From the abstract gets itno little more detail.
Prevention of Growth Deceleration after Withdrawal of Growth Hormone Therapy in Idiopathic Short Stature
Discussion
As the collaborative Israeli study of efficacy and safety of hGH therapy was analyzed (10), we realized that in 65 boys with GH deficiency or idiopathic short stature, aged 3–15 yr, the child’s age was the most significant determinant of therapy outcome; over the course of 3 yr boys in the prepubertal age group gained an average 8 cm of predicted adult height, pubertal boys over the age of 12 yr showed a negative correlation of their predicted height gain against age, and boys over the age of 14 yr showed a loss of predicted height during hGH therapy (10). As others did, we observed a maximal response during the initial 2–3 yr of therapy. The consequence of that study was the hypothesis that in idiopathic short stature, a 2- to 3-yr period of therapy might be beneficial and that the window of opportunity ends before the onset of puberty. In the follow-up study we showed the short-term efficacy of 2–3 yr of hGH therapy in prepubertal children, but identified the well known phenomenon of growth deceleration after treatment withdrawal (4). To understand the mechanism of GH dependence and its withdrawal syndrome, we then studied the GH – IGF-I axis and observed it to be normal during the withdrawal syndrome (4). Assuming that the withdrawal syndrome is related to tolerance that might have developed toward hGH or IGF-I, we tried to prevent it by alternate day treatment. Moreover, hGH doses used in therapy often stimulate IGF-I to supraphysiological serum levels, suggesting that target tissues IGF-I may also be higher than normal. The mechanism seems, therefore, to rest with hGH and IGF-I action at their target tissues. We now show that alternate day therapy with hGH in children with an intact GH-IGF-I axis prevents the withdrawal syndrome.
The design of the study paid special attention to the young age group and conclusion of therapy before the onset of puberty, as well as to matching the two treatment groups by height and growth velocity SD scores. In our previous study we did not observe a different response of patients with intrauterine growth retardation or familial short stature compared with children with normal birth weight and parental height, and the current study followed the same design; inclusion criteria did not include either birth weight or parents’ height. Due to the young age of many of the patients, we could not calculate pretreatment height prediction, and therefore, the final predictions made 4 yr later give unreliable estimates of the true final height gain.
Dependence, often associated with drug abuse, is a biological phenomenon with both psychological and physiological components. During the period of addictive substance use, the body adjusts to a new level of pathologic homeostasis or allostasis. When the drug is abruptly discontinued, this equilibrium is disturbed, and the organism reacts with a constellation of manifestations collectively called a withdrawal syndrome. Dependence is preceded by a phase of tolerance, which signifies a progressively decreased response to the effect of a drug, necessitating ever larger doses to achieve the same effect. Tolerance is largely due to compensatory responses of the organism that mitigate the drug’s pharmacological action. It may result from functional adjustment due to compensatory changes in an effector enzyme or a signal transduction system or from metabolic adjustment due to increased disposition of the drug after chronic use. Endocrine tolerance and withdrawal syndromes have been reported for several hormones (9). The mechanism may lie partly at the inhibitory effect of the drug on endogenous hormone secretion. Yet, GH secretion is normal in children during the withdrawal syndrome (4, 7). It must have to do, then, with the effect of hGH at the target organ, and in the case of childhood growth, the target organ is the growth plate. The molecular and cellular bases of endocrine tolerance and withdrawal syndromes are only partly understood (9). Relatively short-term dependence and addiction result from adaptations in specific target cells caused by prolonged exposure to a supraphysiological level of a hormone or a drug of abuse. The best established mechanism of adaptation is up-regulation of second messenger pathways. Acute opiate exposure inhibits a neuronal cAMP pathway, whereas chronic exposure leads to a compensatory cAMP up-regulation (11). Adaptation in protein kinase A, receptor-G protein coupling, and other components of this signal transduction pathway have also been shown to be involved in the case of opiates and cocaine (12). Long-lasting molecular and cellular adaptations may involve other mechanisms. By analogy with other models of long-term memory and long-term drug addiction and abstinence, such long-lived adaptations to hormones may involve relatively stable changes in molecular switches and transcription factors, such as those implicated in persistent drug-induced long-term neural and behavioral plasticity that occur through alterations in the expression of other genes (9, 11).
The prevention of GH tolerance and withdrawal syndrome by alternate day therapy may implicate the pulsatile nature of GH secretion and serum profile. The latter is preserved in the alternate day regimen and is abrogated by daily treatment. We have previously shown the essential role of GH pulsatility for proper function of the GH receptor. Continuous administration of GH to rats, unlike its pulsatile delivery, up-regulates GH receptors (13, 14) and GH-binding protein (15). In the human, too, GH administration has an up-regulatory effect on GH-binding protein (16), which reflects to a great extent the expression of the GH receptor (17). Moreover, it was shown in a mouse model that hormone pulsation is essential for the signal transduction of GH (18). GH pulses induce synchronized pulses of activated STAT5b, its nuclear translocation, and expression of sex-specific liver CYP genes (19, 20). Long-term interference with GH pulsatility may induce long-lived adaptations to GH that may involve relatively stable changes in molecular switches.GH tolerance is not ubiquitous, as IGF-I and IGF-binding protein-3 levels did not decrease after withdrawal below their pretreatment levels in this (data not shown) and a previous study (4). A possible site of long-term plasticity is the chondroprogenital (reserve) layer of the growth plate. GH promotes differentiation of chondroprogenitor cells to become proliferating chondroblasts in isolated epiphyseal cartilage cells (21) and in epiphyseal organ culture (22) as reviewed recently (23). Chronic exposure to hGH might exhaust these cells, whereas alternate day therapy might enable an intermittent recovery for these cells. The results of the present study suggest that after daily hGH therapy for 24 months, such stable changes may last for over a year.
1. Ackland FM, Jones J, Buckler JM 1990 Growth hormone treatment in non-growth hormone-deficient children: effects of stopping treatment. Acta Paediatr Scand 366(Suppl):32–37
2. Chanoine JP, Vanderschueren-Lodeweyckx M, Maes M, Thiry-Counson G, Craen M, Van Vliet G 1991 Growth hormone (GH) treatment in short normal children: absence of influence of time of injection and resistance to GH autofeedback. J Clin Endocrinol Metab 73:1269–1275[Abstract/Free Full Text]
3. de Zegher F, Albertsson-Wikland K, Wollmann HA, Chatelain P, Chaussain JL, Lofstrom A, Jonsson B, Rosenfeld RG 2000 Growth hormone treatment of short children born small for gestational age: growth responses with continuous and discontinuous regimens over 6 years. J Clin Endocrinol Metab 85:2816–2821[Abstract/Free Full Text]
4. Lampit M. Lorber A, Vilkas DL, Nave T, Hochberg Z 1998 Growth hormone (GH) dependence and GH withdrawal syndrome in GH treatment of short normal children: evidence from growth and cardiac output. Eur J Endocrinol 138:401–407[Abstract]
5. Rudman D, Patterson JH, Gibbas DL 1973 Responsiveness of growth hormone-deficient children to human growth hormone. Effect of replacement therapy for one year. J Clin Invest 52:1108–1112[Medline]
6. Tanner JM, Whitehouse RH, Hughes PC, Vince FP 1971 Effect of human growth hormone treatment for 1 to 7 years on growth of 100 children, with growth hormone deficiency, low birthweight, inherited smallness, Turner’s syndrome, and other complaints. Arch Dis Child 46:745–782[Abstract/Free Full Text]
7. Wu RH, St. Louis Y, DiMartino-Nardi J, Wesoly S, Sobel EH, Sherman B, Saenger P 1990 Preservation of physiological growth hormone (GH) secretion in idiopathic short stature after recombinant GH therapy. J Clin Endocrinol Metab 70:1612–1615[Abstract/Free Full Text]
8. Amatruda Jr TT, Hurst MM, D’Esopo ND 1965 Certain endocrine and metabolic facets of the steroid withdrawal syndrome. J Clin Endocrinol Metab 25:1207–1217[Abstract/Free Full Text]
9. Hochberg Z, Pacak K, Chrousos GP, Endocrine withdrawal syndromes. Endocr Rev, in press
10. Hochberg Z, Leiberman E, Landau H, Koren R, Zadik Z 1994 Age as a determinant of the impact of growth hormone therapy on predicted adult height. Clin Endocrinol (Oxf) 41:331–335[Medline]
11. Nestler EJ, Aghajanian GK 1997 Molecular and cellular basis of addiction. Science 278:58–63[Abstract/Free Full Text]
12. Koob GF, Le Moal M 1997 Drug abuse: hedonic homeostatic dysregulation. Science 278:52–58[Abstract/Free Full Text]
13. Bick T, Youdim MBH, Hochberg Z 1989 Adaptation of liver membrane somatogenic and lactogenic growth hormone (GH) binding to the spontaneous pulsation of GH secretion in the male rat. Endocrinology 125:1711–1717[Abstract/Free Full Text]
14. Hochberg Z, Bick T, Amit T, Barkey RJ, Youdim MBH 1990 Regulation of the GH-receptor turnover by growth hormone. Acta Paediatr Scand 367(Suppl):148–152
15. Bick T, Amit T, Barkey RJ, Hertz P, Youdim MBH, Hochberg Z 1990 The interrelationship of growth hormone (GH), liver membrane GH receptor, serum GH-binding protein activity and insulin-like growth factor-I (IGF-I) in the male rat. Endocrinology 126:1914–1920[Abstract/Free Full Text]
16. Hochberg Z, Phillip M, Youdim MBH, Amit T 1993 Regulation of the growth hormone (GH) receptor and GH-binding protein by GH pulsatility. Metabolism 42:1617–1623[CrossRef][Medline]
17. Amit T, Youdim MBH, Hochberg Z 2000 Clinical Review: does serum growth hormone (GH) binding protein reflect human GH receptor function? J Clin Endocrinol Metab 85:927–932[Abstract/Free Full Text]
18. Gebert CA, Park SH, Waxman DJ 1999 Termination of growth hormone pulse-induced STAT5b signaling. Mol Endocrinol 38–56
19. Gebert CA, Park SH, Waxman DJ 1997 Regulation of signal transducer and activator of transcription (STAT) 5b activation by the temporal pattern of growth hormone stimulation. Mol Endocrinol 11:400–414[Abstract/Free Full Text]
20. Waxman DJ, Zhao S, Choi HK 1996 Interaction of a novel sex-dependent, growth hormone-regulated liver nuclear factor with CYP2C12 promoter. J Biol Chem 271:29978–29987[Abstract/Free Full Text]
21. Ohlsson C, Nilsson A, Isaksson O, Lindahl A 1992 Growth hormone induces multiplication of the slowly cycling germinal cells of the rat tibial growth plate. Proc Natl Acad Sci USA 89:9826–9831[Abstract/Free Full Text]
22. Maor G, Hochberg Z, v d Mark K, Heinegard D, Silbermann M 1989 Human growth hormone enhances chondrogenesis and osteogenesis in a tissue culture system of chondroprogenitor cells. Endocrinology 125:1239–1245[Abstract/Free Full Text]
23. Hochberg Z, Clinical physiology and pathology of the growth plate. Bailliere Clin Endocrinol Metab, in press