The effect of ketamine and saffan on the beta-endorphin and ACTH response to hemorrhage in the minipig.

The endocrine response is an important component of the physiological response to blood loss. There is some variability in reported levels of certain hormones during hemorrhage such as the stress hormone adrenocorticotrophic hormone (ACTH). Therefore, the effect of two anesthetic agents, ketamine and saffan, on ACTH and beta-endorphin levels during hemorrhage was assessed in 12 minipigs. The animals were divided into two groups, group I saffan and group II ketamine (n=6). Pigs were subjected to a continuous fixed volume hemorrhage under one of the above anesthetics while spontaneously breathing. Blood pressure and heart rate responses were recorded together with beta-endorphin and ACTH levels both before and at 10, 20, 30, 40 min after the onset of bleeding. ACTH levels were higher in the ketamine-anesthetized pigs and rose significantly faster with falling blood pressure than ACTH measured in pigs under saffan anesthesia. In contrast, the hemorrhage induced beta-endorphin increase was not significantly different between the two anesthetic groups. These results indicate that choice of anesthetic agent is important when investigating the hormone response to hemorrhage and may account for the variable hormone levels in the published literature to date.

Effects of different anesthetics on the paired-pulse depression of the h reflex in adult rat.

Hyperreflexia is a common feature of spinal cord injury (SCI), and changes in reflex excitability have been reported to be useful in assessing treatments in animal models of cord damage. However, spinal reflexes are known to be dependent on anesthetic level. As a preliminary to its use in SCI, the excitability of the Hoffman reflex (H reflex) has been assessed under several commonly used anesthetics. The H reflex was recorded in the distal foot muscles (dorsal interossei) of adult rats, while the lateral plantar nerve was stimulated. Five different anesthetics were used: ketamine, halothane, Nembutal, Etomidate, and Saffan. Recording and stimulating electrodes were inserted directly through the skin to minimize the surgical procedure for each experiment, allowing repeated recording to be made in the same animal on a weekly basis. Suppression of the H reflex was tested using twin-pulse stimulation. Halothane and ketamine produced suppression of the H response when interpulse intervals were shortened to less than 1 s. The H-reflex suppression profiles recorded under Etomidate, Saffan, and Nembutal anesthesia were less sensitive to the stimulation rate, with little reduction until intervals were 200 ms or less. The suppression profiles of halothane and ketamine resemble that seen in unanesthetized humans, whereas that under the other anesthetics tried here resembles that observed in spinal-cord-injured animals. The results suggest a preferential action of some anesthetics on descending pathways involved in reflex modulation and the importance of assessing reflex excitability under anesthetics such as ketamine or halothane.

Antinociceptive properties of neurosteroids II. Experiments with Saffan and its components alphaxalone and alphadolone to reveal separation of anaesthetic and antinociceptive effects and the involvement of spinal cord GABA(A) receptors.

Studies have shown that the steroid anaesthetic alphaxalone positively modulates gamma-aminobutyric acid (GABA) receptors in vitro. It has also been reported that positive modulation of GABA(A) receptors in the rat spinal cord can produce antinociception in vivo. This present study looks at the interaction of an intraperitoneal injection (i.p.) of the steroid anaesthetic combination Saffan (alphaxalone 9 mg/ml, alphadolone acetate 3 mg/ml) with GABA(A) receptors in the spinal cord. Full recovery from anaesthesia induced by Saffan 2 ml/kg i.p., as assessed by the rotarod test, occurred after 28.78 +/- 0.86 min. Residual antinociceptive effects were assessed by application of electrical current at two skin sites (neck and tail) and also tail withdrawal from noxious heat. Residual antinociception was observed at both skin sites assessed by the electrical test but not when assessed by noxious heat. The antinociceptive effects in the tail but not the neck were suppressed by intrathecal administration of GABA(A) antagonists (bicuculline and SR-95531). In a separate group of experiments alphaxalone and alphadolone were given i.p. individually at the same doses that were given when formulated in Saffan. Alphaxalone produced sedative and anaesthetic effects with no antinociception. Alphadolone caused no sedation but it did cause antinociceptive effects equal in magnitude to those produced by Saffan. We conclude that Saffan produces antinociception in rats when given i.p. by an interaction with spinal GABA(A) receptors. Furthermore, this antinociception is due to the alphadolone content of the neurosteroid anaesthetic and not the alphaxalone.

Anaesthesia of the common marmoset (Callithrix jacchus) using continuous intravenous infusion of alphaxalone/alphadalone.

A safe means of anaesthetizing common marmosets (Callithrix jacchus) for a study using magnetic resonance imaging (MRI) to investigate cerebral ischaemia was required. Continuous infusion of alphaxalone/alphadalone was used to anaesthetize 37 marmosets for non-recovery and recovery experiments. This was found to give safe, reliable anaesthesia when coupled with pulse oximetry and electrocardiographic (ECG) monitoring.

Actions of the anaesthetic Saffan on rat sympathetic preganglionic neurones in vitro.

1. Whole-cell patch-clamp recordings were used to investigate the effects of the anaesthetic Saffan on the electrophysiological properties of sympathetic preganglionic neurones (SPNs) in rat spinal cord slices. 2. Saffan (1-54 microM) abolished or reduced the frequency of spontaneous action potential firing and abolished spontaneous, sub-threshold membrane potential oscillations. Saffan caused dose-dependent decreases in input resistance and depending upon the initial resting membrane potential, either a depolarization, a hyperpolarization or no change in membrane potential. 3. Responses to Saffan were blocked by the GABAA receptor antagonists bicuculline (5-20 microM) and picrotoxin (20 microM), but not by the glycine receptor antagonist strychnine (20 microM) indicating that they were mediated by GABAA receptors. 4. Changes in the properties of SPN action potentials were also observed. In the presence of Saffan the amplitude and duration of the action potential after-hyperpolarization were reduced and larger depolarizations were required in order to evoke trains of action potentials. 5. To examine the effects of Saffan on electrotonic coupling between SPNs, experiments were performed with the Na+ channel blocker QX-314 in the intracellular solution and antidromic oscillations were evoked by ventral root stimulation. Saffan failed to abolish antidromic oscillations, but reduced their amplitude and duration. This indicates that the abolition of spontaneous membrane potential oscillations was not a direct effect on the coupling between SPNs, but was a result of the abolition of spontaneous activity by Saffan. 6. The responses to Saffan occurred within the plasma concentration range of Saffan during anaesthesia, suggesting that the electrophysiological properties of SPNs may be altered during anaesthesia with Saffan. This would be expected to lead to changes in sympathetic tone and in the integration of sympathetic output.

Effect of thiopental, saffan, and propofol anesthesia on cardiovascular parameters and bronchial smooth muscle in the rhesus monkey.

The application of human pediatric equipment for measuring respiratory function in nonhuman primates is rapidly gaining popularity in the evaluation of anti-asthma drugs. An important difference between primate procedures and the human clinical situation is the requirement for anesthesia for some techniques because of poor animal compliance. We studied the actions of three potential maintenance anesthetic agents-thiopental, saffan, and propofol-and their effects on a range of cardiovascular parameters under conditions of a broncho-provocation test in rhesus monkeys. The spasmolytic effect of saffan on bronchial smooth muscle was investigated in smooth muscle preparations in vitro and in the rhesus monkey in vivo. Thiopental proved to be a useful sedating agent for this application. Saffan proved to be a bronchodilator in vitro, but the sedative dose was lower than that required to induce appreciable bronchodilator activity in vivo. In comparison, propofol was not appropriate for this application because of the poor sedative effect at nonbronchodilator doses.

Inhibition of erythrocyte membrane ATPases with antisickling and anaesthetic substances and ionophoric antibiotics.

A study has been carried out into the effects of clinically important antisickling and anaesthetic substances and ionophoric antibiotics on the activities of (Na+, K+)- and (Ca+2, Mg2+)-ATPases of the human erythrocyte membrane. In general, these drugs, with the exception of nystatin, inhibit both types of enzymic activities but with varying degrees of efficacy. (Ca2+, Mg2+)-ATPases was more sensitive to the lipophilic anaesthetics and (Na+,K+)-ATPase to the ionophoric antibiotic, amphotericin B. These results are explained in the light of the partition coefficients of these drugs in erythrocyte membranes, their effects on the fluidity of the erythrocytes membranes, the changes they induce in the permeability properties of erythrocytes and the subsequent effect of procaine on sickling of erythrocytes, and their potential interaction with specific membrane components.

Effects of administration of oxytocin in association with gonadotropin-releasing hormone on luteinizing hormone levels in rats in vivo.

Gonadotropin-releasing hormone (GnRH) and oxytocin both stimulate the secretion of luteinizing hormone (LH), although with different characteristics. Therefore, interaction between oxytocin and GnRH in the control of LH may be postulated. We developed models for investigating whether oxytocin can modulate GnRH action on LH in vivo. Pentobarbitone is known to pharmacologically isolate the pituitary from hypothalamic GnRH. We found that after pentobarbitone anesthesia of female rats at proestrus, oxytocin caused a synergistically enhanced LH response to administered GnRH (p < 0.04). In a second series of experiments, female proestrous rats were anesthetized with althesin. This anesthetic allows transport of endogenous GnRH from the hypothalamus to the pituitary. In control animals, which received no exogenous hormone, there was a surge in the mean LH concentration on the evening of proestrus, indicating the presence of endogenous GnRH activity. Thus, the novel model enables detection of interactions of administered hormones with endogenous GnRH. Administration of GnRH plus oxytocin in the afternoon of proestrus caused a reduction (p < 0.01) in the mean level of LH observed in the evening. The reduction was larger than if GnRH alone was administered. Following althesin anesthesia, rats sometimes had low LH levels on the afternoon of proestrus. There was a statistically significant difference between the number of rats that received oxytocin plus GnRH and had low LH levels and the number with low LH levels in the control group (p < 0.02). Neither of the hormones administered alone had a significant effect. Thus, it appears that oxytocin accentuated the effect of GnRH in reducing LH concentrations in althesin-anesthetized rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaesthetic steroids--a review.

Steroids produce anaesthesia besides producing the well known metabolic and hormonal effects. A number of anaesthetic steroids have been synthesized and tried clinically. Hydroxydione, althesin, minaxolone and pregnanolone are among those studied in detail. They act through GABAergic mechanism and are known to be advantageous over barbiturates.

Effect of physostigmine on the loss of consciousness induced by midazolam, etomidate and althesin.

The effect of physostigmine, a cholinesterase inhibitor, on the loss of consciousness induced by three different intravenous induction anesthetics, namely midazolam, etomidate and althesin at ED50, was studied in three comparable groups of patients. Ten min before induction, the first and second groups received physostigmine 8 micrograms/kg and 16 micrograms/kg, respectively, and the third group received 2 ml of saline solution. Physostigmine 16 micrograms/kg resulted in a significant decrease in the percentage of unconscious patients with midazolam (from 50% to 10%), but it did not modify the incidence with etomidate or althesin. Physostigmine at doses of 8 micrograms/kg and 16 micrograms/kg could cause 6.7% and 10% nausea, respectively. Although the mechanism of the drug interaction of physostigmine and midazolam is unclear, physostigmine could be used clinically to reverse post-anesthetic somnolence induced by midazolam.

Effects of inhalation and intravenous anesthetic agents on pressor response to NG-nitro-L-arginine.

The effects of anaesthetic agents on pressor effect of NG-nitro-L-arginine (L-NNA), a potent inhibitor of nitric oxide (NO) synthesis, were examined in rats. I.v. bolus of L-NNA (1-32 mg/kg) in conscious rats dose dependently increased mean arterial pressure (MAP) to a maximum value of 53 +/- 2 mmHg at 16 mg/kg with ED50 value of 4.7 +/- 0.9 mg/kg. The effects of a single i.v. bolus dose (32 mg/kg) of L-NNA were examined in conscious rats and rats anaesthetised with pentobarbital, chloralose, ketamine, althesin (mixture of alphaxalone and alphadolone), urethane, enflurane or halothane. In conscious rats, peak MAP (51 +/- 3 mmHg) was reached 10 min after i.v. injection and the effect lasted more than two hours. The magnitudes of peak MAP differed under the influence of anaesthetic agents with the following rank order: althesin greater than conscious = pentobarbital = chloralose = ketamine = urethane greater than enflurane much greater than halothane (in which there was negligible change in MAP). The onsets were delayed in rats anaesthetised with pentobarbital, althesin, chloralose and enflurane but not altered with ketamine and urethane compared to that in conscious rats. Therefore, L-NNA caused intense and prolonged pressor response in conscious rats and rats anaesthetised with the i.v. anaesthetic agents pentobarbital, chloralose, ketamine, althesin and urethane. MAP effect of L-NNA was markedly attenuated by the inhalation anaesthetics halothane and enflurane.

Course of murine leukemia retrovirus infection determined in vivo by magnetic resonance imaging.

Magnetic resonance imaging was applied to measure the volumes of spleens and lymph nodes of mice infected with three different leukemia retroviruses (LP-BM5 murine leukemia virus, Friend, and Rauscher) in vivo. Anesthesia by rapid intraperitoneal injection of Saffan was sufficient for magnetic resonance imaging and could be repeated at appropriate intervals. Eleven frontal magnetic resonance images through the abdomen with a center-to-center distance of 1.5 mm between adjacent slices were acquired simultaneously. To optimally demarcate spleens from the surrounding tissues, the magnetic resonance images were mildly T2-weighted for mice infected with LP-BM5 murine leukemia virus and mildly T1-weighted for those infected with Friend and Rauscher virus. Measurements requiring only 3 to 4 hours in groups of 24 to 28 mice were accomplished by using a standardized holder (i) accommodating two animals in the supine position and (ii) ensuring reproducible positioning in the magnetic resonance-instrument, and (iii) by reducing the number of phase-encoding steps of mildly T2-weighted magnetic resonance images from 256 to 128. Volumes of spleens and inguinal lymph nodes were calculated from the respective cross-sectional areas. The weights and magnetic resonance image-derived volumes of spleens and inguinal lymph nodes correlated well (r greater than 0.95). Despite large variations in the extent of splenomegaly and lymphadenopathy at any given time, the progression of the disease could easily be followed by repeating magnetic resonance imaging at intervals. Thus, statistically relevant results can be obtained in an infection model requiring the use of only a few animals.

Anaesthetic suppression of transmitter actions in neocortex.

1. The effects of general anaesthetics were investigated on neuronal sensitivities to transmitter substances, which were determined by iontophoretic applications of acetylcholine, glutamate, N-methyl-D-aspartate (NMDA) and gamma-aminobutyrate (GABA) during intracellular recording in in vitro slice preparations of neocortex (guinea-pig). 2. In most of the 65 neurones studied, perfusion of isoflurane (0.5-2.5 minimum alveolar concentration (MAC)) or Althesin (25-200 microM) and, in some cases, halothane (0.5-2 MAC), markedly reduced the depolarizing responses and associated membrane conductance changes evoked by dendritic applications of acetylcholine, glutamate, NMDA and GABA. 3. The order of depression was acetylcholine greater than glutamate or NMDA much greater than GABA. This selectivity could also be assessed from the EC50 for the isoflurane-induced depression of the just-maximal responses to acetylcholine, which was 0.9 MAC compared with an EC50 = 1.9 MAC for the suppression of glutamate responses. The selectivity was less pronounced in the case of the actions of Althesin, where the EC50s were 75 microM for the depression of acetylcholine responses and 90 microM for the depression of glutamate responses. 4. The hyperpolarizing responses observed when GABA was applied near the perikaryon in 7 neurones, were slightly reduced (approximately 15%) in 4, and unchanged in 3 neurones during anaesthetic application. 5. The pronounced depression of the responsiveness to the putative arousal transmitters and an observed blockade of acetylcholine-induced potentiation of glutamate actions suggest that anaesthetics produce unconsciousness, at least in part, by interfering with subsynaptic mechanisms of neocortical activation.

Contribution of pregnan steroid Althesin to the pathophysiology of epilepsy.

The original study with Althesin in the development of epilepsy was carried out in nine patients. EEG and SEEG records show that sensitivity to Althesin, which is a mixture of pregnandiol and pregnan acetate, precursors of sexual hormones, raises in the direction to the oldest brain formations. A physiological substance in provoking epilepsy was discovered.

Effects of althesin and urethan-chloralose on neurohumoral cardiovascular regulation.

The cardiovascular effects of althesin (ALT) and urethan-chloralose (UC) anesthesia were compared in conscious, chronically instrumented rats. Althesin had no effect on arterial pressure or base-line resistance in the renal, superior mesenteric, and hindquarters vasculatures but increased heart rate. In contrast, UC decreased arterial pressure, heart rate, and mesenteric resistance. Although UC attenuated depressor responses to nitroglycerin, neither anesthetic significantly altered regional vascular reactivity to intravenous phenylephrine and nitroglycerin. The cardiac chronotropic baroreflex was examined by comparing the slope of the curves relating maximal changes (delta) in heart rate (pulse interval) that occurred at the point coinciding in time with the maximal changes in mean arterial pressure produced by phenylephrine and nitroglycerin. Neither anesthetic significantly altered the baroreflex slope (delta pulse interval/delta mean arterial pressure) for pressor and depressor stimuli. Both anesthetics attenuated the sympathoexcitatory response to cerebroventricular angiotensin II, although ALT had less of a depressive effect (pressor response during ALT and UC = 65 and 30%, respectively, of conscious). Plasma renin activity (PRA) and the hemodynamic response to peripheral angiotensin-receptor antagonism were significantly increased (PRA by almost 6-fold) during UC, whereas ALT was without effect. Similarly, UC but not ALT induced vasopressin-dependent vascular tone. Ganglionic blockade indicated that peripheral neurogenic tone was not altered by ALT anesthesia. These data suggest that althesin produces fewer hemodynamic disturbances than urethan-chloralose and largely maintains cardiovascular regulation intact.

Effects of steroid anaesthesia on some liver function tests in goats.

The effect of Saffan, a steroid anaesthetic, on the liver function of goats has been studied. Forty healthy animals were divided into 4 equal groups. The first 2 groups were given 2 and 4 mg Saffan/kg b. wt respectively. A mixture of Saffan (1 mg) and Xylazine (0.1 mg)/kg b. wt was given to the third group and Xylazine alone to the fourth group (0.1 mg/kg b. wt). Serum samples from all groups were analysed for glucose, total protein, total and direct bilirubin and the level of activity of transaminases. Administration of Saffan evoked more hyperglycemia than a mixture with Xylazine, or Xylazine alone. The hyperglycemic effect of both doses of Saffan (2 and 4 mg) was equivocal beyond 2 h. The effect then differed and glucose was increased 4-fold by 2 mg and 3-fold by 4 mg Saffan. Serum total protein, conjugated and total bilirubin, and GPT and GOT were not changed in the four experimental groups. This was good evidence of a normally functioning liver during the course of steroid anaesthesia administration in goats.

Effect of anaesthetic agents on bile flow and biliary excretion of 131I-cholylglycyltyrosine in the rat.

We have compared in the rat the effects of i.v. anaesthetic agents on bile flow rate and on the biliary excretion of a novel bile acid, 131I-cholylglycyltyrosine (131I-cholylgly.tyr.). Etomidate 1-mg bolus and 2-mg h-1 infusion, Althesin 3-mg bolus and 14.5-mg h-1 infusion and propofol 3.3-mg bolus and 3.3-mg h-1 were given via a tail vein cannula and pentobarbitone 50 mg kg-1 was given by the intraperitoneal route, to groups of six rats. Each animal received only one anaesthetic agent. One hour after cannulation of the common bile duct, 131I-cholylgly.tyr. 5 microCi was injected into the jugular vein and bile was collected every 1 min for 10 min. The mean (SD) percentage cumulative biliary excretion of 131I-cholylgly.tyr. at the end of 10 min was: propofol group 74.1 (5.2)%; Althesin group 82.3 (2.2)%; etomidate group 69.4 (17.6)%; pentobarbitone group 76.4 (3.2)%. Propofol and Althesin were relatively more choleretic, causing bile flow rates twice that produced by pentobarbitone. Only Althesin caused a significant increase in biliary excretion of 131I-cholylgly.tyr. relative to that in rats that received pentobarbitone. Bile flow rates for the respective anaesthetic techniques (microliter min-1/100 g body weight) (mean (SD)) were: propofol group 14.1 (1.8); Althesin group 12.5 (1.7); etomidate 8.5 (1.4); pentobarbitone group 7.3 (1.0). There was a marked metabolic acidosis in all rats except in the propofol group, in which normal acid-base status and oxygenation were observed.