β-arrestin biased signaling is not involved in the hypotensive actions of 5-HT7 receptor stimulation: use of Serodolin

The 5-hydroxytryptamine 7 receptor (5-HT7) is necessary for 5-HT to cause a concentration-dependent vascular relaxation and hypotension. 5-HT7 is recognized as having biased signaling, transduced through either Gs or β -arrestin. It is unknown whether 5-HT7 signals in a biased manner to cause vasorelaxation/hypotension. We used the recently described β-arrestin selective 5-HT7 receptor agonist serodolin to test the hypothesis that 5-HT7 activation does not cause vascular relaxation or hypotension via the β -arrestin pathway. Isolated abdominal aorta (no functional 5-HT7) and vena cava (functional 5-HT7) from male Sprague Dawley rats were used in isometric contractility studies. Serodolin (1 nM - 10 μM) did not change baseline tone of isolated tissues and did not relax the endothelin-1 (ET-1)-contracted vena cava or aorta. In the aorta, serodolin acted as a 5-HT2A receptor antagonist, evidenced by a rightward shift in 5-HT-induced concentration response curve [pEC50 5-HT [M]: Veh = 5.2 +/- 0.15; Ser (100 nM) = 4.49 +/- 0.08; p < 0.05]. In the vena cava, serodolin acted as a 5-HT7 receptor antagonist, shifting the concentration response curve to 5-HT left and upward (%10 μM NE contraction; Veh = 3.2 +/- 1.7; Ser (10 nM) = 58 +/- 11; p < 0.05) and blocking relaxation of pre-contracted tissue to the 5-HT1A/7 agonist 5-carboxamidotryptamine. In anesthetized rats, 5-HT or serodolin was infused at 5, 25 and 75 μg/kg/min, iv. Though 5-HT caused concentration-dependent depressor responses, serodolin caused an insignificant small depressor responses at all three infusion rates. With the final dose of serodolin on board, 5-HT was unable to reduce blood pressure. Collectively the data indicate that serodolin functions as a 5-HT7 antagonist with additional 5-HT2A blocking properties. 5-HT7 activation does not cause vascular relaxation or hypotension via the β -arrestin pathway.

Perivascular Adipose Tissue Remodels Only after Elevation of Blood Pressure in the Dahl SS Rat Fed a High-Fat Diet

INTRODUCTION

Tunica media extracellular matrix (ECM) remodeling is well understood to occur in response to elevated blood pressure, unlike the remodeling of other tunicas. We hypothesize that perivascular adipose tissue (PVAT) is responsive to hypertension and remodels as a protective measure.

METHODS

The adventitia and PVAT of the thoracic aorta were used in measuring ECM genes from 5 pairs of Dahl SS male rats on 8 or 24 weeks of feeding from weaning on a control (10% Kcal fat) or high-fat (HF; 60%) diet. A PCR array of ECM genes was performed with cDNA from adventitia and PVAT after 8 and 24 weeks. A gene regulatory network of the differentially expressed genes (DEGs) (HF 2-fold > con) was created using Cytoscape.

RESULTS

After 8 weeks, 29 adventitia but 0 PVAT DEGs were found. By contrast, at 24 weeks, PVAT possessed 47 DEGs while adventitia had 3. Top DEGs at 8 weeks in adventitia were thrombospondin 1 and collagen 8a1. At 24 weeks, thrombospondin 1 was also a top DEG in PVAT. The transcription factor Adarb1 was identified as a regulator of DEGs in 8-week adventitia and 24-week PVAT.

CONCLUSION

These data support that PVAT responds biologically once blood pressure is elevated.

Renal and hypothalamic inflammation in renovascular hypertension: role of afferent renal nerves

Renal denervation (RDN) is a potential therapy for drug-resistant hypertension. However, whether its effects are mediated by ablation of efferent or afferent renal nerves is not clear. Previous studies have implicated that renal inflammation and the sympathetic nervous system are driven by the activation of afferent and efferent renal nerves. RDN attenuated the renal inflammation and sympathetic activity in some animal models of hypertension. In the 2 kidney,1 clip (2K1C) model of renovascular hypertension, RDN also decreased sympathetic activity; however, mechanisms underlying renal and central inflammation are still unclear. We tested the hypothesis that the mechanisms by which total RDN (TRDN; efferent + afferent) and afferent-specific RDN (ARDN) reduce arterial pressure in 2K1C rats are the same. Male Sprague-Dawley rats were instrumented with telemeters to measure mean arterial pressure (MAP), and after 7 days, a clip was placed on the left renal artery. Rats underwent TRDN, ARDN, or sham surgery of the clipped kidney and MAP was measured for 6 wk. Weekly measurements of water intake (WI), urine output (UO), and urinary copeptin were conducted, and urine was analyzed for cytokines/chemokines. Neurogenic pressor activity (NPA) was assessed at the end of the protocol calculated by the depressor response after intraperitoneal injection of hexamethonium. Rats were euthanized and the hypothalamus and kidneys removed for measurement of cytokine content. MAP, NPA, WI, and urinary copeptin were significantly increased in 2K1C-sham rats, and these responses were abolished by both TRDN and ARDN. 2K1C-sham rats presented with renal and hypothalamic inflammation and these responses were largely mitigated by TRDN and ARDN. We conclude that RDN attenuates 2K1C hypertension primarily by ablation of afferent renal nerves which disrupts bidirectional renal neural-immune pathways.NEW & NOTEWORTHY Hypertension resulting from reduced perfusion of the kidney is dependent on renal sensory nerves, which are linked to inflammation in the kidney and hypothalamus. Afferent renal nerves are required for chronic increases in both water intake and vasopressin release observed following renal artery stenosis. Findings from this study suggest an important role of renal sensory nerves that has previously been underestimated in the pathogenesis of 2K1C hypertension.

5-HT7 receptors mediate dilation of rat cremaster muscle arterioles in vivo

OBJECTIVE

Serotonin (5-HT) infusion in vivo causes hypotension and a fall in total peripheral resistance. However, the vascular segment and the receptors that mediate this response remain in question. We hypothesized that 5-HT7 receptors mediate arteriolar dilation to 5-HT in skeletal muscle microcirculation.

METHODS

Cremaster muscles of isoflurane-anesthetized male Sprague-Dawley rats were prepared for in vivo microscopy of third- and fourth-order arterioles and superfused with physiological salt solution at 34°C. Quantitative real-time PCR (RT-PCR) was applied to pooled samples of first- to third-order cremaster arterioles (2-4 rats/sample) to evaluate 5-HT7 receptor expression.

RESULTS

Topical 5-HT (1-10 nmols) or the 5-HT1/7 receptor agonist, 5-carboxamidotryptamine (10-30 nM), dilated third- and fourth-order arterioles, responses that were abolished by 1 μM SB269970, a selective 5-HT7 receptor antagonist. In contrast, dilation induced by the muscarinic agonist, methacholine (100 nmols) was not inhibited by SB269970. Serotonin (10 nmols) failed to dilate cremaster arterioles in 5-HT7 receptor knockout rats whereas arterioles in wild-type litter mates dilated to 1 nmol 5-HT, a response blocked by 1 μM SB269970. Quantitative RT-PCR revealed that cremaster arterioles expressed mRNA for 5-HT7 receptors.

CONCLUSIONS

5-HT7 receptors mediate dilation of small arterioles in skeletal muscle and likely contribute to 5-HT-induced hypotension, in vivo.

Chemerin is resident to vascular tunicas and contributes to vascular tone

The adipokine chemerin may support blood pressure, evidenced by a fall in mean arterial pressure after whole body antisense oligonucleotide (ASO)-mediated knockdown of chemerin protein in rat models of normal and elevated blood pressure. While the liver is the greatest contributor of circulating chemerin, liver-specific ASOs that abolished hepatic-derived chemerin did not change blood pressure. Thus, other sites must produce the chemerin that supports blood pressure. We hypothesize the vasculature as a source of chemerin independent of the liver that supports arterial tone. RNAScope®, PCR, Western analyses, ASOs, isometric contractility, and radiotelemetry were used in the Dahl salt sensitive (SS) rat (male and female) on a normal diet. Rarres2 mRNA was detected in the smooth muscle, adventitia, and perivascular adipose tissue of the thoracic aorta. Chemerin protein was detected immunohistochemically in the endothelium, smooth muscle cells, adventitia, and perivascular adipose tissue. Chemerin colocalized with the vascular smooth muscle marker a-actin and the adipocyte marker perilipin. Importantly, chemerin protein in the thoracic aorta was not reduced when liver-derived chemerin was abolished by a liver-specific ASO against chemerin. Chemerin protein was similarly absent in arteries from a newly created global chemerin knockout in Dahl SS rats. Inhibition of the receptor Chemerin1 by the receptor antagonist CCX832 resulted in loss of vascular tone that supports potential contributions of chemerin by both PVAT and the media. These data suggest that vessel-derived chemerin may support vascular tone locally through constitutive activation of Chemerin1. This posits chemerin as a potential therapeutic target in blood pressure regulation.

A high fat diet does not stimulate blood pressure dependence on chemerin in the Sprague-Dawley rat

The adipokine chemerin is a candidate for connecting obesity to hypertension.

Study objective

To test the hypothesis that a high fat (HF) diet stimulates dependence on chemerin for blood pressure regulation.

Design

Blood pressure in male Sprague Dawley rats fed a control (10 % fat) or HF (60 % fat) diet from weaning was measured using radiotelemetry. Antisense oligonucleotides (ASOs), administered after 17 weeks of feeding, were used to abolish chemerin production.

Results

The HF diet did not increase blood pressure (mm Hg; control = 117.0 ± 2.5; HF = 122.0 ± 2.2). An ASO against chemerin (dosed 1×/week, 4 weeks) similarly reduced blood pressure in the control (-14.0 ± 2.7 mmHg) and HF rat (-12.4 ± 2.3). Chemerin mRNA was abolished in the liver and fats (primary producers of chemerin) from rats given the ASO chemerin vs control.

Conclusion

A HF diet alone is insufficient to stimulate the dependence of blood pressure in the rat on chemerin.

Abstract P344: High Fat Diet Increases Inflammatory Gene Expression In Perivascular Adipose Tissue And Mesenteric Lymph Nodes Prior To Hypertension In Dahl S Rats

There are considerable data to suggest an association between inflammation and cardiovascular disease, including a link between the immune system and hypertension. Our previous studies indicated an increase in the induction of proinflammatory cytokines by activated T cells cultured in media conditioned with perivascular adipose tissue (PVAT) taken from Dahl S rats on a high fat diet (HFD). Notably this effect preceded the development of hypertension in these animals. The purpose of the present studies was to test the hypothesis that high fat diet promotes inflammatory gene expression in immune cells in mesenteric PVAT and mesenteric lymph nodes (mLN) of Dahl S rats prior to the development of hypertension. To test this hypothesis, we isolated the stromal vascular fraction (SVF) from mPVAT and cells from mLN from Dahl S rats on high fat diet for 10 weeks for single cell RNA-sequencing analysis. In the mPVAT SVF we found an increase in the expression of acute inflammatory genes, including Tnfa , and genes associated with T cell chemotaxis, such as Cxcr3 and Cxcl11 . Conversely, there was also an increase in genes that negatively regulate immune response and adipokine expression in mPVAT SVF from Dahl S rats on HFD. In mLN, we found an increase in genes associated with IL-3 signaling in CD8 T cells and in genes associated with NFκB signaling in CD4 T cells (Fig. 1). Taken together, these data suggest an increase in acute inflammatory signaling in cells in mPVAT and mLN from Dahl S rats on HFD.

Abstract P227: A High Fat Diet Does Not Enhance Blood Pressure Dependence On Chemerin In Normotensive Rats

Various humoral factors produced by adipose tissue are suggested to contribute to obesity associated hypertension and cardiovascular pathology. The adipokine chemerin is a frontrunner candidate. Male Dahl SS rats fed a high fat (HF; 60% kCal) diet from weaning develop severe hypertension that is profoundly reduced by weekly treatment with an antisense oligonucleotide (ASO) that disables chemerin mRNA. Here we hypothesized that feeding a HF diet from weaning to male Sprague Dawley (SD) rats would similarly increase the dependence of blood pressure (BP) regulation on chemerin. Over 17 weeks of feeding, HF fed SD rats gained significantly more weight and body fat than those fed control (10% kCal) diet. Radiotelemeters were implanted at 17 weeks of age to measure BP. Two weeks of basal BP was collected, and as we and others have shown previously, the HF diet did not increase BP in SD rats (control = 117±2.5 mm Hg; HF = 122±2.2 mm Hg). Vehicle or Gen 2.5 ASO chemerin (25 mg/kg, sc) were then given once a week for four weeks. Gen 2.5 ASO chemerin caused a slowly developing but significant reduction in BP in control rats (-14.0±2.7 mm Hg) that was not significantly different from the BP fall in HF rats (-12.4±2.3 mm Hg). RT-PCR analyses validated complete loss of chemerin mRNA in the liver and fat (primary producers of chemerin) from rats given the Gen 2.5 ASO chemerin vs control. These data show that in normal, normotensive rats a HF diet alone is insufficient to increase BP dependence on chemerin

Abstract P356: Cutaneous Vasodilation May Contribute To 5-ht-induced Hypotension In The Rat

5-hydroxytryptamine (5-HT, serotonin) is well-recognized to have vasodilator properties. For example, infusion of 5HT at low rates into rats decreases blood pressure acutely and chronically through reduction of total peripheral resistance. We recently showed that vasodilation in the hindquarters contributes to this fall in peripheral resistance. The hindquarter in the rat is mostly made up of skeletal muscle but also includes skin. Therefore, we hypothesized that an increase in blood flow in the skin, measured as an elevated temperature (T) in the thermoregulatory tail and paws, could contribute in part to 5-HT-induced reduction in blood pressure and hindquarters vasodilation. The temperature of thermoregulatory organs in the skin of anesthetized male, Sprague Dawley rats were measured using a Optris PI640 thermal camera. Blood pressure (from a radiotelemeter) and temperature of each paw and four locations along the tail (TL1-4) were recorded for 20 minutes before, during, and after infusion of 5-HT at a rate of 25 μg/min into the femoral vein. With this infusion protocol, the mean arterial blood pressure of rats fell over 30 mm Hg. However, the temperature of the paws (~29-32 o C) and tail (32 o at base, 25 o C at tip) were stable before and during 5-HT infusion, suggesting that flow was maintained, vs reduced, during this time. T increased during the 15-minute recovery time in all tail sections (base = from 32 o to 34 o C; tip from 23.5 o to 25.5 o C). Because the skin circulation exhibits only weak autoregulation, our results suggests that 5-HT infusion causes vasodilation of glabrous skin in the rat but without causing hyperemia. This could play a part in 5-HT induced hypotension.

Abstract P003: Chemerin Supports Basal Blood Pressure In Both Male And Female Dahl SS Rats

Evidence supports that Antisense oligonucleotides (ASO) against the adipokine chemerin reduce the blood pressure of the normal male Sprague Dawley rat and, to a greater magnitude, the hypertensive Dahl SS rat fed a high fat diet. In the Dahl SS rat, chemerin protein concentration in white adipose tissue [mesenteric perivascular adipose tissue (Mes PVAT)] was significantly higher in females vs males. We hypothesized that female Dahl SS rats would be more dependent on chemerin for blood pressure maintenance than males because of the Mes PVAT’s proximity to blood vessels that control total peripheral resistance. Age-matched male and female Dahl SS rats on a standard chow (0.2% NaCl, 6.2% fat) diet were used. Radiotelemeters were implanted to measure blood pressure (MAP) and heart rate (bpm). Following a two-week recovery period after implantation, one week of baseline measures were collected. Knockdown of whole body chemerin was achieved by subcutaneous injections of scrambled control ASO or whole-body ASO against chemerin (both 25 mg/kg) on days 0, 7, 14, and 21. On day 23, the rats were euthanized, and samples were collected for western blot and qPCR of the chemerin gene Rarres2 . Plasma chemerin was abolished in both male and female rats given the ASO against chemerin vs that of rats receiving the control ASO. In males and females, respectively, chemerin mRNA expression (2 -ΔCT ) was reduced from 0.53 to 0.001 ± 0.002 and 0.23 to 0.001 ± 0.02 in liver, 0.05 to 0.01 ± 0.005 and 0.07 to 0.005 ± 0.02 in RP fat, and 0.09 to 0.01 ± 0.003 and 0.05 to 0.001 ± 0.02 in epididymal/uterine fat. MAP in control ASO rats showed no significant change from baseline measurements (M:137.4 ± 3.0 /F: 130.6 ± 1.5 mmHg), while males and females treated with whole-body ASO dropped by 10.7 ± 1.6 and 10.9 ± 2.1 mmHg respectively after four injections, with no significant change in heart rate. Pulse pressure also decreased by 5.6 ± 1.3 and 6.8 ± 1.3 mmHg in whole-body ASO males and females, respectively, with no significant changes from baseline in the control animals. These data suggest, contrary to our hypothesis, that chemerin plays a similar role in basal blood pressure regulation in males and females. This indicates that males and females may be equally dependent on chemerin for high fat diet-induced hypertension.

Abstract MP19: Endogenous 5-hydroxytryptamine May Regulate Skeletal Muscle Vascular Resistance In Normal Healthy Rats

Infusing low doses of 5-hydroxytryptamine (5-HT) into normal rats causes chronic (weeks to months) hypotension and a fall in total peripheral resistance. These effects are mediated by activation of 5-HT 7 receptors. Therefore, we generated 5-HT 7 receptor knockout rats (5-HT 7 KO) to explore possible cardiovascular effects of 5-HT 7 receptors under normal and pathophysiological conditions. We previously reported that healthy 5-HT 7 KO rats have normal blood pressure and total peripheral resistance at rest. This suggested that 5-HT 7 receptors plays no role in cardiovascular regulation under normal conditions. But total peripheral resistance is determined by multiple vascular beds that differ in their sensitivity to 5-HT. Others have indicated that 5-HT 7 receptors in the skeletal muscle vasculature are particularly sensitive to the effects of 5-HT. Therefore, we hypothesized that 5-HT 7 KO rats would show both reduced responsiveness to exogenous 5-HT and increased resting skeletal muscle vascular resistance. Experiments were performed in isoflurane-anesthetized, male Sprague-Dawley (SD) (n=6), 5-HT 7 wild-type (5-HT 7 WT) (n=5) and 5-HT 7 KO (n=6) rats at 7-8 months of age. Arterial pressure was measured with an aortic catheter. Blood flow to the hindquarters (mostly skeletal muscle) was measured with transit-time, ultrasound flowmetry. After 10 minutes of baseline hemodynamic measurements were obtained, 5-HT was infused iv at a rate of 25 μg/kg/min for 15 minutes, followed by a 15-minute recovery period. As expected, 5-HT 7 KO rats did not show a significant fall in hindquarter vascular resistance (HQVR) during 5-HT infusion, while SD and 5-HT 7 WT did. More importantly, HQVR at baseline was significantly (p < 0.05) higher in 5-HT 7 KO rats (16.0 ± 2.0 mmHg/ml/min) than in 5-HT 7 WT rats (10.9 ± 0.06 mmHg/ml/min) or SD rats (7.0 ± 0.03 mmHg/ml/min). These results support our hypothesis that in healthy (albeit anesthetized) rats, 5-HT 7 receptors reduce skeletal muscle vascular resistance.

Abstract MP05: The Mechanism Of The Pvat Pro-inflammatory Micro-environment Formation During The Development Of High Fat Diet-induced Hypertension

There is considerable evidence for a causative role for T cells in hypertension, including studies with immunosuppressive drugs and T cell-deficient models. Our previous studies showed that soluble mediators from mesenteric perivascular adipose tissue (mPVAT) modulate T cell function. Specifically, conditioned media from mPVAT (mPVAT-CM) from Dahl S rats on a high fat diet (HFD) promoted expression of the pro-inflammatory cytokines, IFNg, IL-17a and GM-CSF, by activated T cells. Furthermore, the Dahl S rats on HFD will later develop hypertension.

Hypothesis: mPVAT is stimulated to produce immunomodulatory mediators that promotes Th1/17 differentiation preceding the development of HFD-induced hypertension. We conducted bulk RNA-seq on activated splenocytes cultured in mPVAT-CM from Dahl S rats on either control or HFD for 10 weeks. In accordance with our previous studies, PVAT-CM from HFD-fed rats significantly upregulated many genes associated with IFNg/IL-17 induction, including Mpeg1, Lyz2 and Tnfsf4 (5.0±1.78, 3.70±0.53 and 1.78±0.42 fold over Control diet, respectively). In contrast, Th2/Treg-associated genes, such as Ctla2a (-0.27±0.02) and Ccr4 (-0.41±0.03) were downregulated. We also performed single cell (sc) RNA-seq on the PVAT stromal vascular fraction (SVF) and found that acute inflammatory genes were enriched in the HFD group. Together with the bulk RNA-seq on mPVAT, these data strongly suggest that the pro-inflammatory mPVAT micro-environment may promote Th1/Th17 differentiation. To identify mediators in PVAT-CM that may induce Th1/Th17 differentiation, we compared the bulk RNA-seq on splenocytes cultured in PVAT-CM with bulk RNA-seq conducted on the whole mPVAT itself. We found that a T cell co-stimulatory receptor DPP4 (CD26), which is closely associated with T cell activation was significantly increased in mPVAT from HFD-fed rats (33.4±2.3 HFD vs. 15.3±1.8 Control diet). We also observed an increase in DPP4 global expression from mPVAT SVF in HFD-fed rats, as determined by scRNA-seq.

Conclusion: The data suggest that HFD promotes the IFNg and IL-17a pathways in PVAT, which precedes hypertension in Dahl S rats and correlates with an increase in expression of DPP-4, a gene that promotes T cell activation. (NIH P01 HL070687).

Reduction in Hindquarter Vascular Resistance Supports 5-HT7 Receptor Mediated Hypotension

The 5-HT₇ receptor is the primary mediator of both the acute (<hours) and chronic (day-week) decreases in mean arterial pressure (MAP) during low dose 5-HT infusion in rats. Previous data show the hypotensive response during chronic 5-HT infusion is due to a decrease total peripheral resistance (TPR) and specifically splanchnic vascular resistance. We hypothesized that changes in vascular resistance in both the splanchnic and skeletal muscle vascular beds are critical to the cardiovascular effects mediated by the 5-HT₇ receptor. Systemic and regional hemodynamic data were collected in conscious and anesthetized male rats using radiotelemetry, vascular catheters and transit-time flowmetry. Reversible antagonism of the 5-HT₇ receptor was achieved with the selective antagonist SB269970 (33 μg/kg, iv). From the very beginning and throughout the duration (up to 5 days) of a low dose (25 μg/kg) infusion of 5-HT, TPR, and MAP were decreased while cardiac output (CO) was increased. In a separate group of rats, the contribution of the 5-HT₇ receptor to the regional hemodynamic response was tested during 5-HT-induced hypertension. The decrease in MAP after 24 h of 5-HT (saline 83 ± 3 vs. 5-HT 72 ± 3 mmHg) was associated with a significant decrease in skeletal muscle vascular resistance (saline 6 ± 0.2 vs. 5-HT 4 ± 0.4 mmHg/min/mL) while splanchnic vascular resistance was similar in 5-HT and saline-treated rats. When SB269970 was administered acutely, MAP and skeletal muscle vascular resistance rapidly increased, whereas splanchnic resistance was unaffected. Our work suggests the most prominent regional hemodynamic response to 5-HT₇ receptor activation paralleling the fall in MAP is a decrease in skeletal muscle vascular resistance.

Male and female high-fat diet-fed Dahl SS rats are largely protected from vascular dysfunctions: PVAT contributions reveal sex differences

Vascular dysfunctions are observed in the arteries from hypertensive subjects. The establishment of the Dahl salt-sensitive (SS) male and female rat models to develop a reproducible hypertension with high-fat (HF) diet feeding from weaning allows addressing the question of whether HF diet-associated hypertension results in vascular dysfunction similar to that of essential hypertension in both sexes. We hypothesized that dysfunction of three distinct vascular layers, i.e., endothelial, smooth muscle, and perivascular adipose tissue (PVAT), would be present in the aorta from HF diet-fed versus control diet-fed male and female rats. Dahl SS rats were fed a control (10% kcal of fat) or HF (60%) diet from weaning for 24 wk. Male and female Dahl SS rats became equally hypertensive when placed on a HF diet. For male and female rats, the thoracic aorta exhibited medial hypertrophy in HF diet-induced hypertension versus control, but neither displayed a hyperresponsive contraction to the α-adrenergic agonist phenylephrine nor an endothelial cell dysfunction as measured by acetylcholine-induced relaxation. A beneficial PVAT function, support of stress relaxation, was reduced in the male versus female rats fed a HF diet. PVAT in the aorta of males but not in females retained the anticontractile activity. We conclude that this HF model does not display the same vascular dysfunctions observed in essential hypertension. Moreover, both male and female show significantly different vascular dysfunctions in this HF feeding model.NEW & NOTEWORTHY Although the aorta exhibits medial hypertrophy in response to HF diet-induced hypertension, it did not exhibit hyperresponsive contraction to an α-adrenergic agonist nor endothelial cell dysfunction; this was true for both sexes. Unlike other hypertension models, PVAT around aorta from (male) rats on the HF diet retained significant anticontractile activity. PVAT around aorta of the male on a HF diet was modestly more fibrotic and lost the ability to assist in arterial stress relaxation.

Phenotypic Changes in T Cell and Macrophage Subtypes in Perivascular Adipose Tissues Precede High-Fat Diet-Induced Hypertension

Perivascular adipose tissue (PVAT) may connect adiposity to hypertension because of its vasoactive functions and proximity to blood vessels. We hypothesized that immune cell changes in PVATs precede the development of high fat diet (HFD)-induced hypertension. Both sexes of Dahl S rat become equally hypertensive when fed a HFD. Further, both sexes would have similar immune cell composition in PVATs with the development and progression of hypertension. Male and female Dahl S rats were fed a regular (10% calories from fat; CD) diet or a HFD (60%) from weaning. PVATs from around the thoracic aorta (APVAT) and small mesenteric vessels (MRPVAT) were harvested at 10 weeks (pre-hypertensive), 17 weeks (onset), or 24 (hypertensive) weeks on diet. RNA-sequencing in MRPVAT at 24 weeks indicated sex-differences with HFD (>CD) and diet-differences in males (>females). The top 2 out of 7 immune processes with the maximum number of differentially expressed genes (DEGs) were associated with immune effector processes and leukocyte activation. Macrophages and T cells (and their activation status), neutrophils, mast, B and NK cells were measured by flow cytometry. Sex-specific changes in the number of CD4 memory T cells (males > females) and M2-like macrophages (females > males) in PVATs occur with a HFD before hypertension developed. Sex-differences became more prominent with the development and progression of hypertension, driven by the diet (HFD > CD). These findings suggest that though the magnitudes of increased blood pressure were equivalent in both sexes, the associated phenotypic changes in the immune subsets within the PVATs were different in the male vs. the female with the development and progression of hypertension.

Renal Denervation and Celiac Ganglionectomy Decrease Mean Arterial Pressure Similarly in Genetically Hypertensive Schlager (BPH/2J) Mice

Supplemental Digital Content is available in the text.

Renal denervation (RDNX) lowers mean arterial pressure (MAP) in patients with resistant hypertension. Less well studied is the effect of celiac ganglionectomy (CGX), a procedure which involves the removal of the nerves innervating the splanchnic vascular bed. We hypothesized that RDNX and CGX would both lower MAP in genetically hypertensive Schlager (BPH/2J) mice through a reduction in sympathetic tone. Telemeters were implanted into the femoral artery in mice to monitor MAP before and after RDNX (n=5), CGX (n=6), or SHAM (n=6). MAP, systolic blood pressure, diastolic blood pressure, and heart rate were recorded for 14 days postoperatively. The MAP response to hexamethonium (10 mg/kg, IP) was measured on control day 3 and postoperative day 10 as a measure of global neurogenic pressor activity. The efficacy of denervation was assessed by measurement of tissue norepinephrine. Control MAP was similar among the 3 groups before surgical treatments (≈130 mm Hg). On postoperative day 14, MAP was significantly lower in RDNX (−11±2 mm Hg) and CGX (−11±1 mm Hg) groups compared with their predenervation values. This was not the case in SHAM mice (−5±3 mm Hg). The depressor response to hexamethonium in the RDNX group was significantly smaller on postoperative day 10 (−10±5 mm Hg) compared with baseline control (−25±10 mm Hg). This was not the case in mice in the SHAM (day 10; −28±5 mm Hg) or CGX (day 10; −34±7 mm Hg) group. In conclusion, both renal and splanchnic nerves contribute to hypertension in BPH/2J mice, but likely through different mechanisms.

Vascular reactivity stimulated by TMA and TMAO: Are perivascular adipose tissue and endothelium involved?

Trimethylamine (TMA), formed by intestinal microbiota, and its Flavin-Monooxygenase 3 (FMO3) product Trimethylamine-N-Oxide (TMAO), are potential modulators of host cardiometabolic phenotypes. High circulating levels of TMAO are associated with increased risk for cardiovascular diseases. We hypothesized that TMA/TMAO could directly change the vascular tone. Perivascular adipose tissue (PVAT) helps to regulate vascular homeostasis and may also possess FMO3. Thoracic aorta with(+) or without(-) PVAT, also + or - the endothelium (E), of male Sprague Dawley rats were isolated for measurement of isometric tone in response to TMA/TMAO (1nM-0.5 M). Immunohistochemistry (IHC) studies were done to identify the presence of FMO3. TMA and TMAO elicited concentration-dependent arterial contraction. However, at a maximally achievable concentration (0.2 M), contraction stimulated by TMA was of a greater magnitude (141.5 ± 16% of maximum phenylephrine contraction) than that elicited by TMAO (19.1 ± 4.03%) with PVAT and endothelium intact. When PVAT was preserved, TMAO-induced contraction was extensively reduced the presence (19.1 ± 4.03%) versus absence of E (147.2 ± 20.5%), indicating that the endothelium plays a protective role against TMAO-induced contraction. FMO3 enzyme was present in aortic PVAT, but the FMO3 inhibitor methimazole did not affect contraction stimulated by TMA in aorta + PVAT. However, the l-type calcium channel blocker nifedipine reduced TMA-induced contraction by ∼50% compared to the vehicle. Though a high concentration of these compounds was needed to achieve contraction, the findings that TMA-induced contraction was independent of PVAT and E and mediated by nifedipine-sensitive calcium channels suggest metabolite-induced contraction may be physiologically important.

Activation of the 5-HT7 receptor but not nitric oxide synthase is necessary for chronic 5-hydroxytryptamine-induced hypotension

NEW FINDINGS

What is the central question of this study? What mechanisms account for the hypotension observed during chronic elevations in circulating 5-hydroxytryptamine in rats? What is the main finding and its importance? Chronic 5-hydroxytryptamine-induced hypotension requires continued activation of the 5-HT₇ receptor subtype but does not require NO, an outcome that resolves previous conflicting results. Therapeutic interruption of the hypotensive actions of 5-HT under pathophysiological conditions can only be achieved through blockade of the 5-HT₇ receptor.

ABSTRACT

Low dose infusion of 5-hydroxytryptamine (5-HT) to rats causes both an acute and a chronic fall in arterial blood pressure. The 5-HT₇ receptor subtype plays a critical part in the observed hypotension. Acute (minutes to hours) 5-HT infusion shows no depressor role for nitric oxide (NO), but 5-HT depressor responses under chronic conditions suggest that NO production may be critical. We test the hypothesis that NO contributes to the chronic, but not the acute, depressor response to 5-HT. We compared the role of NO and 5-HT₇ receptors in 5-HT-induced hypotension under acute and chronic conditions in the same animal. Mean arterial pressure and heart rate were measured by radiotelemetry in conscious rats during 5 days of saline or 5-HT (25 μg kg^-1  min^-1 ; osmotic pump) infusion and for 2 days after infusion was stopped. To quantify the contributions of NO and the 5-HT₇ receptor to 5-HT-induced hypotension, the nitric oxide synthase (NOS) inhibitor l-NAME or the selective 5-HT₇ receptor antagonist SB-267790 were given at 1, 3 and 5 days of chronic infusion, and 1 day after 5-HT infusion pumps were removed. N^ω -Nitro-l-arginine methyl ester (l-NAME) caused a pressor response of the same magnitude in the absence or presence of 5-HT infusion. Conversely, SB-269970 did not affect mean arterial pressure in the absence of 5-HT infusion and reversed the 5-HT-induced depressor response at each time point. Our findings demonstrate that acute and chronic 5-HT-induced hypotension does not require NOS activation but does require continued activation of the 5-HT₇ receptor.

Blood pressure changes PVAT function and transcriptome: use of the mid-thoracic aorta coarcted rat

Perivascular adipose tissue (PVAT) modifies the contractile function of the vessel it surrounds (outside-in signaling). Little work points to the vessel actively affecting its surrounding PVAT. We hypothesized that inside-out arterial signaling to PVAT would be evidenced by the response of PVAT to changes in tangential vascular wall stress. Rats coarcted in the mid-thoracic aorta created PVAT tissues that would exemplify pressure-dependent changes (above vs. below coarctation); a sham rat was used as a control. Radiotelemetry revealed a ∼20 mmHg systolic pressure gradient across the coarctation 4 wk after surgery. Four measures (histochemical, adipocyte progenitor proliferation and differentiation, isometric tone, and bulk mRNA sequencing) were used to compare PVAT above versus below the ligature in sham and coarcted rats. Neither aortic collagen deposition in PVAT nor arterial media/radius ratio above coarctation was increased versus below segments. However, differentiated adipocytes derived from PVAT above the coarctation accumulated substantially less triglycerides versus those below; their relative proliferation rate as adipogenic precursors was not different. Functionally, the ability of PVAT to assist stress relaxation of isolated aorta was reduced in rings above versus below the coarctation. Transcriptomic analyses revealed that the coarctation resulted in more differentially expressed genes (DEGs) between PVAT above versus below when compared with sham samples from the same locations. A majority of DEGs were in PVAT below the coarctation and were enriched in neuronal/synaptic terms. These findings provide initial evidence that signaling from the vascular wall, as stimulated by a pressure change, influences the function and transcriptional profile of its PVAT.NEW & NOTEWORTHY A mid-thoracic aorta coarcted rat was created to generate a stable pressure difference above versus below the coarctation ligature. This study determined that the PVAT around the thoracic aorta exposed to a higher pressure has a significantly reduced ability to assist stress relaxation versus that below the ligature and appears to retain the ability to be anticontractile. At the same time, the PVAT around the thoracic aorta exposed to higher pressure had a reduced adipogenic potential versus that below the ligature. Transcriptomics analyses indicated that PVAT below the coarctation showed the greatest number of DEGs with an increased profile of the synaptic neurotransmitter gene network.

Potential role of intermittent functioning of baroreflexes in the etiology of hypertension in spontaneously hypertensive rats

The spontaneously hypertensive rat (SHR) is a genetic model of primary hypertension with an etiology that includes sympathetic overdrive. To elucidate the neurogenic mechanisms underlying the pathophysiology of this model, we analyzed the dynamic baroreflex response to spontaneous fluctuations in arterial pressure in conscious SHRs, as well as in the Wistar-Kyoto (WKY), the Dahl salt-sensitive, the Dahl salt-resistant, and the Sprague-Dawley rat. Observations revealed the existence of long intermittent periods (lasting up to several minutes) of engagement and disengagement of baroreflex control of heart rate. Analysis of these intermittent periods revealed a predictive relationship between increased mean arterial pressure and progressive baroreflex disengagement that was present in the SHR and WKY strains but absent in others. This relationship yielded the hypothesis that a lower proportion of engagement versus disengagement of the baroreflex in SHR compared with WKY contributes to the hypertension (or increased blood pressure) in SHR compared with WKY. Results of experiments using sinoaortic baroreceptor denervation were consistent with the hypothesis that dysfunction of the baroreflex contributes to the etiology of hypertension in the SHR. Thus, this study provides experimental evidence for the roles of the baroreflex in long-term arterial pressure regulation and in the etiology of primary hypertension in this animal model.

Baroreflex dysfunction contributes to the etiology of hypertension in a genetic model of primary hypertension.

Abstract P142: Sex-differences In M1-like Macrophage Counts In Aortic Perivascular Adipose Tissue Precedes High Fat Diet-induced Hypertension In Dahl S Rats

Perivascular adipose tissue (PVAT) may connect adiposity to hypertension because of its functions and proximity to blood vessels. Immune cells in adipose tissue are proposed to couple adiposity to hypertension development in a sex-specific fashion. It is unknown if sex-differences exist in PVAT’s immune community during the onset of adiposity-induced hypertension. Both sexes of the Dahl S rat strain become equally hypertensive (table) when fed a high fat (HFD) diet. We hypothesized that both sexes have similar immune cell composition in PVAT with the development and progression of HFD-induced hypertension. Male and female Dahl S rats were fed a regular (10% calories from fat; CD) diet or a HFD (60%) from weaning. Thoracic aorta PVAT (APVAT) was harvested at 10 (pre-hypertension), 17 (onset) or 24 (chronic) weeks (w) of diet. Macrophages (subtypes), neutrophils, mast, T (subtypes), B, NK cells were measured by flow cytometry. At 10 w, HFD females had 5X the number of M1-like macrophages vs HFD males. At 17 w, CD females had 10X the number of M2-like macrophages vs CD males. At 17 w and 24 w, males had greater number of CD4 (2X) and CD8 (1.5X) memory T cells vs females, independent of the diet (table). In summary, sex-differences in M1-like macrophage counts in APVAT precedes the development of HFD-induced hypertension in Dahl S rats. The progression of hypertension is associated with memory T cells in males and M2-like macrophages in females. This study is foundational to understand the sex-specific roles of these immune cells in regulating vascular tone in HFD-induced hypertension, underscoring the need for novel sex-specific anti-hypertensive immune modulators.

Renal Inflammation in DOCA-Salt Hypertension

Recent reports indicate that, in addition to treating hypertension, renal denervation (RDN) also mitigates renal inflammation. However, because RDN decreases renal perfusion pressure, it is unclear whether these effects are because of the direct effects of RDN on inflammatory signaling or secondary to decreased arterial pressure (AP). Therefore, this study was conducted to elucidate the contribution of renal nerves to renal inflammation in the deoxycorticosterone (DOCA)-salt rat, a model in which RDN decreases AP and abolishes renal inflammation. In Experiment 1, we assessed the temporal changes in renal inflammation by measuring renal cytokines and AP in DOCA-salt rats. Uninephrectomized (1K) adult male Sprague Dawley rats that received surgical RDN or sham (Sham) were administered DOCA (100 mg, SC) and 0.9% saline for 21 days. AP was measured by radiotelemetry, and urinary cytokine excretion was measured repeatedly. In Experiment 2, the contribution of renal nerves in renal inflammation was assessed in a 2-kidney DOCA-salt rat to control for renal perfusion pressure. DOCA-salt treatment was administered after unilateral (U-)RDN. In Experiment 1, DOCA-salt-induced increases in AP and renal inflammation (assessed by urinary cytokines) were attenuated by RDN versus Sham. In Experiment 2, GRO/KC (growth-related oncogene/keratinocyte chemoattractant), MCP (monocyte chemoattractant protein)-1, and macrophage infiltration were lower in the denervated kidney versus the contralateral Sham kidney. No differences in T-cell infiltration were observed. Together, these data support the hypothesis that renal nerves mediate, in part, the development of renal inflammation in the DOCA-salt rat independent of hypertension. The mechanisms and cell-specificity mediating these effects require further investigation.

Effects of high-fat diet on sympathetic neurotransmission in mesenteric arteries from Dahl salt-sensitive rat

Obesity hypertension is driven by sympathetic neurotransmission to the heart and blood vessels. We tested the hypothesis that high-fat diet (HFD)-induced hypertension is driven by sympathetic neurotransmission to mesenteric arteries (MA) in male but not female Dahl salt-sensitive (Dahl ss) rat. Rats were fed a control diet (CD; 10 kcal% from fat) or HFD (60 kcal% from fat) beginning at 3 weeks (wk) of age; measurements were made at 10-, 17- and 24-wk. Body weight increased with HFD, age and sex. Mean arterial pressure (MAP) was higher in HFD versus CD rats from both sexes at 17- and 24-wk. MA constriction measured using pressure myography, and electrical field stimulation (EFS, 0.2-30 Hz) was greater in HFD versus CD in males at 17-wk; this was not due to changes in α2 autoreceptor or norepinephrine transporter (NET) function. Prazosin (α1-AR antagonist) and suramin (P2 receptor antagonist) inhibited neurogenic MA constriction equally in all groups. Arterial reactivity to exogenous norepinephrine (NE; 10^-8 - 10^-5 M) was lower in HFD versus CD at 10-wk in males. Female MA reactivity to exogenous ATP was lower at 24-weeks compared to earlier time points. HFD did not affect tyrosine hydroxylase (TH) or the vesicular nucleotide transporter (VNUT) nerve density in MA from both sexes. NE content was lower in MA but higher in plasma at 24-wk compared to 10- and 17-wk in both sexes. In conclusion, HFD-induced hypertension is not driven by increased sympathetic neurotransmission to MA in male and female Dahl ss rats.

Brain Prostaglandin D2 Increases Neurogenic Pressor Activity and Mean Arterial Pressure in Angiotensin II-Salt Hypertensive Rats

This study tested whether brain L-PGDS (lipocalin-type prostaglandin [PG] D synthase), through prostanoid signaling, might increase neurogenic pressor activity and thereby cause hypertension. Sprague Dawley rats on high-salt diet received either vehicle or Ang II (angiotensin II) infusion. On day 4, the developmental stage of hypertension, brains from different sets of control and Ang II-treated rats were collected for measuring L-PGDS expression, PGD2 levels, and DP1R (type 1 PGD2 receptor) expression. In a different set of 14-day Ang II-salt-treated rats, mini-osmotic pumps were used to infuse either a nonselective COX (cyclooxygenase) inhibitor ketorolac, L-PGDS inhibitor AT56, or DP1R inhibitor BWA868C to test the role of brain COX-PGD2-DP1R signaling in Ang II-salt hypertension. The acute depressor response to ganglion blockade with hexamethonium was used to quantify neurogenic pressor activity. During the developmental stage of Ang II-salt hypertension, L-PGDS expression was higher in cerebrospinal fluid, and PGD2 levels were increased in the choroid plexus, cerebrospinal fluid, and the cardioregulatory brain region rostral ventrolateral medulla. DP1R expression was decreased in rostral ventrolateral medulla. Both brain COX inhibition with ketorolac and L-PGDS inhibition with AT56 lowered mean arterial pressure by altering neurogenic pressor activity compared with vehicle controls. Blockade of DP1R with BWA868C, however, increased the magnitude of Ang II-salt hypertension and significantly increased neurogenic pressor activity. In summary, we establish that the development of Ang II-salt hypertension requires increased COX- and L-PGDS-derived PGD2 production in the brain, making L-PGDS a possible target for treating neurogenic hypertension.

Different blood pressure responses in hypertensive rats following chemerin mRNA inhibition in dietary high fat compared to dietary high-salt conditions

Chemerin is a contractile adipokine, produced in liver and fat, and removal of the protein by antisense oligonucleotides (ASO) lowers blood pressure in the normal Sprague Dawley rat. In humans, chemerin is positively associated with blood pressure and obesity so we hypothesized that in a model of hypertension derived from high-fat (HF) feeding, the chemerin ASO would reduce blood pressure more than a high-salt (HS) model. Male Dahl S rats were given a HF (60% kcal fat; age 3-24 wk) or HS diet (4% salt; age 20-24 wk to match age and blood pressure of HF animals). Scrambled control, whole body, or liver-specific ASOs that knock down chemerin were delivered subcutaneously once per week for 4 wk with tissue and blood collected 2 days after the last injection. Conscious blood pressure was measured 24 h/day by radiotelemetry. By the end of whole body ASO administration, blood pressure of HF animals had fallen 29 ± 2 mmHg below baseline, while blood pressure of HS-diet animals fell by only 12 ± 4 mmHg below baseline. Administration of a liver-specific ASO to HF Dahl S resulted in a 6 ± 2 mmHg fall in blood pressure below baseline. Successful knockdown of chemerin in both the whole body and liver-specific administration was confirmed by Western and PCR. These results suggest that chemerin, not derived from liver but potentially from adipose tissue, is an important driver of hypertension associated with high fat. This knowledge could lead to the development of antihypertensive treatments specifically targeted to obesity-associated hypertension.

Abstract 113: Chemerin Regulates Adipocyte Size in Mesenteric Perivascular Adipose Tissue When on a Normal but Not High Fat Isocaloric Diet

Chemerin is an adipokine, positively associated with blood pressure, and used as a marker for metabolic syndrome. We hypothesized that a global knockout (KO) of chemerin in the rat would lead to a global decrease in white visceral fat mass in both control (C) and high-fat (HF) diets. Wild-type (WT) and KO rats on a Sprague-Dawley background were fed a C (10% kcal fat) or HF (60% kcal fat) diet with weekly monitoring of body weight and food consumption. MicroCT was performed at 8 weeks and 25 weeks of age to measure subcutaneous and intrabdominal fat. Blood pressure was measured by radiotelemetry measuring for 10 seconds every 10 minutes for 24 hours/day. At the end of 25 weeks, fats were dissected and flash frozen for PCR analysis or fixed with paraformaldehyde for histology. There were no physiologically relevant differences in blood pressure (table). Within each diet, there were no significant differences in final total body weight (table). KO-C had reduced intrabdominal fat when compared to WT-C. Histology of the KO-C intrabdominal white fat components revealed a significant leftward shift in mesenteric adipocyte area compared to WT-C (table; p = 0.01 by the Kolmogorov-Smirnov test) but no changes in retroperitoneal adipocytes. RNA expression of perilipin, adiponectin, and fatty acid synthase normalized to beta-2 microglobulin were all undetectable only in the mesenteric fat, not retroperitoneal fat, of KO-C animals compared to WT-C (table). These data are the first to provide in vivo support for the role of chemerin in adipogenesis but also indicates that chemerin’s role in adipocyte development specific to a location vital for blood pressure regulation.

Abstract P3024: Tangential Wall Stress In The Thoracic Aorta Affects The Structure And Function Of Associated Perivascular Adipose Tissue

Perivascular adipose tissue (PVAT) dynamically modifies contractile function of the blood vessel it surrounds (outside-in signaling). Sparse evidence points to inside-out signaling, i.e. the blood vessel actively affecting its surrounding PVAT. We hypothesized that inside-out signaling to PVAT could occur in response to changes in tangential vascular wall stress. We created a coarctation of the thoracic aorta in male Sprague-Dawley rats to chronically expose PVAT to higher (above) and lower (below) pressures (and thus wall stresses). This allows comparison of PVAT from the same animal to different vascular pressures with confounding factors (neurohormonal environment) presumably being equal. In some animals, dual-channel pressure telemeters were used to simultaneously measure arterial pressure in the aorta of conscious rats above and below the coarctation. Post-surgery (4-8 weeks), thoracic aortic samples + PVAT were dissected above and below coarctation to determine elastin and collagen content of PVAT. Functionally, the adipogenic capacity of PVAT preadipocytes, PVAT-assisted stress relaxation and contraction to phenylephrine (PE) were compared. Telemetry revealed a ~22 mmHg systolic pressure gradient across the coarctation. Collagen deposition (picrosirius red) in PVAT above coarctation increased by 92% vs below (above=1.13±0.23% vs below=0.65±0.23% of PVAT area, n=4, P<0.05); elastin content did not change. Differentiated adipocytes derived from the PVAT above the coarctation accumulated 31% less triglycerides vs those below, and vs retroperitoneal adipose tissue [below=1 (set), above=0.69±0.1%, retroperitoneal=4.15±0.1%, n=4 P<0.05]. Finally, the ability of PVAT to assist stress relaxation (greater relaxation in +PVAT vs -PVAT) over a 6 gram tension range was reduced ~50% (N=5) in PVAT above vs below the coarctation; the anti-contractile function of PVAT in PE-induced contraction did not differ above vs below. In summary, PVAT of thoracic aorta under different distending pressures/wall stress exhibit significantly different structural and functional properties. These data support the hypothesis that signaling (factors derived) from the vascular wall influences the function of its PVAT.

5-HT does not lower blood pressure in the 5-HT7 knockout rat

The fall in mean arterial pressure (MAP) after 24 h of 5-HT infusion is associated with a dilation of the portal vein (PV) and abdominal inferior vena cava (Ab IVC); all events were blocked by the selective 5-HT₇ receptor antagonist SB269970. Few studies have investigated the contribution of the 5-HT₇ receptor in long-term cardiovascular control, and this requires an understanding of the chronic activation of the receptor. Using the newly created 5-HT₇ receptor knockout (KO) rat, we presently test the hypothesis that continuous activation of the 5-HT₇ receptor by 5-HT is necessary for the chronic (1 wk) depressor response and splanchnic venodilation. We also address if the 5-HT₇ receptor contributes to endogenous cardiovascular regulation. Conscious MAP (radiotelemeter), splanchnic vessel diameter (ultrasound), and cardiac function (echocardiogram) were measured in ambulatory rats during multiday 5-HT infusion (25 μg·kg^-1·min^-1 via minipump) and after pump removal. 5-HT infusion reduced MAP and caused splanchnic venodilation of wild-type (WT) but not KO rats at any time point. The efficacy of 5-HT-induced contraction was elevated in the isolated abdominal inferior vena cava from the KO compared with WT rats, supporting loss of a relaxant receptor. Similarly, the efficacy of 5-HT causing an acute pressor response to higher doses of 5-HT in vivo was also increased in the KO vs. WT rat. Our work supports a novel mechanism for the cardiovascular effects of 5-HT, activation of 5-HT₇ receptors mediating venodilation in the splanchnic circulation, which could prove useful in the treatment of cardiovascular disease.

Sex Differences in Renal Inflammation and Injury in High-Fat Diet-Fed Dahl Salt-Sensitive Rats

We examined the impact of sex on high-fat diet (HFD)-induced renal alterations in Dahl salt-sensitive and Sprague Dawley rats. In Dahl rats, HFD (60% kcal from fat for 24-26 weeks starting at weaning) significantly and equally increased blood pressure in males and females when compared with rats fed a control diet (10% kcal from fat). Male Dahl rats on HFD exhibited progressive renal histological injury and moderately increased renal macrophage infiltration at 10 and 24 weeks of feeding when compared with males on control diet. Female Dahl rats had lower grade renal injury and less macrophage infiltration (except at 17 weeks) than males regardless of diet. Male Dahl rats on both diets showed progressively increasing numbers of renal T-cells, a pattern not observed in females. HFD per se did not significantly affect renal T-cell number. Male Dahl rats had lower renal regulatory T-cells cell ratio than females at 24 weeks. Renal macrophage and T-cell infiltrations were highly correlated to final mean arterial pressure levels in males but not in females. Sprague Dawley rats fed HFD were normotensive without significant renal injury/inflammation after 24 weeks of feeding. In summary, HFD feeding fails to increase arterial blood pressure in Sprague Dawley rats but strongly promotes hypertension in both male and female Dahl salt-sensitive rats. Only Dahl males, however, exhibited blood pressure-associated renal inflammation and injury. Maintenance of regulatory T-cells ratio may protect against hypertension-associated renal injury/inflammation but not HFD-induced hypertension.

Abstract P305: High Fat Diet With Normal Salt Feeding Does Not Change Renal m-TORC Signaling Activities In Male And Female Dahl Salt Sensitive Rats

We have previously reported that high fat diet (HFD) with normal salt feeding strongly promotes hypertension in both male and female Dahl salt sensitive (SS) rats. Only males, however, exhibit hypertension-associated renal inflammation/injury. The underlying mechanisms responsible for sex differences in HFD associated renal inflammation/injury are undetermined. It has been reported that increased activity of Mammalian Target of Rapamycin Complex 1/2 (mTORC) contribute to high salt diet associated hypertension and renal inflammation/injury in Dahl SS male rats. In this study, we determined whether HFD increases renal mTORC signaling in Dahl SS rats and if there are sex differences in signaling. Renal cortex and medulla were collected from rats fed a control diet (CD, 10% kcal fat) or a HFD (60% kcal fat) with 0.3% NaCl for 10, 17 or 24 weeks (WKs, starting at weaning, the time points correspond to pre-hypertension, developing hypertension and established hypertension phases of the model. Ratio (%) of expression of phospho-S6 ribosomal protein Ser235/236 (pS6)/S6 (a marker for mTORC1), and phospho-AKT Ser473 (pAKT)/AKT (a marker for mTORC2) were used to evaluate mTORC activity. The activity of mTORC1 in CD male cortex and female medulla were slightly increased at 17 and 24WKs of feeding compared to 10 WKs (22±4 and 16±7 vs 2±2, P<0.05), but HFD did not change the activity in cortex and medulla significantly in males (cortex,10±5, 14±5, 20±5; medulla 9±2, 18±6, 25±12) or females (cortex, 4±1, 12±3, 13±2; medulla 13±8, 22±8, 24±16) (P>0.5). The overall activity of mTORC2 in CD males and females were very low and mostly unchanged during 24WKs feeding, except for a slight increase in CD male cortex at 17WKs of feeding compared to 10WKs (4±1 vs 0.1±0.02, P<0.05). HFD caused only a slight increase of mTORC2 in medulla from males (4±1 vs 1±0.5) and a decrease in medulla from females (8±2 vs 0.9±0.3) (P<0.05) at 24WKs compared with 10WKs of feeding. Overall HFD did not cause marked changes in renal mTORC1/2 signaling activities. In addition, there were no significant differences in mTORC signaling activities between males and females. Therefore mTORC signaling pathways are not likely to contribute to the sex differences in HFD associated renal inflammation/injury in Dahl SS rats.

Abstract P212: Splanchnic and Hepatic Portal Hemodynamics in the Hypotensive Actions of 5-HT

Circulating 5-hydroxytryptamine (5-HT) regulates mean arterial pressure (MAP) under some conditions. Infusion of low doses of 5-HT into rats leads to a sustained decrease in MAP which is prevented by the selective 5-HT7 receptor (5-HT7R) antagonist SB269970 or by inhibition of nitric oxide (NO) production. Time-dependent changes in the splanchnic circulation play a critical role in the sustained depressor response to 5-HT. We hypothesized that activation of 5-HT7Rs reduces MAP in part by causing decreased splanchnic vascular resistance and/or increased hepatic portal vascular resistance. Anesthetized male Sprague Dawley rats were instrumented with arterial and venous lines for pressure measurements and 5-HT/SB269970 infusion, and a Transonic probe on the portal vein to measure portal flow. Within 20 minutes of starting an infusion of 5-HT (25 ug/kg/min), MAP was significantly reduced (63±2 vs baseline 82±4 mmHg), whereas splanchnic vascular resistance (4.1±0.6 vs 2.4±0.1 ml/min/mmHg) and portal vascular resistance (0.18±0.08 vs 0.11±0.3) were increased. In a separate group of rats subjected to 24 hours of 5-HT infusion, MAP was reduced compared to control values (70±3 vs 84±2 mmHg), but portal vascular resistance (0.23±0.07 vs 0.17±0.04) and splanchnic vascular resistance (2.6±0.3 vs 2.4±0.1) were near control values. These animals then received an infusion of SB269970 to determine the direct contribution of the 5HT7R to hemodynamics after 24 hours of 5-HT exposure. After 20 minutes of SB269970 infusion, MAP (83±3 mmHg) was completely restored to baseline values while splanchnic vascular resistance (2.1 ±0.1 vs 2.6±0.1) and portal vascular resistance (0.12±0.3 vs 0.23±0.7) were decreased. These data suggest that the ability of 5-HT7R activation to increase splanchnic vascular resistance is effectively opposed over time by an endogenous vasodilator, which we suspect is nitric oxide. The data also indicate that changes in splanchnic vascular resistance are unlikely to participate in the chronic hypotensive effect of 5-HT, whereas increased resistance to flow through the hepatic portal system could play a role.

Abstract P325: High-Fat Feeding Does not Alter the Sparse Sympathetic Nerve Density in Mesenteric Resistance Artery Perivascular Adipose Tissue in Male Sprague-Dawley Rats

Chemical signals from perivascular adipose tissue (PVAT) modulate the structure and function of blood vessels. This may be partially under sympathetic neural control, however, little is known about the density of sympathetic innervation of PVAT. We hypothesized sympathetic nerve (SN) density in PVAT surrounding mesenteric resistance arteries (MRAs) is similar to that in the adventitia of the MRAs, and that high-fat feeding (HFF, 16 weeks) would decrease the density of SNs on MRAs and in PVAT. To test these hypotheses, we labeled SNs on MRAs and in PVAT with rabbit anti-tyrosine hydroxylase (TH) antibodies/AlexaFluor488-conjugated donkey-anti-rabbit antibodies, ex vivo. TH staining density (fraction occupied by TH-labeled structures) was computed from thresholded, background subtracted, maximum intensity z-projections of image stacks. TH staining density was higher at the surface of MRAs (0.21±0.03, n = 14) than within PVAT (0.013±0.003, n = 42, p<0.0001, Fig. 1 - arrows point to TH-positive nerves). HFF increased PVAT adipocyte diameter from 39±0.5μm (n=672) to 72±0.6μm (n = 365, p<0.0001). However, HFF had no effect on TH staining density on MRAs or within PVAT (p=0.83). Thus, while MRA’s are robustly innervated by SNs, only the first layer of adipocytes adjacent to MRA adventitia is exposed to a similar SN density; SN density in PVAT more than one adipocyte away from MRAs is >16 fold lower. HFF does not affect SN density on MRAs or in PVAT. However, given the larger size of adipocytes in HFF rats, this may mean an increase in SN density/adipocyte. Nonetheless, the low density of SNs in mesenteric PVAT suggests limited direct SN control of PVAT function in the bulk of PVAT adipocytes.

Abstract P304: Sex Differences in Mechanisms of Adiposity-Associated Hypertension in Dahl S Rats

In humans, excessive accumulation of visceral adipose tissue is often associated with hypertension, but there is evidence that the mechanisms responsible may differ between men and women. Dahl S rats fed a high fat diet (HFD) from weaning gain visceral fat and develop a progressively higher arterial pressure compared to Dahl S rats fed a control diet (CD). We previously showed that the magnitude of this effect is similar in males and females. Here we used pharmacological interventions to compare in males and females the contributions of brain prostanoids, the renin-angiotensin system and the sympathetic nervous system to the development of hypertension in this rat model. Dahl S rats were placed on CD or HFD at weaning. All rats received telemetry implants at 15-16 weeks of age to measure arterial pressure, heart rate, and activity. Studies were conducted from 19-23 weeks of age, a time when hypertension is still developing. Drug interventions were separated by at least a week. Mean arterial pressure (MAP) was significantly higher in male HFD (156.0+/- 6.5 mmHg) versus male CD (133.3+/-1.6 mmHg) rats, and in female HFD (140+/-2.6 mmHg) versus female CD (131.4+/-1.2 mmHg) rats during the experimental period. Treatment for one week with the ACE inhibitor enalapril (250 mg/L in the drinking water) lowered MAP significantly more in male HFD (-38.3+/-5.9 mmHg) than in male CD (-23.9+/-1.6 mmHg) rats, but female HFD (-33.2+/-2.2 mmHg) and CD (-28.4+/-1.5 mmHg) rats responded similarly. Treatment for one week with the centrally acting sympatholytic clonidine (2 mg/L in the drinking water) reduced MAP more in females than males, but there were no differences between CD and HFD groups. One week treatment with the prostanglandin D synthase inhibitor AT56 (5.8 nmol/hr sc) caused only a slight fall in MAP (~3 mmHg) that was similar in all groups. Finally, a single injection of the ganglion blocker hexamethonium (30 mg/kg, ip) caused a short-term depressor response that was not significantly different in magnitude among the groups. We conclude that the renin-angiotensin system may have a greater role in adiposity-associated hypertension in Dahl S males versus females, but that sympathetic overactivity or prostaglandin D are not factors in either sex in the age range studied here.

Abstract P162: Adiposity-Induced Hypertension is Associated With Sex-Specific Macrophage Infiltration of Mesenteric Perivascular Adipose Tissue in Dahl S Rats

Perivascular adipose tissue (PVAT) may be a key player in mediating adiposity-associated hypertension because of its proximity to blood vessels. Although increased immune cell occupancy in adipose tissue is proposed to couple adiposity to hypertension, little is known about PVAT’s immune complement. We hypothesized that an immune complement exists in PVAT that would become pro-inflammatory with adiposity-induced hypertension. Male and female Dahl S rats were fed a regular (10% calories from fat) diet (control) or a high fat (60%) diet (HFD) from weaning through 24 weeks of age. HFD rats demonstrated significantly higher systolic blood pressure [mm Hg; control: 127±7 (M), 145±8 (F); HFD: 168±9 (M), 184±11 (F); tail cuff] and visceral adiposity (micro-CT scans). PVATs from the thoracic aorta (APVAT), mesenteric resistance vessels (MRPVAT), non-PVAT retroperitoneal fat (RP fat) and spleen (positive control) were harvested from each animal. T cells (CD4 and CD8), B cells, macrophages, mast cells and neutrophils in the stromal vascular fraction were quantified using 7-color flow cytometry. The type and number of immune cells are presented as a percentage (%) of total live singlet cells. Each immune cell type is reported as % of total immune cells, and CD4, CD8 cells as % of T cells. The table illustrates significant (P<0.05) differences with HFD vs respective controls. HFD-induced hypertension in Dahl S rats leads to greater macrophage infiltration of MRPVAT and RP fat in females vs males. Further studies are needed to gain mechanistic insights into how macrophage subtypes and their associated cytokines in PVAT may alter vascular tone and blood pressure.

Abstract P145: The Bacterial Metabolite Trimethylamine (TMA), but Not Trimethylamine N-Oxide (TMAO), Causes Vascular Contraction

Circulating levels of TMAO are elevated in humans with cardiometabolic diseases. The gut microbiota-initiated TMA/flavin-containing monooxygenase 3 (FMO3)/TMAO pathway has been identified as a potential modulator of host cardiometabolic phenotypes. Like TMA/TMAO, FMO3 expression is positively correlated with body mass index and high-fat diet-induced obesity We hypothesized that TMA/TMAO stimulate vascular contraction which could be modified by perivascular adipose tissue (PVAT) expression of FMO3. Our model was the isolated thoracic aorta with (+) or without (-) PVAT, in presence (+) or in absence (+) of endothelium (E) of male Sprague Dawley rat to perform tissue bath studies to measure isometric tone using a large range of TMA/TMAO concentrations: 1 nM-10 -1 M. Immunohistochemistry (IHC) studies were done to identify the presence of FMO3 in aorta. TMA and TMAO, at any concentration, did not relax half maximally contracted tissues when compared to vehicle control. TMA and TMAO elicited arterial contraction independent of PVAT or E status. Interestingly, contractions stimulated by TMA were significantly higher (% PE max 123.7±15.6%) than by TMAO (% PE max 38.3±15.5%). IHC studies revealed FMO3 in aortic PVAT, but the FMO3 inhibitor methimazole (100 μM) did not affect aortic contraction stimulated by TMA (+PVAT). The L type Ca2+ channel antagonist nifedipine (100 nM), reduced the TMA-induced contraction (% PE max: +PVAT: 73±9%; -PVAT: 63±6.7%), compared to vehicle (+PVAT: 149.8±18%; -PVAT: 111.8±9%). These results support that TMA can induce arterial contraction with higher potency and efficacy compared to TMAO, independent of the conversion to TMAO. The contractile mechanism is ≈ 50% dependent of Ca 2+ influx through L-type VOC. Considering the high concentration needed to achieve the contraction it is unlikely that increasing vascular tone is a mechanism that could contribute to CVD but dependence of contraction on Ca 2+ channel activation suggests specific activity of TMA in the vessel wall that warrants further study.

The chemerin knockout rat reveals chemerin dependence in female, but not male, experimental hypertension

Measures of the adipokine chemerin are elevated in multiple cardiovascular diseases, including hypertension, but little mechanistic work has been done to implicate chemerin as being causative in such diseases. The chemerin knockout (KO) rat was created to test the hypothesis that removal of chemerin would reduce pressure in the normal and hypertensive state. Western analyses confirmed loss of chemerin in the plasma and tissues of the KO vs. wild-type (WT) rats. Chemerin concentration in plasma and tissues was lower in WT females than in WT males, as determined by Western analysis. Conscious male and female KO rats had modest differences in baseline measures vs. the WT that included systolic, diastolic, mean arterial and pulse pressures, and heart rate, all measured telemetrically. The mineralocorticoid deoxycorticosterone acetate (DOCA) and salt water, combined with uninephrectomy as a hypertensive stimulus, elevated mean and systolic blood pressures of the male KO higher than the male WT. By contrast, all pressures in the female KO were lower than their WT throughout DOCA-salt treatment. These results revealed an unexpected sex difference in chemerin expression and the ability of chemerin to modify blood pressure in response to a hypertensive challenge.-Watts, S. W., Darios, E. S., Mullick, A. E., Garver, H., Saunders, T. L., Hughes, E. D., Filipiak, W. E., Zeidler, M. G., McMullen, N., Sinal, C. J., Kumar, R. K., Ferland, D. J., Fink, G. D. The chemerin knockout rat reveals chemerin dependence in female, but not male, experimental hypertension.

Targeted afferent renal denervation reduces arterial pressure but not renal inflammation in established DOCA-salt hypertension in the rat

Recent preclinical studies show renal denervation (RDNx) may be an effective treatment for hypertension; however, the mechanism remains unknown. We have recently reported total RDNx (TRDNx) and afferent-selective RDNx (ARDNx) similarly attenuated the development of deoxycorticosterone acetate (DOCA)-salt hypertension. Whereas TRDNx abolished renal inflammation, ARDNx had a minimal effect despite an identical antihypertensive effect. Although this study established that ARDNx attenuates the development of DOCA-salt hypertension, it is unknown whether this mechanism remains operative once hypertension is established. The current study tested the hypothesis that TRDNx and ARDNx would similarly decrease mean arterial pressure (MAP) in the DOCA-salt hypertensive rat, and only TRDNx would mitigate renal inflammation. After 21 days of DOCA-salt treatment, male Sprague-Dawley rats underwent TRDNx ( n = 16), ARDNx ( n = 16), or Sham ( n = 14) treatment and were monitored for 14 days. Compared with baseline, TRDNx and ARDNx decreased MAP similarly (TRDNx -14 ± 4 and ARDNx -15 ± 6 mmHg). After analysis of diurnal rhythm, rhythm-adjusted mean and amplitude of night/day cycle were also reduced in TRDNx and ARDNx groups compared with Sham. Notably, no change in renal inflammation, injury, or function was detected with either treatment. We conclude from these findings that: 1) RDNx mitigates established DOCA-salt hypertension; 2) the MAP responses to RDNx are primarily mediated by ablation of afferent renal nerves; and 3) renal nerves do not contribute to the maintenance of renal inflammation in DOCA-salt hypertension.

Renal perivascular adipose tissue: Form and function

Renal sympathetic activity affects blood pressure in part by increasing renovascular resistance via release of norepinephrine (NE) from sympathetic nerves onto renal arteries. Here we test the idea that adipose tissue adjacent to renal blood vessels, i.e. renal perivascular adipose tissue (RPVAT), contains a pool of NE which can be released to alter renal vascular function. RPVAT was obtained from around the main renal artery/vein of the male Sprague Dawley rats. Thoracic aortic PVAT and mesenteric PVAT also were studied as brown-like and white fat comparators respectively. RPVAT was identified as a mix of white and brown adipocytes, because of expression of both brown-like (e.g. uncoupling protein 1) and white adipogenic genes. All PVATs contained NE (ng/g tissue, RPVAT:524 ± 68, TAPVAT:740 ± 16, MPVAT:96 ± 24). NE was visualized specifically in RPVAT adipocytes by immunohistochemistry. The presence of RPVAT (+RPVAT) did not alter the response of isolated renal arteries to NE compared to responses of arteries without RPVAT (-RPVAT). By contrast, the maximum contraction to the sympathomimetic tyramine was ~2× greater in the renal artery +PVAT versus -PVAT. Tyramine-induced contraction in +RPVAT renal arteries was reduced by the α₁-adrenoceptor antagonist prazosin and the NE transporter inhibitor nisoxetine. These results suggest that tyramine caused release of NE from RPVAT. Renal denervation significantly (>50%) reduced NE content of RPVAT but did not modify tyramine-induced contraction of +RPVAT renal arteries. Collectively, these data support the existence of a releasable pool of NE in RPVAT that is independent of renal sympathetic innervation and has the potential to change renal arterial function.

Abstract P319: 5-HT7 Receptors Mediate 5-HT-induced Hypotension

Serotonin (5-HT, 5-hydroxytrypamine) lowers blood pressure in the conscious rat when given chronically (25 μg/kg/min; > 24 hours). This same dose of 5-HT nearly normalizes the mean arterial blood pressure of hypertensive rats, including the deoxycorticosterone acetate (DOCA) salt hypertensive rat (baseline =166 + 9 vs 112 + 3 mm Hg). We have found that 5-HT causes venodilation through activation of the 5-HT 7 receptor and presently test the hypothesis that the hypotension stimulated by 5-HT in vivo is 5-HT 7 receptor-dependent. Two approaches were made. First, male Sprague Dawley rats were instrumented with radiotelemeters for measurement of blood pressures, HR and activity. Through a venous line, the 5-HT 7 receptor antagonist SB269970 (3 mg/kg, i.v.) was given hours prior to implantation of all rats with an Alzet pump delivering 5-HT (as above). SB269970 abolished the fall in blood pressure during 24 hours of 5-HT-infusion when compared to vehicle (vehicle = -18.73 + 2.0 vs SB269970 = -.7 + 1.51 mm Hg; N=6). Second, we created a global 5-HT 7 receptor knockout (KO) rat through CRISPR-Cas9 technology using a Sprague Dawley background. Genotyping validated creation of deletion of exon 1-2 and/or indel formation on exon 1 and exon 2 of the 5-HT 7 receptor gene. In female KO (N=4) vs WT (N=4), baseline mean arterial blood pressure in radiotelemeter-implanted rats was significantly elevated (KO=111 + 1 mm Hg; WT=103 + 2 mm Hg; p<0.05). Infusion of the same dose of 5-HT (25 μg/kg/min) which lowered mean pressure in the WT rats (baseline: 103.5 + 1.85 to 89.9 + 3.06 mm Hg 24 hours) did not lower blood pressure in the KO at 24 hours (111.7 + 1.1 to 117.5 + 1.0 mm Hg) nor through 6 more days of infusion. Blood pressure reduction in the WT was accompanied with an elevation in heart rate (410 + 8 to 474 + 5 bpm; p<0.05) that was not observed in the 5-HT 7 receptor KO (387 + 10 to 395 + 4.3 bpm; p>0.05). Thus, pharmacological and molecular work powerfully support the necessity of the 5-HT 7 receptor for 5-HT-induced hypotension. The significance of this study capitalizes on the unique pharmacology of the 5HT 7 receptor and provides potential insight into the development of new treatment for CV diseases.