Prolactin stimulated rat hypothalamic corticotropin-releasing hormone and pituitary ACTH secretion in vitro

In rats hyperprolactinemia increases corticotropin-releasing hormone (CRH) concentration and secretion in hypophysial portal blood and the serum concentration of adrenocorticotropic hormone (ACTH). To determine whether the stimulatory effect of prolactin (PRL) on CRH and ACTH in vivo is exerted directly on the hypothalamus, hypothalamic explants and primary anterior pituitary cell cultures from adult male and female rats were used. Hypothalami explanted from male and female rats were preincubated during 90 min and treated for 30 min with rat PRL (rPRL) at concentrations of 10(-8), 10(-7), and 10(-6) M (about 200, 2,000, and 20,000 ng/ml, respectively), corticosterone at concentrations of 10(-7), 10(-6), and 10(-5) M (about 35,350 and 3,500 ng/ml, respectively), ACTH at concentrations ranging from 10(-10) to 10(-7) M (0.46, 4.6, 46, and 460 ng/ml, respectively), and graded concentrations of testosterone or estradiol. Concentrations of immunoreactive CRH (iCRH) were measured by radioimmunoassay. rPRL at 10(-6) M stimulated iCRH secretion by 360 and 400% of the basal iCRH output (about 14 pg/hypothalamus), respectively, from hypothalami explanted from male and female rats. ACTH and corticosterone did not suppress rPRL (10(-6) M) induced iCRH secretion. Corticosterone at the concentration of 10(-6) M potentiated rPRL (10(-6) M) induced iCRH secretion in hypothalami explanted from male, but not female rats. Gonadal steroids had no effect either on the basal or rPRL (10(-6) M) stimulated iCRH secretion, with the exception of estradiol which augmented the response to 10(-6) M rPRL by about fivefold, but only at the concentration of 10(-8) M (about 2.7 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)