Effect of an acute β-adrenergic blockade on the blood glucose response during lactate minimum test

The aim of this study was to determine the relationship between blood lactate and glucose during an incremental test after exercise induced lactic acidosis, under normal and acute β-adrenergic blockade. Eight fit males (cyclists or triathletes) performed a protocol to determine the intensity corresponding to the individual equilibrium point between lactate entry and removal from the blood (incremental test after exercise induced lactic acidosis), determined from the blood lactate (Lacmin) and glucose (Glucmin) response. This protocol was performed twice in a double-blind randomized order by ingesting either propranolol (80 mg) or a placebo (dextrose), 120 min prior to the test. The blood lactate and glucose concentration obtained 7 minutes after anaerobic exercise (Wingate test) was significantly lower (p<0.01) with the acute β-adrenergic blockade (9.1±1.5 mM; 3.9±0.1 mM), respectively than in the placebo condition (12.4±1.8 mM; 5.0±0.1 mM). There was no difference (p>0.05) between the exercise intensity determined by Lacmin (212.1±17.4 W) and Glucmin (218.2±22.1 W) during exercise performed without acute β-adrenergic blockade. The exercise intensity at Lacmin was lowered (p<0.05) from 212.1±17.4 to 181.0±15.6 W and heart rate at Lacmin was reduced (p<0.01) from 161.2±8.4 to 129.3±6.2 beats min-1 as a result of the blockade. It was not possible to determine the exercise intensity corresponding to Glucmin with β-adrenergic blockade, since the blood glucose concentration presented a continuous decrease during the incremental test. We concluded that the similar pattern response of blood lactate and glucose during an incremental test after exercise induced lactic acidosis, is not present during β-adrenergic blockade suggesting that, at least in part, this behavior depends upon adrenergic stimulation.

Effect of furosemide treatment on the central and peripheral pressor responses to cholinergic and adrenergic agonists, angiotensin II, hypertonic solution and vasopressin

The present study was performed to investigate the effect of treatment with furosemide on the pressor response induced by intracerebroventricular (i.c.v.) injections of cholinergic (carbachol) and adrenergic (norepinephrine) agonists, angiotensin II (ANGII) and hypertonic saline (HS, 2 M NaCl). The changes induced by furosemide treatment on the pressor response to intravenous (i.v.) norepinephrine, ANGII and arginine vasopressin (AVP) were also studied. Rats with a stainless-steel cannula implanted into the lateral ventricle (LV) were used. Two injections of furosemide (30 mg/kg b.wt. each) were performed 12 and 1 h before the experiments. Treatment with furosemide reduced the pressor response induced by carbachol, norepinephrine and ANGII i.c.v., but no change was observed in the pressor response to i.c.v. 2 M NaCl. The pressor response to i.v. ANGII and norepinephrine, but not AVP, was also reduced after treatment with furosemide. These results show that the treatment with furosemide impairs the pressor responses induced by central or peripheral administration of adrenergic agonist or ANGII, as well as those induced by central cholinergic activation. The results suggest that the treatment with furosemide impairs central and peripheral pressor responses mediated by sympathetic activation and ANGII, but not those produced by AVP. © 1992.

Role of cholinergic and adrenergic pathways of the medial septal area in the control of water intake and renal excretion in rats

In this study, we investigated an interaction between noradrenergic and cholinergic pathways of the medial septal area (MSA) on the control of water intake and urinary electrolyte excretion by means of injection of their respective agonists. Noradrenaline (a nonspecific α-adrenergic agonist) and clonidine (an α2-adrenergic agonist), but not phenylephrine (an α1-adrenergic agonist), induced natriuresis and kaliuresis. α-Adrenergic activation had no effect on the natriuresis and kaliuresis induced by carbachol (a cholinergic agonist) and it inhibited the antinatriuresis and antikaliuresis induced by isoproterenol (a ß-adrenergic agonist). Interactions related to volume excretion are complex. α-Adrenergic activation induced a mild diuresis and inhibited the antidiuresis induced by isoproterenol, but phenylephrine combined with carbachol induced antidiuresis. The water intake induced by carbachol was inhibited by clonidine and noradrenaline, but not phenylephrine. These results show an asymmetry in the interaction between α-adrenergic and cholinergic receptors concerning water intake and electrolyte excretion. © 1992.

Role of the adrenergic pathways of the lateral hypothalamus on water intake and pressor response induced by the cholinergic activation of the medial septal area in rats

In the present experiments, we investigated a possible involvement of noradrenergic receptors of the lateral hypothalamus (LH) in the water intake and pressor response induced by cholinergic stimulation of the medial septal area (MSA) in rats. The cholinergic agonist carbachol (2 nmol) injected into the MSA induced water intake and pressor response. The injection of an α2-adrenergic agonist, clonidine (20 and 40 nmol), but not of an α1-adrenergic agonist, phenylephrine (80 and 160 nmol), into the LH inhibits the water intake induced by carbachol injected into the MSA. The injection of clonidine or phenylephrine into the LH produced no change in the MAP increase induced by carbachol injected into the MSA. The present results suggest that adrenergic pathways involving the LH are important for the water intake, but not for the pressor response, induced by cholinergic activation of the MSA. © 1994.

Cardiac dysfunction induced by obesity es not related to beta-adrenergic system impairment at the receptor-signalling pathway

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Renal- and calcium-dependent vascular effects of Polybia paulista wasp venom

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Brain monoaminergic neurons and ventilatory control in vertebrates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Cardiovascular changes under normoxic and hypoxic conditions in the air-breathing teleost Synbranchus marmoratus: importance of the venous system

Synbranchus marmoratus is a facultative air-breathing fish, which uses its buccal cavity as well as its gills for air-breathing. S. marmoratus shows a very pronounced tachycardia when it surfaces to air-breathe. An elevation of heart rate decreases cardiac filling time and therefore may cause a decline in stroke volume (VS), but this can be compensated for by an increase in venous tone to maintain stroke volume. Thus, the study on S. marmoratus was undertaken to investigate how stroke volume and venous function are affected during air-breathing. To this end we measured cardiac output (Q), heart rate (fH), central venous blood pressure (PCV), mean circulatory filling pressure (MCFP), and dorsal aortic blood pressures (PDA) in S. marmoratus. Measurements were performed in aerated water (P-O2 > 130 mmHg), when the fish alternated between gill ventilation and prolonged periods of apnoeas, as well as during hypoxia (P-O2 <= 50 mmHg), when the fish changed from gill ventilation to air-breathing. Q increased significantly during gill ventilation compared to apnoea in aerated water through a significant increase in both fH and VS. PCV and MCFP also increased significantly. During hypoxia, when the animals surface to ventilate air, we found a marked rise in fH, PCV, MCFP, Q and VS, whereas PDA decreased significantly. Simultaneous increases in PCV and MCFP in aerated, as well as in hypoxic water, suggests that the venous system plays an important regulatory role for cardiac filling and VS in this species. In addition, we investigated adrenergic regulation of the venous system through bolus infusions of adrenergic agonists (adrenaline, phenylephrine and isoproterenol; 2 mu g kg(-1)). Adrenaline and phenylephrine caused a marked rise in PCV and MCFP, whereas isoproterenol led to a marked decrease in PCV, and tended to decrease MCFP. Thus, it is evident that stimulation of both alpha- and beta-adrenoreceptors affects venous tone in S. marmoratus.

Cardiovascular actions of rattlesnake bradykinin ([Val(1), Thr(6)] bradykinin) in the anesthetized South American rattlesnake Crotalus durissus terrificus

Incubation of heat-denatured plasma from the rattlesnake Crotalus atrox with trypsin generated a bradykinin (BK) that contained two amino acid substitutions (Arg(1) --> Val and Ser(6) --> Thr) compared with mammalian BK. Bolus intra-arterial injections of synthetic rattlesnake BK (0.01-10 nmol/kg) into the anesthetized rattlesnake, Crotalus durissus terrificus, produced a pronounced and concentration-dependent increase in systemic vascular conductance (Gsys). This caused a fall in systemic arterial blood pressure (Psys) and an increase in blood flow. Heart rate and stroke volume also increased. This primary response was followed by a significant rise in Psys and pronounced tachycardia (secondary response). Pretreatment with N-G-nitro-L-arginine methyl ester reduced the NK-induced systemic vasodilatation, indicating that the effect is mediated through increased NO synthesis. The tachycardia associated with the late primary and secondary response to BK was abolished with propranolol and the systemic vasodilatation produced in the primary phase was also significantly attenuated by pretreatment, indicating that the responses are caused, at least in part, by release of cathecholamines and subsequent stimulation of beta-adrenergic receptors. In contrast, the pulmonary circulation was relatively unresponsive to BK.

The autonomic control and functional significance of the changes in heart rate associated with air breathing in the jeju, Hoplerythrinus unitaeniatus

The jeju is a teleost fish with bimodal respiration that utilizes a modified swim bladder as an air-breathing organ (ABO). Like all air-breathing fish studied to date, jeju exhibit pronounced changes in heart rate (f(H)) during air-breathing events, and it is believed that these may facilitate oxygen uptake (M-O2) from the ABO. The current study employed power spectral analysis (PSA) of f(H) patterns, coupled with instantaneous respirometry, to investigate the autonomic control of these phenomena and their functional significance for the efficacy of air breathing. The jeju obtained less than 5% of total M-O2 (M-tO2) from air breathing in normoxia at 26 degrees C, and PSA of beat-to-beat variability in fH revealed a pattern similar to that of unimodal water-breathing fish. In deep aquatic hypoxia (water P-O2=1 kPa) the jeju increased the frequency of air breathing (f(AB)) tenfold and maintained M-tO2 unchanged from normoxia. This was associated with a significant increase in heart rate variability (HRV), each air breath (AB) being preceded by a brief bradycardia and then followed by a brief tachycardia. These f(H) changes are qualitatively similar to those associated with breathing in unimodal air-breathing vertebrates. Within 20 heartbeats after the AB, however, a beat-to-beat variability in f(H) typical of water-breathing fish was re-established. Pharmacological blockade revealed that both adrenergic and cholinergic tone increased simultaneously prior to each AB, and then decreased after it. However, modulation of inhibitory cholinergic tone was responsible for the major proportion of HRV, including the precise beat-to-beat modulation of f(H) around each AB. Pharmacological blockade of all variations in f(H) associated with air breathing in deep hypoxia did not, however, have a significant effect upon f(AB) or the regulation of M-tO2. Thus, the functional significance of the profound HRV during air breathing remains a mystery.

Ractopamine in diets for finishing gilts

Foi realizado um experimento utilizando-se 468 fêmeas, com peso inicial de 84,77 ± 7,20 kg, alojadas em 36 baias, para avaliar os efeitos da adição de ractopamina nas dietas sobre o desempenho, as características e os rendimentos de cortes comerciais da carcaça, a composição e os cortes cárneos do pernil. O desenho experimental usado foi o de blocos ao acaso com quatro níveis de ractopamina (0, 5, 10 e 15 mg/kg de dieta) e nove repetições com 13 animais por unidade experimental. O critério para formação dos blocos foi o peso inicial dos animais. Não foram observados efeitos dos níveis de ractopamina sobre o ganho de peso diário dos animais. O consumo diário de ração apresentou redução linear com o aumento do nível de ractopamina nas dietas. A conversão alimentar dos animais melhorou de forma linear com a inclusão de ractopamina na dieta dos animais. Verificaram-se também diferenças significativas na proporção de gordura e carne na carcaça e nos cortes cárneos. Houve efeito linear decrescente da ractopamina sobre a quantidade e profundidade de gordura e efeito linear crescente sobre a porcentagem de carne magra, de carne no pernil e sobre os pesos de semimembranosus e gluteus medius. Dietas para fêmeas suínas em fase final de terminação devem conter 15 mg de ractopamina por kg.

Eficácia analgésica da dexmedetomidina comparada ao sufentanil em cirurgias intraperitoneais: estudo comparativo

JUSTIFICATIVA E OBJETIVOS: A dexmedetomidina, agonista alfa2-adrenérgico com especificidade alfa1:alfa2 1:1620, não determina depressão respiratória, sendo utilizada no intra-operatório como sedativo e analgésico. Esse fármaco tem sido empregado com os opióides em anestesia de procedimentos com elevado estímulo doloroso, como os abdominais intraperitoneais, não havendo referências sobre seu uso como analgésico único. Comparou-se a dexmedetomidina ao sufentanil em procedimentos intraperitoneais, de pacientes com mais de 60 anos de idade. MÉTODO: Foram estudados 41 pacientes divididos aleatoriamente em dois grupos: GS (n = 21), que recebeu sufentanil, e GD (n = 20), dexmedetomidina, ambos na indução e manutenção da anestesia. Os pacientes receberam etomidato (GS e GD) com midazolam (GD) na indução, isoflurano e óxido nitroso na manutenção da anestesia. Foram avaliados os atributos hemodinâmicos (pressão arterial média e freqüência cardíaca), tempos de despertar e de extubação ao final da anestesia, locais onde os pacientes foram extubados - sala de operação (SO) ou sala de recuperação pós-anestésica (SRPA), tempo de permanência na SRPA, necessidade de analgesia suplementar e antiemético na SRPA, complicações apresentadas na SO e SRPA, índice de Aldrete-Kroulik na alta da SRPA e a necessidade de máscara de oxigênio na alta da SRPA. RESULTADOS: Não houve diferença quanto à estabilidade hemodinâmica e GD apresentou menor tempo de permanência na SRPA e menor necessidade de máscara de oxigênio na alta da SRPA. CONCLUSÕES: A dexmedetomidina pode ser utilizada como analgésico isolado em operações intraperitoneais em pacientes com mais de 60 anos, determinando estabilidade hemodinâmica semelhante à do sufentanil, com melhores características de recuperação.

Efeitos da dexmedetomidina sobre o sistema renal e sobre a concentração plasmática do hormônio antidiurético: estudo experimental em cães

JUSTIFICATIVA E OBJETIVOS: A insuficiência renal aguda peri-operatória é responsável por elevada taxa de morbidade e mortalidade. Os fármacos alfa2-agonistas aumentam o débito urinário e promovem boa estabilidade hemodinâmica nesse período. O objetivo desta pesquisa foi estudar os efeitos renais e sobre a concentração plasmática do hormônio antidiurético (HAD) provocados pela dexmedetomidina no cão anestesiado. MÉTODO: Trinta e seis cães adultos, anestesiados com propofol, fentanil e isoflurano, foram divididos aleatoriamente em três grupos que receberam, de modo encoberto: G1 - injeção de 20 mL de solução de cloreto de sódio a 0,9%, em 10 minutos, seguida de injeção de 20 mL da mesma solução em uma hora; G2 - injeção de 20 mL de solução de cloreto de sódio a 0,9% contendo dexmedetomidina (1 µg.kg-1), em 10 minutos, seguida de injeção de 20 mL da mesma solução, com a mesma dose de dexmedetomidina (1 µg.kg-1), em uma hora e G3 - injeção de 20 mL de solução de cloreto de sódio a 0,9% contendo dexmedetomidina (2 µg.kg-1) em 10 minutos, seguida de injeção de 20 mL da mesma solução, com a mesma dose de dexmedetomidina (2 µg.kg-1), em uma hora. As variáveis renais, hemodinâmicas e a concentração plasmática do HAD foram estudadas em quatro momentos: M1 (controle) - imediatamente após o período de estabilização; M2 - após a injeção inicial de 20 mL da solução em estudo, em 10 minutos, coincidindo com o início da injeção da mesma solução, em uma hora; M3 - 30 minutos após M2 e M4 - 30 minutos após M3. RESULTADOS: A dexmedetomidina reduziu a freqüência cardíaca e promoveu estabilidade hemodinâmica, mantendo constante o débito cardíaco. Houve elevação do débito urinário no G2 e G3, em comparação com o G1. A osmolalidade urinária no G2 e G3 foi menor no M3 e M4 em relação ao M1 e M2. A depuração de água livre aumentou no G3. A concentração plasmática do HAD diminuiu no G3, apresentando valores mais baixos que os observados no G1 e G2 em M2 e M4. CONCLUSÕES: Os cães anestesiados com baixas doses de dexmedetomidina promovem diurese hídrica por inibir a secreção do hormônio antidiurético, havendo potencial para proteção renal em eventos isquêmicos.

Uso de dexmedetomidina em neurocirurgia

JUSTIFICATIVA E OBJETIVOS: Os fármacos alfa2-agonistas são a cada dia mais utilizados em Anestesiologia, seja como adjuvantes ou como agentes anestésicos únicos. Atualmente, o emprego da dexmedetomidina vem se popularizando devido à sua maior seletividade aos receptores alfa2 e, também, ao seu perfil farmacocinético. O objetivo desta revisão foi fazer uma análise do emprego da dexmedetomidina em neurocirurgia. CONTEÚDO: Além das considerações e revisão da literatura quanto ao emprego da dexmedetomidina especificamente em procedimentos neurocirúrgicos, foi realizada descrição dos efeitos do fármaco nos diversos sistemas do organismo. CONCLUSÕES: A dexmedetomidina tem perfil farmacocinético e farmacodinâmico que favorece seu emprego em diversos procedimentos neurocirúrgicos. A utilização clínica em procedimentos cirúrgicos com craniotomia para pinçamento de aneurisma e remoção de tumores é crescente. Além disso, seu uso em intervenções cirúrgicas funcionais é promissor.