Effects of synthetic ovine corticotropin-releasing factor (CRF) on ACTH release in vitro

Abstract

The effect of the synthetic ovine corticotropin-releasing factor (CRF) on adrenocorticotropin (ACTH) release was examined by the perifusion method using rat anterior pituitary tissue and rat monolayer cultured pituitary cells. Quartered anterior pituitaries were placed in a chamber and perifused at a rate of 400 microliters/min with Dulbecco's modified Eagle Medium (DMEM, pH 7.4) bubbled with a mixture of 95% O2 and 5% CO2. The perifused medium was fractionated, and the ACTH concentration was measured by radioimmunoassay. In the monolayer cultured pituitary cells, the amount of ACTH released in the culture medium during three hours incubation was assayed by radioimmunoassay. ACTH was released from the perifused anterior pituitary in a dose-related manner by the pulse administration of CRF or arginine vasopressin (AVP) at the concentration of 1 ng/ml, 10 ng/ml and 100 ng/ml. A significant difference was not found between CRF- and AVP-induced ACTH release. In the monolayer cultured pituitary cells, synthetic ovine CRF induced ACTH release in a dose-related manner between 30 pg/ml and 30 ng/ml, but AVP induced a slight ACTH release. ACTH release was pulsatile during the continuous administration of 2.5 ng/ml of CRF for 150 min, although if gradually increased during the continuous administration of 10 ng/ml or 20 ng/ml of CRF. The continuous administration of AVP also caused pulsatile ACTH release at 10 ng/ml, but the ACTH release gradually decreased during the continuous administration of AVP. The interaction between CRF and AVP on ACTH release was examined by two methods. When CRF and AVP were given simultaneously, a mainly additive effect on ACTH release was observed. However, a low concentration of CRF seemed to potentiate AVP-induced ACTH release. These results show that both CRF and AVP have a significant CRF activity on the perifusion system, that AVP induced a slight ACTH release in monolayer cultured pituitary cells, and that CRF acts additively or potently with AVP to control the ACTH release from the anterior pituitary gland.