The effect of posterior pituitary hormones on the excretion of electrolytes, in dogs

Abstract

The oxytocic substance of posterior pituitary extracts is normally present in equal amounts in both sexes (van Dyke, Adamsons & Engel, 1955). So far two physiological functions have been ascribed to oxytocin, namely, as one of the factors causing contraction of the uterus in parturition, and as the factor responsible for contraction of the mammary myo-epithelial cells in lactation. Several workers have tried to find some other function for this substance. Positive results were obtained by Dicker & Heller (1946) who reported that when Pitocin (oxytocin; Parke, Davis) was given subcutaneously to rats in doses of 3 m-u/100 g rat, glomerular filtration rate (G.F.R.) and renal plasma flOW (R.P.F.) were increased and Cl reabsorption diminished. Demunbrun, Keller, Levkoff & Purser (1954) observed that Pitocin and du Vigneaud's highly purified oxytocin when infused intravenously in large amounts, or given subcutaneously in doses of 2-7-5 i.u., raised renal clearances in dogs with diabetes insipidus, and they suggested that one of the normal functions of oxytocin was to maintain renal blood flow. Brunner, Kuschinsky & Peters (1956) gave doses of 1-50 m-u. oxytocic extract subcutaneously to rats and observed that following hydration with saline solutions, or when the animals were dehydrated, the extract acted as a diuretic and increased Na and K excretion in parallel with the increase in rate of urine flow.The experiments described below were made in another attempt to find out whether oxytocin has some other function than its acknowledged and intermittent ones and whether there is a physiological interdependence of vasopressin and oxytocin. The latter question arises since it has been observed that whatever stimulus is applied to the posterior pituitary-electric, suckling, osmotic etc.-the gland liberates simultaneously both the vasopressor and oxytocic factors, and that the oxytocic one is liberated in greater amounts than the vasopressor by about 4-20 times (Harris, 1955). It was therefore

Synthetic Oxytocin as an Antagonist of Experimental Cardiac Anoxic Changes in Rabbits

“…Geiling, DeLawder & Rosenfeld (1931) and Geiling & DeLawder (1932) have observed an increase in tissue metabolism and oxygen consumption with oxytocic preparations in unanaesthetized dogs, and have also reported that vasopressin and oxytocin have opposite metabolic effects. Fraser (1937) and Brooks & Pickford (1958) have shown that oxytocic preparations can antagonize the antidiuretic effect of the pressor hormone in rats and dogs. It is therefore postulated that the protective cardiac action of oxytocin observed in these experiments might be due to a metabolic action rather than to coronary dilatation.…”

Vasopressin-independent mechanisms in controlling water homeostasis

“…Early studies showed that i.v. administration of oxytocin raised the urinary excretion of sodium two to fourfold and enhance glomerular filtration rate in dogs (Brooks & Pickford 1958) and rats (Dicker & Heller 1946). Recent studies using Vp-deficient Brattleboro rats showed that these animals could respond dose-dependently to oxytocin.…”

“…In recent years, many studies have shown that other hormones also exhibit anti-diuretic functions and these findings add to a growing body of evidence indicating the involvement of Vp-independent mechanisms in regulating renal water reabsorption (Bauman 1965, Jeon et al 2003, Li et al 2006. Secretin (Waldum et al 1980, Chu et al 2007 and oxytocin (Brooks & Pickford 1958, Jeon et al 2003, were previously argued to exert either diuretic or antidiuretic effects, are therefore candidates in regulating renal functions. This review will focus on how these two hormones are potentially involved as Vp-independent mechanisms controlling water homeostasis.…”

The effect of water diuresis on electrolyte excretion in unanaesthetized dogs

“…This provides a tentative explanation for the pattern of electrolyte excretion seen in our experiments. Brooks & Pickford (1958) have shown that oxytocin causes natriuresis and kaluresis when it is given to conscious dogs at high rates of urine flow, if vasopressin is also present. During the early stages of water diuresis, when the plasma concentration of vasopressin is decreasing, the natriuretic effect of the circulating oxytocin would diminish.…”