C. S. Nahorniak

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In the goldfish (Carassius auratus) the two endogenous forms of gonadotropin-releasing hormone (GnRH), namely chicken GnRH II ([His5, Trp7,Tyr8]GnRH) and salmon GnRH ([Trp7,Leu8]GnRH), stimulate the release of both gonadotropins and growth hormone from the pituitary. This control is thought to occur by means of the stimulation of distinct GnRH receptors.(More)
The present study examined the influence of GnRH on the in vivo and in vitro secretion of GH in the goldfish (Carassius auratus). Intraperitoneal injection of several GnRH peptides, including a form native to goldfish, salmon GnRH (sGnRH), elevated circulating GH levels in female goldfish. An analog of mammalian GnRH (mGnRH), [D-Ala6,Pro9-NEt] mGnRH(More)
The seasonal changes in the gonadotrophin-release-inhibitory activity of dopamine and responsiveness to gonadotrophin-releasing hormone were investigated by determining the effects of injection of pimozide, a dopamine receptor antagonist, des-Gly10 [D-Ala6] LH-RH ethylamide (LRH-A), or the combination of pimozide plus LRH-A on serum gonadotrophin (GtH)(More)
The effects of testosterone (T) and estradiol (E2) on serum growth hormone (GH) concentrations were investigated throughout the seasonal reproductive cycle of the female goldfish. Gonad-intact female goldfish were implanted intraperitoneally for 5 days with silastic pellets containing no steroid (blank), T(100 micrograms/g) or E2 (25-100 micrograms/g). In(More)
The elevated serum gonadotropin (GtH) levels in goldfish receiving two injections of des Gly10, [D-Ala6] LH-RH ethylamide (LH-RH-A), given 12-hr apart, were reduced by apomorphine, a dopamine agonist, injected at either the first or the second LH-RH-A injection. Serum GtH concentrations in goldfish given two injections of LH-RH-A at a 3-hr interval were(More)
Two forms of gonadotropin-releasing hormone (GnRH) have been purified from brain extracts of the Thai catfish, Clarias macrocephalus, using reverse-phase high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA). The amino acid sequences of both forms of catfish GnRH (catfish GnRH-I and -II) were determined using Edman degradation. The(More)
The goldfish pituitary contains two classes of gonadotropin-releasing hormone (GnRH) binding sites, a high affinity/low capacity site and a low affinity/high capacity site (Habibiet al. 1987a), whereas the catfish pituitary contains a single class of high affinity GnRH binding sites (De Leeuwet al. 1988a). Seasonal variations in pituitary GnRH receptor(More)
Three natural forms of vertebrate gonadotropin-releasing hormone (GnRH) provided the structural basis upon which to design new GnRH agonists: [His5,Trp7,Leu8]-GnRH, dogfish (df) GnRH; [His5,Asn8]-GnRH, catfish (cf) GnRH; and [His5,Trp7,Tyr8]-GnRH, chicken (c) GnRH-II. The synthetic peptides incorporated the position 6 dextro (D)-isomers D-arginine (D-Arg)(More)
The pars distalis of the pituitary was transplanted from one goldfish to another, of matched gonadal condition and body size, either beside the brain ("juxta" location) or into the brain ventricle in the preoptic region or under the optic tectum. Recipients of a pars distalis had significantly higher serum gonadotropin (GtH) levels than sham-operated(More)