title: Daily patterns of plasma atrial natriuretic peptide, serum osmolality and haematocrit in the rat.
abstract: The present study documents daily rhythms of plasma atrial natriuretic peptide, serum osmolality and haematocrit in the rat. One-hundred and twenty-five Sprague-Dawley rats were used. They were bred under a cycle of 12 h light/12 h dark starting at 07.00 h. Fifty-three rats were decapitated between 09.00 and 16.00 h (study I) and 72 rats in groups of six were decapitated at 2-h intervals for a period of 24 h (study II). In study I, plasma atrial natriuretic peptide was 156 +/- 11 pg mg-1 (mean +/- SEM). In study II, atrial natriuretic peptide was at a control level from 08.00 to 18.00 h and then began to increase. At 22.00 h, atrial natriuretic peptide was 420 +/- 105 pg ml-1, which was significantly higher than at 08.00 h (P less than 0.05). The serum osmolality was over 300 mosmol kg-1 during the day. The highest mean osmolalities (315, 317, 312 mosmol kg-1) were found from 18.00 to 22.00 h. These were significantly different (P less than 0.05) from other groups during the day. The haematocrit was highest at 14.00 h (49.5 +/- 0.7%) and lowest at 24.00 h (43.6 +/- 0.8%) (P less than 0.05). In conclusion, we have shown that there are significant daily rhythms of plasma atrial natriuretic peptide, serum osmolality and haematocrit during a 24-h period and 12 h light/12 h dark cycle in the rat.
authors.affiliation: Department of Physiology, University of Oulu, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Kanervo
authors.forename: O
authors.initials: O
authors.lastname: Arjamaa
authors.forename: O
authors.initials: O
authors.lastname: Vuolteenaho
authors.forename: J
authors.initials: J
authors.lastname: Leppäluoto
mesh_terms: D000818:Animals; D009320:Atrial Natriuretic Factor / Q000097:blood*; D002940:Circadian Rhythm / Q000502:physiology*; D006400:Hematocrit; D008297:Male; D009994:Osmolar Concentration; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D009320:Atrial Natriuretic Factor