Anti-tumoral action of octreotide and bromocriptine on the experimental rat prolactinoma: anti-proliferative and pro-apoptotic effects.

OBJECTIVES: The purpose of the study was to compare the effects of bromocriptine (BC) - D-2 receptor agonist and octreotide (OCT) - somatostatin analog on the tumor weight, prolactin (PRL) secretion, cell proliferation and apoptosis in the diethylstilboestrol (DES)-induced rat prolactinoma.

MATERIAL AND METHODS: Male four-week Fisher 344 rats were used in the experiment. The animals were implanted subcutaneously (s.c.) with capsules containing DES. Six weeks after the implantation the rats were given OCT (2 x 25 microg/animal/24 h s.c.) or BC (3 mg/kg b.w./24 h s.c.) for 10 days. The incorporation of bromodeoxyuridine (BrDU) into the tumor cell nuclei was used as an index of cell proliferation (labeling index - LI). The labeling of nuclear DNA fragmentation according to the TUNEL method was considered as an index of apoptosis (AI). PRL was measured by radioimmunoassay (RIA).

RESULTS: It has been found that OCT and BC significantly decreased the tumor weight and LI of tumor cells to the same extent. Both OCT and BC suppressed the PRL levels, but the inhibitory effect of BC was stronger than that of OCT. BC and OCT significantly enhanced the number of apoptotic cells in the tumor, but the pro-apoptotic effect of BC was more pronounced. The joint treatment exerted additive effects on tumor mass reduction, PRL secretion and cell proliferation, but OCT attenuated the pro-apoptotic effect of BC.

CONCLUSIONS: Summing up, both OCT and BC inhibit PRL secretion and cell proliferation. The anti-tumoral action of BC, and to some extent the action of OCT, is also connected with induction of apoptosis.