Vascular effects of arginine vasotocin in toad skin

Fluid balance in amphibians is regulated, in large part, by arginine vasotocin (AVT). One important action of this hormone is to facilitate water uptake by increasing the water permeability of the skin. Cutaneous blood flow also affects water uptake, but the effects of AVT on skin perfusion are unknown. This study tested the hypothesis that AVT facilitates water uptake, not only by increasing cutaneous water permeability, but also by promoting cutaneous blood flow. The effects of AVT on blood flow through the ventral pelvic skin, a region specialized for water uptake, were assessed in Bufo marinus by determining the conductance of the skin to acetylene (GsAc), an index of cutaneous blood flow. A pump-perfused skin preparation was used to study the effects of AVT on the cutaneous vascular resistance (CVR) of the ventral pelvic skin and the dorsal skin (a region not normally involved in water uptake). Bolus AVT injections (iv) of 10 pmol/kg and below had no significant effect on GsAc (P > 0.45). However, 100 and 300 pmol/kg of AVT decreased GsAc by 39 +/- 7 (P < 0.001) and 63 +/- 6% (P < 0.001), respectively. The higher AVT doses increased mean arterial pressure. AVT increased CVR in both pump-perfused preparations. The lowest concentration of AVT tested that significantly raised CVR was 1 x 10(-10) M for the dorsal skin (P = 0.006) and 3 x 10(-10) M for the ventral pelvic skin (P = 0.038).(ABSTRACT TRUNCATED AT 250 WORDS)