Acute parathyroid hormone increase by oral peptones administration after roux-en Y gastric bypass surgery in obese subject : role of phosphate in the rapid control of parathyroid hormone release

Background. It is generally considered that changes in serum phosphate levels do not alter parathyroid hormone (PTH) secretion in the absence of concomitant changes in ionized serum calcium level in humans. An acute rise in PTH was shown after phosphate administration by intraduodenal gavage in rats. We aimed to study gastrin, phosphate, PTH, ionized calcium (iCa), and blood pH responses to oral peptones in morbidly obese patients before and after roux-en-Y gastric bypass (RYGB) surgery. Methods. These parameters were evaluated in response to an oral peptone load in 24 (18 male and 6 female) obese subjects before and 6 months after RYGB surgery. In 12 gastric bypass patients, we also evaluated PTH and phosphate after peptones plus aluminum hydroxide administration to suppress phosphate absorption. Results. Before RYGB, peptones increased gastrin (P < .001), and decreased iCa (P < .01) without changes in PTH or pH. Both phosphate and PTH markedly increased after RYGB with the peptones oral load (P < .01), without changes in pH, iCa, or gastrin. There was a significant, direct relationship between the increase of phosphate and the increase of PTH in the patients treated with aluminum hydroxide (r2 = 0.78; P < .0001). Conclusion. Rapid delivery of peptones in the jejunum in bypassed obese patients results in a significant rise in phosphate and PTH, in the absence of changes of other PTH regulators, possibly mediated by a signaling from the gastrointestinal tract. RYGB patients provide an opportunity to study the control of PTH secretion, with potential relevant clinical implications.