Cardiovascular changes induced by large doses of clonidine in mice

Influence of Intragastric Administration of Traditional Japanese Medicine, Ninjin'Yoeito, on Cerebral Blood Flow via Muscarinic Acetylcholine Receptors

Ninjin'yoeito (NYT) is a traditional medicine that has been used for mitigating physical frailty, such as fatigue and anorexia, as well as for cognitive dysfunction. Maintenance of adequate cerebral blood flow (CBF) is important for preventing cognitive dysfunction. The present study aimed to examine the effect of NYT on CBF. Male C57BL/6 J mice were anesthetized with urethane and were artificially ventilated. We measured CBF in the neocortex with laser-speckle contrast imaging for 10 min before administration and 60 min after administration. We administered NYT solution (0.25, 0.5, 1, and 2 g/kg) or vehicle (distilled water; DW) over 5 min via an intragastric catheter. We surgically transected the vagus nerve to investigate its contribution as a neural pathway and intraperitoneally injected atropine to block muscarinic acetylcholine receptors. Finally, we tested the CBF response to cutaneous brushing stimulation applied to the left hind paw (30 sec). CBF decreased after DW administration, starting from 30 min onward, whereas CBF did not change after NYT. The averaged CBF change following DW administration differed from that following NYT (1 g/kg) but not from those following the other doses of NYT. Arterial pressure was not affected by either solution. CBF after NYT (1 g/kg) was not affected by vagotomy but was lower following additional atropine. In response to brushing stimulation, CBF in the right (contralateral) parietal cortex increased. The magnitude of CBF increase following NYT was greater than that following DW. These results suggest that NYT prevents CBF decrease via cholinergic activation independent of vagal activity and enhances the CBF response to somatosensory stimulation.

Norepinephrine released by intestinal Paneth cells exacerbates ischemic AKI

Small intestinal Paneth cells play a critical role in acute kidney injury (AKI) and remote organ dysfunction by synthesizing and releasing IL-17A. In addition, intestine-derived norepinephrine is a major mediator of hepatic injury and systemic inflammation in sepsis. We tested the hypothesis that small intestinal Paneth cells synthesize and release norepinephrine to exacerbate ischemic AKI. After ischemic AKI, we demonstrated larger increases in portal venous norepinephrine levels compared with plasma norepinephrine in mice, consistent with an intestinal source of norepinephrine release after renal ischemia and reperfusion. We demonstrated that murine small intestinal Paneth cells express tyrosine hydroxylase mRNA and protein, a critical rate-limiting enzyme for the synthesis of norepinephrine. We also demonstrated mRNA expression for tyrosine hydroxylase in human small intestinal Paneth cells. Moreover, freshly isolated small intestinal crypts expressed significantly higher norepinephrine levels after ischemic AKI compared with sham-operated mice. Suggesting a critical role of IL-17A in Paneth cell-mediated release of norepinephrine, recombinant IL-17A induced norepinephrine release in the small intestine of mice. Furthermore, mice deficient in Paneth cells (SOX9 villin Cre mice) have reduced plasma norepinephrine levels after ischemic AKI. Finally, supporting a critical role for norepinephrine in generating ischemic AKI, treatment with the selective α-adrenergic antagonists yohimbine and phentolamine protected against murine ischemic AKI with significantly reduced renal tubular necrosis, inflammation, and apoptosis and less hepatic dysfunction. Taken together, we identify Paneth cells as a critical source of norepinephrine release that may lead to intestinal and liver injury and systemic inflammation after AKI.

Clonidine Improves Spontaneous Baroreflex Sensitivity in Conscious Mice Through Parasympathetic Activation

α-2 Adrenoceptors are important in baroreflex regulation. We tested the impact of α-2 adrenoceptors on heart rate variability (HRV) and spontaneous baroreflex sensitivity (BRS) in conscious mice with telemetry (TA11PA-C20). Baseline beat-to-beat measurements (2 hours between 8:00 am to 12:00 pm ) were compared with measurements after intraperitoneal α-2 adrenoceptor blockade (yohimbine 2 mg/kg) and α-2 adrenoceptor stimulation (clonidine 1, 10, and 50 mg/kg). Blood pressure (BP) was 128±6/87±6 mm Hg and heart rate (HR) was 548±18 bpm at baseline. BRS, calculated with the cross-spectral method, was 1.2±0.1 ms/mm Hg at baseline. BP increased 20±2/13±2 mm Hg with yohimbine. HR increased by 158±23 bpm. BRS did not change. BP decreased 16±7/5±4 mm Hg with 1 mg/kg of clonidine and did not change with a higher dose. HR decreased with clonidine (176±28, 351±21, 310±29 bpm during 1, 10, and 50 mg/kg of clonidine, P <0.01). HRV (total power=4629±465, 7002±440, and 6452±341 ms 2 during 1, 10, and 50 mg/kg of clonidine, P <0.01) and BRS were profoundly increased with clonidine (14±1, 13±1, and 10±1 ms/mm Hg, P <0.01). The effects of clonidine were abolished with atropine (2 mg/kg plus 50 mg/kg of clonidine) but not with metoprolol (4 mg/kg plus 50 mg/kg of clonidine). These data suggest that α-2 adrenoceptors exert a regulatory influence on autonomic cardiovascular control and baroreflex function. The effect of clonidine on baroreflex HR regulation is mediated by the parasympathetic nervous system. These murine data fit well with recent human observations regarding parasympathetic activation via α-2 adrenoceptors.

The role of alpha-adrenoceptors in the regulation of pentylenetetrazol convulsions in mice

Typical ocular colobomas and associated orbital cysts are relatively common malformations that result from a defect in the fusion of the fetal optic fissure. Three cases studied with computed tomography (CT) are reported, and the spectrum of ocular colobomas, their associated findings, and CT differential diagnosis are reviewed. This experience indicates that the location and extent of colobomas can be determined with high-resolution CT.