AJP - Endocrinology and Metabolism, Vol 241, Issue 1 6-13, Copyright © 1981 by American Physiological Society
Differential effects of cyclic nucleotide analogues and GnRH on LH synthesis and release
T. C. Liu and G. L. Jackson
We compared the effects of gonadotropin-releasing hormone (GnRH) and cyclic
nucleotides on biosynthesis and release of luteinizing hormone (LH) by rat
anterior pituitary glands (APs). APs from ovariectomized rats were
incubated in the presence of test compounds, [3H]glucosamine, and
[14C]alanine. GnRH significantly (P less than 0.01) increased both
incorporation of [3H]glucosamine into LH (glycosylation) and release of
immunoreactive LH (IR-LH) and [3H]LH. None of the cyclic nucleotides alone
at 5 mM significantly stimulated release of IR-LH. Adenosine 3',5'-cyclic
monophosphate (cAMP), N6,O2'-dibutyryl cAMP (DBcAMP), and 8-bromo-adenosine
3',5'-cyclic monophosphate (8-Br-cAMP) stimulated (P less than 0.01)
glycosylation, whereas 8-Br-AMP, 8-bromoguanosine 5'-monophosphate
(8-Br-GMP), cGMP, and 8-Br-cGMP had no detectable effect. Release of [3H]LH
was increased by GnRH, 8-Br-cAMP, and DBcAMP, but not by other nucleotides.
None of the cyclic nucleotides elevated [14C]LH, whereas GnRH elevated it
(P less than 0.01) in the medium. Dose-response curves for glycosylation in
response to 8-Br-cAMP and GnRH were parallel. In contrast, dose-response
curves for release of both [3H]LH and IR-LH were nonparallel. It appears
that cAMP can mimic the action of GnRH on LH glycosylation, but may have
little direct effect on LH release.
