In vivo release of dopamine, luteinizing hormone-releasing hormone and thyrotropin-releasing hormone in male rats bearing a prolactin-secreting tumor.

Abstract

The present study was concerned with the effects of a transplantable prolactin-secreting pituitary tumor (7315b) on the hypothalamic release of dopamine, luteinizing hormone-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH) in gonadectomized, adrenalectomized male rats bearing subcutaneously a testosterone capsule and a corticosterone pellet. Similar male rats not inoculated with tumor served as controls. The rats were studied 3-4 weeks after tumor inoculation, while they were anesthetized with urethane. Compared to the controls, prolactin levels in the tumor-bearing rats had increased 70-fold, whereas the levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) decreased to 20 and 27%, respectively. In tumor-bearing rats, the secretion of dopamine into hypophysial stalk plasma increased from 2.3 to 4.9 ng/h (p less than 0.025), whereas that of LHRH decreased from 127 to 52 ph/h (p less than 0.005). Since the use of urethane anesthesia may change quantitatively and qualitatively the effects of hyperprolactinemia, it was decided to study these effects on the in vivo release of LHRH, dopamine and TRH in conscious rats by a push-pull perfusion of the median eminence-arcuate nucleus area. Using this technique, it was found that in tumor-bearing rats the secretion of LHRH decreased from 20.0 to 9.8 pg/15 min (p less than 0.005), whereas that of dopamine increased from 118 to 246 pg/15 min (p less than 0.025). The secretion of TRH was not altered by hyperprolactinemia (4.1 vs. 4.4 pg/15 min).(ABSTRACT TRUNCATED AT 250 WORDS)