Abstract
A highly sensitive, specific and reproducible double antibody RIA [radioimmunoassay] for measuring oxytocin in unextracted serum of cattle was developed. Serum concentrations of oxytocin were significantly (P < 0.05) elevated from 8.0 .+-. .11 .mu.U[units]/ml to 25 .+-. 7.6 .mu.U/ml (mean .+-. SE) 2 min after commencement of milking. The range of peak oxytocin concentrations seen 2 min after milking in 6 animals was 11.2-65 .mu.U/ml. The T1/2 [half-life] for oxytocin, after milk ejection, was 3.6 min. Simultaneous determinations of oxytocin activity in blood sera and intramammary pressure were monitored in 2 cows before, during and after stimulation of the milk ejection reflex. Ocytocin activity in blood closely paralleled changes in intramammary pressure.