Human Pancreatic Growth Hormone-Releasing Factor-44 Differentially Stimulates Release of Stored and Newly Synthesized Rat Growth Hormone in Vitro*

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Abstract
Effects of synthetic human pancreatic GH[growth hormone]-releasing factor-44 (hpGRF-44) on synthesis and release of rat pituitary GH and PRL [prolactin] were examined in vitro in a static incubation system. A double label, specific immunoprecipitation protocol permitted simultaneous study of hormone synthesis and release of both stored and newly synthesized hormone. Synthetic hpGRF-44 (0.3 and 3.0 nM) stimulated the release of stored GH 240% beyond the basal level, while simultaneously stimulating the release of newly synthesized GH by 610%. Despite the stimulation of release, hpGRF-44 did not alter GH synthesis (102% of control value). A small but statistically significant increase in release of stored PRL occurred in response to hpGRF-44; release of newly synthesized PRL and PRL synthesis were unaffected. (Bu)2cAMP [1 mM] stimulated the release of newly synthesized and stored GH and PRL. hpGRF-44 apparently differentially stimulates GH release from separate intracellular compartment; the lactotroph may also, under certain conditions, respond to this secretagogue.

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