Somatostatin agonist pasireotide inhibits exercise stimulated growth in the male Siberian hamster (Phodopus sungorus)

The Siberian hamster (Phodopus sungorus) is a seasonal mammal, exhibiting a suite of physiologically and behaviourally distinct traits dependent on the time of year and governed by changes in perceived day length (photoperiod). These attributes include significant weight loss, reduced food intake, gonadal atrophy, and pelage change with short day photoperiod as in winter. The central mechanisms driving seasonal phenotype change during winter are mediated by a reduced availability of hypothalamic tri-iodothyronine (T3), but downstream mechanisms responsible for physiological and behavioural changes are yet to be fully elucidated. With access to a running wheel (RW) in short photoperiod, Siberian hamsters which have undergone photoperiod mediated weight loss override photoperiod-drive for reduced body weight and regain weight similar to a hamster held in long days. These changes occur despite retaining the majority of hypothalamic gene expression profiles appropriate for short day hamsters. Utilising the somatostatin agonist pasireotide, we have recently provided evidence for an involvement of the growth hormone axis (GH axis) in the seasonal regulation of bodyweight. In the present study we employed pasireotide to test for the possible involvement of the GH axis in running wheel induced body weight regulation. Pasireotide successfully inhibited exercise stimulated growth in short day hamsters and this was accompanied by altered hypothalamic gene expression of key GH axis components. Our data provides support for an involvement of the GH axis in the RW response in Siberian hamsters.