USE OF A HEAD DOME SYSTEM TO COMPARE IV METHACHOLINE-INDUCED BRONCHOCONSTRICTION IN CONSCIOUS VS ANESTHETIZED RHESUS-MONKEYS

The use of a newly developed head dome system has allowed measurement of pulmonary function in conscious monkeys, Such information is often desired, so that pharmacological or toxicological effects of administe red compounds can be measured in the absence of effects from anestheti c agents. The current study was conducted to gain experience with this method and to allow the determination of the effects of sodium pentob arbital anesthesia (30 mg kg(-1) i.v.) on the bronchoconstriction seen during i.v. infusion of methacholine in rhesus monkeys, Bronchoconstr iction was measured as changes in respiratory resistance using a Buxco LS20 pulmonary mechanics computer, Four mate rhesus monkeys (4.2-5.1 kg) were used, For the anesthetized exposures, the animals were intuba ted with a 4.0-mm cuffed endotracheal tube attached to a size 'O' Flei sch pneumotachograph. For the conscious exposures, the animals sat in restraining chairs with a custom-built head dome attached to the same pneumotachograph. In both cases, transthoracic pressure was monitored with an intrapleural catheter, Each monkey was infused with methacholi ne in stepwise doses, while anesthetized and conscious, until a 75% in crease in respiratory resistance was seen, The ED(50) values of 0.134 and 0.180 mg ml(-l) methacholine were not significantly different in a nesthetized vs conscious monkeys, respectively.