@article{fruchtman_mcvey_borski_2002, title={Characterization of pituitary IGF-I receptors: modulation of prolactin and growth hormone}, volume={283}, ISSN={["1522-1490"]}, DOI={10.1152/ajpregu.00511.2001}, abstractNote={There have been no studies in any vertebrate that have localized insulin-like growth factor (IGF)-I receptors in prolactin (PRL) cells or that have correlated pituitary binding to the potency of IGF-I in regulating both PRL and growth hormone (GH) secretion. We show that IGF-I binds with high affinity and specificity to the pituitary gland of hybrid striped bass ( Morone saxatilis × M. chrysops). IGF-I and IGF-II were equipotent in inhibiting saturable125I-IGF-I binding, whereas insulin was ineffective. IGF-I binds with similar affinity to the rostral pars distalis (>95% PRL cells) as the whole pituitary gland and immunohistochemistry colocalizes IGF-I receptors and PRL in this same region. Des(1–3)IGF-I, a truncated analog of IGF-I that binds with high affinity to IGF-I receptors but weakly to IGF-I binding proteins (IGFBPs), showed a similar inhibition of saturable125I-IGF-I binding, but it was more potent than IGF-I in stimulating PRL and inhibiting GH release. These results are the first to localize IGF-I receptors to PRL cells, correlate IGF-I binding to its efficacy in regulating GH and PRL secretion, as well as demonstrate that IGFBPs may play a significant role in modulating the disparate actions of IGF-I on PRL and GH secretion.}, number={2}, journal={AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY}, author={Fruchtman, S and McVey, DC and Borski, RJ}, year={2002}, month={Aug}, pages={R468–R476} }
 @article{borski_hyde_fruchtman_2002, title={Signal transduction mechanisms mediating rapid, nongenomic effects of cortisol on prolactin release}, volume={67}, ISSN={["0039-128X"]}, DOI={10.1016/S0039-128X(01)00197-0}, abstractNote={While the mechanisms governing genomically mediated glucocorticoid actions are becoming increasingly understood, relatively little is known with regard to the cell signaling pathways that transduce rapid glucocorticoid actions. Studies of the cultured tilapia rostral pars distalis (RPD), a naturally segregated region of the fish pituitary gland that contains a 95–99% pure population of prolactin (PRL) cells and is easily dissected and maintained in a completely defined, serum-free media, indicate that physiological concentrations of cortisol rapidly inhibit PRL release. The attenuative action of cortisol on PRL release occurs within 10–20 min, is insensitive to the protein synthesis inhibitor, cycloheximide, and mimicked by its membrane impermeable analog, cortisol-21 hemisuccinate-conjugated bovine serum albumin (BSA). Cortisol and somatostatin, a peptide known to work through membrane receptors to inhibit PRL release, rapidly and reversibly reduces intracellular free Ca2+ (Cai2+), and inhibits 45Ca2+ influx and BAYK-8644 induced PRL release. Preliminary investigations show cortisol, but not somatostatin, suppresses phospholipase C (PLC) activity in PRL cell membrane preparations. In addition, cortisol and somatostatin reduce intracellular cAMP and membrane adenylyl cyclase activity. These findings indicate that the acute inhibitory effects of cortisol on PRL release occur through a nongenomic mechanism involving interactions with the plasma membrane and inhibition of both the Ca2+ and cAMP signal transduction pathways. Cortisol may reduce Cai2+ by inhibiting influx through L-type voltage-gated channels and possibly release through a PLC/inositol triphosphate sensitive intracellular Ca2+ pool. In addition, it is also likely the steroid inhibits adenylyl cyclase activity in events leading to reduced cAMP production and the subsequent release of PRL.}, number={6}, journal={STEROIDS}, author={Borski, RJ and Hyde, GN and Fruchtman, S}, year={2002}, month={May}, pages={539–548} }
 @article{borski_hyde_fruchtman_tsai_2001, title={Cortisol suppresses prolactin release through a non-genomic mechanism involving interactions with the plasma membrane}, volume={129}, ISSN={["1096-4959"]}, DOI={10.1016/S1096-4959(01)00358-X}, abstractNote={In the classical theory of steroid hormone action, steroids diffuse through the membrane and alter transcription of specific genes resulting in synthesis of proteins important for modulating cell function. Most often, steroids work solely through the genome to exert their physiological actions in a process that normally takes hours or days to occur. In tilapia (Oreochromis mossambicus), cortisol inhibits prolactin (PRL) release within 10-20 min in vitro. This action is accompanied by similarly rapid reductions in cellular Ca(2+) and cAMP levels, second messengers known to transduce the membrane effects of peptide hormones. We further examined whether cortisol might inhibit PRL release through a non-genomic, membrane-associated mechanism using the protein synthesis inhibitor, cycloheximide, and a membrane impermeant form of cortisol, cortisol-21 hemisuccinate BSA (HEF/BSA). Cycloheximide (2 and 10 microg/ml) was ineffective in overcoming PRL release induced by hyposmotic medium or that inhibited by cortisol over 4 h static incubations. These dosages reduced protein synthesis as measured by amino acid incorporation in pituitaries by 75 and 99%, respectively. During 4-h incubation, HEF/BSA and HEF significantly reduced PRL release in a dose-dependent fashion. These studies suggest that cortisol inhibits PRL release through a plasma membrane-associated, protein-synthesis independent (non-genomic) pathway.}, number={2-3}, journal={COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY B-BIOCHEMISTRY & MOLECULAR BIOLOGY}, author={Borski, RJ and Hyde, GN and Fruchtman, S and Tsai, WS}, year={2001}, month={Jun}, pages={533–541} }
 @article{fruchtman_gift_howes_borski_2001, title={Insulin-like growth factor-I augments prolactin and inhibits growth hormone release through distinct as well as overlapping cellular signaling pathways}, volume={129}, ISSN={["1879-1107"]}, DOI={10.1016/S1096-4959(01)00315-3}, abstractNote={We recently discovered a new role for insulin-like growth factor-I (IGF-I) as a specific and direct stimulator of prolactin (PRL) release in addition to its recognized function as an inhibitor of growth hormone (GH) release and synthesis. Little is known of the mechanisms that transduce the actions of IGF-I on PRL and GH release in vertebrates. The present study was undertaken to determine the cellular pathways that mediate the disparate actions of IGF-I on PRL and GH release in hybrid striped bass (Morone saxatilis X M. chrysops). When regulating cellular function, IGF-I may activate two primary pathways, phosphatidylinositol 3-kinase (PI 3-K) and mitogen-activated protein kinase (MAPK). The specific MAPK inhibitor, PD98059, blocked IGF-I-evoked PRL release as well as GH release inhibition over an 18–20-h incubation. LY294002, a specific PI 3-K inhibitor, overcame IGF-I's inhibition of GH release but was ineffective in blocking PRL release stimulated by IGF-I. These studies suggest IGF-I disparately alters PRL and GH by activating distinct as well as overlapping signaling pathways central for mediating actions of growth factors on secretory activity as well as cell proliferation. These results further support a role for IGF-I as a physiological regulator of PRL and GH.}, number={2-3}, journal={COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY B-BIOCHEMISTRY & MOLECULAR BIOLOGY}, author={Fruchtman, S and Gift, B and Howes, B and Borski, R}, year={2001}, month={Jun}, pages={237–242} }
 @article{fruchtman_jackson_borski_2000, title={Insulin-like growth factor I disparately regulates prolactin and growth hormone synthesis and secretion: Studies using the teleost pituitary model}, volume={141}, ISSN={["1945-7170"]}, DOI={10.1210/en.141.8.2886}, abstractNote={Although insulin-like growth factor I (IGF-I)’s inhibition of GH release is well documented, little is known of its control of GH synthesis at the posttranscriptional level. The manner by which IGF-I alters PRL synthesis and secretion is also unclear. This study was undertaken to examine the role IGF-I plays in regulating in vitro PRL and GH synthesis and release using the teleost pituitary model system. This model allows for isolation of nearly homogenous populations of distinct pituitary cell types that can be cultured in a completely defined, hormone-free medium. Tissues containing PRL cells and those consisting of GH cells were dissected from pituitaries of hybrid striped bass and exposed to varying concentrations of IGF-I, IGF-II, and insulin for 18–20 h. Exposure to graded doses of IGF-I markedly stimulated fractional, total, and newly synthesized PRL release in a dose-dependent fashion (ED50 for fractional release, 35 ng/ml or 4.6 nm; P < 0.0001). IGF-II and insulin also increased PRL release, but only at 10-fold higher concentrations than the lowest effective IGF-I dose. The total PRL content in the incubations and PRL synthesis, as measured by [35S]methionine incorporation, were not altered by IGF-I. By contrast, IGF-I potently reduced GH release (ED50, 29 ng/ml or 3.8 nm; P < 0.0001) and synthesis. Both 100 and 1000 ng/ml IGF-I decreased newly synthesized GH and total GH content (P < 0.001). Insulin and IGF-II mimicked IGF’s action in attenuating GH release, but only at 10- to 11-fold higher concentrations. Taken together, these findings clearly indicate that IGF-I disparately regulates PRL and GH synthesis and secretion. We show that the effects of IGF-I on pituitary hormone release occur in a variety of species, suggesting that its actions are well conserved. The inhibition of GH release and synthesis by IGF-I probably reflects a negative feedback loop for maintaining tight control over GH cell function. These findings further indicate that IGF-I is a potent and specific secretagogue of PRL release in vertebrates.}, number={8}, journal={ENDOCRINOLOGY}, author={Fruchtman, S and Jackson, L and Borski, R}, year={2000}, month={Aug}, pages={2886–2894} }
 @article{jackson_swanson_duan_fruchtman_sullivan_2000, title={Purification, characterization, and bioassay of prolactin and growth hormone from temperate basses, genus Morone}, volume={117}, ISSN={["1095-6840"]}, DOI={10.1006/gcen.1999.7399}, abstractNote={Prolactin (PRL) and two variants of growth hormone (GH), purified from pituitaries of striped bass (Morone saxatilis) and its hybrid with white bass (M. saxatilis x M. chrysops) by gel filtration chromatography under alkaline conditions followed by reversed-phase high pressure liquid chromatography, appear similar between species. Both the minor (GH I) and the major (GH II) forms of purified GH appeared as single bands (M(r) approximately 23,000) after sodium dodecyl sulfate-polyacrylamide gel electrophoresis, as did the purified PRL (M(r) approximately 24,000). The molecular weights of GH II and PRL determined by MALDI TOF mass spectroscopy were 21.2 and 21.3 kDa, respectively. In Western blotting experiments, an antiserum against tilapia (Oreochromis mossambicus) 24K PRL specifically recognized Morone PRL, while an antiserum against tilapia GH specifically recognized Morone GH I and II. Chemical identities of the putative PRL and GH I were further confirmed by N-terminal peptide sequencing, while internal sequence analysis was performed on GH II because it was blocked at its N-terminus. Over a stretch of 29 amino acids, Morone PRL was found to be 76% identical to tilapia 24K PRL, 72% identical to tilapia 20K PRL, 72% identical to chum salmon (Oncorhynchus keta) PRL I, and 69% identical to eel (Anguilla japonica) PRL I. Alignment of the hybrid striped bass GH sequences with those of several other advanced marine teleosts indicated 75-85% sequence identity for GH I (40 amino acids) and 95-98% identity for GH II (45 amino acids). Biological activity of striped bass GH II was confirmed using a heterologous in vitro assay of insulin-like growth factor I mRNA production by coho salmon (On. kisutch) hepatocytes. An in vivo bioassay, involving hypophysectomy of hybrid striped bass and treatment of the fish maintained in fresh water with homologous PRL, confirmed that the purified striped bass PRL was also bioactive.}, number={1}, journal={GENERAL AND COMPARATIVE ENDOCRINOLOGY}, author={Jackson, LF and Swanson, P and Duan, CM and Fruchtman, S and Sullivan, CV}, year={2000}, month={Jan}, pages={138–150} }