Oxytocin determination by radioimmunoassay in cattle

Abstract

Abstract. Oxytocin concentration in jugular vein blood was measured radioimmunologically with a detection limit of 3 pg/ml plasma in male and female cattle. Five bulls were tested; during mating a cow in oestrus with intromission and ejaculation, during mounting a dummy or another bull with ejaculation into an artificial vagina or during false mounts. No increase in oxytocin concentrations could be observed, but stimulation with an electro-ejaculator caused an increase ranging from 5–84 pg/ml after a latent period of 3–5 min. A similar response was observed in two cows following the same procedure. The contact with a bull, false mount or mating with intromission and ejaculation was not followed by a measurable oxytocin release in 5 test cows. The following stimulation techniques, massage of vulva and clitoris, massage of cervix and uterus per rectum, artificial insemination, introduction of a speculum into the vagina or insufflation of air into the vagina were performed with 5 cows and 5 heifers. Insufflation of air into the vagina was the most effective stimulus, eleciting an oxytocin release up to 588 pg/ml. All 5 heifers responded positively, as well as 4 cows in oestrus. The other manipulations caused an oxytocin response mainly in heifers (whether in oestrus or dioestrus), whereas only one cow in oestrus responded with an oxytocin release. In general, oxytocin concentrations increase about 30–90 s after the start of the stimulus.