Mammalian and avian antidiuretic hormone: Studies related to possible species variation in osmoregulatory systems

Summary

• 1. In two representative species of the mammalian and avian classes, the dog and Pekin duck, antidiuretic hormone (ADH) concentrations in the blood were measured by a common radioimmunoassay (RIA) making use of an antiserum raised against the mammalian ADH, arginine vasopressin (AVP) which also cross reacted with the avian ADH, arginine vasotocin (AVT), (Fig. 1). The effects of 24 h dehydration on blood osmolality and ADH concentration and the plasma clearance rates of ADH of conscious dogs and Pekin ducks were compared.

• 2. An AVP plasma level of 2.37±0.20 pg·ml⁻¹ (2.18±0.18 fmol·ml⁻¹) (mean±SE) was found in normally hydrated dogs at 298.1±1.0 mOsm· kg⁻¹ plasma osmolality; 24 h water deprivation increased plasma AVP to 6.64±0.96 pg·ml⁻¹ (6.12±0.88 fmol·ml⁻¹) and osmolality to 314.2±2.3 mOsm·kg⁻¹ (Fig. 2). In ducks, osmolality and AVT concentration increased from 297.6±1.2 mOsm·kg⁻¹ and 5.80±0.41 pg·ml⁻¹ (5.51±0.39 fmol·ml⁻¹) in normally hydrated animals to 318.6±3.2 mOsm·kg⁻¹ and 14.46±1.45 pg·ml⁻¹ (13.75±1.38 fmol·ml⁻¹) after 24 h water deprivation (Fig. 3).

• 3. In both species the correlations between plasma osmolality and ADH concentration were highly significant (2 P<0.001) and indicated similar sensitivities of the ADH system to changes in plasma osmolality: 0.24 pg·ml⁻¹ per mOsm·kg⁻¹ in dogs (Fig. 4) and 0.39 pg·ml⁻¹ per mOsm·kg⁻¹ in Pekin ducks (Fig. 5). This interspecies difference in sensitivity was found to be less than the intraspecies variations (Table 1).