Oxytocin increases nociceptive thresholds in a long-term perspective in female and male rats.
Oxytocin (0.1 and 1.0 mg/kg s.c.) given to male rats during 5 days, increased tail-flick latency when measured 1 (P < 0.05) and 7 days (0.1 mg/kg, P < 0.05; 1.0 mg/kg, P < 0.01) after the last injection. The effect was gone 2 weeks after the end of the treatment. If an additional injection of oxytocin was given 10 days after a previous 5 day treatment period, the significant difference persisted after 3 weeks (P < 0.05). Tail-flick latency was significantly delayed also in oxytocin-treated females when measured 1 week after the treatment period (P < 0.05). Naloxone, but not an oxytocin antagonist, temporarily antagonised the oxytocin induced delay in withdrawal latency. This indicates that oxytocin may act by increasing the activity of opioid mechanisms.
Petersson
M
M
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Alster
P
P
Lundeberg
T
T
Uvnäs-Moberg
K
K
D000818:Animals; D005260:Female; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects*; D010121:Oxytocin / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012684:Sensory Thresholds / Q000187:drug effects*; D013997:Time Factors
D009270:Naloxone; D010121:Oxytocin