Cardiac natriuretic peptide response to water restriction in the hormonal adaptation of two semidesert rodents from west Africa (Steatomys caurinus, Taterillus gracilis)

Two African rodents, Taterillus gracilis and Steatomys caurinus, native to regions of alternate dry and wet seasons, were studied under laboratory con ditions. These species differ in estivation behavior, one undergoing pseudo estivation and the other strong estivation. One group of animals of each sp ecies was provided with unlimited access to seed and vegetables rich in wat er, mimicking the food availability of the wet season (control group). A se cond group of animals of each species was subjected to water restriction fo r 8 days, mimicking the natural drought that occurs during the dry-hot seas on. The effects of water restriction on osmoregulation and body water conte nt were assessed from hematocrit, and plasma and urinary osmolalities (PO, UO). Whether the natriuretic peptide system was modified by the osmoregulat or adaptation to aridity of these semidesert rodents tvas examined from mea surements of atrial natriuretic peptide (ANP) levels in plasma, atria, and ventricles, in parallel with morphological studies. In both species, UO was increased by water restriction In water-deprived T. gracilis, ANP levels w ere about twice (right atria: 1.08 +/- 0.16 mug/mg protein vs control: 0.40 +/- 0.06 mug/mg protein) and plasma concentrations half (0.28 +/- 0.06 ng/ ml vs control: 0.64 +/- 0.07 ng/ml) those in control animals. In S. caurinu s these variables were not affected by water availability (right atria wate r restricted: 2.20 +/- 0.15 mug/mg protein vs control: 2.86 +/- 0.37 mug/mg protein; plasma ANP water restricted: 0.80 +/- 0.12 ng/ml vs control: 0.90 +/- 0.16 ng/ml). Consistent with these quantitative results, immunohistoch emical and ultrastructural observations showed an increase in immunostainin g for both the N- and the C-terminal ANP and a larger number of granules in the atria of T. gracilis following water restriction, whereas there was no visible change in S. caurinus. Thus, water restriction induced a decrease in ANP secretion in T. gracilis, increasing cardiac storage alongside a red uced urine production. In contrast, in S. caurinus, the natriuretic system was not affected by an 8-day period of water restriction. (C) 2000 Academic Press.