Effect of subacute cabergoline treatment on prolactin, thyroid stimulating hormone and growth hormone response to simultaneous administration of thyrotrophin-releasing hormone and growth hormone-releasing hormone in hyperprolactinaemic women.

It is known that dopaminergic neurotransmission is involved in the control of PRL, TSH and GH secretion. Cabergoline (CAB) is a new ergolinic derivative with a long-acting dopaminergic activity. We evaluated 11 women with pathological hyperprolactinaemia before and during sub-acute CAB treatment (0.8-1.2 mg/p.o.; 8 weeks). Simultaneous administration of TRH (200 micrograms i.v.) and GHRH 1-44 (50 micrograms i.v.) were carried out before and after 4, 8 and 10 week intervals from the beginning of CAB treatment. Basal PRL levels (2453.5 +/- S.E. 444.5 mU/l) were significantly reduced during CAB administration (week 4: 164.5 +/- 66.5 mU/l; week 8: 168.0 +/- 66.5 mU/l; P less than 0.01) and no variations were observed 2 weeks after drug discontinuation (week 10: 210.0 +/- 98.0 mU/l). PRL percentage change after TRH was increased by CAB (P less than 0.05). No variation in basal and TRH-stimulated TSH levels was found during CAB administration. A slight increase in GH basal levels (3.0 +/- 0.6 mU/l) was found after weeks 4 (6.4 +/- 2.0 mU/l) and 10 (5.8 +/- 1.6 mU/l) (P less than 0.05). GH response to GHRH was significantly enhanced (ANOVA: P less than 0.01) during sub-acute CAB treatment. A positive correlation was found between GH secretory area and weeks of CAB therapy (P less than 0.01). Our data show that CAB is very effective in lowering PRL secretion in hyperprolactinaemia, and is able to modify PRL and GH responses after TRH and GHRH. The increasing trend in GH basal and GHRH-stimulated GH levels seems to indicate that CAB can override the central dopaminergic tone which is operative in hyperprolactinaemia.