The secretion of Growth Hormone (GH) is characterized by distinct periods of elevated secretion dispersed with periods of low secretion. This pulsatile GH secretion pattern is thought to change relative to growth and ageing, with the most pronounced change seen between puberty and adulthood. It is thought that peaks in GH secretion reach maximal levels at puberty, and decline following the completion of linear growth. While the change in GH secretion in humans throughout puberty is well characterised, the underlying mechanisms that account for this remain largely unknown. To address this, we assessed pulsatile GH secretion in early-pubertal (5-week old) and early-adult (10-week old) wild-type C57BL/6J mice (between 0700h and 1300h). Raw values were processed via deconvolution and approximate entropy (ApEn) analysis as described previously [1]. Basal and peak GH secretion per pulse, and total GH secreted over the sampling period did not change between early-pubertal and early-adult mice. Compared to early-pubertal mice, an increase in the regularity of the secretory pattern of GH was observed in early-adult mice. This was reflected by an increase in the mode of pulsatile GH release, and a decrease in the number and ApEn of GH pulses. Observations suggest that while peak levels of GH secretion are similar between early-pubertal and early-adult mice, the regular pattern of pulsatile GH secretion only becomes established once mice transition into early-adulthood. Compared to early-adult mice, we observed higher levels of IGF-1 within the muscle of early-pubertal mice. This coincides with peak periods of linear growth. Our observations imply that the synchronous pulsatile release pattern of GH is established by early-adulthood, and that an increase in pulse frequency of GH secretion may underlie the promotion of rapid pubertal growth in the mouse.

This work is supported by the National Health and Medical Research Council (NHMRC) and University of Queensland. Kevin Lee is a recipient of the Australian Postgraduate Awards (APA) scholarship. Dr Shyuan Ngo is a Motor Neurone Disease Research Institute of Australia (MNDRIA) Bill Gole Postdoctoral Fellow.