Our objective was to determine whether electrical neuromodulation using spinal cord stimulation (SCS) mitigates transient ischemia-induced ventricular infarction and, if so, whether adrenergic neurons are involved in such cardioprotection. The hearts of anesthetized rabbits, subjected to 30 min of left anterior descending coronary arterial occlusion (CAO) followed by 3 h of reperfusion (control), were compared with those with preemptive SCS (starting 15 min before and continuing throughout the 30-min CAO) or reactive SCS (started at 1 or 28 min of CAO). For SCS, the dorsal C8-T2 segments of the spinal cord were stimulated electrically (50 Hz, 0.2 ms, 90% of motor threshold). For preemptive SCS, separate groups of animals were pretreated 15 min before SCS onset with 1) vehicle, 2) prazosin (α1-adrenoceptor blockade), or 3) timolol (β-adrenoceptor blockade). Infarct size (IS), measured with tetrazolium, was expressed as a percentage of risk zone. In controls exposed to 30 min of CAO, IS was 36.4 ± 9.5% (SD). Preemptive SCS reduced IS to 21.8 ± 6.8% (P < 0.001). Preemptive SCS-mediated infarct reduction was eliminated by prazosin (36.6 ± 8.8%) and blunted by timolol (29.4 ± 7.5%). Reactive SCS did not reduce IS. SCS increased phosphorylation of cardiac PKC. SCS did not alter blood pressure or heart rate. We conclude that preemptive SCS reduces the size of infarcts induced by transient CAO; such cardioprotection involves cardiac adrenergic neurons.

The aim of this project was to study changes in cardiovascular responses brought about by long term oral treatment of Wistar rats with beta adrenoceptor antagonists. After chronic treatment with propranolol (12 or 60 mg/kg/day for up to 6 weeks) or timolol (1.2, 2.5, 5 or 25 mg/kg/day for up to 17 weeks), the log dose-response curves for mean rises in heart rate and mean arterial pressure on stimulation of the postsynaptic adrenoceptors of the pithed rat by I.V. noradrenaline or isoprenaline were not significantly changed. Chronic propranolol treatment significantly reduced the response of the heart to electrical stimulation of the whole sympathetic outflow but treatment with timolol failed to alter the cardiac chronotropic response. The rises in mean arterial pressure on stimulation of the whole sympathetic outflow were not altered by long term treatment with either propranolol or timolol. The high dose of propranolol significantly reduced the heart rate of conscious rats. However neither the lower dose of propranolol nor any dose of timolol affected heart rate. The systolic pressure of conscious rats was unaltered by treatment with the beta adrenoceptor blockers. The threshold for release of tritiated noradrenaline from the sympathetic nerves on stimulation of the whole spinal outflow was raised by chronic treatment with propranolol or timolol. Timolol significantly increased the concentration of 3H noradrenaline in the blood and decreased the heart content of tritium. Chronic propranolol treatment did not alter the blood or heart levels of 3H noradrenaline. Thus, although the plasma levels of the beta adrenoceptor blocking drugs were probably insufficient to ensure prolonged blockade of postsynaptic receptors, significant changes in presynaptic function were observed. It remains to be seen whether these changes play any significant part in cardiovascular responses to beta adrenoceptor antagonists in clinical practice.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第19565号 / 医博第4072号 / 新制||医||1013(附属図書館) / 32601 / 京都大学大学院医学研究科医学専攻 / (主査)教授 江藤 浩之, 教授 前川 平, 教授 髙折 晃史 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

The effect of chloroethylclonidine on nodrenaline-induced contractions of the rat aorta was studied. Chloroethylclonidine (1.5 × 10-5 M) shifted noradrenaline dose-response curve to the right approximately 5000-fold without depressing the maximum. The response to noradrenaline after chloroethylclonidine was not antagonized by phenoxybenzamine (10-7 M), prazosin (10-7 M), WB 4101 (10-7 M) nor yohimbine (10-5 M) and is therefore not mediated via α1-adrenoceptors. These results would suggest that there is a homogenous population of chloroethylclonidine-sensitive α1-adrenoceptors in the rat aorta and that chloroethylclonidine treatment reveals a non-α-adrenoceptor noradrenaline binding site in this tissue.

The interactions of 5,6- and 6,7-dihydroxy derivatives of 2-aminotetralin with [3H]clonidine and [3H]clonidine and [3H]prazosin as well as with [3H]spiperone binding sites in rat cerebral cortex membrane preparations were investigated. The hydroxy derivatives of 2-aminotetralin tested showed significant interaction with [3H]clonidine as well as with [3H]spiperone binding sites while for [3H]prazosin binding site these agents appeared virtually inactive. For interaction with [3H]clonidine binding site 6,7-dihydroxy substitutions impart greater potency that 5,6-dihydroxy substitutions and N-alkyl substitutions either make no difference or reduce the affinity of these compounds. N-alkyl substitutions, however, markedly enhance the affinity of 5,6-dihydroxy derivatives for interactions with [3H]spiperone binding site. The results suggest that some hydroxy derivatives of aminotetralin have significant interaction with both central α2-adrenoceptor and D2-dopamine receptor systems.

Diabetes mellitus (DM) and hyperglycemia contribute to sympathetic nervous system (SNS) activation and cardiovascular dysfunction. SNS activation and increased norepinephrine levels downregulate cardiac β-adrenergic receptors (β-AR). The ADMIRE-HF trial identified reduced cardiac SNS innervation as an independent prognostic marker in heart failure. The β-AR antagonist [3H]-CGP12177 was used to quantify cardiac β-AR in ex vivo biodistribution studies in streptozotocin (STZ)-treated rats after 8 weeks of sustained hyperglycemia, and in the Zucker Diabetic Fatty (ZDF) rat model of type-2 diabetes at the onset of hyperglycemia (10 weeks of age) and after a sustained period of hyperglycemia (16 weeks of age). In some STZ rats, insulin was provided at the onset of hyperglycemia, or after a sustained period of hyperglycemia. Insulin treatment at both time points prevented reduced [3H]-CGP12177 binding (33-38% compared to controls) observed in STZ hyperglycemics. ZDF β-ARs were intact at 10 weeks but became reduced (16-25% relative to the Zucker leans) following 6 weeks of hyperglycemia. This work supports that cardiac β-AR are reduced in models of DM and that restoring insulin signalling to maintain glycemic control can normalize β-AR density whether provided early or after a period of sustained hyperglycemia.

In der vorliegenden Arbeit wurden die Effekte einer frühzeitigen Zelltherapie im Langzeit in-vivo Infarktmodell studiert. Erstmals wurden dabei auch Veränderungen der kardialen -Adrenozeptoren untersucht und Zelltherapie mit einer reversiblen präinfarziösen Ischämie kombiniert. Initial wurden dafür bei 38 männlichen weißen Neuseeländer Kaninchen Knochenmarkspunktionen durchgeführt, MSC durch Kultur isoliert und 60 Minuten nach induziertem Infarkt und ohne Reperfusion in den Randbereich des Infarktgebietes injiziert. Zur Untersuchung möglicher Interaktionen zwischen Zelltherapie und Präinfarktgeschehen wurde bei einigen Tieren das Myokard durch eine kurzzeitige Präinfarktischämie präkonditioniert. Die Ergebnisse der vorliegenden Arbeit zeigen, dass auch die frühzeitige Zellinjektion ohne Reperfusion mit signifikanten Effekten auf die Kontraktilität und spezifischen sympathoadrenergen Veränderungen verbunden ist.

Diabetes mellitus (DM) and hyperglycemia contribute to sympathetic nervous system (SNS) activation and cardiovascular dysfunction. SNS activation and increased norepinephrine levels downregulate cardiac β-adrenergic receptors (β-AR). The ADMIRE-HF trial identified reduced cardiac SNS innervation as an independent prognostic marker in heart failure. The β-AR antagonist [3H]-CGP12177 was used to quantify cardiac β-AR in ex vivo biodistribution studies in streptozotocin (STZ)-treated rats after 8 weeks of sustained hyperglycemia, and in the Zucker Diabetic Fatty (ZDF) rat model of type-2 diabetes at the onset of hyperglycemia (10 weeks of age) and after a sustained period of hyperglycemia (16 weeks of age). In some STZ rats, insulin was provided at the onset of hyperglycemia, or after a sustained period of hyperglycemia. Insulin treatment at both time points prevented reduced [3H]-CGP12177 binding (33-38% compared to controls) observed in STZ hyperglycemics. ZDF β-ARs were intact at 10 weeks but became reduced (16-25% relative to the Zucker leans) following 6 weeks of hyperglycemia. This work supports that cardiac β-AR are reduced in models of DM and that restoring insulin signalling to maintain glycemic control can normalize β-AR density whether provided early or after a period of sustained hyperglycemia.

The influence of the membrane environment on the α1-adrenoceptor has been investigated by examining the effect of phospholipase digestion on the binding of [3H]prazosin to aortic and hepatic membranes. Membrane digestion by phospholipase A2 and phospholipase C was found to markedly reduce prazosin binding to the α1-adrenoceptor whereas phospholipase D had comparatively little effect. In addition, there were differences between membrane preparations since the aortic α1-adrenoceptor was less sensitive to phospholipase A2 and phospholipase C than the hepatic receptor. The results support a major role for hydrophobic groups and the negatively charged, hydrophilic phosphate moiety of phospholipids in the interaction between prazosin and the α1-adrenoceptor.