Release of stored, pre-labeled growth hormone and prolactin from perifused rat pituitary: effect of human pancreatic growth hormone-releasing factor-44.
Human pancreatic growth hormone-releasing factor-44 (hpGRF-44) differentially stimulates release of stored and newly synthesized rGH without altering rGH synthesis over 3 h in static in vitro incubation; hpGRF-44 also stimulates release of stored, but not newly synthesized, rPRL. To study the time course of pre-labeled, stored hormone release without pharmacologically interrupting synthesis, the current experiments were performed in perifusion. Fifteen minute pulses of 0.1 to 10 nM hpGRF-44 stimulated stored [3H]rGH release (to 890% of base); 1.0 to 10 nM hpGRF-44 stimulated stored [3H]rPRL release (to 440% of base). Pulses of 0.1 to 1.0 mM (Bu) 2cAMP also stimulated release of [3H]rGH (to 570% of base) and [3H]rPRL (to 410% of base). However, peak [3H]rGH and [3H]rPRL responses to hpGRF-44 required 10 min, while peak responses to (Bu) 2cAMP required 25 min. Continuous hpGRF-44 stimulated an initial surge of stored [3H]rGH release which was not sustained; the diminishing release was not explained by hpGRF-44 degradation. Total radioimmunoassayable (RIA) hormone release roughly paralleled release of stored immunoprecipitable (IPn) hormone.


CONCLUSIONS
in pituitary perifusion, hpGRF-44 stimulates release of both stored rGH and rPRL as shown in static incubation, but the response is biphasic: initial rapid release is followed by a progressively lesser response; and the response is both more acute and less well sustained than that resulting from exposure to (Bu) 2cAMP.
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D010187:Pancreatic Hormones / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D010477:Perfusion; D010903:Pituitary Gland, Anterior / Q000187:drug effects* / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D010187:Pancreatic Hormones; D010446:Peptide Fragments; D003994:Bucladesine; D011388:Prolactin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone