Thiol Regulation of Protein, Growth Hormone, and Prolactin Release from Isolated Adenohypophysial Secretory Granules*

Administration of Additional Phosphorylated Prolactin During Pregnancy Inhibits Mammary Ductal Branching and Promotes Premare Lobuloalveolus Development

“…Prolactin secretory granules from bovine and rat were obtained as previously described [42,43]. Briefly, the production of rat granules mvolyed homogemzation in 0.32 M sucrose, removal of debris and nuclei by low-speed centrifugation, pelleting of organelles by centri-.…”

“…The biological activity of PRL has previously been shown to be regulated, in part, by the state of phosphorylation [30,42]. Non-phosphorylated PRL promotes growth, while phosphorylated PRL induces cytostasis.…”

“…Clearly, species differences in hormone and receptors (42), endogenous production of PRL, tissue origin and oncogenic mutations, as y/e\l as PRLR isoform complement, can confound results and will take some time to unravel. In the current study, we have eliminated the complication of endogenous PRL production and have used species appropriate hormone preparations.…”

Preferential Interaction of [³⁵S]Cysteamine with Pituitary Secretory Granule Storage Forms of Prolactin

“…Depletion is not due to release of hor mone from the pituitary in vivo [1,2], from cultured cells in vitro [I, 3-5], or from isolated secretory granules [6,7], and no major morphological alteration of secretory granules has been discernible [ 1], Bovine PRL is stored in granules in large part as disulfide-linked oligomers which are poorly detected by antibodies raised against monomeric hormone [8]. Thiol :disulfide interchange mechanisms have been proposed as necessary for the conversion to releasable and immunoassayable hormone [6,8,9], Presumably via such a mechanism, treatment of chromatographically isolated hor mone storage oligomers with reduced glutathione (GSH) at alkaline pH increases the amount of detectable PRL ap proximately 40-fold [7], Exposure of such isolated oligo mers to CySH reduces the GSH effect to only about a 6-fold enhancement [7], In contrast, CySH does not appreciably influence the immunoactivity of standard monomeric PRL or of monomeric PRL released from granules [I, 7]. Based on these data, we have suggested that CySH may interact with storage forms of PRL and interfere with the conver sion of stored hormone to releasable PRL [6,7].…”

“…Thiol :disulfide interchange mechanisms have been proposed as necessary for the conversion to releasable and immunoassayable hormone [6,8,9], Presumably via such a mechanism, treatment of chromatographically isolated hor mone storage oligomers with reduced glutathione (GSH) at alkaline pH increases the amount of detectable PRL ap proximately 40-fold [7], Exposure of such isolated oligo mers to CySH reduces the GSH effect to only about a 6-fold enhancement [7], In contrast, CySH does not appreciably influence the immunoactivity of standard monomeric PRL or of monomeric PRL released from granules [I, 7]. Based on these data, we have suggested that CySH may interact with storage forms of PRL and interfere with the conver sion of stored hormone to releasable PRL [6,7]. The present studies with [35S]CySH were undertaken to determine whe ther preferential binding or interaction could be demon strated between CySH and storage hormone forms as op posed to monomeric PRL.…”