Recent studies have revealed that TRH-like immunoreactivity (TRH-LI) in
human serum is predominantly pGlu-Glu-ProNH2 (< EEP-NH2), a peptide
previously found in, among others tissues, the pituitary gland of various
mammalian species. In the rat pituitary, < EEP-NH2 is present in
gonadotrophs and its pituitary content is regulated by gonadal steroids
and gonadotrophin-releasing hormone (GnRH). Hence, we reasoned that <
EEP-NH2 in human serum may also arise, at least in part, from the
pituitary, and that its secretion may correlate with that of
gonadotrophins. Therefore, blood was simultaneously sampled from both
inferior petrosal sinuses, which are major sites of the venous drainage of
the pituitary gland, and a peripheral vein from seven patients with
suspected adrenocorticotrophin-secreting pituitary tumours. In addition,
in six postmenopausal and six cyclic women, peripheral vein blood was
collected at 10-min intervals for 6 h, then a standard 100 micrograms GnRH
test was performed. In the sera, TRH-LI was estimated by RIA with
antiserum 4319, which binds most tripeptides that share the N- and
C-terminal amino acids with TRH (pGlu-His-ProNH2). In addition, LH and FSH
were measured in these sera b
