Persisting suppression of prolactin secretion after long-term treatment with bromocriptine in patients with prolactinomas.

The effect of bromocriptine withdrawal after long-term treatment on prolactin levels has been investigated in thirty-seven patients with prolactinomas. In ten patients with macroprolactinomas and post-operatively excessively high prolactin levels persisting suppression of prolactin secretion after bromocriptine withdrawal has been observed. This effect was not observed in patients with microprolactinomas or macroprolactinomas with only moderately elevated prolactin levels. The degree of persisting suppression correlated to the height of prolactin levels before treatment and to the duration of bromocriptine therapy. No correlation was found between the rise of prolactin levels after bromocriptine withdrawal and withdrawal time. It is suggested that the persisting suppression of prolactin levels is a sequence of reduction in tumour size. This anti-proliferative action of bromocriptine seems to be specific for the prolactin secreting cells in macroprolactinomas with high proliferation rate and high prolactin turn-over. These findings offer new possibilities in the management of patients with macroprolactinomas.