Release of growth hormone from purified somatotrophs: effects of the calcium channel antagonists diltiazem and nifedipine on release induced by growth hormone-releasing factor.
We examined the effect of the voltage-sensitive Ca2+ channel antagonists, diltiazem and nifedipine, on basal and stimulated growth hormone (GH) release from purified somatotrophs. Our aim was to ascertain whether an influx of Ca2+ from the extracellular to the intracellular compartment is essential for augmented release. Basal release was decreased in a concentration-dependent manner by both diltiazem and nifedipine, while cAMP accumulation was unaffected. The release of GH induced by 29 mM K+ was blocked by diltiazem and nifedipine, at 10(-7) and 10(-8) M, respectively. Again cAMP was unaffected. The release of GH induced by growth hormone-releasing factor was significantly reduced by 10(-4) M diltiazem and completely blocked by nifedipine at a concentration of 10(-6) M or greater. Where the antagonists were effective, the growth hormone-releasing factor induced increase in cAMP accumulation was augmented. We conclude that an influx of Ca2+ from the extracellular compartment is essential for stimulated GH release.
Lussier
B T
BT
Department of Physiology, University of Western Ontario, London, Canada.
Moor
B C
BC
French
M B
MB
Kraicer
J
J
D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004110:Diltiazem / Q000494:pharmacology*; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D009543:Nifedipine / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains
D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D000242:Cyclic AMP; D004110:Diltiazem; D009543:Nifedipine