Comparison of morphine tolerance in body temperature and luteinizing hormone secretion.
Small doses of morphine induce a hyperthermic response that does not change with repeated injections, whereas higher doses induce a hypothermia that changes to hyperthermia with repeated treatment. Experiment 1 confirmed these results in ovariectomized rats, using 6 repeated injections of morphine at 5 or 30 mg/kg. Using the same treatment regimen. Experiment 2 showed that the low dose of morphine induced a transient suppression of LH levels followed by a hypersecretion, and that repeated injections did not affect this response. The high dose (30 mg/kg) of morphine initially induced a sustained suppression of LH. Following the sixth injection of the high dose, subjects showed an intact or exaggerated suppression of LH, but an accelerated recovery to control levels. Experiment 3 extended the phase of repeated treatment of the high dose to 12 days and replicated the results of Experiment 2.
Ganesan
R
R
Department of Pharmacodynamics, University of Florida, Gainesville 32610.
Romano
T
T
Simpkins
J W
JW
D000818:Animals; D001831:Body Temperature / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood*; D009020:Morphine / Q000097:blood / Q000494:pharmacology*; D010052:Ovariectomy; D051381:Rats; D011919:Rats, Inbred Strains
D009020:Morphine; D007986:Luteinizing Hormone