Effects of GH and IGF-I administration on GHRH and somatostatin mRNA levels: II. A study in the infant rat

Abstract

It is generally accepted that growth hormone influences its own secretion by modulating the activity of GHRH and SRIF neurons. To investigate if GH feedback mechanisms are already operating in the early postnatal life of the rat, we have studied in 10-day-old pups the effects of rhGH and rhIGF-I administration on GHRH and somatostatin mRNA levels. The same experiment was also performed in pups passively immunized with an anti-GHRH antiserum from the day of birth. The latter animal model had been previously characterized for presenting reduced levels of circulating GH and IGF-I. In control pups, neither rhGH (250 micrograms/kg, b.i.d., sc) nor rhIGF-I (150 micrograms/kg, b.i.d., sc) administration induced significant changes of GHRH and SRIF gene expression. The passive immunization against GHRH induced per se a trend toward an increase and a reduction of GHRH and SRIF mRNA levels, respectively. Also in these rats the treatment for 3 days with rhGH and rhIGF-I did not further modify the GHRH and SRIF mRNA levels. Based on these results, we conclude that in the 10-day-old rat GH feedback mechanisms are poorly operative, though a direct ultra-short loop mechanism involving the GHRH and SRIF systems seems already operating.

Hexarelin Modulates the Expression of Growth Hormone Secretagogue Receptor Type 1a mRNA at Hypothalamic and Pituitary Sites

“…In addition, it has been demonstrated that in newborn rats, a lower sensitivity of the GH feedback to GH-secreting stimuli is due to an immaturity of the somatostatinergic system [38, 39]. The results of these studies [18, 37, 38, 39]as well as the results found in our study are suggestive of an age-dependent change in the sensitivity of the hypothalamic GHS-R1a mRNA expression to the GH negative feedback.…”

“…Similarly, in GH-deficient dw/dw rats, with chronic severe isolated GH deficiency, the basal GHS-R1a expression in the arcuate nucleus of the hypothalamus was markedly increased and, conversely, treatment with exogenous GH reduced GHS-R1a transcript abundance to levels lower than normal, a likely indication that hypothalamic GHS-R1a expression was sensitive to the GH inhibitory feedback [37]. In addition, it has been demonstrated that in newborn rats, a lower sensitivity of the GH feedback to GH-secreting stimuli is due to an immaturity of the somatostatinergic system [38, 39]. The results of these studies [18, 37, 38, 39]as well as the results found in our study are suggestive of an age-dependent change in the sensitivity of the hypothalamic GHS-R1a mRNA expression to the GH negative feedback.…”

Growth Hormone Effects in Intestinal Adaptation After Massive Bowel Resection in the Suckling Rat

“…Growth hormone influences its own secretion by modulating the activity of GH releasing hormone and somatostatin (17). However, in the early postnatal life of the rat, GH feedback mechanisms are poorly operative compared with those of adults (18). Muscle protein synthesis is stimulated by insulin-like growth factor 1 and GH in adults but by insulin in growing rats (19).…”

Growth hormone and growth hormone gene of the American mink (Neovison vison) – the current state of knowledge of one of the key hormones in one of the most intensively economically exploited species

“…The factors inhibiting the growth hormone secretion include hyperglycaemia, cortisol, chronic lack of sleep, free fatty acids, neuropeptide Y (NPY), vitamin D, thyroid hormones and melatonin (Rettori et al, 1990;Barb et al, 1995;Giustina, Wehrenberg, 1995;Thompson et al, 1995;Seoane et al, 2002;Karasek et al, 2007;Kim et al, 2010;Skrzypczak et al, 2011). An important, inhibitory effect on the secretion activity of acid-absorbant cells of the pituitary gland is shown, in the mechanism of the negative feedback, by GH and IGF-1 present in the peripheral circulation (Yamasaki et al, 1991;Grilli et al, 1997;Skottner, 2012).…”