EFFECT OF MORPHINE AND NALOXONE ON LH RESPONSE AND SEXUAL-BEHAVIOR OFRAMS (OVIS-ARIES)

Effects of the opiate agonist, morphine, and antagonist, naloxone, on LH release, courtship behavior and ejaculation frequency of mature, se xually active or sexually inactive rams were investigated. Plasma LH c oncentrations were monitored from blood samples collected every 15 min for 10 hr (0800 to 1800 hr) from eight rams that were isolated from o r in contact with estrous females. Plasma LH concentration was higher (P<.05) in sexually active rams exposed to receptive females compared with hormone concentration of rams isolated from ewes. Intravenous inf usion of morphine sulphate (1 mg/kg) into rams 4 and 6 hr after exposu re to ewes reduced (P<.05) plasma LH concentration as compared to rams given saline. Morphine did not affect (P>.05) courtship behavior (inv estigatory sniff, mount attempt, foreleg kick, flehmen, vocalization) but diminished (P<.05) number of ejaculations. In another trial, LH co ncentrations were higher (P<.05) in seven sexually active rams given n aloxone iv or when given to three rams through an intracerebroventricu lar cannula (icv) as compared to LH response of sexually inactive rams . LH did not differ (P>.05) in seven sexually inactive rams before or after administration of naloxone. Investigatory sniffs by sexually act ive rams were increased (P<.03) after treatment with the opiate antago nist. Four of the seven sexually active rams had more ejaculations aft er naloxone compared with the pretreatment period, but mean ejaculatio n frequency after treatment did not differ (P=.31). Naloxone did not s timulate courtship behavior of sexually inactive males. These data sug gest that the effect of opiates on sexual behavior and LH secretion de pends upon the inherent level of sexual activity among rams.