Changes in hemodynamic and neurohumoral control cause cardiac damage in one-kidney, one-clip hypertensive mice

Sympathovagal balance and baroreflex control of heart rate (HR) were evaluated during the development (1 and 4 wk) of one-kidney, one-clip (1K1C) hypertension in conscious mice. The development of cardiac hypertrophy and fibrosis was also examined. Overall variability of systolic arterial pressure (AP) and HR in the time domain and baroreflex sensitivity were calculated from basal recordings. Methyl atropine and propranolol allowed the evaluation of the sympathovagal balance to the heart and the intrinsic HR. Staining of renal ANG II in the kidney and plasma renin activity (PRA) were also evaluated. One and four weeks after clipping, the mice were hypertensive and tachycardic, and they exhibited elevated sympathetic and reduced vagal tone. The intrinsic HR was elevated only 1 wk after clipping. Systolic AP variability was elevated, while HR variability and baroreflex sensitivity were reduced 1 and 4 wk after clipping. Renal ANG II staining and PRA were elevated only 1 wk after clipping. Concentric cardiac hypertrophy was observed at 1 and 4 wk, while cardiac fibrosis was observed only at 4 wk after clipping. In conclusion, these data further support previous findings in the literature and provide new features of neurohumoral changes during the development of 1K1C hypertension in mice. In addition, the 1K1C hypertensive model in mice can be an important tool for studies evaluating the role of specific genes relating to dependent and nondependent ANG II hypertension in transgenic mice.     

Aortic depressor nerve unmyelinated fibers in spontaneously hypertensive rats

The objective of the present study was to compare the morphology of the unmyelinated fibers in the aortic depressor nerves (ADN) of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). In anesthetized rats, the ADN was identified by its spontaneous activity synchronous with the arterial pulses. Thin sections of the proximal and distal segments of the ADN were analyzed by electron microscopy, and a morphometric study of the unmyelinated fibers and Schwann cells was performed. The proximal segments of WKY and SHR ADN contain an average of 335 +/- 68 and 130 +/- 14 unmyelinated fibers, respectively (P < 0.05), and the distal segments contain an average of 337 +/- 46 and 242 +/- 77 unmyelinated fibers, respectively (P < 0.05). The distribution of the diameters of unmyelinated fibers was unimodal for both strains, with the histogram from the SHR significantly shifted to the left. Because the unmyelinated fibers play a role in the tonic inhibition of the medullary vasomotor centers, especially in the presence of hypertension, the morphological differences observed in the ADN from SHR may account, at least in part, for the blunted baroreflex of SHR.     

Studies on the partial characterization of extracted glycosaminoglycans from fish waste and its potentiality in modulating obesity through in-vitro and in-vivo

Glycoconjugate Journal - Glycosaminoglycans (GAGs) are bioactive polysaccharides or glycoconjugates found in the fish waste having significant health impacts. In the present study it has been...     

From glacial refugia to hydrological microrefugia: Factors and processes driving the persistence of the climate relict tree Zelkova sicula

With only two tiny populations, the climate relict Zelkova sicula (Sicily, Italy) is one of the rarest trees in the world. It also represents the most marginal member of genus Zelkova that was widespread in the broadleaved forests thriving in warm–temperate climates throughout Eurasia until the Last Glacial Age. Occurring at the westernmost range of the genus under typical Mediterranean climate, the micro‐topographic settings have always appeared crucial for the survival of this relict. However, the factors and processes actually involved in its persistence in the current refugia, as well as the response of similar relict trees in arid environments, are poorly understood worldwide. In the aim to elucidate these aspects, in the two sites hosting Z. sicula analyses of topographical attributes were combined with investigations on soil moisture dynamics. Additionally, plants’ growth and spatial distribution patterns were analyzed to detect fine‐scale differences between populations and assess the possible ecological amplitude of the species. Results revealed that convergent topographies are basic determinants of microrefugia in arid environments. Within the investigated sites, underground moisture never decreases below 25%, buffering seasonal rainfall fluctuations. Therefore, hydrological microrefugia play a key role in decoupling from regional climate, supporting the target species in coping with an unsuitable climatic envelope. Additionally, the inter‐population variability of biometric attributes showed that individual growth is site‐dependent and the species retains a relative ecological plasticity, whereas the strongly clumped spatial patterns confirmed the common clonal growth. On one hand, deeply incised landforms have acted as effective hydrologic microrefugia, on the other clonality coupled with triploidy supposedly improved the resistance of Z. sicula to harsh environments, though entailing inability to reproduce sexually. Most likely, sterility and environmental/physical barriers that have existed for millennia have prevented this relict from leaving the last suitable microrefugia, resulting in the two current rear edge populations.     

International student exchange and the medical curriculum: evaluation of a medical sciences translational physiology course in Brazil

The objective of the present study was to conduct a short-term international course on translational physiology for medical students from Wright State University and the University of Iowa. The goals were to 1) provide students with an exposure to the academic, cultural, and medical environments in Brazil; 2) promote awareness of the global medical community; and 3) provide an academic course focused on translational physiology. An evaluation of the students was conducted to determine whether such a short-term course might be useful in the medical curriculum. The 2-wk course was held in the summer of 2005 at the University of S?o Paulo School of Medicine in Ribeir?o Preto, Brazil, for 23 American students. The program included presentations of basic and clinical topics, meetings with medical students, and clinical presentations. The program finished with student attendance at a scientific meeting sponsored by the Brazilian Society of Hypertension. Student surveys evaluated issues related to perceived treatment, Brazilian medical school environment, culture and personal attributes, and career aspirations. The international Medical Sciences Translational Physiology course for medical students provided a brief, but intense, experience. It gave students a picture of the medical environment in Brazil and an appreciation for the differences and similarities in cultures. Most students reported that it was a positive experience that would be beneficial to their careers. In conclusion, a short-term international course provides an efficient means for medical students to experience aspects of global medical science.     

A Novel Central Pathway Links Arterial Baroreceptors and Pontine Parasympathetic Neurons in Cerebrovascular Control

1. We tested the hypothesis that arterial baroreceptor reflexes modulate cerebrovascular tone through a pathway that connects the cardiovascular nucleus tractus solitarii with parasympathetic preganglionic neurons in the pons.2. Anesthetized rats were used in all studies. Laser flowmetry was used to measure cerebral blood flow. We assessed cerebrovascular responses to increases in arterial blood pressure in animals with lesions of baroreceptor nerves, the nucleus tractus solitarii itself, the pontine preganglionic parasympathetic neurons, or the parasympathetic ganglionic nerves to the cerebral vessels. Similar assessments were made in animals after blockade of synthesis of nitric oxide, which is released by the parasympathetic nerves from the pterygopalatine ganglia. Finally the effects on cerebral blood flow of glutamate stimulation of pontine preganglionic parasympathetic neurons were evaluated.3. We found that lesions at any one of the sites in the putative pathway or interruption of nitric oxide synthesis led to prolongation of autoregulation as mean arterial pressure was increased to levels as high as 200 mmHg. Conversely, stimulation of pontine parasympathetic preganglionic neurons led to cerebral vasodilatation. The second series of studies utilized classic anatomical tracing methods to determine at the light and electron microscopic level whether neurons in the cardiovascular nucleus tractus solitarii, the site of termination of baroreceptor afferents, projected to the pontine preganglionic neurons. Fibers were traced with anterograde tracer from the nucleus tractus solitarii to the pons and with retrograde tracer from the pons to the nucleus tractus solitarii. Using double labeling techniques we further studied synapses made between labeled projections from the nucleus tractus solitarii and preganglionic neurons that were themselves labeled with retrograde tracer placed into the pterygopalatine ganglion.4. These anatomical studies showed that the nucleus tractus solitarii directly projects to pontine preganglionic neurons and makes asymmetric, seemingly excitatory, synapses with those neurons. These studies provide strong evidence that arterial baroreceptors may modulate cerebral blood flow through direct connections with pontine parasympathetic neurons. Further study is needed to clarify the role this pathway plays in integrative physiology.     

Yield and quality of forage maize (<i>Zea mays</i> L.) with different levels of subsurface drip irrigation and plant density

The scarcity of water in arid and semiarid regions of the world is a problem that every day increases by climate change. The subsurface drip irrigation (SDI) and changes in population density of plants are alternatives that can be used to make a sustainable use of water. Therefore, the objectives of this study were to determine the combination that allows for an increased corn performance and efficient use of water without losing the quality of forage. Three different irrigation levels were applied through a system of a SDI at three different densities of forage maize plants in an arid region. The results demonstrated that by applying different levels of water, either enough or lack of soil moisture is created, which is directly reflected in crop yield, and its determining variables such as green forage and dry matter yield, and nutritional quality. The irrigation level to a 100% of potential evapotranspiration (PET), at a density of 80000 plants/ha, increased yield of green forage to 57664 kg/ha; crude protein was 8.59%, while the rest of the quality parameters decreased. This study allowed to conclude that the irrigation level was the major factor in the response of the crop.     

Cardiovascular autonomic control in mice lacking angiotensin AT1a receptors

Studies examined the role of angiotensin (ANG) AT1a receptors in cardiovascular autonomic control by measuring arterial pressure (AP) and heart rate (HR) variability and the effect of autonomic blockade in mice lacking AT1a receptors (AT1a -/-). Using radiotelemetry in conscious AT1a +/+ and AT1a -/- mice, we determined 1) AP and pulse interval (PI) variability in time and frequency (spectral analysis) domains, 2) AP response to alpha(1)-adrenergic and ganglionic blockade, and 3) intrinsic HR after ganglionic blockade. Pulsatile AP was recorded (5 kHz) for measurement of AP and PI and respective variability. Steady-state AP responses to prazosin (1 microg/g ip) and hexamethonium (30 microg/g ip) were also measured. AP was lower in AT1a -/- vs. AT1a +/+, whereas HR was not changed. Prazosin and hexamethonium produced greater decreases in mean AP in AT1a -/- than in AT1a +/+. The blood pressure difference was marked after ganglionic blockade (change in mean AP of -44 +/- 10 vs. -18 +/- 2 mmHg, AT1a -/- vs. AT1a +/+ mice). Intrinsic HR was also lower in AT1a -/- mice (431 +/- 32 vs. 524 +/- 22 beats/min, AT1a -/- vs. AT1a +/+). Beat-by-beat series of systolic AP and PI were submitted to autoregressive spectral estimation with variability quantified in low-frequency (LF: 0.1-1 Hz) and high-frequency (HF: 1-5 Hz) ranges. AT1a -/- mice showed a reduction in systolic AP LF variability (4.3 +/- 0.8 vs. 9.8 +/- 1.3 mmHg(2)), with no change in HF (2.7 +/- 0.3 vs. 3.3 +/- 0.6 mmHg(2)). There was a reduction in PI variability of AT1a -/- in both LF (18.7 +/- 3.7 vs. 32.1 +/- 4.2 ms(2)) and HF (17.7 +/- 1.9 vs. 40.3 +/- 7.3 ms(2)) ranges. The association of lower AP and PI variability in AT1a -/- mice with enhanced AP response to alpha(1)-adrenergic and ganglionic blockade suggests that removal of the ANG AT1a receptor produces autonomic imbalance. This is seen as enhanced sympathetic drive to compensate for the lack of ANG signaling.     

Hemodynamic responses to aortic depressor nerve stimulation in conscious L-NAME-induced hypertensive rats

The present study investigated whether baroreflex control of autonomic function is impaired when there is a deficiency in NO production and the role of adrenergic and cholinergic mechanisms in mediating reflex responses. Electrical stimulation of the aortic depressor nerve in conscious normotensive and nitro-l-arginine methyl ester (L-NAME)-induced hypertensive rats was applied before and after administration of methylatropine, atenolol, and prazosin alone or in combination. The hypotensive response to progressive electrical stimulation (5 to 90 Hz) was greater in hypertensive (-27 ± 2 to -64 ± 3 mmHg) than in normotensive rats (-17 ± 1 to -46 ± 2 mmHg), whereas the bradycardic response was similar in both groups (-34 ± 5 to -92 ± 9 and -21 ± 2 to -79 ± 7 beats/min, respectively). Methylatropine and atenolol showed no effect in the hypotensive response in either group. Methylatropine blunted the bradycardic response in both groups, whereas atenolol attenuated only in hypertensive rats. Prazosin blunted the hypotensive response in both normotensive (43%) and hypertensive rats (53%) but did not affect the bradycardic response in either group. Prazosin plus angiotensin II, used to restore basal arterial pressure, provided hemodynamic responses similar to those of prazosin alone. The triple pharmacological blockade abolished the bradycardic response in both groups but displayed similar residual hypotensive response in hypertensive (-13 ± 2 to -27 ± 2 mmHg) and normotensive rats (-10 ± 1 to -25 ± 3 mmHg). In conclusion, electrical stimulation produced a well-preserved baroreflex-mediated decrease in arterial pressure and heart rate in conscious l-NAME-induced hypertensive rats. Moreover, withdrawal of the sympathetic drive played a role in the reflex bradycardia only in hypertensive rats. The residual fall in pressure after the triple pharmacological blockade suggests the involvement of a vasodilatory mechanism unrelated to NO or deactivation of α(1)-adrenergic receptor.     

Baroreflex responses to electrical stimulation of aortic depressor nerve in conscious SHR

Baroreflex responses to changes in arterial pressure are impaired in spontaneously hypertensive rats (SHR). Mean arterial pressure (MAP), heart rate (HR), and regional vascular resistances were measured before and during electrical stimulation (5-90 Hz) of the left aortic depressor nerve (ADN) in conscious SHR and normotensive control rats (NCR). The protocol was repeated after beta-adrenergic-receptor blockade with atenolol. SHR exhibited higher basal MAP (150 +/- 5 vs. 103 +/- 2 mmHg) and HR (393 +/- 9 vs. 360 +/- 5 beats/min). The frequency-dependent hypotensive response to ADN stimulation was preserved or enhanced in SHR. The greater absolute fall in MAP at higher frequencies (-68 +/- 5 vs. -38 +/- 3 mmHg at 90-Hz stimulation) in SHR was associated with a preferential decrease in hindquarter (-43 +/- 5%) vs. mesenteric (-27 +/- 3%) resistance. In contrast, ADN stimulation decreased hindquarter and mesenteric resistances equivalently in NCR (-33 +/- 7% and -30 +/- 7%). Reflex bradycardia was also preserved in SHR, although its mechanism differed. Atenolol attenuated the bradycardia in SHR (-88 +/- 14 vs. -129 +/- 18 beats/min at 90-Hz stimulation) but did not alter the bradycardia in NCR (-116 +/- 16 vs. -133 +/- 13 beats/min). The residual bradycardia under atenolol (parasympathetic component) was reduced in SHR. MAP and HR responses to ADN stimulation were also preserved or enhanced in SHR vs. NCR after deafferentation of carotid sinuses and contralateral right ADN. The results demonstrate distinct differences in central baroreflex control in conscious SHR vs. NCR. Inhibition of cardiac sympathetic tone maintains reflex bradycardia during ADN stimulation in SHR despite impaired parasympathetic activation, and depressor responses to ADN stimulation are equivalent or even greater in SHR due to augmented hindquarter vasodilation.