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Stimulation of Lipolysis by Phosphate In Vitro and In Vivo¹

Department of Nutrition, College of Biological Science University of Guelph, Guelph, Ontario, Canada N1G 2W1

As part of a study on the mechanism whereby high phosphorus diets depress food intake and weight gain in adult animals, the effect of such diets on mouse and rat adipose tissue lipolysis in vitro and in vivo was investigated. High phosphorus diets cause a rise in serum phosphate and parathyroid hormone (PTH), both of which have been reported to stimulate lipolysis in vitro. Enhancement of epididymal adipose tissue lipolysis by PTH and phosphate in vitro was confirmed, but no effect of feeding low calcium or high phosphorus diets on lipolysis could be detected in vitro or in vivo. However, oral administration of a phosphate load equivalent to that present in a high phosphorus meal led to a significant rise in serum free fatty acids. It was concluded that the concentrations of PTH required to stimulate lipolysis in vitro (10^-9 M) are not attained in animals fed low calcium or high phosphorus diets. Although lipolysis was stimulated in vivo under conditions of phosphate loading, and in vitro by concentrations of phosphate which occur in the serum of animals fed high phosphorus diets, under normal physiological conditions the lipolytic potential of such diets may be blunted by the antilipolytic action of insulin secreted in response to ingested carbohydrate.

KEY WORDS: • phosphate • parathyroid hormone • lipolysis • adipose tissue

¹ Supported by the National Sciences and Engineering Research Council of Canada and The Ontario Ministry of Agriculture and Food.

² To whom reprints should be sent.

Manuscript received 28 July 1981.