Vasodilator responses to enflurane in the small intestine

Local effects of enflurane on intestinal vascular resistance were studied in vivo in cats. A jejunal segment was prepared and perfused at constant flow with blood from the femoral arteries. The intestine was either: (1) left with intact sympathetic innervation, (2) denervated and exposed to electrical post-ganglionic vasoconstrictor nerve stimulation, or (3) excluded from neurogenic remote control by post-ganglionic denervation. Enflurane dissolved in lipid and intra-arterially administered to the jejunal segment in doses comparable to those clinically encountered, decreased intestinal vascular resistance in relation to the intra-arterial concentration of the drug. The vasodilator response was, at the highest enflurane doses studied (blood concentration: 400 and 800 mg X 1(-1], most pronounced in the intestine with intact sympathetic innervation. Otherwise, no differences were observed in vasodilator responses between the three different investigated modes of neurogenic influence on the intestine. In vitro enflurane (-in-lipid) did not affect the vasoconstrictor response to electrical field stimulation in the rat mesenteric arterioles. Enflurane, however, dose-dependently reduced spontaneous contractile activity in the rat portal veins.

Intestinal vascular effects of inhaled and locally administered enflurane in the cat

The effects of enflurane on intestinal vascular resistance and blood flow in the intestine were studied in cats during basal chloralose anaesthesia. A jejunal segment was prepared and perfused with blood from both femoral arteries, allowing control of intestinal inflow pressure. Mesenteric venous blood flow was measured with an optical drop recorder. During constant intestinal arterial pressure (75 mmHg; 10 kPa), intestinal vascular resistance was calculated during enflurane inhalation at MAC 0.5 and 1.0 before and after postganglionic denervation of the jejunal segment. Inhalation of enflurane reduced intestinal vascular resistance in a dose-dependent fashion. The decrease in vascular resistance was attenuated but not abolished by post-ganglionic denervation, indicating both peripheral and central nervous sites of action for enflurane. Furthermore, with the intestinal segment perfused at systemic arterial pressure, the effects of locally intraarterially infused enflurane dissolved in a fat emulsion was studied. A vasodilator response was elicited in the intestine when exposed to local arterial enflurane concentrations in the same range as encountered during surgical anaesthesia in man, supporting the hypothesis of a peripheral site of action.

Cardiovascular studies during controlled baroreflex activation in the dog: II. Effects of metoprolol and enflurane

An experimental model was designed to study circulatory drug effects with or without barostatic reflex influences. In dogs anaesthetized with chloralose, both carotid sinuses were perfused from a femoral by-pass either with systemic arterial pressure or with a pump in order to control the sinus pressure. Cardiac and aortic baroreceptors were denervated. I.v. metoprolol (240 micrograms X kg-1 + 102 micrograms X kg-1 X h-1) with constant carotid sinus pressure and thereby constant baroreceptor activation reduced cardiac output, heart rate, cardiac contractility and left ventricular stroke work index. Systemic vascular resistance increased. This response was independent of the degree of baroreflex activation. During the combined administration of enflurane (1.6% end-tidal concentration) and metoprolol, cardiac performance (cardiac output, stroke volume, heart rate, cardiac contractility and left ventricular stroke work index) was depressed independent of the degree of baroreflex activation. Barostatic reflexes, however, counteracted an observed decrease in systemic vascular resistance. This reflex vascular response was, during metoprolol-enflurane administration, associated with an increased left ventricular end-diastolic pressure.

Adrenergic hyperactivity and epidural block in severe tetanus. A case report

In a 69-year-old man with severe tetanus, sympatho-adrenal overactivity was successfully treated with a lumbar epidural block. Cardiovascular disturbances were reduced and fluctuations in plasma catecholamines were decreased. The duration of other manifestations of tetanus was, however, not influenced by the epidural block in this case.

Effects of TRH and TRH analogues on the central regulation of breathing in the rat

Respiratory activity was studied in rats during light halothane anesthesia. Thyrotropin releasing hormone (TRH) and two TRH analogues: the desamidated form (TRH-OH) and gamma-butyrolactone-gamma-carbonyl-L-histidyl-L-prolinamide citrate (DN 1417) were administered intracerebroventricularly. TRH 0.5-5 micrograms induced a marked tachypnoea with a rapid onset and a duration of at least 20 min. DN 1417, a potent analogue of TRH with a very low TSH (thyroid stimulating hormone) releasing activity was more effective in stimulating respiratory frequency, while TRH-OH, regarded to have neither TSH releasing nor extra hypothalamic effects, at equimolar doses was unable to induce any changes in the respiratory pattern. When TRH was given into the fourth ventricle the dose response curve was slightly shifted to the left. In experiments employing the occluded breath technique, P0.1 was increased in the same magnitude as the mean inspiratory flow (VT/T1). The results also indicated an increase in the gain of the inflation reflex loop whereas the central bulbopontine setting for T1 and TTOT were not significantly changed. Local injection of TRH into the nucleus tractus solitarii induced a stimulation of respiratory frequency which was slower in onset compared to the response seen after injection into the lateral or fourth ventricles. Concomitantly to the respiratory changes, i.c.v. TRH injection induced a hypocarbia and an alkalosis. No changes in blood pressure or heart rate were seen. The respiratory stimulant effect of TRH could be potentiated by pretreatment with naloxone, methylatropine or a low dose of GABA. Haloperidol or propranolol did not significantly change the respiratory effects of TRH, while reserpine pretreatment seemed to blunt some of the ventilatory effects of TRH. It seems likely that TRH has few direct effects on brain stem neurones involved in the central regulation of respiration, but the main effects seem to be elicited in areas rostral to the brain stem. The respiratory stimulating effect of TRH is unrelated to TSH. Furthermore, other neurotransmitter systems might also be involved in modulation of the respiratory stimulation evoked by TRH.

beta-Receptor blockade and neurolept anaesthesia. Withdrawal vs continuation of long-term therapy in gall-bladder and carotid artery surgery

Forty-eight chronically (greater than 3 months) beta-receptor-blocked patients with ischaemic heart disease and/or hypertension were studied on 49 occasions after random distribution to a 4-day, gradual preoperative withdrawal (n = 26) or a continuation (n = 23) of beta-receptor blockers. The patients were scheduled for either a cholecystectomy (n = 28) or a carotid thrombendarterectomy (n = 21) under neurolept anaesthesia. Three patients were excluded from the randomized part of the study due to complications (tachycardia, hypertension, severe angina) after therapy withdrawal. In subgroups, central haemodynamics (beta-receptor blockers withdrawn n = 6, continued n = 8) and creatinine-kinase B (beta-receptor blockers withdrawn n = 9, continued n = 11) were studied. Withdrawal of beta-receptor blockers was associated with high heart rates, supraventricular tachyarrhythmias and a hyperkinetic circulation during pain stimuli. Significantly more postoperative ECG changes (P less than 0.02) indicative of myocardial ischaemia were found than in beta-receptor blocked patients. These patients had low heart rates but also pronounced increases in pulmonary capillary wedge pressures, which in single patients could be associated with myocardial damage. These results imply that beta-receptor blockers should be continued before surgery and that a concomitant vasodilatatory therapy is likely to avoid the drawbacks of an increased cardiac afterload.

Long-term beta-receptor blockade--adrenergic and metabolic response to surgery and neurolept anaesthesia

Twenty-six patients on chronic (greater than 3 months) beta-receptor blocking therapy due to ischaemic heart disease and/or hypertension were randomly distributed to a 4-day gradual withdrawal (n = 13) or a continuation of ordinary therapy until a planned cholecystectomy under neurolept anaesthesia (n = 13). Plasma-adrenaline, -noradrenaline, -potassium, -glycerol, -FFA, -insulin and b-glucose were determined perioperatively. The metabolic response to surgery was as expected with hyperglycaemia and depressed insulin levels, which did not differ significantly between the two groups of patients. Plasma-catecholamines showed the highest mean values during emergence from anaesthesia. Plasma-adrenaline and -potassium were constantly highest in the beta-receptor-blocked patients, who also showed indices of a relatively depressed lipolysis compared to patients in whom beta-receptor blockers had been withdrawn. These discrepancies between withdrawal versus continuation of preoperative beta-receptor blockade seemed to be of small clinical importance and did not oppose the present view that beta-receptor blockers should generally be continued during surgery. However, findings in individual patients suggest that beta-receptor blockade may maintain hypoglycaemia in catabolic patients.

Beta-receptor blockade and spinal anaesthesia. Withdrawal versus continuation of long-term therapy

A prospective study was performed in 43 men scheduled for transurethral resections under spinal anaesthesia. All patients were on chronic beta-receptor blockade because of hypertension and/or ischaemic heart disease. The patients were randomly subjected to either a gradual preoperative withdrawal or a continuation of the beta-receptor blockade. Haemodynamics were measured non-invasively. Spinal anaesthesia was performed and an i.v. injection of atropine given. The patients were then placed in a lithotomy position. Mean anaesthetic level included T6. After beta-receptor blocker withdrawal consistently elevated heart rates, a high incidence of arhythmias, angina pectoris and postoperative ST-T changes indicating myocardial ischaemia were seen. These changes were not seen in patients with continued beta-receptor blockade. Withdrawal of beta-receptor blockers was also associated with an increased total peripheral vascular resistance in connection with spinal anaesthesia. These results suggest that patients on long-term beta-receptor blockade should continue the therapy during and after spinal anaesthesia.

Evidence for a dopamine interaction with the central respiratory control system in the rat

Respiratory activity was studied in adult rats during light halothane anesthesia. Dopamine agonists and antagonists were injected intracerebroventricularly (i.c.v.) or systemically. The respiratory parameters were recorded after exposure to O2 or to CO2 in O2. Apomorphine (i.c.v. 300 microgram) induced a biphasic response with an initial decrease in respiratory frequency (f) followed by pronounced tachypnoea after 5 min. The changes in tidal volume (VT) showed an inverse pattern. When apomorphine was administered into the fourth ventricle, only the later phase of the biphasic response was observed. Haloperidol (2 mg/kg i.p.) antagonized the apomorphine-induced response in contrast to domperidone (2 mg/kg i.v.), a dopamine receptor blocking agent which does not pass the blood brain barrier. Administered i.c.v., haloperidol as well as domperidone induced a decrease in f while VT was increased. The same response was observed after the presynaptic dopamine receptor agonist 3-PPP, 3-(3-hydroxyphenyl)-N-n-propylpiperidine. Hypercapnea was found to decrease the tachypnea in apomorphine-treated animals. Apomorphine also induced a decrease in blood pressure and heart rate, which was not reversed by haloperidol. It is concluded that there is a centrally located, tonically activated dopamine system involved in respiratory regulation. The predominant effect seems to be of a respiratory stimulating nature. The possible role of presynaptic and different postsynaptic dopamine receptor mechanisms is discussed.

Respiratory effects of TRH in preterm rabbits

The respiratory activity in newborn preterm (29 days gestation) rabbits was studied after administration of thyrotropic releasing hormone. Intraperitoneal injection induced an increase in respiratory frequency (f) and a decrease in tidal volume (VT) resulting in a slight increase in pulmonary ventilation (VE). These effects were seen in parallel to a decrease in expiratory time (TE) and respiratory time (TTOT). An increase in the TI/TTOT ratio but (unaffected) VT/TI ratio indicates that thyrotropic releasing hormone affects "respiratory timing" mechanisms rather than "inspiratory drive." The changes in respiratory parameters are most probably due to an effect on the central respiratory controlling centers in the brain stem.

Hemodynamic effects of massive doses of dexamethasone in controlled hypovolemic shock in the dog

The hemodynamic effects of massive doses of dexamethasone in combination with the alpha-adrenergic blocking agent phenoxybenzamine were studied in dogs subjected to hemorrhagic hypotension. Previously it has been shown that the glucocorticoid methylprednisolone, but not the glucocorticoid betamethasone, induces a pronounced vasodilation in combination with phenoxybenzamine. In the present study it was found that also dexamethasone (a stereoisomer of betamethasone) is unable to increase the peripheral blood flow after phenoxybenzamine. Since equivalent doses were used in relation to glucocorticoid activity, it seems reasonable to conclude that the different hemodynamic patterns are unrelated to the glucocorticoid ability of the drugs. Furthermore, it is unlikely that possible beneficial effects of dexamethasone in hypovolemic shock are due to a direct vascular influence.

Effects of vagotomy and glossopharyngectomy on respiratory response to dopamine-agonists

In normal rats lightly anesthetized with halothane apomorphine increased both resting and CO2-dependent minute ventilation (VM) by stimulating respiratory frequency (RF) whereas tidal volume (VT) was slightly decreased. Acute bilateral glossopharyngectomy, which impaired carotid body function, did not change the apomorphine effects in contrast to bilateral vagotomy, which abolished the RF response of the drug, but now increased VT. Intravenous infusion of dopamine increased VM by elevating RF, and this effect was only slightly blunted by bilateral glossopharyngectomy but nearly abolished by vagotomy and totally eliminated by the combined procedures. The respiratory response to dopamine was depressed in rats with chronically destroyed central catecholaminergic neurons. These findings indicate that there may be two different dopaminergic stimulatory mechanisms that modulate RF-one peripheral and one central-and both depend upon afferent vagal activity. With impaired vagal function, however, two other dopaminergic stimulatory mechanisms effecting VT are evident-one central, and one peripheral which involves the carotid body.

Myositis ossificans circumscripta in para/tetraplegics

At the Hospital of Physical Medicine, Hornbaek, we analysed in retrospect 52 cases of myositis ossificans circumscripta (MOC) among 605 patients with para/tetraplegia. MOC proved significantly more common after total than after subtotal spinal cord injuries. MOC was not observed in any case above the motor level of the spinal cord lesion. This neurological relationship appears to "explain" the finding that MOC is more common in para/tetraplegia of traumatic origin (more complete spinal cord lesions) than among those caused by slipped discs or tumours. Twenty-five per cent of the patients ended up with fairly mild and 12% with more severe hip contractures, the latter causing recurrent, contralateral decubital ulcers over the ischial tuberosity and protracted hospitalization. To aid diagnosis, the authors suggest a simple programme for all para/tetraplegics. In our opinion, routine X-ray examination is not necessary. Intensified research into the causative factors and treatment is needed, not only to facilitate these patients' social adaptation, but also for socio-economic reasons.

GABA-ergic mechanisms in central respiratory control in the anesthetized rat

Rats lightly anesthetized with halothane were injected intracerebroventricularly (i.c.v.) with gamma aminobutyric acid (GABA) and the GABA-like drugs muscimol, baclofen, and gamma-hydroxybutyric acid (GHBA). Respiratory frequency (f) was reduced after GABA (1 mg) but increased after baclofen (0.5 microgram), while muscimol (0.5 microgram) or GHBA (1 mg) did no affect f. However, GHBA administered repeatedly caused a dose-dependent increase in f. Tidal volume (VT) decreased in a dose-dependent fashion after i.c.v. administration of all the drugs used. Taken together, these changes in f and VT resulted mainly in a dose dependent decrease in minute volume (VE) after GABA and muscimol while after baclofen and GHBA VE was increased due to the marked stimulation of f after repeated administration. Mean arterial pressure (MAP) decreased after GABA and muscimol while no effect or a slight increase was seen after baclofen and GHBA. Heart rate (HR) was unaltered after muscimol, decreased after gaba but slightly increased after GHBA and baclofen. No alterations were seen in blood gases except after administration of GABA which induced a slight hypoxia, hypercapnia and acidosis. The data indicate that an activation of GABA-ergic mechanisms results in a respiratory depression. Moreover, the effects of GABA and muscimol are probably due to a direct GABA-ergic receptor activation while the effects elicited by baclofen and GHBA are due to other mechanisms than direct GABA receptor activation or indirect effects via other system on respiratory regulating centers.

Central respiratory stimulant effect by thyrotropin in releasing hormone in the rat

Anaesthetized male rats were injected intracerebroventricularly with the tripeptide, thyrotropin releasing hormone (TRH). Respiratory frequency (f), tidal volume (VT) and minute volume (VE) were measured in a closed whole body plethysmograph by a low pressure transducer connected to a Grass polygraph. TRH induced an approximately 50% increase in f, while VT was not altered. VE increased in the same proportion as f. Our results indicate that TRH neurons or TRH-sensitive receptors may be involved in the regulation of central respiratory activity.

Vascular and metabolic effects of methylprednisolone and phenoxybenzamine during controlled hypotension in the dog

The relationship between central haemodynamics and vascular and metabolic parameters in skeletal muscle was studied in dogs subjected to controlled haemorrhagic hypotension and treated with cumulative doses of methylprednisolone (4-32 mg x kg-1), (or saline in the control group), followed by phenoxybenzamine. There were no significant haemodynamic or metabolic changes between the groups during the injections of steroid or saline. The alpha-adrenergic receptor blockade caused, as found earlier, a pronounced vasodilation in the steroid group, which was parallelled by an increase in muscle blood flow in the same order of magnitude. There was no clearcut relationship between metabolic and vascular effects in the groups. Despite the significant difference in blood flow between the groups after phenoxybenzamine, only small and insignificant differences were seen in muscle metabolites, with the exception of muscle lactate which showed higher values in the steroid group. The study provides further evidence in support of the hypothesis that the haemodynamic effects of the combination of methylprednisolone and phenoxybenzamine are of neurogenic origin.

Neuronal and extraneuronal uptake of 3H-noradrenaline in rat portal vein in vitro

Rat portal veins were incubated with 3 different concentrations of 3H-l-noradrenaline (3H-l-NA) and the radioactive material retained in the tissue as well as that present in the postincubation medium was analyzed after a postincubation period in substrate-free medium. Inhibition of the neuronal amine uptake mechanism (by preincubation with LU 3-010) reduced the retention of radioactivity in the tissue more at low than at high substrate concentrations. At increasing substrate concentrations the relative role of the extraneuronal amine uptake was increased. Corticosterone and hydrocortisone reduced extraneuronal accumulation whereas betamethasone and methylprednisolone in the concentrations used were ineffective, indicating that the inhibition of extraneuronal uptake by the corticosteroids is unrelated to their glucocorticoid potency. When the composition of the retained radioactivity was analyzed, NA was found to be the major component of the retained radioactivity after inhibition of extraneuronal uptake, whereas tritiated catabolites were found to be the predominating constituent of the retained radioactivity after neuronal uptake inhibition. The possible role of inactivation of the adrenergic transmitter by the extraneuronal uptake mechanism in different situations is discussed.

Transient apnea after an enkephalin analogue in the preterm rabbit

FK 33-824, a potent enkephalin analogue was administered systemically, 0.5-5 mg/kg to preterm neonatal rabbits. A marked decrease in respiratory frequency as well as irregular breathing and apneic spells was recorded at 5 mg/kg. Tidal volume was not affected. The enkephalin-induced respiratory depression was restored immediately after naloxone (10 mg/kg). Bases on the results it may be speculated upon whether brain stem enkephalin neurons are involved in the pathogenesis of neonatal transient apnea and irregular breathing.

Effects of adrenergic neuron and ganglion blockers on hemodynamics and plasma catecholamine levels after corticosteroids during hemorrhagic shock in the dog

The involvement of adrenergic mechanisms in the ability of massive doses of methylprednisolone to potentiate the vasodilatory effects of phenoxybenzamine during controlled hemorrhagic shock was investigated. Dogs were subjected to ligation of the adrenals and, with the exception of the controls, were pretreated with either hexamethonium or bretylium. Despite careful surgery, the adrenal ligation, per se, failed to alter the concentration of plasma catecholamines. Hexamethonium and bretylium, on the other hand, both decreased the levels of plasma catecholamines: noradrenaline to a greater extent than adrenaline. Methylprednisolone was almost ineffective after ganglionic or adrenergic neuron blockade. Furthermore, the degree of vasodilation after methylprednisolone and phenoxybenzamine seemed to correlate better with plasma noradrenaline than with adrenaline. These findings indicate that the ability of methylprednisolone to induce vasodilation in the presence of adrenergic alpha-receptor blockade in hypovolemic shock in the dog relies on an intact release of noradrenaline from postganglionic adrenergic nerve terminals.

Respiratory depression by GABA-ergic drugs in the preterm rabbit

Respiratory parameters were studied in preterm rabbits (gestational age 29 days) after intraperitoneal administration of the GABA-like drugs gamma-hydroxybutyric acid and muscimol. The animals were anaesthetized with 0.7% halothane in oxygen and studied in a closed body plethysmograph. Both drugs induced a decreased respiratory frequency and minute volume. Tidal volume decreased after muscimol, but not after gamma-hydroxybutyric acid administration. The present results indicate that an increased GABA-ergic activity causes respiratory depression in the preterm neonatal rabbit, presumably by an action on central nervous frequency and tidal volume modulating systems. Central GABA neurons may thus be involved in the pathogenesis of neonatal respiratory depression and irregular breathing.

Effects of different monoamine oxidase inhibitors on respiratory activity in rats with chronically impaired central serotonergic function

Resting and CO2 stimulated respiration were measured by means of a whole-body plethysmograph in rats lightly anaesthetized with halothane. Rats pretreated neonatally with intracisternal 5,7-dihydroxytryptamine (5,7-DHT) to destruct permanently central serotonergic neurones had significantly lower resting and CO2 stimulated respiratory frequency (RF) and minute volume (VM) than naive rats. In the 5,7-DHT pretreated rats, but not in naive rats, the monoamine oxidase inhibitors clorgyline and pargyline further reduced both resting and CO2 stimulated RF and VM, whereas 1-deprenyl stimulated respiration. The results provide additional evidence that monoaminergic mechanisms are involved in central modulation of respiration in which activation of a serotonergic neuronal system depresses, and dopaminergic activation stimulates respiration.