Exercise-induced hyperphagia in the hamster is associated with elevated plasma somatostatin-like immunoreactivity

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 triiodothyronine (T3), although the downstream mechanisms responsible for physiological and behavioural changes are yet to be fully clarified. With access to a running wheel (RW) in short photoperiod, Siberian hamsters that have undergone photoperiod-mediated weight loss over-ride 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 recently provided evidence for an involvement of the growth hormone (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 RW-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 provide support for an involvement of the GH axis in the RW response in Siberian hamsters.

Preclinical and clinical studies with somatostatin related to the central nervous system

1. The tetradecapeptide somatostatin (SS) has a widespread, uneven distribution within several organs including the central nervous system (CNS), with particularly high concentration in the hypothalamus. 2. The SS-related peptides (SS28, SS28(1-12), SS28(15-28)) are originated from the precursor pre-prosomatostatin. 3. SS is suggested to be involved in a large number of CNS functions, locomotion, sedation, excitation, catatonia, body temperature, feeding, nociception, paradoxical sleep, self-stimulation, seizure, learning and memory. 4. SS influences central neurochemical processes. 5. It is possible that SS is related to various neurological and psychiatric illnesses, like Huntington's disease, multiple sclerosis, Parkinson's disease, epilepsy, eating disorders, Alzheimer's disease, schizophrenia and major depressive illness.

Somatostatin-immunoreactive nerve fibers in close association with capillaries in the small intestine

Electron microscopic immunocytochemistry was used to identify somatostatin-immunoreactive nerve profiles around the capillary system of the small intestine in the rat and cat. The highest density of somatostatin-immunoreactive nerve profiles was seen in the mucosa, and 25-30% of all immunoreactive profiles were found immediately adjacent to the endothelial cells of capillary blood vessels. About half of the capillary endothelial cells were fenestrated. The majority of the immunoreactive nerve profiles were varicosities, containing synaptic vesicles. These observations suggest that somatostatin might be released from varicose nerve fibers and may contribute to the elevated levels of the peptide measured in portal blood as compared to peripheral blood.