Neuropeptide Y (NPY) modulatesin vitro gonadotropin in release from rainbow trout pituitary glands

Abstract

This work investigated the action of neuropeptide Y (NPY) on thein vitro pituitary release of the maturing gonadotropic hormone (GtH) of the rainbow trout using a perifusion system employing trout balanced salt solution (pH 7.5) at 15°C and a 12.5 ml/h flow rate. In vitellogenic females a 20 minutes NPY application (10(-7) M) induced a 20-30% decrease in GtH secretion. Removal of NPY was followed by a rebound in GTH secretion. On the contrary, in ovulated females, NPY (15 minutes, 10(-7) M) directly stimulated GTH secretion. The greatest stimulation was obtained the day of ovulation where the stimulatory effect of NPY was similar to those induced by s.GnRH in the same conditions, reaching 400% of the basal GTH level. In vitellogenic females treated with 1-4-6 androstadien 3-7 dione, an inhibitor of aromatase activity, the pituitary response to NPY was similar to that obtained in ovulated females. Thus thein vitro action of NPY might depend on thein vivo steroidogenic environment.

Neuropeptide Y stimulates in vivo gonadotropin secretion in teleost fish

“…This agrees with in vitro results in the goldfish (Kah et al, 1989) and the rainbow trout (Breton et al, 1989). There were no apparent differences in the dynamics of the responses between these two species.…”

“…Thus in mammals NPY modulation of LH secretion depends on the steroidogenic environment, especially estradiol (Crowley et al, 1985;Crowley and Kahra, 1987;Wehrenberg et al, 1989), under which NPY stimulates LH secretion. In previous in vitro studied (Breton et al, 1989) the findings were opposite to those in mammals; estradiol inhibited GtH2 secretion under the action of NPY. The present in vivo experimental conditions in the rainbow trout gave estradiol levels that were lower around ovulation (Fostier et al, 1978), and also a stimulatory effect of NPY on GtH secretion was observed, indicating possibly different modulatory actions of NPY and estradiol in fish and mammals.…”

“…In these last two species NPY stimulates in vitro gonadotropin (GtH2 secretion from perifused pituitary fragments (Kah et al, 1989;Breton et al, 1989). In the rainbow trout its in vitro action is pleiotropic (Breton et al, 1990).…”

“…NPY also acts directly on dispersed pituitary cells, or indirectly via GnKH (Breton et al, 1990). Moreover the peptide's in vitro action depends on the in vivo steroidogenic environ-' Present address: Department of Ichthyobiology, Academy of Agriculture, 30149 Krakow-MydIniki, Poland. ment (Breton et al, 1989). In fish, unlike in mammals, all results to date concern NPY's in vitro actions.…”

Distribution of Neuropeptide Y and Gonadotropin-Releasing Hormone Immunoreactivities in the Brain and Hypophysis of the Ayu, Plecoglossus altivelis (Teleostei).

“…Among them, at least two neurohormones have been essentially implicated in the regulation of gonadotropin secretion: the gonadotropin-releasing hormone (GnRH), and dopamine, a gonadotropin release-inhibiting factor (PETER, 1983;KAH, 1986). Recently, it has been reported that neuropeptide Y (NPY) stimulates gonadotropin release in the rainbow trout (BRETON et al, 1989(BRETON et al, ,1991DANGER et al, 1991), the common carp (BRETON et al, 1991) and the goldfish (KAH et al, 1989;PENG et al, 1990PENG et al, , 1993a and also growth hormone release in the goldfish (PENG et al, 1990(PENG et al, , 1993a. Innervation of the teleostean hypophysis by NPY-immunoreactive fibers has been demonstrated by immunohistochemistry in different species: the sea bass (MooNs et al, 1989), the goldfish (PoNTET et al, 1989), the trout (DANGER et al, 1991), and the platyfish (MAGLIURO-CEPRIANO and SCHREIBMAN, 1993).…”