No abstract

Some of the effects of inhalational anacsthetics may be mcdiatcd by 13-endorphins acting on opioid receptors. Stimulation of such receptors has been shown both to promote and to inhibit the release of arginine vasopressin (AVP). Ten rabbits were studied to determine the response of plasma AVP to a predetermined time/concentration "dose" of halothane, enflurane or isoflurane. Abolition of corneal rcflex was used as a standard end-point. Plasma samples were obtained from awake animals and after exposure to the anaesthetics, the sequence being randomly assigned. No significant changes in plasma AVP concentrations were observed when predetermined time/concentration "doses" of the agents were administered to the rabbits. Anaesthesia produced by halothane, enflurane or isoflurane, therefore, is not necessarily accompanied by changes in plasma AVP.

The specificity, the potency, and the duration of action of [1-(beta-mercapto-beta, beta-cyclopentamethylenepropionic acid) 2-(O-methyl)tyrosine]arginine-vasopressin[d(CH2)5Tyr(Me)AVP] to antagonize pressor responses to arginine vasopressin (AVP) was examined in pentobarbital-anaesthetized rats. Injection of the compound (4 micrograms.kg-1 i.v.) prevented pressor responses to i.v. infusions of supramaximal doses of AVP, but not to i.v. infusions of another peptide, angiotensin II (Ag II). The antagonism of AVP persisted for at least 3 h. Since i.v. injection of the compound in the absence of exogenous administration of AVP did not cause any change in the arterial pressure of rats, it appears that the compound is devoid of agonistic pressor activity. The results show that d(CH2)5Tyr(Me)AVP is a potent and a specific antagonist of pressor responses to AVP.

Cyanosig it a sign for which the anaesthetist must be alert. Intraoperative eyanosis requires rapid and definitive diagnostic manoeuvres to rule out hypoxaemia prior to considering more exotic causes. The following case illustrates the course of such an investigation. Case reportA 15-year-old boy from France, while attending an international church conference, developed periumbilieal pain. After 48 hours the pain localized to the right lower quadrant and he was taken late at night to the emergency department. A diagnosis of appendicitis was made. Intravenous fluids were started and he was given metronidazole 5(~0 rag, tobmmycin 60 rag, meperidine 50 mg and dimenhydrinate 50 rag.The patient gave a history of essential hypertension and

THE STATE OF AWARENESS is known to have a functional relationship with the brain stem reticular formation. This follows the work of Moruzzi and Magoun. 1 The concept of the ascending (reticular activating) fibres arising from the reticular formation and influencing widespread central nervous system centres is illustrated in Figure 1. It is known that thalamocurtieal trafl~e is multidirectional. 1 The state of awareness is characterized in electroencephalographic recordings obtained from the cerebral cortex of man and experimental animals by the pattern of activation. 1 This consists of fast, low amplitude waves in the EEC tracing. Sleep, on the other hand, is associated with the EEC pattern of deactivation which is characterized by higher amplitude and slower electrical recordings. During the production and maintenance of anaesthesia, there is a graded pattern of fast