Gonadal sex steroids modulate GH synthesis and secretion with effects on both the hypothalamus and anterior pituitary. In the post-pubertal animal, androgens and oestrogens modulate hypothalamic somatostatin (SS) and GHRH synthesis respectively. These effects may be direct as SS neurons express the androgen receptor and many GHRH neurons are oestrogen receptor positive. The neonatal steroid environment modulates the number of GHRH neurons in the adult hypothalamus, as well as their responsivity to post-pubertal steroids. Furthermore, both neonatal and post-pubertal steroids modulate hypothalamic synaptic organisation affecting the number of synaptic inputs and the morphology of glial cells. This in turn has important effects on the ability of the hypothalamus to drive the secretory pulsatility of anterior pituitary hormone release. At the level of the somatotroph, androgens and oestrogens have been reported to stimulate, inhibit or have no effect on GH synthesis. In primary cultures, we found no effect of either androgens or oestrogens on GH mRNA levels. However, the sex steroid environment significantly modified the response of somatotrophs to SS. Furthermore, males have more somatotrophs compared with female rats and this partially depends on the neonatal sex steroid environment. In conclusion, sex steroids have both organisational and activational effects on the GH axis. These effects range from modulating the number of hypothalamic neurons controlling GH secretion, their responsiveness to later steroids, and the synaptic connectivity and neuropeptide production, to modulation of somatotroph numbers in the anterior pituitary and their responsiveness to inputs controlling GH synthesis and secretion.
JA Chowen, LM Frago and J Argente
L Goya, LM Garcia-Segura, S Ramos, AM Pascual-Leone, J Argente, MA Martin and JA Chowen
OBJECTIVE: In malnutrition both the GH-IGF and reproductive axes are greatly affected. Because the actions of IGF and sex steroids are inter-dependent in many tissues, we have examined how ovariectomy modulates the response of the systemic IGF system to undernutrition. DESIGN AND METHODS: Peripubertal (30 days of age) female rats were either sham operated or ovariectomized. Five days later half of each group was submitted to a protein-caloric restriction diet. All rats were killed at 60 days of age. RESULTS: Growth was decreased in all rats submitted to calorie restriction and this was consistent with a decrease in circulating IGF-I concentrations and liver IGF-I mRNA expression. While in normally fed rats ovariectomy had no significant effect on serum IGF-I concentrations, ovariectomized and underfed rats had significantly higher levels than intact underfed rats. In undernourished rats, serum IGF-binding proteins (IGFBP)-1, -2 and -3 concentrations were significantly reduced and this was not modified by ovariectomy. In contrast, liver mRNA concentrations of IGFBP-1 and -2 were increased and IGFBP-3 unchanged in intact undernourished animals, suggesting that undernutrition could be affecting the proteolysis of these binding proteins, and this response was significantly modulated by ovariectomy. CONCLUSION: These results indicate that the presence of circulating ovarian hormones significantly affects the response of the IGF system to undernutrition.
V Barrios, J Argente, MT Munoz, J Pozo, JA Chowen and M Hernandez
OBJECTIVE: To analyze the possible utility of measuring acid-labile subunit (ALS) in some types of pathologies in which the IGF system is altered and to compare it with the clinical implications of measurements of other components of this axis. DESIGN AND METHODS: We studied serum ALS concentrations in 20 children with normal variants of short stature (NVSS) at diagnosis and 24 with growth hormone deficiency (GHD), 18 obese patients and 18 girls with anorexia nervosa at diagnosis and during a follow-up period. RESULTS: In patients with GHD and anorexia nervosa, mean ALS concentrations were significantly reduced, but there was a high percentage of overlap with control values. At diagnosis, ALS concentrations were normal in obese patients and children with NVSS. During follow-up, these values normalized in children with GHD who were treated with GH, tended to normalize in those with anorexia nervosa who showed weight gain, and did not change in obese children upon weight loss. However, ALS measurement was less accurate than that of IGF-I or IGF binding protein (IGFBP)-3 in diagnosis of GHD. The correlations found between ALS and some IGF system components at diagnosis either decreased or were non-significant during follow-up of these clinical conditions. CONCLUSION: ALS adds little information to that obtained with IGF-I and IGFBP-3 determinations.
L Soriano-Guillen, V Barrios, G Martos, JA Chowen, A Campos-Barros and J Argente
OBJECTIVE: Coexpression of GH secretagogue receptor and ghrelin in the pancreas suggests that this peptide is involved in glucose metabolism. Previous reports in adult humans have demonstrated that plasma ghrelin levels decrease after oral glucose administration. However, no data are available in children. Therefore, the aim of this study was to analyze the response of plasma ghrelin levels in obese children after oral glucose administration. SUBJECTS AND METHODS: Twenty-eight obese children ranging from Tanner I to Tanner V were studied. All subjects were given 0.75 g/kg (maximum 75 g) glucose solution after overnight fasting. Ghrelin, insulin, glucose and IGF-binding-protein-1 were determined at 0, 30, 60 and 120 min of the oral glucose tolerance test (OGTT). RESULTS: Basal plasma ghrelin levels were significantly lower than in the respective control groups. These levels decreased significantly during OGTT in obese children, reaching a nadir of 28+/-9% at 60 min in parallel with the maximum increase in glucose levels and previous to maximum insulin levels. CONCLUSION: The rapid fall in plasma ghrelin concentration in obese children after glucose load suggests a mechanism for the control of appetite after food intake.