Effects of atropine and pyridostigmine in heat-stressed patas monkeys

Abstract

The effects of a single intramuscular atropine injection (0.03 mg.kg-1) and a chronic oral pyridostigmine treatment (0.4 mg.kg-1, 3 times/day over a period of 7 d) on the thermoregulatory effector responses of unanesthetized patas monkeys were investigated using indirect calorimetry. The effects of atropine treatment on the thermoregulatory effector responses of patas monkeys exposed to 25 degrees and 35 degrees C were qualitatively similar but quantitatively greater at 35 degrees C. At 35 degrees C atropine decreased sweating (Esw) 52%, increased rectal temperature (Tre), mean skin temperature (Tsk), metabolic rate (MR), and whole body conductance (K), and elicited a consistent 11% increase in heart rate (HR). Daily oral pyridostigmine treatment to patas monkeys produced a significant 25-30% drop in serum cholinesterase activity with no chronic effects on thermoregulatory or cardiovascular functions. The acute effects of oral pyridostigmine treatment in this species included transient 12% and 15% decreases in MR and HR, respectively, and a transient 25% increase in Esw. The latter was associated with significant acute reductions in Tre and Tsk which lasted at least 120 min following pyridostigmine administration. It is concluded that the patas monkey is an excellent animal model for studies to evaluate the effects of neuroactive agents on thermoregulatory and other physiological functions which are difficult, if not impossible, to perform on humans.