Daily rhythm of NaCl intake in rats fed low-Ca2+ diet: relation to plasma and urinary minerals and hormones.
To assess daily rhythms of salt appetite, we measured spontaneous 300 mM NaCl intake of male Sprague-Dawley rats fed a diet containing 150 or 25 mmol Ca2+/kg. Both groups drank most NaCl at night, but, as the dark period progressed, intakes of controls remained constant or diminished, whereas intakes of rats fed low-Ca2+ diet increased. During the late dark period, when the difference in NaCl intake between the two dietary groups was greatest, rats fed a low-Ca2+ diet lost more corticosterone and sodium in urine, had lower plasma osmolarity, and had higher plasma adrenocorticotropic hormone (ACTH) and corticosterone concentrations than did controls. Over the 24-h cycle, rats fed the low-Ca2+ diet excreted less Ca2+ and more corticosterone in urine than did controls. They also had consistently lower plasma concentrations of Ca2+ and renin activity and consistently higher plasma phosphorus, arginine vasopressin, parathyroid hormone, thyroxine, calcitonin, and 1,25-dihydroxyvitamin D3. These findings support the hypothesis that salt appetite induced by dietary Ca2+ deficiency involves a subtle dysfunction of the ACTH-corticosterone axis, but they also raise several other possibilities.
Tordoff
M G
MG
Monell Chemical Senses Center, Philadelphia, Pennsylvania 19104, USA.
Okiyama
A
A
D000818:Animals; D002136:Calcium, Dietary / Q000008:administration & dosage*; D002940:Circadian Rhythm; D006728:Hormones / Q000097:blood / Q000652:urine; D008297:Male; D008903:Minerals / Q000097:blood / Q000652:urine; D051381:Rats; D017207:Rats, Sprague-Dawley; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage / Q000378:metabolism*
D002136:Calcium, Dietary; D006728:Hormones; D008903:Minerals; D017673:Sodium Chloride, Dietary