Effects of hypertonic stimuli and arginine vasotocin (AVT) on water absorption response in Japanese treefrog, Hyla japonica.
Anuran amphibians do not drink orally but absorb water osmotically through the highly permeable ventral skin. In this cutaneous water absorption, roles of the putative cerebral osmoreceptors and functions of arginine vasotocin (AVT) were examined in the central nervous system of the Japanese treefrog, Hyla japonica. Intracerebroventricular (ICV) or intralymphatic sac (ILS) administration of various hypertonic solutions (NaCl, mannitol and urea) significantly extended the residence time in water in a dose-dependent manner, suggesting facilitation of water absorption in frogs. ICV injection of AVT also increased significantly the residence time in a dose-dependent manner. The water absorption effect of AVT was significantly inhibited by pretreatment of ICV OPC-21268, a vasopressin V(1) receptor antagonist. But pre-ICV injection of OPC-31260, a vasopressin V(2) receptor antagonist, did not block the water absorption effect of AVT. Extension of the residence time induced by hyperosmotic NaCl (1000 mOsm) ICV injection was significantly inhibited by pretreatment of ICV OPC-21268. The present results showed that increases of osmotic pressure in plasma and/or cerebrospinal fluid stimulate water absorption response, suggesting that osmoreceptors are certainly present in the central nervous system and AVT may directly stimulate water absorption in the treefrog. It is also suggested that AVT activates cellular mechanisms via V(1)-like but not V(2)-like receptors in the central nervous system and facilitates water absorption response in the treefrog.
Department of Biological Science, Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 9308555, Japan.
Sho
S
Maejima
Toshiki
T
Yamada
Takayuki
T
Hamada
Kouhei
K
Matsuda
Minoru
M
Uchiyama
D000818:Animals; D065092:Antidiuretic Hormone Receptor Antagonists; D001552:Benzazepines / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002490:Central Nervous System / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005950:Glucose Solution, Hypertonic / Q000494:pharmacology*; D006982:Hypertonic Solutions / Q000008:administration & dosage / Q000494:pharmacology; D009997:Osmotic Pressure / Q000187:drug effects; D010880:Piperidines / Q000494:pharmacology; D015363:Quinolones / Q000494:pharmacology; D011898:Ranidae; D017483:Receptors, Vasopressin / Q000502:physiology; D012462:Saline Solution, Hypertonic / Q000494:pharmacology*; D014668:Vasotocin / Q000494:pharmacology*; D014867:Water / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000187:drug effects
D065092:Antidiuretic Hormone Receptor Antagonists; D001552:Benzazepines; D005950:Glucose Solution, Hypertonic; D006982:Hypertonic Solutions; D010880:Piperidines; D015363:Quinolones; D017483:Receptors, Vasopressin; D012462:Saline Solution, Hypertonic; D014867:Water; C068644:OPC 21268; C076251:mozavaptan; D014668:Vasotocin