Effect of magnesium ions on rat pineal N-acetyltransferase (EC 2.3.1.5) activity

N-Acetyltransferase (NAT) activity at night and following isoproterenol treatment in intact animals was higher in rats pretreated with magnesium than in controls. This effect was probably due to enhancement of agonist binding and/or adenylate cyclase activation caused by magnesium ions. A similar effect was observed in vitro, where magnesium increased norepinephrine-stimulated NAT activity in organ-cultured pineal glands, suggesting that magnesium acts primarily on the pineal gland as opposed to some other peripheral or central site. This enhancement of NAT activity by magnesium would presumably lead to increased melatonin production; and as melatonin has been shown to decrease serum magnesium levels, a negative feedback mechanism may exist.

Anesthetic considerations at moderate altitude

The influence that changes in altitude may have on various aspects of anesthetic practice are discussed. The consequences of alterations in the partial pressure and density of anesthetic gases are described, as well as the problems that may arise as a result of using measuring devices calibrated in percentages that actually measure partial pressure. The performance of vaporizers under conditions of reduced barometric pressure is considered. The behavior of flowmeters at altitude was studied. The increase in flow produced by flowmeters under hypobaric conditions is not a constant factor dependent on density, but is variable at flow rates below 4 L/min. The following suggestions are put forward. Anesthetists should be encouraged to think in terms of the partial pressures of gases that they are using rather than concentrations. Measuring devices and vaporizers that are dependent on partial pressure and not on concentration should be calibrated in the appropriate units. The term MAC could be replaced by MAPP, which would more accurately represent the important factor in the delivery of anesthetic gases. The value of nitrous oxide in anesthetic practice at altitude needs to be reassessed.

Apparent traumatic perforation of the bowel in tetanus. A case report

A case of severe tetanus complicated by intestinal perforation is described. Because of the nature of the treatment in tetanus, the diagnosis was missed for several weeks and the patient's life consequently put at great risk. The possibility that the perforation may have resulted from extreme intra-abdominal pressure changes during spasms is discussed as well as the difficulties of managing such complications in an intensive care unit.

Effects of halothane or enflurane with controlled ventilation on auditory evoked potentials

The effects of increasing concentrations of halothane and enflurane on selected components of the auditory evoked response were studied in 12 patients; six received halothane and six enflurane. After the induction of anaesthesia with thiopentone, anaesthesia was maintained with 70% nitrous oxide in oxygen. Ventilation was controlled. The inspired concentration of the inhalation agent was increased incrementally, halothane in steps of 0.5% up to 2.5%, and enflurane in steps of 1% up to 5%. With both agents, linear dose-related increases were seen in the latencies of waves III, V, Pa and Nb and the interpeak intervals I-V and III-V, with decreases in the amplitudes of Pa and Nb. In five of the patients the inhalation agent was discontinued at the end of the test period, resulting in reversal of the changes in some or all of these waves. End-tidal carbon dioxide tension was controlled and variations of temperature and arterial pressure were insufficient to produce the observed changes. The results show that halothane and enflurane delay neural transmission along the brainstem and cortical sections of the auditory pathway and that the effects of these agents are approximately related to their known anaesthetic potencies.

Role of prolactin in vitamin D metabolism and calcium absorption during lactation in the rat

Intestinal calcium absorption and plasma levels of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) were measured in lactating and non-lacting rats and the effects of bromocriptine and exogenous prolactin treatment were evaluated. In lacting rats calcium absorption and plasma levels of parathyroid hormone, 1,25(OH)2D3 and alkaline phosphatase activity were significantly increased. Bromocriptine treatment significantly reduced the enhanced calcium absorption and levels of plasma 1,25(OH)2D3 and alkaline phosphatase but had no significant effect on plasma levels of parathyroid hormone. Prolactin administered with bromocriptine to lactating animals prevented all the changes observed with bromocriptine treatment alone. It was concluded that the increased plasma levels of prolacting during lactation lead to high plasma levels of 1,25(OH)2D3 which are responsible for the enhanced intestinal calcium absorption.

Nitrous oxide analgesia and altitude

The analgesic effectiveness of 50% nitrous oxide and oxygen or oxygen-enriched air, measured by variations in pain threshold, was studied at an altitude of 1460 m and simulated altitudes of sea level and 3300 m. At sea level pressures, 50% nitrous oxide exerted a similar analgesic effect to that found for morphine, raising the pain thresholds by a mean of 71.5%. At 1460 m, the increase in pain threshold produced was 40% and at 3300 m the increase in pain threshold was only 19%. The difference between the analgesic effects of nitrous oxide at each altitude was statistically significant. It is concluded that moderate altitudes significantly reduce the effectiveness of nitrous oxide in a manner directly related to the partial pressure of nitrous oxide at each altitude.

A study of the thermogenic effect of ethanol in the hypothermic rat

1. The hypothesis that ethanol may exert a thermogenic effect in cold environments was studied by infusing ethanol, dextrose or saline into hypothermic rats and observing the rate of rewarming in each group. 2. No difference was found in the rate of heat gain in any of the three groups.

The use of the Cape Minor ventilator with the circle absorber system

Various methods by which the Cape Minor ventilator may be used in the circle absorber system are described and the problems of the circuits described are considered. A new valve system is described which overcomes most of the problems encountered with other circuits. The economic advantages of an inexpensive ventilator and absorber system which is economical are obvious.

Analgesic effect of ethyl alcohol

The analgesic properties of ethyl alcohol administered i.v. were investigated, using elevation of the pain threshold for applied somatic stimuli as an index. Alcohol proved markedly superior to saline in this respect and produced an effect equivalent to that of i.v. morphine.