SECRETION OF DOPAMINE INTO HYPOPHYSEAL PORTAL BLOOD BY RATS BEARING PROLACTIN-SECRETING TUMORS OR ECTOPIC PITUITARY-GLANDS

Catecholamines were quantified in hypophyseal portal plasma obtained from cycling diestrous rats and from noncycling diestrous rats with hyperprolactinemia due to PRL[prolactin]-secreting pituitary explants or a PRL-secreting pituitary tumor. In rats bearing PRL-secreting tumors, the plasma concentration of PRL was 4450 .+-. 938 ng/ml (mean .+-. SE), whereas in cycling diestrous animals the plasma level of PRL was 16 .+-. 2.2 ng/ml. The concentration of dopamine in hypophysial portal plasma of tumor-bearing rats (2.0 .+-. 0.3 ng/ml) was significantly greater (P < 0.05) than that in diestrous rats (1.1 .+-. 0.2 ng/ml). The anterior pituitary content of PRL was 18 .+-. 1.5 .mu.g in cycling diestrous animals and 9 .+-. 0.8 .mu.g in tumor-bearing rats. The adrenals from tumor-bearing animals were much heavier (155 .+-. 14 mg) than those from cycling diestrous rats (58 .+-. 1.2 mg). The concentration of dopamine in portal plasma from tumor-bearing adrenalectomized rats was 2.0 .+-. 0.5 ng/ml, similar to that in portal plasma from tumor-bearing intact animals. The arterial plasma concentration of PRL in rats bearing 4 anterior pituitary explants maintained under the renal capsule was 178 .+-. 20 ng/ml. The pituitary content of PRL was 11 .+-. 1.6 .mu.g, which was significantly less (P < 0.01) than that in cycling diestrous animals (19 .+-. 1.9 .mu.g). The dopamine concentration in portal plasma from cycling diestrous rats was 1.3 .+-. 0.23 ng/ml and was 1.3 .+-. 0.36 ng/ml in the rats bearing ectopic pituitary glands. Agents secreted by the tumor, possibly PRL and/or an ACTH-like substance, apparently can lead to an increased secretion of dopamine by the hypothalamus.