NT Rats Research Articles

P049 RENOVASCULAR HYPERTENSIVE RATS (2K1C) HAVE REDUCED INTRACRANIAL COMPLIANCE INDUCED BY RAISED VENTRICULAR VOLUME COMPARED TO NORMOTENSIVE RATS

Background and Objective: Intracerebroventricular (ICV) infusions of increased volumes of saline can be used to study intracranial compliance (ICC). Since the two-kidneys,1-clip (2K1C) rat model of renovascular hypertension has an enhanced baseline level of intracranial pressure (ICP), the present study aimed to verify the effect of ICV infusions of 0.15 M NaCl on ICP and ICC in 2K1C rats. Methods: Male Holtzman rats (180-210 g) were randomly separated to be normotensive (NT; sham surgery, n = 5) or with 2K1C (n = 5), done by a partial left renal artery occlusion. Six weeks after, rats were anaesthetized with urethane (1.2 g/kg body weight, i.v.), tracheostomized, placed under artificial ventilation, and had an ICP sensor and a needle inserted into the lateral ventricle for, respectively, ICP recording and ICV 0.15 M infusions (30, 60 and 90 μL, at 100 μL/min). There was a 20-minute interval between each infusion. ICC was calculated by the ratio of volume change to ICP change [ICC = ΔV (μL)/Δ ICP (mmHg)]. Results: Baseline MAP, ICP, and P2/P1 ratio of 2K1C rats (166 ± 6 mmHg; 15.7 ± 1.7 mmHg; 1.6 ± 0.1, respectively) were higher than the ones in NT rats (94 ± 5 mmHg; 10.1 ±1.4 mmHg; 0.7 ± 0.1 respectively; p<0.05 vs 2K-1C). ICV infusions induced increased ICP in 2K1C rats (19 ±0.5; 42 ±1.2 and 55 ±5.5 mmHg, vs NT: 8 ±0.6; 25 ±3.2 and 36 ± 4.9 mmHg, respectively at 30, 60 and 90 μL infusion; p<0.05). In addition, 2K1C rats presented a reduced ICC only at 30 μl infusion (5.6 ±1.4, vs NT: 11.4 ±0.9; p<0.05). Conclusions: These findings suggest that renovascular hypertension impairs ICC to the well-documented increase in ICP. Support: FAPESP, CNPq.

P171 WATER DEPRIVATION REDUCES WATER INTAKE AND INCREASES SUCROSE INTAKE IN SPONTANEOUSLY HYPERTENSIVE RATS: POSSIBLE MECHANISMS

Background and Objective: Water deprivation (WD), a common situation in wild and human lives, can induce an increase in sucrose palatability in SHR. However, it is not known if SHR also has an increase in sucrose intake after WD and if this intake is related to energy intake, as WD reduces food intake, or to the change in sucrose palatability. Methods: Adult (∼12 weeks) male Holtzman (normotensive, NT) or SHR rats (n = 20/strain) were used. In protocol 1, all rats were first subjected to 24-h WD. Food consumption was measured during WD and was used for the non-water deprived (ND)/food restricted (FD) group to equal energy consumption. Three days after the WD, rats were randomly assigned to the 24-hour WD or the ND/FR group. In protocol 2, animals were implanted with an intraoral cannula and were randomly assigned as above. Results: In the WD condition, water intake was greater in NT (15.9 ± 1.1, vs. SHR: 8.6 ± 0.2 mL/120 min, p < 0.05), whereas sucrose intake was greater in SHR (8.8 ± 0.7, vs. NT: 2.1 ± 1 mL/120 min, p< 0.05). In the ND/FR condition, water intake was very low in both strains, however, SHR had a higher sucrose intake compared to NT (11.5 ± 2.0, vs. NT: 3.3 ± 1.8 mL/120 min; p < 0.05). In NT rats, in the WD condition, there was a decrease in sucrose palatability compared to the ND/FR condition, whereas in SHR palatability was similar in the WD or ND/FR condition. SHR have a greater mean arterial pressure than NT (167 ± 3 vs, NT: 105 ± 2 mmHg). Conclusions: Our results suggest that SHR favours energy intake during WD, since during ND/FR they drank equivalent amount of sucrose. This suggestion is supported by the absence of a greater palatability to sucrose in SHR when food is restricted. Support: CAPES PrINT, FAPESP, CNPq

Breathing irregularities in spontaneously hypertensive neonate rats

An excessive sympathetic drive is commonly observed in hypertensive patients and critically contributes to increasing arterial pressure levels. The quality of postnatal life can impact sympathetic control in adulthood. Spontaneously hypertensive (SH) rats, an experimental model of neurogenic hypertension, exhibit breathing irregularities in adult life. In this study, we investigated whether SH rats display breathing abnormalities after birth, which could be a risk factor for developing sympathetic overactivity. Using head-out plethysmography, we found that the neonate (P0-2, male and female) SH rats (n=9) exhibited lower minute ventilation than age-matched normotensive rats (NT, n=14; 816±177 vs 1261±189 ml/min/kg, P<0.05) under resting conditions, mainly due to reductions in respiratory frequency (93±15 vs 132±13 cpm, P<0.05). The reduced baseline ventilation in the SH group was accompanied by a greater prevalence of periods of apneas and respiratory irregularities (P<0.05). Under hypoxia conditions (10% O2, 10 min), SH and NT rats (n=9/each) mounted similar transient increases in minute ventilation during the initial period of exposure due to increments in tidal volume. In contrast, the respiratory frequency in the SH rats decreased progressively below baseline levels during hypoxia exposure (42% reduction, P<0.05), while it remained similar to pre-hypoxia values in the control group. In rhythmic in vitro preparations from neonate SH rats (n=2), we identified ectopic bursts in the hypoglossal activity and prolonged inspiratory-related bursts in the preBötzinger complex compared to preparations from NT rats (n=2). Our findings indicate that breathing irregularities in SH rats are present from birth and could be linked to dysfunctions in the inspiratory rhythm-generating network. Financial support: FAPESP, CNPq. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effects of the Opioid Analgesic, Sufentanil, on Respiration after Extremity Trauma and Severe Conscious Hemorrhage in Rats

Background: Currently, opioid analgesics such as Sufentanil are not recommended for use on the battlefield for Soldiers with severe hemorrhage and respiratory difficulties, although they are still used during such situations (Schauer et al., Prehosp Emerg Care 21: 744, 2017). Moreover, there have been no controlled, preclinical studies conducted using analgesic doses of Sufentanil to support these guidelines. The current study was conducted to evaluate effects of the opioid analgesic Sufentanil on multiple components of respiration after severe hemorrhage in conscious rats in the absence or presence of extremity trauma. We hypothesized that Sufentanil would negatively impact respiration under such experimental conditions.MethodsRats were randomly assigned to receive either 0.9% saline vehicle (VEH), or 1μg/kg Sufentanil (SUF; 0.1μg/100 μl). These treatments were subdivided into rats that were (T) or were not (NT) exposed to trauma (n=9–10 rats/each of the 4 groups). All rats (male; ~ 380grams) were surgically implanted with a carotid catheter. After 24 hours, rats were anesthetized briefly (10 min) to undergo trauma (crushing of the right gastrocnemius and semimembranosus muscles for 30 sec with forceps, T) and fibula fracture. NT rats were anesthetized for 10 min only. Rats were allowed to awaken, and 90 min later underwent a conscious hemorrhage (~55% of blood volume during 25 min) within a whole body plethysmography chamber via the indwelling carotid catheter. At the end of hemorrhage, rats received either VEH or SUFvia the carotid catheter. Respiratory measures were collected and recorded over 1 min intervals and analyzed via Data Sciences International FinePointe software. Primary respiratory measures were respiration rate (RR; breaths/min), tidal volume (TV; ml), and minute volume (MV; ml/min; RR x TV). TV and MV were normalized to the average body weight of all rats used in the study (377 grams). Rats were observed for 1 hr after the start of the hemorrhage. Data were analyzed via multiway analysis of variance (ANOVA) for repeated measures using the Statistical Analysis System.ResultsFor RR, there was no effect of trauma (P = 0.43) so data were combined across T and NT groups for each treatment. For a brief period (2–15 min) after SUF injection, RR was lower (P < 0.04) compared with VEH. For TV and MV, there were interactions between treatment and trauma groups. Hence, compared with VEH‐rats, TV in SUF‐rats was intermittently depressed in T‐rats (P < 0.04) but briefly increased in NT‐rats (P < .03) for up to 15 min post injection. In T‐rats only, SUF transiently (12 min) decreased MV (P<0.05) starting 3 min after injection. All respiratory effects induced by SUF were resolved within 15 min.ConclusionsAt the analgesic dose given – previously shown to ameliorate behavioral indices of pain in rats (Xiang, J Trauma Acute care Surg 85: S49, 2018) – and at the times measured, SUF had primarily transient inhibitory effects on respiration that often depended on the presence of previous extremity trauma.Support or Funding InformationThis study was funded by the US Army Medical and Materiel Command, Clinical and Rehabilitative Medicine Research Program.

Therapeutic mild hypothermia improves early outcomes in rats subjected to severe sepsis

AimsTherapeutic hypothermia has shown beneficial effects in sepsis. This study focused on its mechanism. Main methodsSixteen male Sprague-Dawley rats underwent cecal ligation and perforation and subsequently were treated with either hypothermia (HT; body temperature cooled and maintained at 34 °C by ice pad for 10 h; n = 8) or normothermia (NT; n = 8). Three additional rats underwent sham surgery. The body temperatures of the sham-operated and NT groups were maintained at 38 °C with a thermal pad. After the hypothermia treatment, the HT rats were rewarmed for 2 h. The groups were compared for circulating cytokines (IL-6, IL-10), lactate, high mobility group box-1 protein (HMGB1), and lung and intestinal lesions. Animals were observed for 24 h. Key findingsCompared with the sham-operated group, the 2 sepsis group rats had significantly higher circulating IL-6, HMGB1, and lactate levels, and tissue injury. In the HT rats, the levels of IL-6, HMGB1, and lactate, the lung wet-to-dry ratio, and lung and intestinal damage were significantly lower than that of the NT group. Circulating IL-10 levels increased significantly after 12 h in the sepsis groups compared with sham animals, while that of the NT and HT groups were comparable. The survival rates of the NT and HT rats were also comparable. SignificanceTherapeutic hypothermia in a rat model of sepsis was associated with lower levels of circulating IL-6 and HMGB1, and less capillary leakage and tissue edema. These results suggest that mild hypothermia has potential as a therapy in sepsis.

Treadmill training modifies KIF5B motor protein in the STZ-induced diabetic rat spinal cord and sciatic nerve.

Previous research has demonstrated diabetic-induced axonal transport deficits. However, the mechanism of axonal transport impairment induced by diabetes is poorly understood. Kinesin motor proteins have been shown to transport various cargos along highly polarized neurons. In the present study, we investigated the effect of regular treadmill exercise on KIF5B and Sunday Driver (SYD) mRNA levels in sensory and motor parts of spinal cord and KIF5B content in sciatic nerves of streptozotocin (STZ)-induced diabetic rats. Forty male Wistar rats were divided into four groups: (1) diabetic trained (DT: n = 10); (2) Non-trained diabetic (NTD: n = 10); (3) normal control (NC: n = 10), and (4) normal trained (NT: n = 10). Two weeks after STZ injection (45 mg/kg, i.p.), the rats were subjected to treadmill exercise for 5 days a week over 6 weeks. We determined mRNA levels and protein content by Real time- PCR and ELISA. Exercise training decreased blood glucose levels in the DT rats. Diabetes increased the KIF5B and SYD mRNA in both sensory and motor parts and KIF5B content in sciatic nerves in the NTD. Moreover, exercise training modulated the KIF5B and SYD mRNA and KIF5B content to normal levels in the DT. Exercise training in NT rats increased KIF5B and SYD mRNA in sensory and motor parts and KIF5B content in sciatic nerves. Our results suggest that diabetes seems to change spinal cord KIF5B and SYD mRNA and sciatic nerves KIF5B content and exercise training modifies it, which may be attributable to the training-induced decreased hyperglycemia.

Modulation expression of tumor necrosis factor α in the radiation-induced lung injury by glycyrrhizic acid.

To evaluate the ability of glycyrrhizic acid (GLA) to reduce the tumor necrosis factor α (TNF-α), release on messenger ribonucleic acid (mRNA) and protein production in the lungs using GLA in response to irradiation were studied. The animals were divided into four groups: No treatment (NT group), GLA treatment only (GLA group), irradiation only (XRT group), and GLA treatment plus irradiation (GLA/XRT group). Rats were killed at different time points. Real-time reverse transcriptase polymerase chain reaction (RT-PCR) was used to evaluate the mRNA expression of TNF-α in the lungs (compared with non-irradiated lungs). An enzyme-linked immunosorbant assay (ELISA) assay was used to measure the TNF-α protein level. The TNF-α mRNA expression in the lungs of the XRT rats was clearly higher at all-time points compared to the NT rats. The TNF-α mRNA expression in the lungs of the GLA/XRT rats was lower at all-time points compared to the XRT rats. Release of the TNF-α on protein level in the lungs of the XRT rats increased at all-time points compared to the NT rats. In contrast to the XRT rats, the lungs of the GLA/XRT rats revealed a reduction on TNF-α protein level at 6 h after irradiation. This study has clearly showed the immediate down-regulation of the TNF-α mRNA and protein production in the lungs using GLA in response to irradiation.

Renal angiotensin II type 1 receptor expression and associated hypertension in rats with minimal SHR nuclear genome

Angiotensin II (AII) has been linked as a causal factor in several experimental models of hypertension (HT) including Okamoto spontaneously hypertensive rats (SHR). The transmission and expression of AII type 1 receptors (AT1r) in SHR and the development of genetic HT remain unknown. It is hypothesized that tissue-specific expression of renin–angiotensin system (RAS) genes derived from SHR are linked to HT in offspring of SHR crossed with Brown Norway (BN) rats. Hypertensive female progeny of BN/SHR matings was backcrossed with founder BN males to generate the F1 and five backcross generations (BN/SHR-mtSHR). Progeny were phenotyped according to normotension (NT: systolic arterial pressure [SAP] ≤ 124 mmHg), borderline hypertension (BHT: 124 ≤ SAP < 145 mmHg), and HT (SAP ≥ 145 mmHg). Six generations produced more HT (n = 88; 46%) than NT (n = 21; 11%) offspring. The mRNA expression of the RAS was evaluated in NT (n = 20) and HT (n = 20) BN/SHR-mtSHR across several generations. Quantitative real-time polymerase chain reaction analysis of kidney tissue showed increased expression of AII, type 1 receptors (Agtr1a) (∼2.5-fold) in HT versus NT rats, while other members of both the renal and systemic RAS pathway were not different. Western blot analysis from kidney homogenates showed that AT1r protein levels were higher (P < 0.05) in backcross generation 3 (BC3) HT versus NT rats. Evaluation of SAP as a function of AT1r expression by linear regression indicated positive correlation (P < 0.05) in kidney of BC3 BN/SHR-mtSHR rats. Thus, elevated kidney AT1r expression may be involved in the development of HT in BN/SHR-mtSHR rats.

Cytokines in the Hypothalamic Paraventricular Nucleus (PVN) are Not Required for Maintenance of Angiotensin II‐Salt Hypertension

Rats consuming high salt and treated with systemic angiotensin II (Ang II) develop neurogenic hypertension mediated by elevation of sympathetic nerve activity (SNA) derived from a forebrain‐hypothalamic circuit. Cytokines are proposed to increase SNA and arterial blood pressure (ABP) and we therefore sought to determine their role within PVN in maintenance of AngII+salt hypertension. We first focused on tumor necrosis factor α (TNFα), which was microinjected into the PVN (0.3 pmol in 50 nl/side) of anesthetized normotensive (NT, 0.4% NaCl diet, n=10) rats. Although this increased lumbar SNA (18±7%), splanchnic SNA (49±9%) and mean ABP (4±2 mmHg) compared to vehicle (P&lt;0.05), interfering with TNFα binding by PVN injection of etanercept (20 μg in 100 nl/side) did not affect recorded variables either in NT rats or in Ang II (150 ng/kg/min, sc) + salt (2% NaCl diet) hypertensive (HT, n=12) rats. Given this apparent lack of TNFα “tone” in PVN, we next non‐selectively inhibited local cytokine release by microinjection of minocycline (1 μg in 100 nl/side). This too failed to alter lumbar SNA (HT: 13±9% vs NT: 0±3%), splanchnic SNA (HT: 12±4% vs NT: 6±2%) or mean ABP (HT: 3±2 mmHg vs NT: −1±1 mmHg) in NT or HT rats. These findings indicate that whereas TNFα can act in PVN to increase SNA; maintenance of Ang II‐salt hypertension does not depend on either PVN actions of TNFα or microglia derived cytokines. Support: HL102310 &amp; HL 088052 (GMT)

Tissue Angiotensin II Type 1 Receptor Expression in Development of Hypertension in SHR/Brown Norway Backcross Rats

Angiotensin II (AII) has been linked to hypertension in Okamoto Spontaneously Hypertensive Rats (SHR). The transmission and tissue specific progeny expression of AII Type 1 receptors (AT1r) in SHR and the development of genetic hypertension remains unknown. It is hypothesized that tissue AT1r expression of genes derived from SHR are linked to elevated blood pressure in offspring of SHR crossed with normotensive Brown Norway rats. A rat colony was developed by breeding a female Okamoto‐Aoki SHR (MAP=160mmHg) with a BN male (MAP=91mmHg). Hypertensive F1 female progeny were backcrossed with the founder BN to generate 5 subsequent backcross generations. F1 and backcross generation 3 (BC3) tissue AT1r protein expression were evaluated. Progeny were grouped as normotensive (NT&lt;105mmHg; F1 n=0, BC4 n=8), borderline hypertension (BHT 105 ≤ MAP &lt; 122 mmHg; F1 n=18, BC4 n=21) and hypertensive (HT MAP ≥ 122 mmHg; F1 n=15, BC4 n=16). AT1r protein expression between HT and BHT F1 progeny were similar in kidney, hypothalamus or forebrain. HT BC3 rats had greater kidney and hypothalamic AT1r expression but not FB compared to NT rats. There was a positive correlation between MAP and AT1r expression in kidney and hypothalami. These results demonstrate that tissue specific elevated AT1r expression may contribute to spontaneous hypertension in SHR/BN rats with minimal SHR genome inheritance.

Role of alpha adrenoceptors and nitric oxide on cardiovascular responses in acute and chronic hypertension

The contribution of α-adrenoceptors and nitric oxide (NO) on the alterations of sympathetically mediated cardiovascular responses after acute (AcH) and chronic (ChH) hypertension was evaluated in pithed aortic coarcted hypertensive rats. Pressor and tachycardia response produced by electrical stimulation of preganglionic sympathetic fibers or exogenous noradrenaline (NA) were recorded in the absence and presence of prazosin (α(1)-antagonist), rauwolscine (α(2)-antagonist), or N (G)-nitro-L-arginine methyl ester (L-NAME; an inhibitor of NO synthase). Compared with age-matched sham-operated rats (Nt), the pressor response produced by electrical stimulation or NA was smaller in AcH rats and larger in ChH rats. Prazosin caused a decrease of pressor response elicited by electrical stimulation or NA in all groups. However, this effect was higher in ChH. Rauwolscine produced a similar increase of sympathetically mediated pressor response in Nt and AcH rats. Nevertheless, this antagonist did not affect the sympathetically mediated pressor response in ChH rats. In addition, rauwolscine did not affect the NA-induced pressor response in all groups. The pressor response elicited by L-NAME was larger in all groups compared without L-NAME and in presence of L-arginine. Moreover, L-NAME in the presence of NA increased sympathetically mediated pressor response is in all groups, compared without it or in the presence of L-arginine. Compared with Nt, basally produced NO in aortic rings was increased in AcH but decreased in ChH. Collectively, our data suggest that decreased cardiovascular reactivity in AcH is due to an increase in basally produced NO. In ChH, enhanced cardiovascular response appears to be associated with a decrease in produced NO and an increase in released NA from sympathetic nerves.

Indomethacin enhances reactivity to vasopressin in normotensive and hypertensive rats, while PGE2 receptor blockade only attenuates reactivity in normotensive rats.

Previously, we reported that in female (F) rats 17‐β‐estradiol and aortic coarctation‐induced hypertension (ACIH) increase release of thromboxane (TXA2) and prostacyclin from mesenteric arterioles (MA), and that constrictor responses of aorta to vasopressin (VP) are reduced ~40% by TP receptor antagonist SQ 29,548 (SQ). Thus, the roles of TXA2 and PGE2 in constrictor responses to VP were studied in MA. F Sprague‐Dawley rats (14–16 wks age) underwent ACIH (hypertensive; HT) or sham (normotensive; NT). Rats were sacrificed 12–14 days post‐ACIH and reactivity to VP was measured in MA (150–200 μm dia.) using isometric myography. Data are means ± S.E. (n = 4–5 rats/group). Maximal contractile responses of MA to VP did not differ between NT (9.97 ± 0.75 mN/mm) and HT (11.77 ± 1.40). SQ (40 μM) did not alter responses in NT (9.16 ± 1.53) or HT (12.69 ± 1.77). In separate rats, maximal responses to VP did not differ between NT and HT. AH6809, a PGE2 receptor blocker (EP1, 2, 3) reduced maximal responses of MA from NT (8.95 ± 0.36 vs. 10.24 ± 0.63) but not HT (9.73 ± 0.81 vs. 9.36 ± 0.61). Indomethacin (non‐specific COX inhibitor; 10 μM) increased contractions to VP in NT and HT (11.74 ± 0.84 and 12.75 ± 0.79, respectively). While TXA2 potentiates constrictor responses of aorta to VP, the role of TXA2 in reactivity of MA to VP is less certain. However, it appears that PGE2 may also play a role in modulating MA responses to VP in NT rats. (NIH:HL‐080402)

Effects of high-altitude exercise training on contractile function of rat skinned cardiomyocyte

Previous studies have questioned whether there is an improved cardiac function after high-altitude training. Accordingly, the present study was designed specifically to test whether this apparent blunted response of the whole heart to training can be accounted for by altered mechanical properties at the cellular level. Adult rats were trained for 5 weeks under normoxic (N, NT for sedentary and trained animals, respectively) or hypobaric hypoxic (H, HT) conditions. Cardiac morphology and function were evaluated by echocardiography. Calcium Ca2+ sensitivity of the contractile machinery was estimated in skinned cardiomyocytes isolated from the left ventricular (LV) sub-epicardium (Epi) and sub-endocardium (Endo) at short and long sarcomere lengths (SL). Cardiac remodelling was harmonious (increase in wall thickness with chamber dilatation) in NT rats and disharmonious (hypertrophy without chamber dilatation) in HT rats. Contrary to NT rats, HT rats did not exhibit enhancement in global cardiac performance evaluated by echocardiography. Stretch- dependent Ca2+ sensitization of the myofilaments (cellular index of the Frank-Starling mechanism) increased from Epi to Endo in N rats. Training in normoxic conditions further increased this stretch-dependent Ca2+ sensitization. Chronic hypoxia did not significantly affect myofibrilar Ca2+ sensitivity. In contrast, high-altitude training decreased Ca2+ sensitivity of the myofilaments at both SL, mostly in Endo cells, resulting in a loss of the transmural gradient of the stretch-dependent Ca2+ sensitization. Expression of myosin heavy chain isoforms was affected both by training and chronic hypoxia but did not correlate with mechanical data. Training at sea level increased the transmural gradient of stretch-dependent Ca2+ sensitization of the myofilaments, accounting for an improved Frank-Starling mechanism. High-altitude training depressed myofilament response to Ca2+, especially in the Endo layer. This led to a reduction in this transmural gradient that may contribute to the lack of improvement in LV function via the Frank-Starling mechanism.

Effects of ingested fruiting bodies, submerged culture biomass, and acidic polysaccharide glucuronoxylomannan of Tremella mesenterica Retz.:Fr. on glycemic responses in normal and diabetic rats

Mushroom polysaccharides have been shown to regulate glucose metabolism. Using male Wistar rats injected with saline (normal rats), streptozotocin (STZ − NT rats), or streptozotocin plus nicotinamide (STZ + NT rats), we investigated the hypoglycemic activity of orally ingested fruiting bodies (FB), submerged culture biomass (CM), or the acidic polysaccharide glucuronoxylomannan (GXM) of Tremella mesenterica, an edible jelly mushroom. Our results demonstrated that FB ingestion significantly attenuated the elevated blood glucose levels in an oral glucose tolerance test (OGTT) in STZ − NT rats. However, in STZ + NT rats, FB, CM, and GXM ingestion significantly attenuated the increases in food and water intake, 2-h postprandial blood glucose concentrations, and blood glucose levels in OGTT. Moreover, FB and GXM ingestion significantly decreased serum concentration of fructosamine in STZ + NT rats. Our results indicated that T. mesenterica might be developed as a potential oral hypoglycemic agent or functional food for diabetic patients and for persons with high risk for diabetes mellitus.

Chronic hypoxia exposure depresses aortic endothelium-dependent vasorelaxation in both sedentary and trained rats: involvement of l-arginine

This study was designed to test the hypothesis that the previously demonstrated training-induced improvement of the endothelium vasodilator function would be blunted under conditions of chronic hypoxia exposure as a result of deleterious effects of hypoxia per se on the nitric oxide pathway. Sea-level-native rats were randomly assigned to N (living in normoxia), NT (living and training 5 days/wk for 5 wk in normoxia), CH (living in hypoxia, 2,800 m), and CHT (living and training 5 days/wk for 5 wk in hypoxia, 2,800 m) groups. Concentration-response curves to acetylcholine (ACh; 10(-9) to 10(-4) M) with or without L-arginine (10(-3) to 10(-5) M) and/or nitro-L-arginine methyl ester (10(-5) M) were assessed on aortic isolated rings. The main finding was that chronic hypoxia severely depressed maximal ACh-responses of aortic rings in both sedentary and trained groups. However, chronic hypoxia did not interfere with training-induced increases in maximal ACh responses, considering that maximal ACh vasorelaxation was improved in CHT rats to the same extent as in NT rats when both groups were directly compared with their sedentary counterparts. It should be pointed out that the vasodilator response to ACh was restored in CH and CHT rats to the level obtained in N and NT rats, respectively, by an in vitro L-arginine addition. A hypoxia-induced decrease in L-arginine bioavailability resulting from acclimatization at altitude may be involved in this limitation of the NO pathway in CH and CHT rats. These results are of importance for aerobic performance as the specific vascular adaptations to training at altitude could contribute to limit peripheral vasodilatation and subsequently blood flow during exercise.

Responses to GABA(A) receptor activation are altered in NTS neurons isolated from renal-wrap hypertensive rats.

The inhibitory amino acid GABA is a potent modulator of the spontaneous discharge and the responses to afferent inputs of neurons in the nucleus of the solitary tract (NTS). To determine if responses to activation of GABA(A) receptors are altered in hypertension, GABA(A) receptor-evoked whole cell currents were measured in enzymatically dispersed NTS neurons from 33 normotensive (NT, 109+/-4 mm Hg, n=7) and 24 hypertensive (HT, 167+/-5 mm Hg, n=24) rats. GABA(A) receptor-evoked currents reversed at the calculated equilibrium potential for chloride and were blocked by bicuculline (n=6). Membrane capacitance was the same in neurons from NT (7.5+/-0.6 pF, n=62) and HT (6.8+/-0.6 pF, n=51) rats. The EC50 for peak GABA-evoked currents cells was significantly greater in neurons from HT (21.0+/-2.6 micromol/L, n=16) compared with NT rats (13.0+/-1.8 micromol/L, n=14, P=0.01). The EC50 of neurons exhibiting DiA labeling of presumptive aortic nerve terminals was no different than that observed in the nonlabeled cells (19.0+/-4.9 micromol/L, n=4). The time constant for desensitization of GABA(A)-evoked currents was the same in neurons from HT (4.5+/-0.3 seconds, n=17) and NT rats (3.8+/-0.3 seconds, n=17, P>0.05). Repetitive pulse application of GABA revealed a more rapid decline in the evoked current in neurons from HT compared with NT rats. The amplitude of the 5th pulse of GABA (5-second duration, 2-second interval) was 21+/-2% the amplitude of the 1st pulse in NT rats (n=10) and 14+/-2% in HT rats (n=11, P<0.05). These alterations in GABAA-receptor evoked currents could render the neurons less sensitive to GABA(A) receptor inhibition and influence afferent integration by NTS neurons in HT.

Interaction of exercise and diet on GLUT-4 protein and gene expression in Type I and Type II rat skeletal muscle.

We determined the interaction of exercise and diet on glucose transporter (GLUT-4) protein and mRNA expression in type I (soleus) and type II [extensor digitorum longus (EDL)] skeletal muscle. Forty-eight Sprague Dawley rats were randomly assigned to one of two dietary conditions: high-fat (FAT, n=24) or high-carbohydrate (CHO, n=24). Animals in each dietary condition were allocated to one of two groups: control (NT, n=8) or a group that performed 8 weeks of treadmill running (4 sessions week-1 of 1000 m @ 28 m min-1, RUN, n=16). Eight trained rats were killed after their final exercise bout for determination of GLUT-4 protein and mRNA expression: the remainder were killed 48 h after their last session for measurement of muscle glycogen and triacylglycerol concentration. GLUT-4 protein expression in NT rats was similar in both muscles after 8 weeks of either diet. However, there was a main effect of training such that GLUT-4 protein was increased in the soleus of rats fed with either diet (P < 0.05) and in the EDL in animals fed with CHO (P < 0.05). There was a significant diet-training interaction on GLUT-4 mRNA, such that expression was increased in both the soleus (100% upward arrowP < 0.05) and EDL (142% upward arrowP < 0.01) in CHO-fed animals. Trained rats fed with FAT decreased mRNA expression in the EDL ( downward arrow 45%, P < 0.05) but not the soleus ( downward arrow 14%, NS). We conclude that exercise training in CHO-fed rats increased both GLUT-4 protein and mRNA expression in type I and type II skeletal muscle. Despite lower GLUT-4 mRNA in muscles from fat-fed animals, exercise-induced increases in GLUT-4 protein were largely preserved, suggesting that control of GLUT-4 protein and gene expression are modified independently by exercise and diet.

Disodium chlodronate prevents bone resorption in experimental periodontitis in rats.

Periodontitis is a chronic disease characterized by alveolar bone loss and inflammatory changes. We studied the effect of disodium chlodronate (CD), a bisphosphonate used in metastatic and metabolic bone disease as a bone resorbing drug, in an experimental periodontitis model (EPD) focusing on anti-resorptive and anti-inflammatory parameters. A nylon thread ligature was placed around the left maxillary molars of 72 male Wistar rats who were sacrificed after 7 or 11 days. Groups were treated daily with CD (1, 5, or 25 mg/kg/sc) starting at day 0 until day 7 (prophylactic CD) or from day 5 until day 11 (curative CD) after periodontitis induction. Non-treated group (NT) consisted of rats subjected to periodontitis that received no pharmacological treatment. Alveolar bone loss (ABL) was measured as the distance between the cuspid tips and the alveolar bone. The right jaw was used as control. The hemiarcades were processed for histopathologic analysis. In NT group there was significant ABL, severe mononuclear cells influx, and increase in osteoclast numbers. Prophylactic CD treatment decreased the ABL 25.8%, 61.6%, and 75.5% as compared to NT for the 1, 5, and 25 mg/kg CD doses, respectively. Curative CD treatment decreased the ABL 20%, 62%, and 69% as compared to NT for the 1, 5 and 25 mg/kg CD doses, respectively. Both prophylactic and curative CD decreased histological changes, as compared to NT rats (P <0.01). CD has both bone sparing and anti-inflammatory activity in EPD in rats when administered as a pretreatment or in an ongoing process. The possibility of using CD as an alternative treatment in human periodontitis should be considered.

Microvascular flow and tissue PO(2) in skeletal muscle of chronic reduced renal mass hypertensive rats.

This study determined whether arteriolar blood flow, capillary red blood cell (RBC) velocity, capillary hematocrit (Hct(cap)), and tissue PO(2) are altered in cremaster muscles of rats with chronic reduced renal mass hypertension (RRM-HT) relative to normotensive rats on high- or low-salt (NT-HS vs. NT-LS) diet. The blood flow in first- through third-order arterioles was not different between NT and HT rats, either at rest or during maximal relaxation of the vessels with 10(-4) M adenosine. Capillary RBC velocity was similar between the groups at rest but was elevated in RRM-HT and NT-HS rats during adenosine superfusion. Hct(cap) was reduced at rest in RRM-HT and NT-HS rats compared with NT-LS and was reduced in RRM-HT rats during adenosine-induced dilation. Tissue PO(2) was reduced in RRM-HT and NT-HS rats compared with NT-LS rats during control conditions and was lower in RRM-HT than in NT-LS rats during adenosine-induced dilation. These results indicate that both RRM-HT and chronic exposure of normotensive rats to a high-salt diet lead to reduced tissue oxygenation, despite the maintenance of normal arteriolar blood flow.

Hypertension in transgenic (mREN2)27 rats is not associated with the presence of B1 receptors.

B1 receptors are inducible receptors expressed only in stressful conditions. The aim of this study was to determine if, in (mREN2)27 transgenic rats, hypertension is associated with the presence of B1 receptors in the cardiovascular system and if a heat stress inducible effect is preserved during hypertension. Age-matched (16 weeks old) heterozygous hypertensive transgenic (mREN2)27 rats (HT rats) and the normotensive control animals (homozygous Sprague-Dawley rats, NT rats) were used. The study was conducted in two parts: in the first part the responsiveness of B1 receptors was studied in rats submitted to heat stress (42 degrees C rectal temperature, 20 min) or sham anaesthesia 24 h before, by recording changes in isometric tension in aortic rings in response to [des-Arg9]-bradykinin, a B1 receptor agonist. In the second part, we studied whether B1 receptor mRNA was present in aorta, heart and kidneys, using a semi-quantitative RT-PCR technique. [des-Arg9]-Bradykinin induced a concentration-dependent relaxation of aortic rings only from animals submitted to prior heat stress. This response was significantly higher in aortic rings from heat stressed HT rats than from heat stressed NT ones. B1 receptor mRNA was undetectable in organs from rats not submitted to heat stress but they were present 5 h after heat stress in aorta, heart and kidneys from both NT and HT rats. In conclusion, arterial hypertension observed in (mREN2)27 rats is not associated with the presence of B1 receptors. However, after heat stress, we observed an increase in responsiveness from HT rat aortas compared to NT ones.