Characterization of Mild Delayed Gestational Hypertension in Rats Following Ozone Exposure

The contribution of air pollution induced cardio-pulmonary damage on the development of hypertensive disorders of pregnancy and other adverse outcomes of pregnancy has gained increased attention as epidemiological data continues to highlight spatiotemporal pregnancy trends related to air pollution exposure. However clinical mechanistic data surrounding gestational complications remains sparse, necessitating the need for the use of animal models to study these types of complications of pregnancy. The current study seeks to examine the real-time effects of mid-gestational ozone exposure on maternal blood pressure and body temperature through the use of radiotelemetry in a rat model. The exposure resulted in acute depression of heart rate and core body temperature as compared to control animals. Ozone exposed animals also presented with a slight but significant increase in arterial blood pressure which was perpetuated until term. The data presented here illustrates the feasibility of murine models to assess cardiovascular complications caused by inhaled toxicants during the window of pregnancy.

Abstract 288: Impaired Ischemic Myocutaneous Wound Revascularization And Transdermal H 2 S Emissions In Diabetic Rats

Introduction: Hydrogen sulfide (H 2 S) has been recognized as an important signaling molecule in cellular O 2 sensing, wound healing and angiogenesis. Studies have shown abnormal H 2 S levels in diabetic patients with cardiovascular disease. Diminished H 2 S signaling may play a causative role in diabetic foot wounds. The Transdermal Arterial Gasotransmitter Sensor (TAGS) device measures real-time H 2 S emissions through the skin. In this work, we utilize the novel TAGS device to characterize transdermal H 2 S emissions during diabetic and non-diabetic wound healing for the first time.

Methods: Dorsal peninsular-shaped myocutaneous ischemic flap wounds were created under anesthesia. Sprague Dawley (SD) and Zucker Diabetic Fatty (ZDF) rats (n=10 each) were compared. Transdermal H 2 S emissions, laser speckle contrast images (LSCI) and planimetric photos were serially taken from the wound flap area over 14 days. After animal sacrifice, healed flap tissue was collected for histologic (H&E) analysis of panniculus carnosus (skin muscle) viability as a proxy for degree of ischemic insult.

Results: ZDF rats were significantly hyperglycemic (mean 516 mg/dL vs. 201 mg/dL for SD, P=0.002). Similar mean baseline (preoperative) H 2 S emissions were observed in SD (16 ppb) and ZDF (12 ppb) rats (P=0.25). During revascularization and healing, ZDF wounds emitted significantly less H 2 S (10 ppb at day 14) as compared to SD (28 ppb at day 14, P<0.01). ZDF wounds demonstrated impaired flap engraftment and revascularization by LSCI (mean 65.6 Perfusion Units (PU) for ZDF vs. 188.0 PU for SD at day 14, p<0.01) and planimetric analysis (mean 16.6% necrosis for ZDF vs. 5.3% necrosis for SD at day 14, p=0.01). Panniculus carnosus mean myofibril count, myofibril diameter, and layer thickness were significantly decreased (p<0.01) in the ZDF cohort, suggesting greater tissue ischemic insult and muscle loss.

Conclusion: Diabetic rats have impaired wound H 2 S production and poor revascularization. These physiologic alterations are accompanied by greater wound necrosis and histologic ischemic insult. This suggests H 2 S abnormalities in diabetes may play a role in the pathogenesis of impaired wound healing and could represent a potential future therapeutic target for these difficult wounds.

Portal Venous Flow Is Increased by Jejunal but Not Colonic Hydrogen Sulfide in a Nitric Oxide-Dependent Fashion in Rats

Hydrogen sulfide (H2S) is a recently discerned endogenous signaling molecule that modulates the vascular system. Endogenous hydrogen sulfide has been shown to dilate both the mesenteric and portal vasculature. Gut microbiome, via sulfur reducing bacteria, is another source of H2S production within the gut lumen; this source of H2S is primarily produced and detoxified in the colon under physiologic conditions. Nitric oxide (NO), a major endogenous vasodilator in the portal circulation, participates in H2S-induced vasodilation in some vascular beds. We hypothesize that jejunal but not colonic H2S increases portal vein flow in a NO-dependent fashion. To evaluate the effects of luminal H2S, venous blood flow, portal venous pressure, and systemic venous pressure were measured in rats after administration of either vehicle or an H2S donor (NaHS) into the jejunum or the colon. We found that portal venous pressure and systemic pressure did not change and were similar between the three study groups. However, portal venous blood flow significantly increased following jejunal administration of NaHS but not in response to colonic NaHS or vehicle administration. To test the contribution of NO production to this response, another group of animals was treated with either an NO synthase inhibitor (N-Ω-nitro-L-arginine, L-NNA) or saline prior to jejunal NaHS infusion. After L-NNA pretreatment, NaHS caused a significant fall rather than increase in portal venous flow compared to saline pretreatment. These data demonstrate that H2S within the small intestine significantly increases portal venous blood flow in a NO-dependent fashion.

Abstract P131: Transdermal Detection of Low Concentrations of Hydrogen Sulfide

We report here a novel approach to measure circulating hydrogen sulfide (H 2 S) non-invasively as a potential way to diagnose and monitor endothelial dysfunction and peripheral artery disease (PAD). PAD is a life-threatening condition caused by arterial constriction and obstruction of blood flow leading to limb ischemia. Current methods to diagnose and monitor PAD lack sensitivity, are expensive, and technically difficult. Recent studies indicate that decreased H 2 S production is an underlying cause of PAD. Also, reduced plasma H 2 S correlates with endothelial dysfunction in individuals with untreated hypertension, diabetes, sleep apnea and other cardiovascular diseases. The TAGS device was designed to measure transdermal H 2 S to test the hypothesis that the diffusion rate (and therefore gas phase concentration) of H 2 S is directly proportional to dermal blood flow. Healthy volunteers between the ages of 21-65 were recruited. Exclusion criteria included subjects currently treated for hypertension, hyperlipidemia, and diabetes. Smokers and pregnant women were also excluded. We demonstrate that H 2 S can be detected in healthy volunteers (n=11) at 10.8 part per billion (ppb). Interestingly, there is a positive correlation between age and TAGS readings in male volunteers (r=0.614; n= 6) and a negative correlation in female volunteers (r=0.482, n=5). The TAGS device has the potential, therefore, to serve as a more sensitive, economical, and easy to use diagnostic tool to detect H 2 S and predict dermal blood flow.

NFATc3 is required for intermittent hypoxia-induced hypertension

Sleep apnea, defined as intermittent respiratory arrest during sleep, is associated with increased incidence of hypertension and peripheral vascular disease. Exposure of rodents to brief periods of intermittent hypercarbia/hypoxia (H-IH) during sleep mimics the cyclical hypoxia-normoxia of sleep apnea. Endothelin-1, an upstream activator of nuclear factor of activated T cells (NFAT), is increased during H-IH. Therefore, we hypothesized that NFATc3 is activated by H-IH and is required for H-IH-induced hypertension. Consistent with this hypothesis, we found that H-IH (20 brief exposures per hour to 5% O(2)-5% CO(2) for 7 h/day) induces systemic hypertension in mice [mean arterial pressure (MAP) = 97 +/- 2 vs. 124 +/- 2 mmHg, P < 0.05, n = 5] and increases NFATc3 transcriptional activity in aorta and mesenteric arteries. Cyclosporin A, an NFAT inhibitor, and genetic ablation of NFATc3 [NFATc3 knockout (KO)] prevented NFAT activation. More importantly, H-IH-induced hypertension was attenuated in cyclosporin A-treated mice and prevented in NFATc3 KO mice. MAP was significantly elevated in wild-type mice (Delta = 23.5 +/- 6.1 mmHg), but not in KO mice (Delta = -3.9 +/- 5.7). These results indicate that H-IH-induced increases in MAP require NFATc3 and that NFATc3 may contribute to the vascular changes associated with H-IH-induced hypertension.