三种国产藜芦碱(邢氏藜芦碱、毛叶藜芦碱、马氏藜芦碱)的降血压作用及其机制

1.麻醉猫靜脉注射馬氏藜芦碱(5—25微克/公斤)毛叶藜芦碱(25微克/公斤)邢氏藜芦碱(50微克/公斤)能使血压下降20—70%,历时5—80分钟,降压时伴有心率減慢,呼吸抑制或暫停。肌肉注射10倍于靜脉注射降压量,口服15倍于靜脉注射降压量有降压作用,可維持2—3小时,唯部分动物死于实驗中。无明显快速耐受現象。2.降压作用与腎上腺素、去甲腎上腺素无关,而与迷走神經、毒蕈碱-胆碱反应系統有关。3.降压过程中,頸动脉加压反射減弱,刺激迷走神經及坐骨神經向中端引起的血压效应被抑制。4.舌下动脉給药,或結扎頸內、外动脉从甲状腺上动脉給药,結果馬氏藜芦碱1微克/公斤,毛叶藜芦碱2微克/公斤,邢氏藜芦碱5微克/公斤,均可引起血压下降。5.三种国产藜芦碱于离体兔耳及猫后肢未見直接血管扩张作用。6.三种国产藜芦碱大量时(馬氏碱75—200微克/公斤,毛叶碱200微克/公斤,邢氏碱400微克/公斤)除引起明显的哑噁心、呕吐外,未見其他特殊症状。氯丙嗪預先应用可防止此反应。     

狭叶萝芙木根生物碱的降压作用及机制

继中国蘿芙木之后,最近在云南又发現狹叶蘿芙木(Rauwolfia yunnanensis Tsiang var.angustifolia C.Y.Wu.)。其根生物碱对麻醉动物具降压作用,給犬靜脉注射1毫克/公斤后2小时內的降压面积为-32%,給猫靜脉注射3毫克/公斤的降压面积为-30%。同时測得中国蘿芙木根生物碱在犬的降压面积为-45%,猫为-29%。重复給药有快速耐受性。降压的同时呼吸呈兴奋,对心率影响不明显。降压作用与M-胆碱能反应系統、N-胆碱能反应系統以及內感受器都无关系?匝芤参拗苯幼饔?单側頸交感神經切除兔耳試驗发現,扩张血管的作用与交感神經有关。狹叶蘿芙木根生物碱可抑制腎上腺素或去甲腎上腺素的加压反应,也可抑制阻断頸总动脉血流和电刺激迷走神經或胫骨神經中枢端所致的加压反射。用脊猫試驗吋其降压作用大为減弱,但并不完全消除,降压面积仅为-14%。因此,其降压机制包括中枢和外周两方面,即对血管运动中枢的抑制作用和抗腎上腺素的作用。急性毒性試驗証明,狹叶蘿芙木根生物碱的毒性很小,小鼠口服2000毫克/公斤无死亡发生,动物呈現安靜状态。     

国产乙酰普马嗪的药理作用研究——加强作用及对交感神经末梢介质释放的影响

(1)采用热水刺激小白鼠尾巴法試驗鎮痛作用,乙酰普馬嗪0.5毫克/公斤可使“疼痛”反应出現时間延迟,較盐酸嗎啡(2毫克/公斤)为弱;二者均以半量合并应用,鎮痛作用强度虽未見加强,但鎮痛时間則延长。(2)脑室內注射乙鮂振R嗪,可立即引起小白鼠安靜,并使其体溫明显下降;皮下注射同剂量时,安靜及降溫作用均不显著,但可明显加强安替比林及水合氯醛的降溫作用。(3)乙酰普馬嗪局部滴药及皮下注射均可产生角膜麻醉,并可加强普魯卡因的表面麻醉作用,尤以皮下注射法为强。(4)乙酰普馬嗪2.5微克/公斤即可減弱腎上腺素的升压作用;5微克/公斤时,使后者作用翻轉,并使电刺激交感神經节前纤維及注射腎上腺素所引起的瞬膜收縮反应減弱。(5)在离体兔神經——迴腸标本,电刺激交感神經节后纤維引起腸张力下降,运动減弱,乙酰普馬嗪及氯丙嗪均可加强此交感反应。     

四种苯骈二氧六环化合物的腎上腺素能阻断作用

四种苯駢二氧六环化合物的結构式为: 小白鼠腹腔注射BD-3,933F,BD-1和BD-5的LD₅₀分別为0.1,0.20,0.26和0.22克/公斤,BD-3和933F組死亡多在1—3小时內,而BD-1和BD-5組死亡多在1—3天內。BD-5在小鼠能显著減低腎上腺素的毒性,而其他3药则不能。麻醉大白鼠和猫靜脉注射4药后均可引起降压,但4药间差异均不显著。BD-3,933F和BD-1使麻醉猫靜脉注射腎上腺素的升压引起反轉作用,而BD-5仅具抑制作用。对酪胺及去甲腎上腺素的升压,4药均可抑制。麻醉猫靜脉注射10毫克/公斤的933F有增血糖作用,BD-5注射20毫克/公斤才增高血糖。933F和BD-5对腎上腺素所引起的血糖及乳酸均无明显的抑制作用。因为BD-5同时阻断收縮和舒张血管的作用,但不引起腎上腺素的反轉作用,因此在治疗血管痙攣性疾患中可能比933F效果更好。     

维生素C对大白鼠条件反射活动的影响

利用大白鼠运动防御性条件反射方法,研究了大剂量維生素C对健康动物高級神經活动的影响。結果証明,每日腹腔注射維生素C 0.2克/公斤能加速大白鼠阳性条件反射的形成。維生素C 0.1—1克/公斤可使大白鼠阳性条件反射潛伏期縮短,靜脉給药較腹腔給药效果显著。腹腔注射維生素C 0.2克/公斤与咖啡因(25毫克/公斤,皮下注射)并用对条件反射无明显协同作用;与氯丙嗪(3毫克/公斤,腹腔注射)并用有一定拮抗作用。当靜脉注射維生素C 0.2/公斤时,对氯丙嗪有明显的拮抗作用。腹腔注射維生紊C 0.4克/公斤对消退性抑制,以及靜脉注射維生素C 0.1克/公斤对分化性抑制皆无显著影响。     

汉防己甲素及乙素降压的机制

1.甲素及乙素預先作靜脉注射,能使乙醯胆硷的降压作用加强及作用时間延長,同时阿託品可部分取消甲素及乙素的降压作用,可以認为其有拟似胆硷反应系統(M-系統)的作用。2.甲素及乙素对腎上腺素之升压作用並無影响。3.甲素及乙素对交感神經节並無阻断作用,相反,当甲素及乙素产生显著血压下降时,往往引起交感神經节的短暫兴奋現象。4.甲素及乙素可取消或減弱因压迫頸动脉所引起的升压反射,二者的降压作用並不受切断二侧竇神經所影响,可以推想其对血管运动中樞或交感神經中樞有抑制作用。5.甲素及乙素对血管的直接及反射性舒張作用,对血管运动中樞或交感中樞之抑制及对胆硷反应系統的拟似作用等,应可視为它們降压作用之主要机制。6.甲素及乙素之药理性質相似,但乙素之降压作用較甲素为弱且易产生急速耐受現象。     

汉防己甲素及乙素对心血管系统的作用

1.以汉防已甲素或乙素3毫克/公斤靜脉注射、肌肉注射或灌胃,均可使麻醉猫的血压明显下降,甲素之降压作用較乙素大而持久,甲素靜脉注射时,降压作用急驟而持久,可維持1—5小时;肌肉注射及灌胃时,降压作用較緩慢,但亦甚持久。2.乙素之降压作用較甲素弱而短暫,靜脉給药之作用較肌肉注射为强,灌胃之降压作用又較肌肉注射为弱。3.静脉注射甲素或乙素3毫克/公斤,在血压下降的同时,可見暫时性心收縮力減弱;但肌肉注射同样或更大剂量(5毫克/公斤),則不出現心力抑制現象,甲素对心率之影响較少,乙素則往往引起心率減慢,心动电流圖上仅見R波幅度之減小,对P-R間歇及T波等均無影响。4.甲素及乙素可使脾容积增加,但在血压急剧下降时,則可使脾容积縮小。5.甲素及乙素均可使离体兎耳血管扩張,直接对平滑肌之抑制作用及神經反射机制均参加在內.甲素之血管扩張作用較乙素及罂粟硷为大而持久。     

猪毛菜(茨蓬)浸膏对实验动物的药理研究

猪毛菜浸膏对麻醉动物有明显持久降压作用,无明显快速耐受現象。猪毛菜对乙酰胆碱及刺激迷走神經离中端所致降压作用无影响,阿託品不阻断猪毛菜的降压作用。双側迷走神經切断后,猪毛菜降压作用略減弱。猪毛菜不阻断頸上交感神經传导,亦无明显抗腎上腺素作用。猪毛菜抑制因压迫頸总动脉及刺激坐骨神經向中端所致的升压反射,二側竇神經切除亦不影响其降压作用。在猪毛菜引起降压作用时,带神經离体兔耳血管反射性扩张,因此推测猪毛菜对血管运动中枢或交感中枢有抑制作用。猪毛菜5,10克/公斤皮下注射能显著减少小白鼠自由活动。20克/公斤延长戊巴比妥鈉(35毫克/公斤)催眠作用的时間,并使非催眠剂量的水合氯醛(200毫克/公斤)产生催眠作用。但不能对抗中枢惊厥药(戊四氮及士的宁)的惊厥及致死作用。在小白鼠防御运动条件反射实驗中,皮下注射猪毛菜3克/公斤,对条件反射活动无明显影响。5克/公斤,10克/公斤时能使条件反射时延长,強化次数增加,分化相无变化。20克/公斤时条件反射显著抑制。5,10克/公斤皮下注射均能加速阳性条件反射消褪过程。小白鼠皮下注射猪毛菜LD₅₀为56克/公斤,大白鼠腹腔注射8克/公斤卽死亡。家兔口服(灌胃)40克/公斤未見毒性反应,80克/公斤时可見死亡。     

广地龙的降压作用和降压机制的探讨

本文对广地龙毒性、降压作用和降压机制作了初步探討。广地龙热浸剂给小鼠靜脉注射时,LD₅₀=38.5克/公斤。热浸剂(0.1克/公斤)連續給大鼠灌胃45天,未发現毒性反应。給麻醉狗按0.1克/公斤靜脉注射热浸剂或乙醇浸出液,在給药30—45分钟出現血压下降,一般可維持2—3小时。正常大鼠一次用大剂量(10克/公斤)灌胃或腎型高血压大鼠用个剂量(50毫克/公斤)长时間(2周)灌胃,均有明显的降血压作用。在后一种情况下,多数大鼠血压下降出現于給药的第3—7天,并于停药后第2周回升到用药前水平。广地龙降压机制可能是由于它直接作用于脊髓以上的中枢神經系統或通过某些內感受器反射地影响中枢神經系統,引起部分內脏血管的扩张而使血压下降。     

广地龙中促进子宫收缩的成分

本文研究了自广地龙中提出来的一种引湿性、淡黄色針状結晶(含量約0.2%)对平滑肌器官(特别是对子宮)的作用。介紹了該結晶的提取方法。該結晶0.1毫克加入25毫升Locke液中,能使已孕和未孕大鼠或豚鼠离体子宮角紧张度明显升高,0.3毫克可使之呈痙攣收縮状态。按1毫克/公斤給已孕和未孕麻醉家兔靜脉注射后15—30分钟,在位子宮紧张度升高,作用維持1.5—3小时。按8—10毫克/公斤注射,子宮紧张度立卽升高和血压急剧下降到零而死亡。9只慢性子宫瘻家兔靜脉注射(3—6毫克/公斤)或灌胃給药(10—20毫克/公斤)后15—45分钟,子宮收縮明显增强,作用維持1.5—3小时(注射給药)和7小时以上(灌胃給药)。多数实驗家兔在子宮兴奋同时有排便現象。該結晶对家兔在位腸管和大鼠后肢血管均有强烈兴奋作用,但对豚鼠支气管肌作用极弱。当給小鼠靜脉注射时,LD₅₀为38.7毫克/公斤。     

Intravenously injected CDP-choline increases blood pressure and reverses hypotension in haemorrhagic shock: effect is mediated by central cholinergic activation

Intravenous (i.v.) administration of cytidine-5′-diphosphate choline (CDP-choline) (100, 250 and 500 mg/kg) increased blood pressure in normal rats and reversed hypotension in haemorrhagic shock. Choline (54 mg/kg; i.v.), at the dose equimolar to 250 mg/kg CDP-choline decreased blood pressure of rats in both conditions and caused the death of all hypotensive animals within 2-5 min. Equimolar dose of cytidine (124 mg/kg; i.v.) did not change cardiovascular parameters. Choline levels in plasma, lateral cerebral ventricle and hypothalamus increased after CDP-choline administration. Intracerebroventricular (i.c.v.) hemicholinium-3 pretreatment (20 μg), greatly attenuated the pressor effect of CDP-choline in both conditions. Atropine pretreatment (10 μg; i.c.v.) did not change the pressor effect of CDP-choline while mecamylamine (50 μg; i.c.v.) abolished the pressor response to drug. Besides, acetylcholine (1 μmol; i.c.v.) produced similar increases in blood pressure in normal and hypotensive conditions to that observed in CDP-choline given rats. CDP-choline (250 mg/kg; i.v.) increased plasma catecholamines and vasopressin levels but not plasma renin activity. Pretreatment of rats with either prazosin (0.5 mg/kg; i.v.) or vasopressin V₁ receptor antagonist, [β-mercapto,β,β-cyclopentamethylenepropionyl¹,O-Me-Tyr²-Arg⁸]vasopressin (10 μg/kg; i.v.), attenuated the pressor response to CDP-choline while simultaneous administration of these antagonists before CDP-choline injection completely blocked the pressor effect. Results show that i.v. CDP-choline increases blood pressure and reverses hypotension in haemorrhagic shock. Activation of central nicotinic cholinergic mechanisms by the increases in plasma and brain choline concentrations appears to be involved in the pressor effect of this drug. Moreover, the increases in plasma catecholamines and vasopressin levels mediate these effects.     

云南萝芙木的药理研究,—云南萝芙木的降压作用及其机制

自从夹竹桃科植物印度蛇木(Rauwolfia Serpentina Benth.)的各种制剂(特别是Reserpine)对高血压的疗效引起全世界医、药学家的重视后,我国学者也从本国寻找其代替品,并在云南、广东、广西及海南岛找到了同属植物蘿芙木R. Verticillata (Lour.) Baill.李承祜等及云南药用植物研究所曾做过其生药学的研究。赵承嘏等曾从广东蘿芙木提出一种生物硷,名为蘿芙甲素(Rauwolfia A),经夏炳南等,林吉强等进行了药理研     

溴苄乙铵及其有关化合物的一些药理观察

本文就国产溴苄乙铵进行了药理观察,证实了前人报告的降压作用以及对交感神经的选择作用,并发现用药后交感末梢的介质释放量显著减少;大剂量能明显改变猫、兔在位心脏的功能;在一般降压剂量时不仅增敏儿茶酚胺的升压作用,并且也能增敏其降压作用。初步试验了溴苄乙铵的异构体与类似物5个,发现间位与对位异构体同溴苄乙胺(邻位)对血压的作用相反,用药后血压略降后卽显著上升,并伴有瞬膜收缩和唾液分泌增加,阿托品能取消其降压和唾液分泌作用,而溴苄乙铵则能取消其升压作用。     

Modification of certain vascular responses to dopamine by morphine

Alteration by morphine of two specific vascular responses to dopamine, systemic hypotension in cats and renal vasodilation in dogs, were characterized in α-adrenergically blocked (phenoxybenzamine) anesthetized animals. Morphine sulfate (15–30 mg/kg, i.v.) converted the vasodepressor response to dopamine (50–100 μg/kg, i.v.) to a pressor response in intact cats, whereas in spinal cats dopamine-induced vasodepression was not significantly altered by morphine (15–60 mg/kg, i.v.). Haloperidol, a putative peripheral dopaminergic receptor antagonist, briefly but significantly attenuated the hypotensive response to dopamine in spinal cats. Canine renal vasodilator responses to intrarenal arterial dopamine (0.09–96 μg) were significantly reduced after morphine (2–6 mg/kg, i.a.). Morphine produced a non-parallel shift in the dopamine dose-response curve, whereas a parallel shift was obtained when haloperidol was used as the antagonist in the canine renal test system. These results do not support the concept that morphine may be a competitive antagonist of dopamine at peripheral dopaminergic receptors in these species.     

Cardiovascular effects of intracerebroventricularly injected CDP-choline in normotensive and hypotensive animals: the involvement of cholinergic system

Intracerebroventricular (i.c.v.) administration of CDP-choline (0.25, 0.5, 1 and 2 micromol) induced prompt, dose- and time-dependent increase in blood pressure in normotensive rats. Equimolar dose of CDP-choline (1 micromol; i.c.v.) and choline (1 micromol; i.c.v.) caused similar increases in blood pressure while cytidine (1 micromol; i.c.v.) failed to produce any pressor effect. In haemorrhagic shock, CDP-choline (0.1, 0.25, 0.5 and 1 micromol; i.c.v.) increased blood pressure dose- and time-dependently. The complete reversal of hypotension was observed with the i.c.v. injection of CDP-choline (1 micromol) and choline (1 micromol). Cytidine (1 micromol; i.c.v.) produced small, but significant ( P<0.05) increase in blood pressure in haemorrhaged rats. Dose-related bradycardia was observed with the injection of CDP-choline in normotensive rats, but the changes in heart rate were not significantly different ( P>0.05) in hypotensive conditions. Choline levels in lateral cerebral ventricle and hypothalamus increased about nine- and fivefold, respectively, after CDP-choline (1 micromol) administration in normotensive rats. In haemorrhagic shock extracellular choline levels in hypothalamus increased sevenfold after an i.c.v. administration of CDP-choline (1 micromol). Hemicholinium-3 (20 microg; i.c.v.), a neuronal high affinity choline uptake blocker, and mecamylamine (50 microg; i.c.v.), nicotinic receptor antagonist, pretreatment abolished the pressor effect of CDP-choline in normal rats. The increase in blood pressure was also attenuated by atropine (10 microg; i.c.v.) pretreatment. Atropine blocked the bradycardic response observed after CDP-choline. In haemorrhaged rats, the pressor effect of CDP-choline was attenuated by hemicholinium-3 and mecamylamine while atropine failed to alter the pressor response to CDP-choline. I.c.v. CDP-choline increased plasma adrenaline and vasopressin levels in normal rats. Haemorrhage, itself, increased plasma catecholamines and vasopressin levels. CDP-choline (1 micromol) produced additional increases in the elevated plasma levels of these hormones. An alpha(1)-adrenoceptor blocker, prazosin (0.5 mg/kg; i.v.), or vasopressin V(1) receptor antagonist, [beta-mercapto, beta,beta-cyclopenta-methylenepropionyl(1), O-Me-Tyr(2)-Arg(8)]-vasopressin (10 micro/kg; i.v.), pretreatments partially blocked the pressor response to CDP-choline (1 micromol; i.c.v.). Simultaneous administration of these two antagonists completely blocked the pressor effect of CDP-choline in haemorrhagic shock. These results show that the exogenous administration of CDP-choline increases blood pressure and reverses hypotension in haemorrhagic shock. In normotensive conditions, increase in blood pressure appears to be due to the activation of both nicotinic and muscarinic central cholinergic receptors through the activation of presynaptic cholinergic mechanisms. In hypotensive rats, activation of nicotinic cholinergic receptors is solely involved in the pressor effect. Increase in plasma vasopressin and adrenaline mediates the pressor response of CDP-choline in both normotensive and hypotensive conditions.     

Involvement of 5-hydroxytryptamine in the central control of respiration, blood pressure and heart rate in the anaesthetized rat.

5-Hydroxytryptamine (5-HT, 1 ng-25 μg) injected into the cerebral ventricles of urethananaesthetized rats produced a rise in blood pressure, a biphasic change in heart rate and a decrease in ventilation. Responses were largest after injections into the 3rd ventricle. Lateral ventricle injections produced smaller responses while 4th ventricle injections produced the least response. The cardiovascular responses were prevented or reduced by prior intraventricular injection of bromolysergic acid diethylamide. The pressor response was not blocked by hexamethonium (10 mg/kg i.v.) and was only partly reduced by pretreatment with either 6-hydroxydopamine (3 × 100 mg/kg i.v.) or atropine methonitrate (10 mg/kg i.v.). The pressor response was prevented by spinal transection at C1 or C3 but only slightly reduced by transection at C5 or C7. In animals curarized and artificially respired with air, the blood pressure response was reduced. It is conjectured that the rise in blood pressure may involve a direct effect of hypoxia or hypercapnia resulting from a decrease in respiratory activity which is in turn mediated by a direct action of 5-HT on structures lining the 3rd ventricles. There appears to be little or no involvement of the autonomic nervous system in the response. The fall in heart rate is mediated sympathetically.     

Blood pressure effects of intravenous apomorphine in conscious deoxycorticosterone-acetate salt-hypertensive rats

SUMMARY: The present study reports the effects of apomorphine (APO) on blood pressure and the principal site of action of this agonist in 4-week deoxycorticosterone-acetate (DOCA)-hypertensive conscious rats. In these preprations, intravenous (i.v.) administration of APO (0.50-1 mg/kg) induced short-lasting and dose-dependent decreases in mean arterial pressure. The hypotensive response to APO (0.3 mg/kg) was reversed into a significant pressor effect by i.v. hexamethonium (30 mg/kg), whereas it was enhanced by i.v. pretreatment with the vasopressor antagonist of arginine vasopressin (AVP) d(CH2)5Tyr(Me)AVP (10 microg/kg) and/or prazosin (1 mg/kg). This depressor effect was suppressed by the central and peripheral dopamine D2 receptor antagonist metoclopramide (5 mg/kg i.v.), unaffected by the selective dopamine D1 receptor antagonist SCH 23390 (0.2 mg/kg i.v.), partly reduced by intrathecal domperidone (40 microg per rat at T9-T10 level), a dopamine D2 receptor antagonist which does not cross the blood-brain barrier, and reversed into a significant pressor effect by i.v. domperidone (0.5 mg/kg). The latter pressor effect was fully abolished by combined i.v. pretreatment with the vasopressor antagonist of AVP and prazosin. These results show that, in conscious DOCA salt-hypertensive rats, APO induced a brief, initial depressor effect, which is opposed to a central pressor component. The depressor component is related to an inhibition of norepinephrine transmission through activation of dopamine D2 receptors, some of which are located in the spinal cord and some of which are located in the peripheral circulation. The central pressor component, which became manifest after peripheral dopamine D2 receptor blockade, appears to be related to an increase in vasopressin release and sympathetic tone through activation of brain dopamine D2 receptors.     

Intrinsic sympathomimetic activity of labetalol

In intact cats, cumulative doses (0.1-10 mg/kg i.v.) of labetalol produced dose-dependent decreases in heart rate and arterial blood pressure and dose-dependently reduced i.v. phenylephrine induced pressor responses. In spinal cats devoid of resting sympathetic tone, labetalol (1 mg/kg i.v.) produced a sustained elevation of heart rate and a transient fall in arterial blood pressure. In reserpine-pretreated, adrenalectomized cats, labetalol produced quantitatively the same effects as in spinal cats, indicating that the cardiovascular effects observed in cats with no resting sympathetic tone are due to a direct action of labetalol rather than via catecholamine release. The elevated heart rate due to labetalol in spinal cats was reduced by subsequent administration of the beta-adrenergic receptor antagonist, propranolol. Further, pretreatment with propranolol prevented the tachycardic and depressor effects of labetalol in spinal cats. In a separate group of spinal cats, labetalol administered in cumulative doses of up to 1 mg/kg i.v., produced graded increases in heart rate and also dose dependently reduced i.v. isoproterenol-induced tachycardic responses. Pindolol, a beta-adrenergic receptor antagonist with partial beta-agonist activity, produced similar effects in spinal cats at cumulative doses of 1-30 micrograms/kg. These results indicate that the alpha- and beta-adrenergic receptor antagonist, labetalol possesses partial beta-adrenergic receptor agonist activity. This intrinsic sympathomimetic action of labetalol appears to be more sustained on cardiac than on vascular beta-adrenergic receptors.     

On the mechanism of L-dopa-induced postural hypotension in the cat

1. The effects of L-DOPA on postural hypotension and carotid occlusion pressor effect were studied, mainly in cats; the recovery of the blood pressure upon tilting was used as a measure of postural hypotension.2. L-DOPA (30 mg/kg) partially depressed the carotid occlusion pressor effect and caused some degree of postural hypotension, L-DOPA (100 mg/kg) had more marked effects; the responses returned to control after 90 to 150 minutes. L-DOPA itself caused a pressor response in all cats.3. The dopa decarboxylase inhibitor N¹-(DL-seryl)-N²-(2,3,4-trihydroxybenzyl) hydrazine (RO4-4602, 50 and 10 mg/kg) had no effect itself on the tilt response but completely prevented the effects of L-DOPA on the carotid occlusion pressor effect and postural hypotension.4. After RO4-4602 (3 and 1 mg/kg), L-DOPA (100 mg/kg) caused a brief rise of blood pressure followed by a longer lasting fall in horizontally-orientated cats (i.e. `supine'' hypotension). No postural hypotension was observed after L-DOPA under these conditions.5. Noradrenaline elicited only small and transient effects on postural hypotension, but dopamine''s effects were more marked and longer lasting. Pressor dose-response relationships for noradrenaline were the same before and after L-DOPA, as well as in cats pretreated with L-DOPA for 4 days.6. In cats with kidneys and intestines removed, the tilt reflex was still present. Dose-response curves to L-DOPA were the same as in normal animals. RO4-4602 (3 mg/kg) prevented postural hypotension and block of the carotid occlusion pressor effect; supine hypotension was also observed after L-DOPA.7. The recovery response to tilting in spinal cats was markedly depressed or absent unless the blood pressure was elevated by angiotensin, in which experiments L-DOPA depressed the recovery upon tilting (i.e. induced postural hypotension).8. Blood pressure responses to tyramine were increased after 10 mg/kg of L-DOPA, but depressed after 100 mg/kg. The response to tyramine was not depressed, however, when RO4-4602 was given to block the dopa-dopamine conversion.9. The response to sympathetic stimulation in pithed rats was depressed after L-DOPA and dopamine, but not after α-methyldopa.10. α-Methyldopa (300 mg/kg) given acutely caused a moderate degree of postural hypotension and a more marked postural hypotension if given for two days.11. It is concluded that it is possible to differentiate between the supine and postural hypotension caused by L-DOPA and that supine hypotension is due to a central effect and postural hypotension to an extracerebral effect. Postural hypotension is discussed in relation to six hypotheses presented to explain its effect. Postural hypotension after L-DOPA is probably not due to a-adrenoceptor blockade, a central effect or any effect on the kidney. The most likely hypothesis is that L-DOPA forms dopamine which acts as a false transmitter in the peripheral sympathetic nervous system.     

Involvement of central alpha-adrenoceptors in the hypotensive and bradycardic effects of (--)-delta 9-trans-tetrahydrocannabinol.

I.v. administration of (--)-delta9-trans-tetrahydrocannabinol (delta 9-THC) to chloralose-anesthetized cats produced a decrease in blood pressure and heart rate. Studies conducted to investigate the mechanism of these changes revealed that the hypotensive and bradycardic effects of delta 9-THC (0.1 mg/kg, i.v.) could be significantly antagonized following intraventricular (i.v.t.) perfusion with alpha-adrenergic receptor blocking agent phentolamine, while a larger dose of delta 9-THC (0.25 mg/kg, i.v.) still produced significant hypotension and bradycardia. I.v.t. perfusion of phentolamine (100 mug/min for 30 min) caused a fall in blood pressure and heart rate which were reversible and produced blockade of central alpha-adrenergic receptors. These results provide evidence for the involvement of central alpha-adrenergic receptors in the hypotensive and bradycardic actions of delta 9-THC and indicate that other receptor mechanisms may also be involved in mediating these responses observed following administration of delta 9-THC.