Anomalous prolactin release in vitro in response to cold and its specific blockade by a purified hypothalamic-inhibiting factor.

Bovine anterior pituitary slices were incubated in Krebs—Ringer—Bicarbonate for 2 hr and TSH, LH, FSH, ACTH, GH and prolactin (PRL) released into the medium were estimated by radioimmunoassay. During continuous incubation at 0 C, release of hormones was increased 10 to 60 times the release at 37 C, except for PRL release which was unaltered. A 5–min exposure to cold resulted, during subsequent incubation at 37 C, in a similar augmentation of release of all hormones including PRL. The enhanced release upon exposure to cold resulted in depletion of total cellular hormone stores by 8, 16, 21, 43, 45 and 61 percent for PRL, FSH, TSH, LH, GH and ACTH, respectively. A purified “prolactin—inhibiting factor” reduced the effect of the 5–min cold pulse on the release of PRL by 50%, but had no significant effect on the enhanced release of the other hormones. These findings suggest that unusual properties of the plasma membrane of the PRL cell provide the basis for the unique response of the lactotrope to hypothalami...