CCK/gastrin-like immunoreactivity in the goldfish pituitary: regulation of pituitary hormone secretion by CCK-like peptides in vitro.
The presence and distribution of cholecystokinin (CCK)/gastrin-like immunoreactivity (IR) was examined in the goldfish pituitary. Intense CCK/gastrin-like IR was consistently observed within fibers of the proximal pars distalis (PD), with fewer IR fibers localized in the rostral PD. Within the proximal PD CCK/gastrin-like IR fibers were distributed among both the gonadotrophs and somatotrophs, suggesting a possible role for CCK-like peptides in the regulation of gonadotropin-II (GtH-II) and growth hormone (GH) secretion. Exposure of pituitary fragments from either sexually gonadal recrudescing (maturing) or regressed goldfish to three 5-min pulses of 1.0 or 10 nM sulfated CCK8 (CCK8-s), at 55-min interpulse intervals, resulted in an increased secretion of both GtH-II and GH. Independent of the dose perifused, the GtH-II release responses to the second and third pulses of CCK8-s were always of similar magnitude to the first pulse at a given dose. For GH, repeated challenges of pituitary fragments to 0.1 or 1.0 nM CCK8-s stimulated release responses of similar magnitude; however, successive pulses of 10 nM CCK8-s resulted in a desensitization in the GH release response to the second or the third pulse. Fragments from sexually regressed goldfish exhibited an overall greater release response of GtH-II to CCK8-s relative to fragments from sexually recrudescing fish, whereas the GH release responses to CCK8-s were similar between the two sexual stages. A dose-dependent release of GtH-II was present in pituitary fragments from sexually regressed goldfish following five 5-min pulses of increasing (0.1 to 100 nM) doses of CCK8-s. Finally, the sulfated forms of CCK8 and gastrin 17 (G17-s) exhibited greater stimulatory abilities than the nonsulfated form of CCK8 in releasing GtH-II and GH from fragments of sexually recrudescing fish. Additionally, CCK8-s and G17-s were equal in their capacity to stimulate the release of GtH-II, whereas G17-s was slightly more effective than CCK8-s in stimulating the release of GH. Overall, these studies are the first to provide evidence that IR CCK/gastrin-like fibers are codistributed among the gonadotrophs and somatotrophs, and that CCK-like peptides are highly effective in stimulating GtH-II and GH release from the goldfish pituitary.
Himick
B A
BA
Department of Zoology, University of Alberta, Edmonton, Canada.
Golosinski
A A
AA
Jonsson
A C
AC
Peter
R E
RE
D000704:Analysis of Variance; D000818:Animals; D002766:Cholecystokinin / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology*; D005260:Female; D005455:Fluorescent Antibody Technique; D005755:Gastrins / Q000032:analysis / Q000378:metabolism*; D006054:Goldfish / Q000502:physiology*; D006065:Gonadotropins, Pituitary / Q000378:metabolism*; D013006:Growth Hormone / Q000378:metabolism*; D007106:Immune Sera; D007124:Immunoenzyme Techniques; D007150:Immunohistochemistry; D008297:Male; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012844:Sincalide / Q000494:pharmacology*
D005755:Gastrins; D006065:Gonadotropins, Pituitary; D007106:Immune Sera; D013006:Growth Hormone; D002766:Cholecystokinin; D012844:Sincalide