The factors that control oxytocin secretion in men and in non pregnant, non suckling women are unclear (Fig. 5.10). Recent studies in animals show that osmotic stimulation releases oxytocin in similar quantities to vasopressin, but that the quantity of oxytocin released after haemorrhage is considerably smaller than the quantity of vasopressin released. Oxytocin secretion appears to increase with the duration of pregnancy, but the regulating factors that are involved are unknown. Suckling is a specific stimulus for oxytocin release. Plasma oxytocin concentrations rise to very high values at the end of parturition, release being stimulated by cervical dilatation (the Ferguson reflex).
