The Mechanism of Action of Parathyroid Hormone: Lack of Evidence for the Mediation by Cyclic Adenosine 3′, 5′-Monophosphate of Parathyroid Hormone-Stimulated Phosphaturia

Sallis, John D.

doi:10.1677/joe.0.0460185

Cited by 5 publications

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References 10 publications

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“…The rapidity of the response to PTH by the isolated parotid gland was similar to that seen in the kidney [Sallis, 1970] for phosphate excretion and is consistent with the rate of increase in activity of adenyl cyclase following PTH addition to tissue in vitro [Streeto, 1969;Chase and Aurbach, 1968]. Cyclic AMP is thought to be a mediator in the action of PTH in bone and kidney [see Major and Kilpatrick, 1972] and this may also be the case with parotid salivary glands in sheep.…”

Section: Disclussionsupporting

confidence: 62%

The Influence of Parathyroid Hormone on the Secretion of Phosphate by the Parotid Salivary Gland of Sheep

Fürst

1974

Exp Physiol

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The effect of parathyroid hormone on phosphate secretion by the parotid salivary gland in sheep has been examined in three separate studies: the first, with 3 sheep, used freeflow salivary collection under anaesthesia and intravenous infusion of hormone; the second involved 4 sheep in which 'stop-flow' techniques were applied to one parotid gland; the third was carried out using 6 sheep in which the blood vessels to one parotid gland were isolated and hormone infused at graded rates directly into the arterial supply to the gland.Parathyroid hormone infusion caused an increase in parotid salivary phosphate concentration and secretion rate in all experiments. The response was rapid (within 2-4 min) and also declined rapidly following cessation of infusion. During hormone administration the ratio of salivary to plasma phosphate concentrations for stopped-flow samples was significantly higher than for controls (22-0 ± 2-1 (S.E.M.) Vs 16-0 ± 2.2).Hormone infusion into the blood supply of the isolated parotid gland at rates estimated to give rise to plasma parathyroid hormone levels of about 5, 10 or 20 ng/ml. caused salivary phosphate concentration to rise by 11-6, 19-6 and 25-7 m-mole/litre respectively.The increment, whether expressed as a percentage or on an absolute basis, was directly related to the dose rate.Parathyroid hormone infusion also altered the secretion of sodium, potassium and bicarbonate, but not of calcium or magnesium. These changes, and those of phosphate, are discussed in relation to the mode of action of parathyroid hormone.Reabsorption of phosphate by the renal tubules and absorption of phosphate from the gut are known to be affected by parathyroid hormone (PTH) [see Arnaud, Tenenhouse and Rasmussen, 1967]. The transport of phosphate by the renal tubules is inhibited by PTH in a direct and rapid manner [Pullman, Lavender, Aho and Rasmussen, 1960; Sallis, Hoperoft and Opit, 1967] but the exact mechanism for this action is not yet known. In contrast to the renal effect is the evidence for an enhancing effect of PTH upon gastro-intestinal phosphate transport [Cramer, 1963;Lifshitz, Harrison and Harrison, 1969] but, as in the case of renal transport, the mechanisms are not defined.Since the parotid salivary glands in ruminants actively secrete considerable quantities of phosphorus [McDougall, 1948;Kay, 1966] and since the secretion of phosphorus to the gut appears to play a major role in the regulation of phosphorus homeostasis in ruminants [Compere, 1966; Tomas, 1974] it seems plausible that PTH may exert an action on this secretion. Mayer, Ramberg and Kronfeld [1968] suggested this possibility to explain, in part, the effect of PTH on phosphorus excretion in cows.

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