Secretion of dopamine into hypophysial portal blood by rats bearing prolactin-secreting tumors or ectopic pituitary glands

Catecholamines were quantified in hypophysial portal plasma obtained from cycling diestrous rats and from noncycling diestrous rats with hyperprolactinemia due to PRLsecreting 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 μg in cycling diestrous animals and 9 ± 0.8 μg 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 four anterior pituitary explants maintained under the renal capsule was 178 ± 20 ng/ ml. In these same animals, the pituitary content of PRL was 11 ± 1.6 μg, which was significantly less (P μ 0.01) than that in cycling diestrous animals (19 ± 1.9 fig). 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. It is concluded that agents secreted by the tumor, possibly PRL and/or an ACTH-like substance, can lead to an increased secretion of dopamine by the hypothalamus.