Obestatin, a product of post-translational processing of the ghrelin prohormone, has been reported to act in the brain to inhibit thirst. We extended our initial studies on water drinking by examining the effects of obestatin on hypovolemia-induced water and saline drinking and vasopressin release in male rats. Intracerebroventricular administration of obestatin significantly inhibited water, but not saline (0.3 M NaCl) drinking in response to a hypovolemic challenge. Obestatin also inhibited, in a dose-related fashion, dehydration-induced vasopressin secretion without affecting plasma oxytocin levels. Vasopressin release induced by central angiotensin II administration was attenuated significantly by prior administration of obestatin. Finally, central administration of an antiserum specific to obestatin resulted in an exaggerated basal vasopressin release and an increased vasopressin response to overnight water deprivation. Antiserum treatment also resulted in significantly increased ad libitum water drinking and drinking in response to dehydration. We conclude that this product of post-translational processing of the ghrelin prohormone may be an important contributor to the physiologic regulation of fluid and electrolyte homeostasis.
Willis K Samson, Gina L C Yosten, Jaw-Kang Chang, Alastair V Ferguson and Meghan M White
Gina L C Yosten, Grant R Kolar, Lauren J Redlinger and Willis K Samson
Microvascular diseases, such as retinopathies, neuropathies, and nephropathies, are a devastating consequence of type 1 and type 2 diabetes. The etiology of diabetes-associated microvascular dysfunction is poorly understood, and, likewise, treatment modalities for these disorders are limited. Interestingly, proinsulin C-peptide has been shown to play a protective role against diabetes-associated complications in experimental animals and in diabetic humans and is thus an attractive therapeutic target. However, an important step in the development of C-peptide-based therapeutics is identification of the C-peptide receptor, which is likely a G protein-coupled receptor (GPCR). Using a unique Deductive Ligand-Receptor Matching Strategy, we sought to determine whether one of the known orphan GPCRs is essential for C-peptide signaling. Knockdown of GPR146, but not GPR107 or GPR160, blocked C-peptide-induced cFos expression in KATOIII cells. Furthermore, stimulation with C-peptide caused internalization of GPR146, and examples of punctate colocalization were observed between C-peptide and GPR146 on KATOIII cell membranes. These data indicate that GPR146 is likely a part of the C-peptide signaling complex and provide a platform for the elucidation of the C-peptide signalosome.