Evidence for a Direct Action of Cholecalciferol and 25-Hydroxycholecalciferol on the Renal Transport of Phosphate, Sodium, and Calcium

Abstract

A B S T R A C T

Study of the Renal Tubular Interactions of Thyrocalcitonin, Cyclic Adenosine 3′, 5′ -Monophosphate, 25-Hydroxycholecalciferol, and Calcium Ion

“…In these studies, animals were expanded with 25-30 ml/kg physiological saline solution 2Kindly supplied by Dr. James Bastian, Armour Pharmaceutical Co., Kankakee, Ill. containing 4-4.5 mEq/liter calcium over a 20-30 min period, after which the infusion rate was adjusted constantly to match urine flow. As in previous studies from this laboratory (24,25), this moderate degree of volume expansion (approximately 2.5% body wt) was utilized as the "control" situation because, in hydropenic, TPTX animals, phosphate excretion is so low as to render any further decline difficult or impossible to detect (24). Steady-state expansion was considered to have been achieved when the urinary flow rate of five to seven consecutive 10-min urine collections did not vary by more than +5%o.…”

“…In Table I, part A, are given the results of those studies in which the infusion of TCT was superimposed upon the renal effects of 25HCC. It has previously been determined in this laboratory that the administration of propylene glycol alone, during sustained volume expansion of this degree leads either to no change (25) or a slight rise (24) in the excretion of phosphate, sodium, and calcium as the expanded state is maintained. Similar to the findings in the former studies (24), the administration of 25HCC to the saline-expanded animals resulted in an invariable fall in the absolute and fractional excretion rates for phosphate, sodium, and calcium in each of the nine studies.…”

“…The experiments described in this comlimulnication were prompted by the findings obtained in this laboratory during a previous study of the renial actions of vitamin D and PTH (24,25). When base line phosplhate excretion in TPTX animals was elevated by means of mild volume expansion, it was possible to demonstrate that the acute effect of vitamin D and its metabolites on the kidney is the enhancement of phosphate, sodium, and calcium reabsorption (24,25).…”

“…An endotracheal tube was passed anfd the dogs were ventilated with a Harvard respirator. Inulin, p-aminohippurate (PAH) and aqueous vasopressin (ADH) were infused in physiological saline solution at a rate of 1 ml/min in quantities sufficient to provide plasma levels of [20][21][22][23][24][25][26][27][28][29][30] mg/100 ml and 1-3 mg/100 ml for the former two substances, and to deliver 30-60 mU/kg per h of the latter. After an equilibration period of 50-60 min, the following experimental maneuvers were performed.…”

“…Urine was collected every 10-30 min by means of air washout and/or manual bladder compression. Blood and urine samples were analyzed for inulin, PAH, calcium, phosphate, sodium, and potassium by methods previously described (24).…”