AJP - Endocrinology and Metabolism, Vol 240, Issue 5 504-E509, Copyright © 1981 by American Physiological Society
Perifusion of rat pituitaries: requirements for optimal GnRH-stimulated LH release
J. E. Stern and P. M. Conn
Perifusion of rat hemipituitaries was used as an in vitro model for
luteinizing hormone (LH) release in response to gonadotropin-releasing
hormone (GnRH). LH release during continuous stimulation with GnRH (10(-7)
M) was inhibited by EGTA (1.5 or 5 mM given 1 h prior to GnRH) or by D-600
(methoxyverapamil, 1 mM, given concomitantly with GnRH). These findings
suggested that GnRH-stimulated LH release was a Ca2+-dependent process.
Inhibition of LH release caused by Ca2+ chelation with EGTA was reversed
when hemipituitaries were returned to medium without EGTA. Elevation of
medium K+ (to 50 mM, without GnRH) stimulated Ca2+-dependent LH release
during the 1st h. GnRH-stimulated LH release was 60% inhibited by
cycloheximide (25 micrograms/ml) after the 1st h. LH release was not
stimulated by dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP),
although this cyclic nucleotide was shown to have biological activity and
to enter pituitary cells as judged by its ability to stimulate prolactin
release from the same tissue. The data suggest that optimal LH release in
response to GnRH requires extracellular Ca2+ and depends on protein
synthesis.
