Metabolism of gonadotropin-releasing hormone in goldfish: serum clearance and tissue uptake studies.
The metabolic clearance rate (MCR) and initial half-disappearance time (T(1/2)i) of salmon gonadotropin-releasing hormone (sGnRH) and its agonist analog [D-Arg6,Pro9-NEt]-sGnRH (sGnRH-A) were investigated in goldfish, following a single intraarterial injection of radioiodinated sGnRH and sGnRH-A. The tissue uptake of radioiodinated sGnRH-A was also investigated. 125I-sGnRH had a MCR of 0.01173 ml min-1 35 g-1 and a (T(1/2)i) of 32.38 min; 125I-sGnRH-A had a MCR of 0.0192 ml min-1 35 g-1 and a (T(1/2)i) of 72.95 min. In the tissue uptake experiments, high levels of accumulated labeled sGnRH-A were generally found in the gills, kidney, liver, and pituitary compared to air bladder, brain, gonad, eyes, and muscle. Coinjection of excess amount of cold sGnRH-A caused decreased uptake of labeled sGnRH-A only in pituitary, but increased accumulation of labeled sGnRH-A in some other tissues. Our results show a correlation between the T(1/2)i and the affinity of the peptides for a serum GnRH binding protein present in the goldfish, suggesting that the formation of a hormone-binding protein complex may decrease the MCR of GnRH in the circulation in goldfish. Our data also indicate specific uptake of 125I-sGnRH-A by the pituitaries of both male and female goldfish, confirming the pituitary as a major target organ of GnRH in goldfish.
Huang
Y P
YP
Department of Zoology, University of Alberta, Edmonton, Canada.
Peng
C
C
Peter
R E
RE
D000400:Air Sacs; D000818:Animals; D005260:Female; D005880:Gills / Q000378:metabolism; D006054:Goldfish / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000378:metabolism*; D007269:Injections, Intra-Arterial; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D008657:Metabolic Clearance Rate; D009206:Myocardium / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism; D011966:Receptors, LHRH / Q000032:analysis*; D012044:Regression Analysis; D014018:Tissue Distribution; D017329:Triptorelin Pamoate / Q000031:analogs & derivatives*
D011966:Receptors, LHRH; D017329:Triptorelin Pamoate; D007987:Gonadotropin-Releasing Hormone; C019176:Tryptal