Respiratory function in rats restrained for extended periods: assessment of the effects of bethanecol.
BACKGROUND
The ICH guideline S7A recommends that the effects of drugs on the respiratory system are evaluated in laboratory mammals prior to administration in man. Previously, animals have been placed in plethysmography chambers for short durations. This study investigates the possibility of restraining animals in chambers for a longer duration to assess respiratory function over extended periods.


METHODS
Respiratory function in conscious rats was assessed using plethysmography chambers where the rat body was enclosed in a sealed chamber while the head was free. Thoracic movements were measured by pressure transducers linked to a Buxco amplifier system and respiratory parameters were captured and analyzed by the Notocord HEM data acquisition system. Each animal was subjected to 5 acclimatization sessions of escalating duration (1, 2, 4, 5, and 6 hours (h)) over 5 days prior to testing, with a baseline recording session conducted the day prior to dosing. Animals (8 males/group) were dosed subcutaneously with saline or bethanecol (3, 10, or 30 mg/kg) and placed in the chambers for 6 h of continuous recording. Additionally, a recording session was conducted at 24 h post-dose.


RESULTS
Subcutaneous administration of 30 mg/kg bethanecol decreased respiration rate by up to 33% during the first 1.5 h post-dose and increased tidal volume by up to 46% from 0.25 to 1.25 h post-dose when compared to vehicle group data. A decrease in minute volume of up to 33% was observed 0.25 h following administration of the 10 and 30 mg/kg doses.


CONCLUSIONS
These data show a respiratory depression caused by the cholinergic agonist bethanecol, an effect partially compensated for by an increase in tidal volume. This also demonstrates the ability to continuously restrain and record respiratory parameters in conscious rats for up to 6 h without any negative impact on the quality of the data.
Harris
David
D
Department of Pharmacology, Quintiles Limited, Heriot-Watt University Research Park, Riccarton, Edinburgh EH14 4AP, UK. david.harris@quintiles.com
Graham
Mags
M
Price
Joanne
J
Munro
Fiona
F
Templeton
Alison
A
Young
Ross
R
Paterson
Kirsty
K
Anderson
Lynne
L
Gillies
Susanne
S
McKendrick
Sue
S
Low
Gill
G
Patmore
Leslie
L
Bodine
Rebeccah
R
Jeanne Kallman
Mary
M
Hoffman
Wherly P
WP
Lee
Cindy
C
Wolff
Ronald K
RK
D000818:Animals; D018723:Bethanechol / Q000633:toxicity*; D004353:Drug Evaluation, Preclinical / Q000379:methods*; D064420:Drug-Related Side Effects and Adverse Reactions; D007279:Injections, Subcutaneous; D008297:Male; D018721:Muscarinic Agonists / Q000633:toxicity*; D010993:Plethysmography, Whole Body / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D012143:Respiratory Physiological Phenomena / Q000187:drug effects*; D012149:Restraint, Physical; D013990:Tidal Volume / Q000187:drug effects
D018721:Muscarinic Agonists; D018723:Bethanechol