Int. J. Dev. Biol. 45: S159 - S160 (2001)

Vol 45, Issue S1

Modulation of the control of the hypothalamic growth hormone (GH)-releasing factor (GRF) on the GH secretion in fetal and neonatal pigs

Published: 1 June 2001

R Torronteras, F Gracia-Navarro, D Martinez-Dominguez, F Cordoba-Garcia, F Elsaesser

Univ Huelva, Fac Ciencias Expt, Dept Biol Ambiental & Salud Publ, Huelva, Spain; Univ Cordoba, Fac Ciencias, Dept Biol Celular Fisiol & Immunol, Cordoba, Spain; FAL, Inst Tierzucht & Tierverhalten, Hannover, Germany

Abstract

An ontogenic aspect of the growth hormone (GH) secretion was studied in fetal and neonatal pigs, It is known that GH secretion is under the dual control of hypothalamic peptides: a GH-releasing factor (GRF) and somatostatin (SRIF), which exerts a major inhibitory influence (Frohman and Jansson, 1986). It has been also reported that chronic treatments (continuous or pulsatile) of pituitary cells to GRF caused a loss of responsiveness of somatotropes to the secretagogue (Hulse etal., 1986). This phenomenon was explained by desensitization (Bilezikjian and Vale, 1983). Then, we have studied the role of hypothalamic GRF to maintain the responsiveness of somatotrope cells to the secretagogue during animal development. For this purpose, we compared the effects of 3-days pulsatile treatments of anterior pituitary (AP) tissue cultures from 95 days female fetuses, 110-days fetuses and 12-days neonatal pigs to GRF on GH response to this secretagogue, using a in vitro superfusion system. Every day, pulsatile treatments of GRF maintained GRF-estimulated GH secretion in neonatal female pigs with a similar response. However, a significant reduction in GH response was observed day to day in fetuses. In previous reports, when we exposured AP tissue to GRF resulted in a rapid GH release in fetuses and neonates. However, somatostatin and IGF-1 given during a GRF pulse inhibited the GH response in neonates but not in fetuses. Therefore, the relative resistance of the fetal somatotropes to the inhibitory effects of somatostatin and IGF-1 showed an immaturity of regulatory mechanism in fetuses which, at least in part, could be responsible for the desensitization effects of GRF in fetuses, but not in piglets. These data suggest a fundamental difference between the GH regulatory process of fetuses and piglet pituitaries. The ability of the somatotrope to maintain GH response to GRF is developmentally regulated, and the presence of the mature stimulatory (GRF)/ inhibitory(SRIF or IGF-1) mechanism might contribute to avoid the desensitization effects to the secretagogues.

Keywords

Somatostatin