Prolactin release in dairy heifers relative to duration of teat stimulation.

Experiments have shown that the prolactin response specific to sustained teat stimulation is strictly dependent upon the duration of stimulation. There is some evidence for assuming two principally different patterns of prolactin response, namely high sensitivity to the stimulus with an initial maximal response, and poor sensitivity to the stimulus with a gradually intensifying response. Hyperstimulation of teats results in relative refractoriness of neural receptors for specific prolactin impulses. Refractoriness of one teat leads to a reduction in the release of prolactin which can be overcome by the stimulation of another as yet unstimulated teat.