Atrial-natriuretic-peptide (anp) Increases In the Mangrove Crab Ucides-cordatus When Exposed To Increased Environmental Salinity

1. Haemolymph taken from the basal joints of the walking legs of the mangrove Brazilian crab Ucides cordatus, was analysed using a very sensitive radioimmunoassay (RIA) technique, before and after specific extraction and purification methods (Vycor-Glass) for immunoreactive atrial natriuretic peptide (IR-ANP) determinations. 2. The mangrove crabs (N = 20) were randomly distributed in four groups, exposed to four different salinities, all of them included in the ecological Brazilian mangrove range: 9, 17, 26, 34 parts-per-thousand of seawater. 3. The smallest IR-ANP value, found in the 26 parts-per-thousand salinity (1.25 +/- 0.2 pg/ml) was coincident with the isosomotic gradient for haemolymph and external medium, where the crab is not submitted to osmoregulatory disbalances. 4. The IR-ANP values found in the 9 and 17 parts-per-thousand salinity, did not show any significant differences when compared with values obtained at the isosmotic point 26 parts-per-thousand. 5. IR-ANP level increased significantly with the external salinity level, from 26 to 34 parts-per-thousand (7.5 +/- 5 pg/ml; N = 5). There was a significant positive Kendall Correlation Coefficient (P = 0.035) between the IR-ANP values found at 26 and 34 parts-per-thousand salinity. 6. ANP could participate in the osmoregulation of the Brazilian crab. U. cordatus, contributing towards NaCl extrusion in hyperosmotic environmental salinity.