© 2008, Editrice Kurtis © 2008, Editrice Kurtis NOT PRINTABLE 520 J. Endocrinol. Invest. 31: 520-524, 2008 ABSTRACT. Ten healthy subjects used to performing regular physical activity and eight subjects affected by idiopathic isolat- ed GH deficiency (GHD) were enrolled; 22- and 20-kDa GH se- cretion and its biological activity were evaluated in response to pharmacological stimuli such as arginine, L-dopa or glucagon in GHD children, while the hormonal response to exercise was studied according to Bruce protocol in healthy subjects. We found a significant increase in 22- and 20-kDa GH level in health- y subjects after monitored physical exercise (MPE; basal 0.28±0.12 vs 7.37±2.08 ng/ml and basal 0.076±0.04 vs 0.18±0.05 ng/ml, respectively). Furthermore, the 22-kDa/20- kDa ratio significantly increased in children who had undergone MPE and the GH bioactivity basal mean value also increased significantly after exercise (basal 2.86±0.76 vs 7.64±1.9 ng/ml). The mean value of 22-kDa GH in GHD patients increased sig- nificantly following GH pharmacological stimulation (2.78±0.63 ng/ml) when compared with mean basal (0.20±0.11 ng/ml) val- ue. In the GHD group the basal concentration of 20-kDa GH significantly increased following GH pharmacological stimula- tion (0.34±0.11 vs 0.72±0.2 ng/ml); the 22-kDa/20-kDa ratio significantly increased too. Likewise, GH bioactivity in children with GHD increased significantly after pharmacological stimu- lation test (basal 2.53±0.56 vs 7.33±1.26 ng/ml). Both GH iso- form concentrations and their biological activity are significantly increased in healthy subjects after submaximal exercise proto- col and in GHD children after pharmacological stimuli. (J. Endocrinol. Invest. 31: 520-524, 2008) ©2008, Editrice Kurtis INTRODUCTION The most powerful, non-pharmacological stimuli for GH secretion are both sleep and exercise. Since the initial observation by Hunter et al. in Science in 1965 (1), it has been clearly recognized that physical activity is a naturally occurring stimulator of GH release into the cir- culation. Studies have reported that exercise of suffi- cient intensity and duration elicits a significant increase in GH secretion immediately after physical activity (2). Experimental evidence has also suggested that inten- sity and duration of exercise, work output and muscle strength used during exercise, training state and age may influence the GH response to exercise; but the physiological role of the exercise-induced rise in GH is not known (3). GH is a potent anabolic agent, and the natural response to exercise is, therefore, of great interest to sports per- formers who are trying to maximize the anabolic effect of their training regimen. Similarly, the use of exercise as a way of contributing to the maintenance of functional capacity could have a major impact in the current climate of an aging western society. Therefore, there are many reasons why it is important to understand the relation- ship between exercise and GH release (4). The insight most studies have provided concerning GH secretory dynamics has been limited because they have measured only the 22-kDa molecular isoform of GH. A unique characteristic of GH that has been considered on- ly recently with regard to exercise is the fact that GH ex- ists as a family of molecular isoforms (2). The major isoform is 22-kDa in molecular size, whereas the second most abundant isoform is 20-kDa in size and accounts for ~10% of the total GH in the pituitary. This isoform is generated by alternative splicing of the GH pri- mary transcript and has growth-promoting and lipolytic activities similar to those of 22-kDa (5, 6) but has reduced antinatriuretic activity (7). Although these observations suggest that it has a slightly different metabolic profile, the physiological role of 20-kDa GH is not known (8). Salient findings from studies by Wallace et al. (9) showed that all forms of GH increased during and at the end of exercise and demonstrate that the proportion of GH iso- forms changed across acute exercise and into recovery. The authors postulated that the increase in the propor- tion of isoforms other than 22-kDa after exercise may be attributed to differential pituitary isoform secretion, the appearance of isoforms from non-pituitary sources, gen- eration of fragments, dimers and oligomers in the circu- lation, and differences in clearance rates of the different isoforms. The importance of possessing a greater understanding of the exercise-mediated influences on GH molecular het- erogeneity resides in the fact that the GH isoforms have different downstream metabolic and anabolic actions in target tissue (2). Recently, studies using a highly specific enzyme-linked immunosorbent assay (ELISA) for 20-kDa GH have re- vealed that it circulates at a constant proportion to 22- kDa GH under a variety of physiological and pathophys- iological conditions (8, 10). In fact, no changes in the percentage of 20-KDa were found in normal children and patients with GH deficien- cy (GHD), non-GHD short stature and Turner’s syndrome throughout provocative tests and during deep sleep (11). However, it remains to be determined whether 20-kDa GH is regulated differently from 22-kDa GH. The aims of our study were: 1) to evaluate if the main iso- Key-words: Growth hormone, exercise, GHD, GH isoforms, bioactivity. Correspondence: M. Bozzola, Dipartimento di Scienze Pediatriche, Università degli Studi di Pavia, Piazzale C. Golgi 19, 27100 Pavia, Italy. E-mail: mauro.bozzola@unipv.it Accepted August 3, 2007. Growth hormone isoforms release in response to physiological and pharmacological stimuli S. Pagani 1 , M. Cappa 2 , C. Meazza 1 , G. Ubertini 2 , P. Travaglino 1 , E. Bozzola 1 , and M. Bozzola 1 1 Department of Pediatric, University of Pavia, Pavia; 2 Unit of Endocrinology, Department of Pediatric Medicine, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy