title: Oxytocin release from isolated posterior pituitary lobes of adult male rats as determined by radioimmunoassay.
abstract: In vitro oxytocin (OXT) release from isolated posterior pituitary lobes (PPL) of adult male Wistar rats was measured under basal and K+- stimulated conditions using a specific, sensitive radioimmunoassay. A basal release of 0.95 +/- 0.20 ng OXT/lobe/10 min was estimated in standard Locke's bathing solution. An excess of K+ (56 mmol/l) augmented the OXT secretion to 18.1 +/- 2.24 ng OXT/lobe/10 min in the presence of 2.2 mmol/Ca++. A stimulatory effect of K+ excess was also determined in Ca++-free medium and in Ca++ free medium enriched with 0.7 mmol/l EGTA. An inhibitory effect on K+-stimulated OXT release was achieved by raising the Mg++ concentration from 1.0-8.0 mmol/l of bathing fluid. During prolonged K+ stimulation the rate of OXT release declined exponentially. Estimation of the OXT content of PPLs after prolonged stimulation with K+ excess revealed that the lobes still contained 80% of their original OXT content.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D008297:Male; D010121:Oxytocin / Q000378:metabolism*; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011863:Radioimmunoassay; D051381:Rats; D012636:Secretory Rate / Q000187:drug effects
chemical_list: D010121:Oxytocin; D011188:Potassium; D002118:Calcium