Relative Importance of Newly Synthesized and Stored Hormone to Basal Secretion by Growth Hormone and Prolactin Cells*

Abstract

It is generally accepted that under basal conditions there is preferential release of newly synthesized hormone by a number of endocrine cell type, including those that secrete GH or PRL. However, the cellular basis for this phenomenon along with the relative contribution of stored hormone to basal secretion has yet to be clearly established. In the present study, we employed reverse hemolytic plaque assays to monitor basal and stimulated release of GH and PRL from individual cells in which de novo protein synthesis had been blocked. Monodispersed pituitaries from adult male rats were cultured for 21 h in the absence or presence of maximally effective doses of puromycin (100 microM) or cycloheximide (36 microM) and were then subjected to separate plaque assays for GH or PRL. Treatment with puromycin reduced the percentage of GH or PRL secretors (plaque formers) by about half. Coincubation with stimulatory secretagogues did not increase the percentages of GH or PRL secretors in control cultures, but returned the proportion in puromycin-treated cells to normal, demonstrating that cells which failed to secrete basally could still release hormone from their stored pools when stimulated. Very similar results were obtained when these experiments were repeated with cycloheximide. Taken together, these results demonstrate that only a fraction of the cells that release GH or PRL are dependent upon newly synthesized hormone for basal secretion; the remainder appear capable of mobilizing stored hormone for this purpose even in the absence of stimulation.

Red, yellow, green go! – a novel tool for microscopic segregation of secretory vesicle pools according to their age

“…This has made it possible to segregate LDCVs into different subpopulations according to their age. We have shown that newly synthesized LDCVs are located in peripheral areas, from which they are preferentially released by nicotine, which explains previous reports that newly synthesized peptides are secreted quickly [13,14]. The swift translocation of newly synthesized LDCVs from the Golgi to the cell membrane agrees with a recent analysis of vesicle dynamics in PC12 cells [15].…”

Vesicular Release of Prolactin from Preformed Prolactin Granules Is Stimulated by Soluble Factor(s) from the Anterior Pituitary of Lactating Rats

“…To evaluate the role of protein synthesis on CM-induced stimulation of PRL release, male pituitary fragments were incubated in control Earle’s medium or in CM, either with or without 50 µg/ml CHx, a specific inhibitor of RNA protein translation that has been employed previously for inhibiting PRL synthesis [24, 25]. As shown in figure 8, basal PRL secretion (about 1.8 µg/mg tissue) was not affected by the presence of CHx in the medium.…”

“…To evaluate the participation of protein synthesis on CM-induced stimulation of PRL release from male pituitary fragments, the inhibitor CHx [24, 25] was used (50 µg/ml; Sigma). Similarly, to examine the role of vesicle trafficking to the plasma membrane, a mixture of inhibitors was used (50 µ M colchicine, 5 µ M vincristine and 20 µ M cytochalasin D; Sigma) [26,27,28,29].…”

Retention and stimulus-dependent recycling of dense core vesicle content in neuroendocrine cells

“…Newly synthesized hormones in endocrine cells, including PRL in pituitary cells, can be preferentially released (Walker and Farquhar, 1980;Gold et al, 1982;Rhodes and Halban, 1987;Chen at al., 1989). It may be possible that newly synthesized hormone merged with the recycling granules in an intermediate compartment such as immature granules or the endosomal recycling compartment..…”