The Effect of Vasopressin Upon the Excretion of Calcium by the Sheep

Abstract

Vasopressin (140 ,U/min) was infused intravenously into 12 conscious merino ewes for 2 hr. Urine flow rate and free water clearance were consistently reduced. There was no effect upon renal plasma flow, glomerular filtration rate or the rate of excretion of sodium, potassium, magnesium, chloride or phosphate. Although all animals received 75 mmol calcium chloride into the rumen on the previous day, five commenced the experiment with calcium excretion rates of less than 1 ,umol/min. In these, vasopressin further decreased calcium exeretion. In seven animals with calcium excretion rates between 2 and 20 ,umol/min vasopressin had no effect upon either total calcium or free ionized calcium excretion rate.A number of workers have observed that administration of arginine vasopressin increases electrolyte excretion. Brooks and Pickford [1958] described an increased sodium excretion in the dog and Cross, Thornton and Tweddell [1963] demonstrated that vasopressin administered as a single intravenous injection of 40 mU caused an increase in potassium excretion in the sheep. Thorn [1961] administered similarly large doses of vasopressin in the dog and observed increases in calcium excretion. Dicker and Eggleton [1961] demonstrated a similar effect in humans. They used these findings to support an hypothesis that vasopressin acted upon renal tubule hyaluronidase and claimed that the increased calcium excretion was secondary to depolymerization of the intercellular matrix. They certainly demonstrated a good inverse relationship between urine flow and calcium excretion. Kuhn [1966] reinvestigated the phenomenon in the sheep. He used much smaller doses of arginine vasopressin than did previous workers (0-012 mU/kg/ min infused for 40 min). He observed a consistent anti-diuretic effect but noted a decrease in calcium excretion. Kuhn and Peeters [1967] confirmed that this low dose of vasopressin did cause consistent increases in potassium excretion.In the course of a study of calcium metabolism in the sheep the present authors took the opportunity to reinvestigate the phenomenon using low doses of vasopressin infused for long periods of time. METHODSExperiments were conducted on 12 conscious merino ewes. All animals were given an oral dose of calcium chloride (75 mmol) 15 hr before the start of the experiment. The animals were subsequently deprived of food but allowed water. At 08.00 hr on the day of the experiment 3 1 tap water was administered into the rumen. An intravenous infusion of sucrose (210 mmol/l), para amino hippurate (30 mmol/l) and NaCl (60 mmol/l) was maintained at the rate of 2 ml/min for the entire experiment. When 121

Renal calcium and magnesium excretion during vasopressin administration into sheep with acid or alkaline urine.

“…When this phenomenon was investigated in water-loaded sheep using hormone dose rates closer to 'physiological' than those of the previous authors, Kuhn (1966) found that antidiuresis produced by the administration of vasopressin or oxytocin was always associated with significant decreases in renal calcium excretion whereas Beal, Clark, Cross & French (1976) reported significant decreases in excretion after vasopressin only in sheep with calcium excretion rates less than 1 #smole/min. At higher rates of calcium excretion, vasopressin infusion did not alter calcium excretion although antidiuresis still occurred.…”