/mg protein, p<0.05) in IIS of PRE vs IIS of SD. These data demonstrate a synergistic up-regulation of the RAS and ECS associated with reduced uterine permeability at early pregnancy in a PRE model. These changes precede the hypertensive phenotype and are consistent with a critical role for the disrupted RAS and alterations in the ECS in early pregnancy.

Abstract 579: Increased Role of COX-derived Prostanoids in Regulating Ang II Induced Uterine Artery Contraction at Early Pregnancy in a Transgenic Model of Preeclampsia

The balance between vasodilatory and vasoconstrictor prostanoids contributes to vascular control during pregnancy. Alterations in this balance are involved in the development of hypertensive pregnancy. The transgenic female rat containing the human angiotensinogen (hAGN) gene mated with the male transgenic containing human renin (hREN) is a model of preeclampsia (TgA), and shows hypertension and proteinuria at late gestation. We investigated the role COX-derived mediators have on contractility of the uterine artery (UA) in TgA rats before the hypertensive phenotype develops. UA were isolated from transgenic TgA (n=9) and Sprague-Dawley (n=7) control rats at 7 days of gestation. UA were mounted in a wire myograph for determinations of isometric tension (DMT USA, 620M). Responses to acetylcholine (ACh), phenylephrine (Phe) and sodium nitroprusside (SNP) were measured in control conditions and after preincubation with indomethacin (Indo, 10-5M). Data were fitted to a dose response curve, vasodilatation was expressed as percent of pre-constriction and sensitivity as pD2 (pD2= -Log [EC50]). Responses to ACh reached similar maximal relaxations (64±8 vs 75±6%, p>0.05), and an increased contraction in TgA UA at ACh >10μM (p<0.05) was eliminated by Indo. Contraction to Phe was similar in both groups with an inhibitory effect of Indo on TgA UA (p<0.05). Relaxation to SNP was lower in TgA vs SD UA (92±2 vs 74±5%, p<0.05), this difference was abolished by Indo. Thus, inhibition of COX enzymes had a greater effect on TgA UA suggesting an imbalance towards an increased prostanoids-derived constrictor tone in TgA UA. This imbalance appears before the hypertensive phenotype is established.

Abstract 092: Uterine Artery Dysfunction in ACE2 Deficient Mice is Associated with Placental Hypoxia and Reduced Umbilical Flow

Intrauterine fetal growth restriction (IUGR), one of the serious complications of pregnancy, increases the risk for perinatal morbidity and mortality, and cardiovascular and renal abnormalities later in life. The components of the renin-angiotensin system (RAS) are important mediators of uteroplacental vasculature during pregnancy. The distribution of angiotensin converting enzyme 2 (ACE2), a key enzyme of the RAS, is described in the invading and intravascular trophoblasts, decidual cells and in the umbilical cord. Deletion of ACE2 restricts fetal weight gain and reduces fetal-to-placental weights ratio. ACE2 deficiency results in augmented uterine artery contractility to Ang II at mid-gestation. In this study we determined whether uterine artery dysfunction is associated with placental abnormalities in ACE2 KO mice at mid-gestation. Systolic blood pressures were higher in pregnant ACE2 KO vs. C57BL/6 wild type (WT) (102.3±5.1 vs. 85.1±1.9 mmHg). Urinary protein excretion, serum creatinine, mean kidney or heart weights were not different in ACE2 KO vs. WT. Fetal weight, normalized to tibia length, and pup-to-placental weight ratio were lower in ACE2 KO vs. WT (p<0.05). A higher sensitivity to Ang II (pD 2 8.64±0.04 vs. 8.5±0.03, p<0.05) concomitantly with a greater active uterine arterial tension tested as the response to KCl 75 mM (1.90±0.15 vs. 1.13±0.12 mN/mm, p<0.05) were associated with lower Ang II receptor 2 (AT2R) protein expression (0.2±0.01 vs. 0.4±0.01, p<0.05) in uterine arteries from pregnant ACE2 KO. In the placenta, trophoblast invasion as assessed by the distribution of cytokeratin in trophospongium and decidual areas was not different between ACE2 KO and WT mice. The staining for pimonidazole, a marker of placental hypoxia, was significantly increased in the trophospongium and placental labyrinth of the ACE2 KO vs. WT (p<0.05). Umbilical artery velocities measured using VEVO 2100 ultrasound were lower in the ACE2 KO vs. WT mice (82.2±13.1 vs. 162.6±35.4 mm/s, p<0.05). In summary, ACE2 deficiency induces uterine artery dysfunction associated with placental hypoxia and reduced umbilical flow. These changes develop before the major growth of fetus occurs and may contribute to the exacerbation of IUGR in the ACE2 KO mice.

Increased angiotensin II contraction of the uterine artery at early gestation in a transgenic model of hypertensive pregnancy is reduced by inhibition of endocannabinoid hydrolysis

Increased vascular sensitivity to angiotensin II (Ang II) is a marker of a hypertensive human pregnancy. Recent evidence of interactions between the renin-angiotensin system and the endocannabinoid system suggests that anandamide and 2-arachidonoylglycerol may modulate Ang II contraction. We hypothesized that these interactions may contribute to the enhanced vascular responses in hypertensive pregnancy. We studied Ang II contraction in isolated uterine artery (UA) at early gestation in a rat model that mimics many features of preeclampsia, the transgenic human angiotensinogen×human renin (TgA), and control Sprague-Dawley rats. We determined the role of the cannabinoid receptor 1 by blockade with SR171416A, and the contribution of anandamide and 2-arachidonoylglycerol degradation to Ang II contraction by inhibiting their hydrolyzing enzyme fatty acid amide hydrolase (with URB597) or monoacylglycerol lipase (with JZL184), respectively. TgA UA showed increased maximal contraction and sensitivity to Ang II that was inhibited by indomethacin. Fatty acid amide hydrolase blockade decreased Ang IIMAX in Sprague-Dawley UA, and decreased both Ang IIMAX and sensitivity in TgA UA. Monoacylglycerol lipase blockade had no effect on Sprague-Dawley UA and decreased Ang IIMAX and sensitivity in TgA UA. Blockade of the cannabinoid receptor 1 in TgA UA had no effect. Immunolocalization of fatty acid amide hydrolase and monoacylglycerol lipase showed a similar pattern between groups; fatty acid amide hydrolase predominantly localized in endothelium and monoacylglycerol lipase in smooth muscle cells. We demonstrated an increased Ang II contraction in TgA UA before initiation of the hypertensive phenotype. Anandamide and 2-arachidonoylglycerol reduced Ang II contraction in a cannabinoid receptor 1-independent manner. These renin-angiotensin system-endocannabinoid system interactions may contribute to the enhanced vascular reactivity in early stages of hypertensive pregnancy.

Vascular effects of diphenylmethoxypiperidine-derived dopamine uptake inhibitors

Vascular effects of 4-aryl methoxypiperidinol compounds previously shown to share with cocaine the ability to inhibit the dopamine transporter are described. All the compounds tested inhibit KCl-induced and noradrenaline-dependent contractions in mesenteric arteries ex vivo. Thus, diphenylpyraline and its analogs may have a role as therapeutic options for the treatment of some of the cardiotoxic effects of cocaine intoxications.

Can upwelling signals be detected in intertidal fishes of different trophic levels?

For intertidal fishes belonging to three species, the herbivore Scartichthys viridis (Blenniidae), the omnivore Girella laevifrons (Kyphosidae) and the carnivore Graus nigra (Kyphosidae), mass and body size relationships were higher in individuals from an upwelling zone compared with those from a non-upwelling zone. RNA:DNA were higher in the herbivores and omnivores from the upwelling zone. Higher biomass and RNA:DNA in the upwelling intertidal fishes may be a consequence of an increased exposure to higher nutrient availability, suggesting that increased physiological conditioning in vertebrates from upwelling areas can be detected and measured using intertidal fishes of different trophic levels.

Abstract 416: Inhibition of Metabolism of Endogenous AEA and 2-AG Reduces Ang II Induced Uterine Artery Contraction at Early Pregnancy in a Transgenic Model of Preeclampsia

Recent evidence of interactions between the renin-angiotensin and the endocannabinoid systems suggests a regulatory role for endogenous cannabinoids (ECs) in modulating Ang II vascular responses. Endogenous levels of the ECs, AEA and 2-AG, are controlled by the hydrolytic enzymes FAAH and MAGL, respectively. We investigated the role of AEA and 2-AG as modulators of Ang II contraction in uterine arteries (UA) in a transgenic pregnant rat, in which the female expressing human angiotensinogen (AGT) is mated to the male with human renin (REN), producing a preeclamptic pregnancy. Uterine arteries were isolated from pregnant transgenic h AGTx h REN rats at 7 days of gestational age (n=4). Arterial segments were mounted in a wire myograph for determinations of isometric tension (DMT USA, 620M). Concentration response curves to Ang II (10 -11 -10 -8 M) were performed in control conditions and after preincubation with enzyme inhibitors: URB597 (FAAH) or JZL184 (MAGL) at 10 -6 M. Data were fitted to a dose response curve, maximal responses (Ang II MAX ) were expressed as percent of maximal response to 75 mM KCl (% K MAX ) and sensitivity as pD 2 (pD 2 = -Log [EC 50 ]). Inhibition of FAAH attenuated both maximal response and sensitivity (Ang II MAX 76±9 vs 105±3, p<0.05; pD 2 8.7±0.09 vs 9.1±0.04, p<0.05) and inhibition of MAGL lowered Ang II sensitivity (Ang II MAX 83±15; pD 2 8.8±0.01, p<0.05), Figure. Thus, by inhibiting the enzymes involved in breakdown of ECs, we demonstrate a functional EC system in the UA that counteracts Ang II contraction. Whether the buffering capacity of the EC system is altered in this model of preeclampsia relative to normal pregnancy is under investigation.

Abstract 644: The Endothelin B Receptor Attenuates Endothelin Contraction Via An Endothelium Independent Mechanism In Mesenteric Arteries Of (mRen2)27 Rats

Endothelin-1 (ET-1) and Angiotensin II (Ang II) are important modulators of vascular tone. Contraction to ET-1 is dependent on the activation of ETA and ETB receptors. The contractile receptor ETA is localized in the smooth muscle cells whereas ETB receptors are predominantly found in the endothelium. We investigated the role of ETB receptors in ET-1 contraction in a model of Ang II-dependent hypertension, the (mRen2)27 rat. Third branch mesenteric arteries were isolated from 12 weeks old male Sprague-Dawley (SD) control and (mRen2)27 hypertensive rats and mounted on a wire Multi Myograph (Model 620, DMT) for determination of isometric force. Dose response curves to ET-1 (10 -11 -10 -7 M) were performed in arterial segments that were either intact, endothelium denuded or preincubated with the ETB specific antagonist BQ788 10 -6 M. Endothelial denudation was performed by passing a human hair through the arterial lumen and functional loss of the endothelium was confirmed by the absence of vasodilatation to acetylcholine. Maximal responses were expressed as percent of maximal response to 75mM KCl (%K MAX ) and the sensitivity as pD 2 (pD 2 = -Log[EC 50 ]). In SD control rats, addition of BQ788 significantly increased ET-1 sensitivity in intact arteries (8.9±0.1 vs 9.3±0.1, p<0.05) and the increase was abolished by endothelial denudation with no change in maximal response. However, the ETB blocker BQ788 increased the maximal tension in both intact (127±2 vs 154±13 %K MAX , p<0.05); and denuded (156±9 vs 188±12 %K MAX , p<0.05) arteries from (mRen2)27 rats with no change in sensitivity. In summary, the present results demonstrate that endothelial ETB receptors influence vasodilatory function in control SD rats, but apparently attenuate the contraction to ET-1 in the (mRen2)27 rats. We conclude that the expression of ETB receptors in the endothelium and smooth muscle of resistance vessels in the (mRen2)27 rats may function as a compensatory mechanism to the increased blood pressure or activated angiotensin system found in this model of hypertension.

Abstract 543: Local Uterine Ang-(1-7) Infusion Augments Expression of Cannabinoid Receptors and Differentially Alters Endocannabinoid Metabolizing Enzymes in the Decidualized Uterus of Pseudopregnant Rats

Endocannabinoids (ECs) are important contributors to implantation and decidualization and are suppressed in early pregnancy. Elevated levels of anandamine (AEA), the endogenous ligand for the CB 1 and CB 2 receptor (R), interfere with receptivity of the blastocyst. Ang-(1-7) is present in the decidualized zones of the implantation site (IS) at early pregnancy and is down-regulated in the IS in normal pregnancy. We determined the effects of intra-uterine Ang-(1-7) on the EC system in the decidualized uterus. Ovariectomized rats were sensitized for the decidual cell reaction by steroid treatment. Decidualization was induced by infusion of phosphate buffered saline into the left horn (infused); the right horn was non-infused. Ang-(1-7) (24 μg/kg/hr) or vehicle was given into one of the two uterine horns. CB 1 R mRNA was reduced by decidualization but increased in the presence of Ang-(1-7) . CB 2 R mRNA was increased by decidualization and by Ang-(1-7) ( Figure). The enzyme metabolizing AEA, fatty acid amide hydrolase (FAAH), was reduced by decidualization (1.0 ± 0.07 vs. 0.13 ± 0.03 U, p<0.01) and remained reduced by Ang-(1-7), whereas the enzyme metabolizing 2-arachidonylglycerol, monoacyl glycerol lipase (MAGL), was unchanged by decidualization (1.06 ± 0.11 vs. 1.34 ± 0.13 U, ns) and increased by Ang-(1-7) (1.32 ± 0.19 vs. 2.27 ± 0.23 U, p<0.01). These findings report for the first time that Ang-(1-7) augments the expression of CB 1 R, CB 2 R and MAGL in the decidualized uterus. The effects of Ang-(1-7) to disrupt regulation of the EC system may interfere with the early events of decidualization, including alterations in angiogenesis, apoptosis, permeability, and receptivity.

Antenatal glucocorticoid exposure enhances the inhibition of adrenal steroidogenesis by leptin in a sex-specific fashion

Antenatal treatment with glucocorticoids (GC) poses long-lasting effects on endocrine and cardiovascular function. Given that leptin attenuates adrenal function and the reported sex differences in plasma leptin concentration, we hypothesized that antenatal GC will affect leptin levels and leptin modulation of adrenal function in a sex-specific manner. Pregnant sheep were randomly given betamethasone or vehicle at 80 days of gestational age, and offspring were allowed to deliver at term. Adrenocortical cells (ADC) were studied from male and female animals at 1.5 yr of age. Plasma leptin was increased 66% in male and 41% in female GC-treated animals (P < 0.05), but adrenal leptin mRNA was increased only in GC-treated males (P < 0.05). Whereas mRNA expression of adrenal leptin receptor isoforms showed sex (Ob-Ra and Ob-Rb) and treatment-dependent (Ob-Rb) differences, protein expression remained unchanged. GC-treated females showed greater plasma cortisol and greater ACTH-stimulated cortisol production (P < 0.05) in ADC. Leptin exerted a greater inhibitory effect on basal and stimulated cortisol by ADC from GC-treated males (P < 0.05), with no differences in females. Similarly, greater inhibitory effects on basal and ACTH-stimulated StAR and ACTH-R mRNA expression by leptin were observed in cells from GC males (P < 0.05), with no changes in females. Persistent effects of antenatal GC on leptin levels and leptin modulation of adrenal function are expressed in a sex-specific manner; males are more sensitive than females to the inhibitory influences of leptin on adrenal function, and this effect appears to be mediated by a greater inhibition of StAR and ACTH-R expression in adrenals of adult GC-treated males.

Cellular and molecular mechanisms in the hypoxic tissue: role of HIF-1 and ROS

Reactive oxygen species such as superoxide anion radicals (O2 (-) ) and hydrogen peroxide (H2 O2 ) have for long time been recognized as undesirable by-products of the oxidative mitochondrial generation of adenosine triphosphate (ATP). Recently, these highly reactive species have been associated to important signaling pathways in diverse physiological conditions such as those activated in hypoxic microenvironments. The molecular response to hypoxia requires fast-acting mechanisms acting within a wide range of partial pressures of oxygen (O2 ). Intracellular O2 sensing is an evolutionary preserved feature, and the best characterized molecular responses to hypoxia are mediated through transcriptional activation. The transcription factor, hypoxia-inducible factor 1 (HIF-1), is a critical mediator of these adaptive responses, and its activation by hypoxia involves O2 -dependent posttranslational modifications and nuclear translocation. Through the induction of the expression of its target genes, HIF-1 coordinately regulates tissue O2 supply and energetic metabolism. Other transcription factors such as nuclear factor κB are also redox sensitive and are activated in pro-oxidant and hypoxic conditions. The purpose of this review is to summarize new developments in HIF-mediated O2 sensing mechanisms and their interactions with reactive oxygen species-generating pathways in normal and abnormal physiology.

Abstract 317: ACE2 Deficiency Enhances Angiotensin II-Induced Vasoconstriction Of The Uterine Artery at Mid-Gestation In Mice

Fetal growth restriction (FGR) remains a leading cause of perinatal morbidity and mortality in humans. Angiotensin converting enzyme 2 (ACE2) is a key enzyme of the renin-angiotensin system that influences the balance between angiotensin II (Ang II) and angiotensin-(1-7) (Ang-(1-7)). ACE2 is highly expressed in the human placenta and maternal stromal tissue in normal pregnancy; however its role in pregnancy is not well understood. Our previous studies revealed that pregnancy in ACE2-deficient mice (ACE2KO) is associated with restricted maternal and fetal weight, attenuated circulating Ang-(1-7), and increased placental Ang II at the end of pregnancy. Since the loss of ACE2 may lead to vascular dysfunction and FGR, we compared the uterine artery reactivity in ACE2KO versus wild-type C57Bl/6 (WT) pregnant mice using wire myography. Maternal and fetal weights and pup-to-placenta ratio were not altered in ACE2KO at day 14 of gestation. However, the number of pups was reduced in ACE2KO [ACE2KO: 7.2±0.2 vs. WT: 9.8±0.7 pups, n=4-5; *p<0.05]. Uterine artery diameters were similar between the two mouse strains. Maximal vasoconstriction to 10 μM phenylephrine (PE) or 80 mM potassium chloride (KCl) and maximal endothelium-dependent relaxation (1 μM acetylcholine) were not altered in pregnant ACE2KO versus pregnant WT. Pregnancy tended to reduce the uterine artery sensitivity to Ang II in WT [virgin: LogEC50: -9.0 vs. 14d pregnant: -8.0, p=0.09], but not in ACE2KO [virgin: LogEC50: -9.1 vs. 14d pregnant: -8.6, p=0.46]. Moreover, the concentration-dependent vasoconstriction to Ang II (0.1 nM-1 μM) was greater in the uterine arteries from pregnant ACE2KO as compared to pregnant WT [ACE2KO: LogEC50: -8.6 vs. WT: -8.0, n=4-5; *p<0.05]. Pretreatment with 1μM Ang-(1-7) for 5 minutes partially attenuated the Ang II-induced vasoconstriction and tended to reduce the sensitivity to Ang II in pregnant ACE2KO [n=2-4]. These results show that the loss of ACE2 in pregnancy is associated with increased constriction and sensitivity of the uterine artery to Ang II. Absence of enhanced constriction to PE or KCl in ACE2KO suggests the specificity of the Ang II-induced response. In conclusion, ACE2 deficiency may contribute to FGR via Ang II-mediated uterine artery dysfunction.

Leptin alters adrenal responsiveness by decreasing expression of ACTH-R, StAR, and P450c21 in hypoxemic fetal sheep

The late gestation increase in adrenal responsiveness to adrenocorticotropin (ACTH) is dependent upon the upregulation of the ACTH receptor (ACTH-R), steroidogenic acute regulatory protein (StAR), and steroidogenic enzymes in the fetal adrenal. Long-term hypoxia decreases the expression of these and adrenal responsiveness to ACTH in vivo. Leptin, an adipocyte-derived hormone which attenuates the peripartum increase in fetal plasma cortisol is elevated in hypoxic fetuses. Therefore, we hypothesized that increases in plasma leptin will inhibit the expression of the ACTH-R, StAR, and steroidogenic enzymes and attenuate adrenal responsiveness in hypoxic fetuses. Spontaneously hypoxemic fetal sheep (132 days of gestation, PO(2) ≈ 15 mm Hg) were infused with recombinant human leptin (n = 8) or saline (n = 7) for 96 hours. An ACTH challenge was performed at 72 hours of infusion to assess adrenal responsiveness. Plasma cortisol and ACTH were measured daily and adrenals were collected after 96 hours infusion for messenger RNA (mRNA) and protein expression measurement. Plasma cortisol concentrations were lower in leptin- compared with saline-infused fetuses (14.8 ± 3.2 vs 42.3 ± 9.6 ng/mL, P < .05), as was the cortisol:ACTH ratio (0.9 ± 0.074 vs 46 ± 1.49, P < .05). Increases in cortisol concentrations were blunted in the leptin-treated group after ACTH(1-24) challenge (F = 12.2, P < .0001). Adrenal ACTH-R, StAR, and P450c21 expression levels were reduced in leptin-treated fetuses (P < .05), whereas the expression of Ob-Ra and Ob-Rb leptin receptor isoforms remained unchanged. Our results indicate that leptin blunts adrenal responsiveness in the late gestation hypoxemic fetus, and this effect appears mediated by decreased adrenal ACTH-R, StAR, and P450c21 expression.

Role of the AT2 receptor in modulating the angiotensin II contractile response of the uterine artery at mid-gestation

INTRODUCTION

During human pregnancy, circulating concentrations of components of the renin-angiotensin system increase, but pressor refractoriness to angiotensin II (Ang-II) is observed. Given the importance of the Ang-II pressor response in deciding susceptibility to preeclampsia and of the Ang-II system for controlling uterine vasoreactivity, we sought to address the effects of pregnancy on the reactivity of the isolated uterine artery (UA) in mice.

MATERIALS AND METHODS

Blood pressure was measured throughout pregnancy in awake C57BL/6J mice. UA segments were isolated from three groups of animals (non-pregnant, mid [day 12-13] and late [day 18-19] gestation) and studied by wire myography.

RESULTS

UA diameters, KCl-mediated responses, and acetylcholine-dependent vasorelaxation were greater at mid and late gestation than in non-pregnant animals. Ang-II responses were also greater during pregnancy, with an increased contraction in response to AT2 receptor blockade at mid-gestation. AT1 receptor blockade abolished the Ang-II response in all groups.

CONCLUSIONS

Study findings are consistent with the possibility that AT2 receptor-mediated vasodilatation plays a role in modulating Ang-II contractile responses in pregnancy.

Mild chronic hypoxemia modifies expression of brain stem angiotensin peptide receptors and reflex responses in fetal sheep

The effects of chronic mild hypoxemia on the binding of angiotensin receptors in selected brain stem nuclei and reflex responses were studied in fetal sheep. Fetal and maternal catheters were placed at 120 days' gestation, and animals received intratracheal maternal administration of nitrogen (n = 16) or compressed air in controls (n = 19). Nitrogen infusion was adjusted to reduce fetal brachial artery PO(2) by 25% during 5 days. Spontaneous baroreflex sensitivity and spectral analysis of the pulse interval were analyzed during the 5 days hypoxemia period using 90 min of daily recording. Brains of control and hypoxemic animals were collected, and brain stem angiotensin receptor binding was studied by in vitro autoradiography at 130 days of gestation. After 5 days of hypoxemia, some animals in each group were submitted to one complete umbilical cord occlusion during 5 min. [(125)I]sarthran binding showed that chronic mild hypoxemia significantly increases angiotensin type 1 receptor, angiotensin type 2 receptor, and ANG-(1-7) angiotensin receptor binding sites in the nucleus tractus solitarius and dorsal motor nucleus of the vagus (P < 0.05). Hypoxemia induced lower baroreflex sensitivity and a higher low frequency-to-high frequency ratio in the fetus, consistent with a shift from vagal to sympathetic autonomic cardiac regulation. Cord occlusion to elicit a chemoreflex response induced a greater bradycardic response in hypoxemic fetuses (slope of the initial fall in heart rate; 11.3 +/- 1.9 vs. 6.4 +/- 1.2 beats x min(-1) x s(-1), P < 0.05). In summary, chronic mild hypoxemia increased binding of angiotensin receptors in brain stem nuclei, decreased spontaneous baroreflex gain, and increased chemoreflex responses to asphyxia in the fetus. These results suggest hypoxemia-induced alterations in brain stem mechanisms for cardiovascular control.

Carbon monoxide: a novel pulmonary artery vasodilator in neonatal llamas of the Andean altiplano

AIMS

To study the nitric oxide (NO) and carbon monoxide roles in the regulation of the pulmonary circulation in lowland and highland newborn sheep and llamas.

METHODS AND RESULTS

We used neonatal sheep (Ovis aries) and llamas (Lama glama) whose gestation and delivery took place at low (580 m) or high (3600 m) altitude. In vivo, we measured the cardiopulmonary function basally and with a NO synthase (NOS) blockade and calculated the production of carbon monoxide by the lung. In vitro, we determined NOS and soluble guanylate cyclase (sGC) expression, NOS activity, and haemoxygenase (HO) expression in the lung. Pulmonary arterial pressure was elevated at high altitude in sheep but not in llamas. Sheep at high altitude relative to sea level had significantly greater total lung NOS activity and eNOS protein, but reduced sGC and HO expression and carbon monoxide production. In contrast, llamas showed no difference in NO function between altitudes, but a pronounced increase in pulmonary carbon monoxide production and HO expression at high altitude.

CONCLUSIONS

In the llama, enhanced pulmonary carbon monoxide, rather than NO, protects against pulmonary hypertension in the newborn period at high altitude. This shift in pulmonary dilator strategy from NO to carbon monoxide has not been previously described, and it may give insight into new treatments for excessive pulmonary vasoconstriction.

Mild chronic hypoxia modifies the fetal sheep neural and cardiovascular responses to repeated umbilical cord occlusion

We have shown that 5 days of mild hypoxia has significant effects on fetal ECoG activity, heart rate and blood pressure. We now studied if mild prolonged hypoxemia had an adverse effect on the fetal cardiovascular and neural responses to repeated cord occlusion and on the magnitude of neuronal damage. Fetal and maternal catheters were placed at 120 days' gestation and animals allocated at random to receive intratracheal maternal administration of nitrogen (n=8) or compressed air in controls (n=7). Five days after surgery, nitrogen infusion was adjusted to reduce fetal brachial artery pO(2) by 25%. After 5 days of chronic hypoxemia, the umbilical cord was completely occluded for 5 min every 30 min for a total of four occlusions. Data are presented as mean+/-SEM and were analyzed by two-way ANOVA or two-sample t-test. Nitrogen infusion decreased fetal pO(2) by 26% (20.5+/-1.7 vs. 14.3+/-0.8 mm Hg) without changing fetal pCO(2) or pH. Pre-existing hypoxia fetuses had a greater terminal fall in heart rate in occlusions II, III and IV, and also had a more severe terminal hypotension in the final occlusion. Pre-existing hypoxia was associated with a greater fall in spectral edge frequency during occlusions from 14.4+/-0.9 Hz to 6.9+/-0.4 Hz vs. 13.6+/-1.64 Hz to 10.6+/-0.77 Hz in controls, p<0.05. In addition, during the three-day post-occlusion period, the contribution of theta and alpha band frequencies to total ECoG activity was significantly lower in the pre-existing hypoxia fetuses (p<0.05). These effects were associated with increased neuronal loss in the striatum (p<0.05). In summary, the cardiovascular and neural response indicates a detrimental effect of pre-existing mild hypoxia on fetal outcome following repeated umbilical cord occlusions.

Antenatal betamethasone administration has a dual effect on adult sheep vascular reactivity

The effect of antenatal steroids on blood pressure in humans remains an unresolved question. Here we report the effects of prenatal exposure to clinically relevant doses of betamethasone on endothelial and/or vascular smooth muscle function. Pregnant sheep were randomly treated with betamethasone (0.17 mg/kg) or vehicle at 80 and 81 d of gestation. We studied arterial segments (4th-5th generation) of the right brachial artery obtained at 1-2 y of age under general anesthesia. We demonstrate that in brachial arteries of steroid exposed offspring: KCl induced contraction is increased after endothelium removal or incubation with inhibitors of nitric oxide synthase or cyclooxygenase; acetylcholine-induced relaxation is increased; sensitivity to endothelin-1 (ET-1) is increased and this effect is decreased by the ETB antagonist BQ-788. These data suggest that, in sheep treated with clinically relevant doses of betamethasone at a gestational stage when human fetuses are routinely exposed to glucocorticoids, there is a dual effect of betamethasone on the adult sheep brachial artery, i.e. endothelial dysfunction with an impairment of endothelin-1 ETB receptor-induced release of nitric oxide and an increased contribution of the ETB receptor in smooth muscle to the contractile effects of ET-1.

The fetal llama versus the fetal sheep: different strategies to withstand hypoxia

The pregnant llama (Lama glama) has walked for millions of years through the thin oxygen trail of the Andean altiplano. We hypothesize that a pool of genes has been selected in the llama that express efficient mechanisms to withstand this low-oxygen milieu. The llama fetus responds to acute hypoxia with an intense peripheral vasoconstriction that is not affected by bilateral section of the carotid sinus nerves. Moreover, the increase in fetal plasma concentrations of vasoconstrictor hormones, such as catecholamines, neuropeptide Y, and vasopressin, is much greater in the llama than in the sheep fetus. Furthermore, treatment of fetal llamas with an alpha-adrenergic antagonist abolished the peripheral vasoconstriction and resulted in fetal cardiovascular collapse and death during acute hypoxia, suggesting an indispensable upregulation of alpha-adrenergic mechanisms in this high altitude species. Local endothelial factors such as nitric oxide (NO) also play a key role in the regulation of fetal adrenal blood flow and in the adrenal secretion of catecholamines and cortisol. Interestingly, in contrast to the human or sheep fetus, the llama fetus showed a small increase in brain blood flow during acute hypoxia, with no increase in oxygen extraction across the brain, and thereby a decrease in brain oxygen consumption. These results suggest that the llama fetus responds to acute hypoxia with hypometabolism. How this reduction in metabolism is produced and how the cells are preserved during this condition remain to be elucidated.