Hyperprolactinemia Exerts a Negative Effect on theβ-Endorphin Content of the Rat Neurointermediate Pituitary Lobe*

Publisher Website
Google Scholar
Abstract
Implantation of the prolactin [PRL], ACTH, .beta.-endorphin (.beta.-EP), and .beta.-lipotropin (.beta.-LPH)-secreting transplantable rat pituitary tumor 7315a resulted in a suppression of the PRL and the ACTH content of the anterior pituitary gland and also of the .beta.-EP/.beta.-LPH content of the neurointermediate (NI) lobe. Treatment with bromocriptine further diminished the anterior lobe PRL content, whereas haloperidol partially inhibited this tumor-mediated diminution. The administration of these drugs did not influence the suppressed ACTH content of the anterior pituitary lobe. The diminished .beta.-EP/.BETA.-LPH content of the NI lobe of tumor-bearing rats became completely normal after treatment with haloperidol, whereas bromocriptine administration further diminished the NI lobe .beta.-EP/.beta.-LPH content. There was a close correlation between the anterior pituitary lobe PRL content and the .beta.-EP/.beta.-LPH content of the NI lobe in all 4 groups of rats taken together (including nontumor-bearing controls, control tumor rats, and tumor rats treated with bromocriptine or haloperidol; P < 0.01). Implantation of the pure PRL-secreting pituitary tumor 7315b resulted in hyerprolactinemia and a suppression of the PRL content of the anterior lobe and the .beta.-EP/.beta.-LPH content of the NI lobe, without affecting the ACTH content of the anterior pituitary lobe. There was a negative correlation between the level of the circulating PRL concentration and the .beta.-EP/.beta.-LPH content of the NI lobe. A possible relationship between the synthesis of PRL by the anterior-pituitary lactotroph and of the hormones of the NI lobe is suggested. The level of the circulating PRL concentration may play, directly or indirectly, a role in the regulation of both systems.