Influence of Gonadoliberin on the Differentiation of Rat Gonadotrophs: An in vivo and in vitro Study

Abstract

The influence of gonadoliberin (GnRH) on the differentiation of rat gonadotrophs in early fetal life was studied both in vivo and in vitro by immunocytology with anti-porcine luteinizing hormone β (pLHβ) serum. Adenohypophysial primordia explanted from 11 to 13 days of gestation were maintained in organ culture in synthetic Parker’s 199 medium enriched with insulin (0.5 µg/ml) and transferrin (5 µg/ml). Cultures lasted to approximate the usual gestation period (21 days). Synthetic GnRH (10^–9 or 10^–12M) was added to the culture medium during the first day of culture only. In contrast to a previous report, immunoreactive cells were detected in the primordia explanted either at 11 or 12 days of gestation only when cultured in the presence of GnRH. The appearance of positive localization was seen by 17 days. No differences due to GnRH dosage were observed in the mean cytoplasmic area of the cells in the different experimental groups as seen at the equivalent of 21 days. GnRH was not effective in a medium deprived of insulin. GnRH, added 6 h before the end of the culture, could also release the secretory product of gonadotrophs which recently developed the presence of immunoreactive pLHβ material. In these conditions, GnRH was shown to enter the cells as observed by immunocytochemistry on sections obtained after cryoultramicrotomy. Endogenous GnRH was also detected by the same technique in fetal pituitary glands removed from 14 to 21 days of gestation. It was always localized in agranular cells and from 18 days in some granular cells considered as gonadotrophs. In the early fetal life transfer of GnRH from the maternal to the fetal side is very unlikely since very small amounts of radioactivity were detected in 11-day-old fetuses after injection of [¹²⁵I]-GnRH into pregnant rats. These results suggest that GnRH can stimulate the differentiation of gonadotrophs in early fetal life in synergy with insulin. This is supported by the intracellular presence of GnRH which is most likely of fetal origin, the possibility of the existence of a placental GnRH-like substance being not completely excluded.

Parotid gland tissue is able partially to assume pituitary functions under the influence of hypothalamic factors: in vivo and in vitro studies

“…Also, it was demonstrated that a single hypothalamic hormone was able to induce the differentiation of more than one pituitary cell type (Heritier & Dubois 1994). Conversely, one pituitary cell phenotype could be induced by more than one factor (Begeot et al 1984, Heritier & Dubois 1994.…”

Induction of Pituitary Cell Type Differentiation by Delta Sleep-Inducing Peptide

“…Pituitary primordia were removed from 11-day-old fetuses and cultured in a synthetic medium as previously described [13]. The Parker's 199 medium (Gibco BRL, Cergy-Pontoise, France), en riched with Hepes (Gibco), insulin (monopic, Organon, St-Denis, France) and transferrin (Sigma, L'Isle d'Abeau, France), was used as control culture medium.…”

“…The effects ofDSIPwerc compared to those of GnRH or TRH as previously published [17,18]. The peptides (GnRH, DSIP or TRH) were tested on day 1 of culture [13,17,18]. The medium was then replaced by the control medium.…”

“…Recent immu nocytochemical studies using light and electron microsco-py have shown that in the adult DSIP colocalizes with GnRH in neurons of several species including man [9], rabbit [10], guinea pig [11] and rat [12]. GnRH is known to influence the differentiation of gonadotropes in vitro [13], and is detected as early as embryonic day (ED) 12 in the rat hypothalamus [14]. In contrast ontogenesis of hypothalamic DSIP containing neurons is still poorly doc umented.…”

“…Nevertheless, early detection of DSIP in GnRH neurons in guinea pig [15] suggests that similarly to GnRH, DSIP may be also involved in pituitary cell differ entiation. In the present study, effects of DSIP on the pituitary cells were compared to those of GnRH or TRH [13,[16][17][18]. Rat pituitary primordia were cultured as pre viously described [13,[16][17][18], and the tested peptides were added in the culture medium during the first day of culture [13,17,18].…”