DEMONSTRATION OF GONADOTROPIN-RELEASING-HORMONE RECEPTORS ON GONADOTROPHS AND SOMATOTROPHS OF THE GOLDFISH - AN ELECTRON-MICROSCOPE STUDY

Dispersed pituitary cells of the goldfish were incubated with biotinylated [D-Lys6, Pro9-N-ethylamide] salmon gonadotropin-releasing hormone (sGnRH-A) then avidin-gold (10 nm), and were fixed, embedded and sectioned. Cells were identified as gonadotrophs, somatotrophs, or prolactin cells using specific hormone antisera and protein-A gold (20 nm) as a marker. Attachment of the biotinylated sGnRH-A to the pituitary cell sections was determined by scanning cell surfaces for the smaller gold particles using the transmission electron microscope. Attachment was observed on gonadotrophs and somatotrophs, but was negligible on prolactin cells. Preincubation with unlabelled salmon gonadotropin-releasing hormone or chicken II gonadotropin-releasing hormone, or omission of the salmon gonadotropin-releasing hormone analog, prevented the reaction. The direct visualization of specific gonadotropin-releasing hormone receptors on gonadotrophs and somatotrophs supports the existence of direct stimulatory actions of gonadotropin-releasing hormone on gonadotropin and somatotropin release in goldfish.