In-vivo and ex-vivo studies on region-specific remodeling of large elastic arteries due to simulated weightlessness and its prevention by gravity-based countermeasure / 生理学报

The present study was designed to test the hypothesis that a medium-term simulated microgravity can induce region-specific remodeling in large elastic arteries with their innermost smooth muscle (SM) layers being most profoundly affected. The second purpose was to examine whether these changes can be prevented by a simulated intermittent artificial gravity (IAG). The third purpose was to elucidate whether vascular local renin-angiotensin system (L-RAS) plays an important role in the regional vascular remodeling and its prevention by the gravity-based countermeasure. This study consisted of two interconnected series of in-vivo and ex-vivo experiments. In the in-vivo experiments, the tail-suspended, hindlimb unloaded rat model was used to simulate microgravity-induced cardiovascular deconditioning for 28 days (SUS group); and during the simulation period, another group was subjected to daily 1-hour dorso-ventral (-G(x)) gravitation provided by restoring to normal standing posture (S + D group). The activity of vascular L-RAS was evaluated by examining the gene and protein expression of angiotensinogen (Ao) and angiotensin II receptor type 1 (AT1R) in the arterial wall tissue. The results showed that SUS induced an increase in the media thickness of the common carotid artery due to hypertrophy of the four SM layers and a decrease in the total cross-sectional area of the nine SM layers of the abdominal aorta without significant change in its media thickness. And for both arteries, the most prominent changes were in the innermost SM layers. Immunohistochemistry and in situ hybridization revealed that SUS induced an up- and down-regulation of Ao and AT1R expression in the vessel wall of common carotid artery and abdominal aorta, respectively, which was further confirmed by Western blot analysis and real time PCR analysis. Daily 1-hour restoring to normal standing posture over 28 days fully prevented these remodeling and L-RAS changes in the large elastic arteries that might occur due to SUS alone. In the ex-vivo experiments, to elucidate the important role of transmural pressure in vascular regional remodeling and differential regulation of L-RAS activity, we established an organ culture system in which rat common carotid artery, held at in-vivo length, can be perfused and pressurized at varied flow and pressure for 7 days. In arteries perfused at a flow rate of 7.9 mL/min and pressurized at 150 mmHg, but not at 0 or 80 mmHg, for 3 days led to an augmentation of c-fibronectin (c-FN) expression, which was also more markedly expressed in the innermost SM layers, and an increase in Ang II production detected in the perfusion fluid. However, the enhanced c-FN expression and increased Ang II production that might occur due to a sustained high perfusion pressure alone were fully prevented by daily restoration to 0 or 80 mmHg for a short duration. These findings from in-vivo and ex-vivo experiments have provided evidence supporting our hypothesis that redistribution of transmural pressures might be the primary factor that initiates region-specific remodeling of arteries during microgravity and the mechanism of IAG is associated with an intermittent restoration of the transmural pressures to their normal distribution. And they also provide support to the hypothesis that L-RAS plays an important role in vascular adaptation to microgravity and its prevention by the IAG countermeasure.

Chronic blockade of angiotensin II type 1 receptor cannot completely prevent structural adaptation in vessels of simulated weightless rats / 生理学报

Our previous studies suggest that the vascular local renin-angiotensin system (L-RAS) plays a pivotal role in the region-specific vascular adaptation due to simulated weightlessness. The present study was designed to determine whether simulated weightlessness still induced adaptive changes in rat vessels when angiotensin II type 1 receptor (AT(1)R) was chronically blocked by the administration of losartan, and whether the expressions of key elements in the L-RAS in the large arteries would change. Tail suspension for 4 weeks was used to simulate the physiological effect of weightlessness. The responses of the basilar, anterior tibial, carotid arteries and abdominal aorta were observed by morphometric technique with light microscopy. The expressions of angiotensinogen (AGT) and AT(1)R in the walls of common carotid artery and abdominal aorta were determined using immunohistochemical technique. The results showed that simulated weightlessness induced hypertrophy of the media of basilar artery and smooth muscle layers of carotid artery, but atrophic change in the anterior tibial artery and abdominal aorta. After 4 weeks of losartan treatment, all these arteries showed significant atrophic changes. However, simulated weightlessness still induced relative hypertrophy of the basilar artery and carotid artery and atrophy of the abdominal aorta when AT(1)R was blocked. After 4 weeks of simulated weightlessness, the expressions of AGT and AT(1)R were upregualted in the wall of carotid artery, but downregulated in the wall of abdominal aorta and perivascular tissues. Losartan decreased AGT and AT(1)R expressions only in the wall of abdominal aorta; whereas simulated weightlessness further decreased AT(1)R expression in the wall of abdominal aorta when AT(1)R was blocked. We conclude that simulated weightlessness for 4 weeks still induces structural changes and upregulates or downregulates the key elements in L-RAS in the large and medium-sized arteries from fore and hind body parts of rats when AT(1)R is blocked. The results suggest that the L-RAS in arterial tissue plays a pivotal role in these differential structural changes. However, there still exist other regulatory pathways to mediate the adaptive regulation of cerebral vessels when AT(1)R is blocked.

EFFECT OF HAEMORRHAGIC SHOCK ON SOMATOSTATINIMMUNOREACTIVE CELLS IN RAT PANCREAS / 解剖学报

Effect of haemorrhagic shock on somatostatin (ss)-immunoreactive cells in rat pancreas was studied with the immunohistochemical PAP method. The results showed that at different time from 30 mins to 6 hours after haemorrhagic shock the number of SS-immunoreactive cells in pancreas was decreased significant. It is suggested that after haemorrhagic shock the releasing rate of somatostatin from the pancreatic D cells is increased. Therefore, the pancreatic D cells may play a role in the regulation of the pathological process of haemorrhagic shock.