Volumetric control of arginine vasotocin and mesotocin release in the frog (Rana ridibunda)

Abstract

Adult male frogs (Rana ridibunda) were subjected to several volumetric and osmometric stimuli and the influence on circulating concentrations of arginine vasotocin (AVT) and mesotocin was studied by the use of highly specific radioimmunoassays. During progressive blood withdrawal (haemorrhage group) urine flow decreased to zero, whereas no change occurred in the plasma and urine osmolality. Control levels of 34.3 +/- 7.3 pmol AVT/1 gradually increased up to 638.3 +/- 179.1 pmol/1 (P less than 0.001) after a blood loss of up to 50-60% of the blood volume. Plasma mesotocin concentrations also increased from 42.4 +/- 9.2 to 70.8 +/- 12.0 pmol/1 (n = 7). Hypervolaemia, produced by the repeated intravenous injection of isotonic Ringer solution, increased the urine flow and osmolality compared to controls but had no influence on the plasma levels of AVT and mesotocin. Hypernatraemia without volume change profoundly increased the urine osmolality but the urine flow was not affected; the plasma concentrations of AVT and mesotocin remained at the control level. Finally, during a 1-h immobilization stress a pronounced antidiuresis occurred in the presence of a constant plasma and urine osmolality and control plasma levels of AVT and mesotocin. It is concluded that the release of AVT and, to a smaller extent, of mesotocin is under volumetric control.

Water balance of field-excavated aestivating Australian desert frogs, the cocoon-formingNeobatrachus aquiloniusand the non-cocooningNotaden nichollsi(Amphibia: Myobatrachidae)

“…Generally, the two species had similar plasma AVT concentrations (9.4-164·pg·ml -1 ) and most excavated individuals had mean concentrations not significantly different from control individuals. Concentrations were also similar to that of hydrated Rana ridibunda and Bufo marinus (Nouwen and Kühn, 1983;Nouwen and Kühn, 1985;Konno et al, 2005) but higher than hydrated Rana catesbeiana (Rosenbloom and Fisher, 1974;Sawyer and Pang, 1975;Pang, 1977). One cocooned N. aquilonius was found to have much higher AVT concentrations than any other frog (394·pg·ml -1 ).…”

“…While there have been few studies to measure circulating AVT concentrations in relation to plasma osmolality, there has been a consistent finding of increased AVT with high osmolality in amphibians (e.g. Nouwen and Kühn, 1983;Nouwen and Kühn, 1985;Konno et al, 2005) and reptiles (Rice, 1982;Ford and Bradshaw, 2006;Ladyman et al, 2006). The increased AVT concentration of frogs with the greatest osmolalities suggests that a similar relationship is likely for the desert-aestivating species of this study; however, it appears that the majority of frogs had not yet been pushed to the threshold where AVT release was stimulated.…”

“…However, the stimulus for AVT release varies among species. For Bufo marinus, an increase in plasma osmolality is sufficient to increase plasma AVT (Konno et al, 2005), while for Rana ridibunda only an increase in osmolality accompanied by haemorrhage/hypovolaemia elicits increases in AVT (Nouwen and Kühn, 1985). There have been no measurements of AVT in aestivating frogs.…”

Water Balance and Arginine Vasotocin in the Cocooning FrogCyclorana platycephala(Hylidae)

“…Cocooning frogs make a particularly interesting case for the study of AVT because its normal role in regulating cutaneous permeability is nullified by the presence of the cocoon. Circulating concentrations of AVT have been measured for only a few frog species (e.g., Ratia catesbeiana [Rosenbloom and Fisher 1974;Sawyer and Pang 1975], Rana ridibunda [Nouwen andKuhn 1983, 1985]), and Bufo marinus appears to be the only terrestrial species for which circulating concentrations have been measured (Konno et al 2005). In the first report of AVT concentrations in a cocooned estivating frog, N. aquilonius excavated in the field were found to have relatively low plasma AVT concentrations (7.1-164 pg mL"') except for a single individual with a concentration of 394 pg mL"' (Cartledge et al 2006).…”

Expression of the vasotocin gene in the hypothalamus of intact and osmotically stimulated bullfrogs during metamorphosis

“…In adult bullfrogs and toads, hyperosmotic stimulation increased plasma vasotocin (VT) levels (Bentley 1969, Pang 1977. The release of VT has been considered to be regulated by both plasma osmolality and blood volume; however, a volemic control seems to predominate in adult amphibians (Nouwen & Kuhn 1985). Injection of VT induced water absorption and reabsorption by the skin, kidney, and urinary bladder, resulting in a weight increase (Alvarado & Johnson 1966, Shoemaker & Nagy 1977.…”