Effects of Thyrotropin-Releasing Hormone on Prolactin Compartments in Clonal Rat Pituitary Tumor Cells

Abstract

PRL compartments were studied in a clonal strain of rat pituitary tumor cells (GH3B6). The cells were pulse-labeled for 10 min with 35S-methionine and then chased for 20 h in the absence or presence of TRH (30 nM) or cycloheximide (3.6 X 10(-5) M), or both. The specific radioactivity (SA) of PRL was followed in the cells and chase medium as a function of chase time and treatments. The transit of labeled and unlabeled PRL has been investigated in cells treated with monensin (1 microM), a drug which is known to perturb the Golgi zone. Newly synthesized PRL was rapidly (15 min of chase) and preferentially released in basal conditions. The pattern of the decay of the SA of PRL released in the medium suggested the existence of at least two PRL pools with different half-lives: 15 min and 3 h, respectively. TRH induced the preferential release of a PRL pool synthesized before the labeling pulse. Monensin decreased the basal release of total radioimmunoassayable PRL without affecting that of the newly synthesized PRL. In contrast, it did not affect the stimulating effect of TRH on the release of unlabeled PRL. These results are in favor of the existence of different intracellular routes for the basal release of PRL (mostly newly synthesized) and the TRH-stimulated release of PRL (mostly stored). Moreover, after 20 h of chase a large fraction (approximately 80%) of the labeled immunoprecipitated material remained intracellularly located and not degraded. This material was not mobilizable by TRH even in the presence of cycloheximide. Polyacrylamide gel electrophoresis analysis revealed that it consisted of large immunoreactive proteins (mol wt, 45,000 and 50,000) instead of mol wt 23,000 PRL which was found in the medium.

Axons Containing a Prolactin-Like Peptide Project into the Perivascular Layer of the Median Eminence: An Immunocytochemical Light and Electron Microscope Study in Adult and Infant Rats

“…I). In good agreement with data obtained in GH.iBi, cell lines [16] and in pituitary cells in primary culture [17], immunostaining was found here to be essentially associated with a protein band corresponding exactly to the prolactin reference (mo lecular weight 23 kilodaltons; kD), and with two minor bands of higher molecular weight (45 and 70 kD) which may possibly repre sent the dimeric and polymeric forms of prolactin previously re ported [20]. On the other hand, no immunostaining could be delec ted in protein bands lighter than 23 kD.…”

Significant Qualitative Differences Exist between Thyrotropin and Prolactin Secretory Dynamics Induced by Pituitary Cell Swelling

“…The secretion kinetics of labeled PRL from GH cells suggest that continuous unregulated exocytosis of PRL represents more recently synthesized hormone than does the PRL secreted in response to secretagogues, indicating that there are at least two intracellular PRL pools in lactotrophs (14)(15)(16). Our data seem in accord with this hypothesis and additionally suggest that the two PRL pools may each be affected differently by cell swelling and Ca2+ influx.…”

Release of big and small molecular forms of prolactin: dependence upon dynamic state of the lactotroph

“…This indi¬ cated that the organdie was still involved in hormone transport and provided strong, though circumstantial, evidence that direct hormone release from the RER to the extracellular space did not take place (Osamura, Komatsu, Izumi et al 1982). Moreover, the presence of an unexplained and rapidly releaseable pool of pro¬ lactin reported in experiments with labelled hormone in pituitary glands in vitro (Swearingen, 1971;Shenai & Wallis, 1979;Walker & Farquhar, 1980;Piercy & Shin, 1981;Morin, Rosenbaum & Tixier-Vidal, 1984) can be ascribed to suppression of hypothalamic inhibitory controls and consequent hyperstimulation of lactotrophs similar to that described for pituitary grafts (Torres & Aoki, 1985). The similarities found under various experimental and physiological conditions reveal common secre¬ tory patterns in lactotrophic activity.…”