Objective: To investigate the influence of psychological stress on suckling-induced oxytocin release.
Methods: The pulsatile release of suckling-induced oxytocin was measured in 22 puerperal women. The blood samples for oxytocin assay were collected at 2-minute intervals in a manner that minimized degradation by plasma oxytocinase, and were used for radioimmunoassay after extraction.
Results: The release of suckling-induced oxytocin during nursing is pulsatile, with discrete, short pulses. The frequency of pulsatile release of oxytocin was significantly lower in the two groups in which stress was imposed by mental calculation or noise than in the control group without stress (mental calculation group, 1.28 +/- 0.76 pulses/20-minute suckling period; noise group, 1.14 +/- 0.38; control group, 2.25 +/- 0.71). However, there were no differences among the three groups in the increase of prolactin during nursing or in the milk yield.
Conclusions: The release of suckling-induced oxytocin is pulsatile, and psychological stress reduces the pulsatile oxytocin release. Our data suggest that suckling-induced oxytocin release may be modulated by the central nervous system and that psychological relaxation is necessary for an adequate let-down response.