Circulating inhibitor of gonadotropin releasing hormone secretion by hypothalamic neurons in uremia.
BACKGROUND
Previous studies have suggested a neuroendocrine defect underlying uremic hypogonadism, characterized by a reduced secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH).


METHODS
We studied the GnRH-producing GT1-7 cell line and the LH-producing LbetaT-2 pituitary cell line under uremic conditions to investigate whether substances circulating in uremic plasma directly affect hypothalamic or pituitary hormone secretion. The cells were incubated with serum from 5/6-nephrectomized or sham-nephrectomized castrated rats, respectively. Furthermore, GT1 cells were incubated with delipidated sera, serum subfractions separated by molecular weight, or several peptide hormones. Cellular viability, apoptosis rate and extracellular hormone degradation were assessed separately. GnRH and LH were measured by RIA in supernatants and cell lysates. GnRH gene expression was assessed by Northern blot.


RESULTS
Uremic serum caused a reduction of extracellular GnRH concentration by 31%, whereas intracellular GnRH increased by 12%. This effect was independent of serum lipids and enzymatic GnRH degradation but was abolished by trypsin digestion. Cellular viability, apoptosis rates and GnRH gene expression did not differ between the two groups. The inhibitory activity was recovered from the high-molecular weight fraction, whereas the fraction <5 kD had stimulatory activity. In contrast, uremic serum did not affect LH secretion from LbetaT-2 cells, indicating that the hypoactivity of the hypothalamo-pituitary gonadotrope unit results from an inhibition at the hypothalamic rather than the pituitary level.


CONCLUSIONS
Our results suggest that uremic serum contains macromolecular and hydrophilic peptide(s) able to specifically suppress the neurosecretion of GnRH from GT1-7 cells.
Daschner
Markus
M
Division of Pediatric Nephrology, Children's Hospital, University of Heidelberg, Heidelberg, Germany.
Philippin
Bärbel
B
Nguyen
Trang
T
Wiesner
Rudolf J
RJ
Walz
Claudia
C
Oh
Jun
J
Sandow
Jürgen
J
Mehls
Otto
O
Schaefer
Franz
F
D000818:Animals; D001798:Blood Proteins / Q000378:metabolism*; D002460:Cell Line; D003404:Creatinine / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004921:Erythropoietin / Q000494:pharmacology; D015870:Gene Expression / Q000502:physiology; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism*; D013006:Growth Hormone / Q000494:pharmacology; D006358:Hot Temperature; D007031:Hypothalamus / Q000166:cytology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D020738:Leptin / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology; D011388:Prolactin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014508:Urea / Q000097:blood; D014511:Uremia / Q000378:metabolism*
D001798:Blood Proteins; D020738:Leptin; D010281:Parathyroid Hormone; D004921:Erythropoietin; D007987:Gonadotropin-Releasing Hormone; D007334:Insulin-Like Growth Factor I; D014508:Urea; D011388:Prolactin; D007986:Luteinizing Hormone; D013006:Growth Hormone; D003404:Creatinine