Effects of arginine vasotocin, cortisol and adrenergic factors on water balance in the toad Bufo bufo: Physiology or pharmacology?

Water Potential Receptors in the Skin Regulate Blood Perfusion in the Ventral Pelvic Patch of Toads

Blood cell flux (BCF) in ventral pelvic skin capillaries was measured in conscious unrestrained Bufo bufo, using a laser Doppler flowcytometer. Hydrated toads responded to water contact with a small but significant increase in BCF. Dehydration alone did not change the BCF in seat patch skin before water contact. However, water contact by dehydrated toads elicited a rapid 600% increase in BCF. The BCF and water uptake of dehydrated toads rehydrating in water declined over 2 h but remained significantly above the low, constant values measured in hydrated toads. Arginine vasotocin injection in hydrated toads did not change skin BCF, but water uptake increased, and urine production decreased. Injection of the beta -adrenergic agonist isoproterenol increased BCF in hydrated toads by 900% and also increased the rate of water uptake. These increases corresponded in magnitude and duration to the response to water contact observed in dehydrated toads. Injection of dehydrated toads with the beta -adrenergic antagonist propranolol significantly reduced both BCF and water uptake. These results are consistent with an autonomic reflex mediated by skin water potential receptors that regulate blood perfusion of ventral pelvic skin.

Amphibian emergency and critical care

Amphibians present unique challenges for the clinician in the diagnosis and treatment of life-threatening conditions. Their adaptability to both aquatic and terrestrial lifestyles leaves them vulnerable to dehydration and fluid overload, either of which may accompany serious disease. This article presents the most common emergency conditions in amphibians, the physiologic basis of disease, and a guide to the diagnosis and treatment of amphibian emergencies.

Solid-phase extraction of arginine vasotocin and isotocin in fish samples and subsequent gradient reversed-phase high-performance liquid chromatographic separation

Gradient high-performance liquid chromatography (HPLC) preceded by a solid-phase extraction (SPE) step is described for determining arginine vasotocin and isotocin, the neurohypophysial nonapeptides, in fish plasma samples. The combination of these two methods significantly improves the separation and increases the sensitivity of the assay. The proposed assay may be a useful alternative for analysis of similar nonapeptides in plasma without the use of radioisotopes, while taking into consideration a difference in detection sensitivity.

Empty bladder and dehydrated pelvic patch water uptake in Bufo marinus: inhibition by captopril

Dehydration (10.3 +/- 2.2%, N = 7) caused a significant increase in pelvic patch water uptake (Jv) from 875 +/- 86 (N = 21) to 2130 +/- 150 (N = 21) cm3.cm-2 x 10(-7), while the pectoral Jv increased from 258 +/- 31 (N = 21) to 545 +/- 75 (N = 21 cm3.cm-2 x 10(-7). Captopril inhibited the pelvic patch Jv in empty bladder toads decreasing the Jv from 978 +/- 45 (N = 27) to 607 +/- 38 (N = 27) cm3.cm-2 x 10(-7). In dehydrated toads (15 +/- 2%, N = 14), captopril reduced the pelvic patch Jv from 1807 +/- 213 (N = 21) to 957 +/- 91 (N = 21) cm3.cm-2 x 10(-7). Captopril injection decreased the blood pressure in dehydrated toads from 25.6 +/- 1.9 (N = 21) to 16.9 +/- 1.5 (N = 21) mmHg with no change in heart rate.

Role of pars nervosa of the hypophysis in amphibian water economy: a re-assessment

1. Responses in renal function and in water permeability of skin and bladder to wet and dry environments are accomplished within the range of normal hydration of the amphibian organism. 2. Urine production is discontinued at moderate dehydration. 3. Strong dehydration is needed to raise plasma arginine vasotocin (AVT). 4. Surgical interference with hypophysial function may repress water balance responses because of pars distalis dysfunction, with no clear effect of elimination of pars nervosa function. 5. Antidiuretic hormones, along with adrenergic agonists, may be potent stimulators of the water permeability of membranes of variable permeability, such as skin of terrestrial anurans. 6. AVT does not play a key role in amphibian water economy, but may exert a modulatory role in the control of renal function, secondary to nervous control.

Effect of breeding state, moulting, dehydration, exposure to saturated atmosphere, and arginine vasotocin on cutaneous water permeability in the toad Bufo bufo

Cutaneous water permeability was assessed in hydrated male toads under a variety of conditions, including dehydration and rehydration, and the effects of exogenous arginine vasotocin (AVT) were determined. Cutaneous water permeability (the rate of water uptake by toads in water) was high in toads collected in the breeding pond and declined steeply during the first week, coincident with reduced activity of the cutaneous mucus glands. The slopes of the dose-response curves relating AVT to cutaneous water influx were about the same at the transition from the breeding to the nonbreeding state, but the level of influx was higher in the breeding state. The dose-response relationship in long-term terrestrial-acclimated toads was similar to that in water-acclimated toads. The threshold dose for effect on the cutaneous water permeability was about 1 ng AVT. Dehydration had a substantially greater effect on the cutaneous water permeability than AVT. The ratio between dehydration and AVT responses tended to increase with increasing water transport capacity of the skin. Moulting and acclimation to a saturated atmosphere in fully hydrated toads more than doubled the water permeability and abolished the response to AVT. It is suggested that AVT and other factors increase the cutaneous water permeability by similar mechanisms, such as insertion of water channels in the apical membrane of the epidermal cells. The effect of AVT on the toad skin is interpreted as reflecting the general high potency of neurohypophysial hormones in stimulating the water permeability of membranes of variable permeability.