Plasma Calcium and Inorganic Phosphate Response of Laying Hens to Parathyroid Hormone1

Abstract

The plasma calcium and phosphate response to iv injection of PTH was studied in laying hens fed diets containing 2.26% or 5.00% calcium, both during periods of egg shell formation and when no egg was in the shell gland. Compared with results for mammals, the response was considerably larger, more rapid and more transient. With PTH injection at 0 min, plasma calcium (5.00% calcium diet only) and phosphate were significantly decreased at 5 min. This was followed by an increase in the concentration of both ions until a maximum was reached between 20 and 30 min. After 60 min, plasma levels of pullets fed the 2.26% calcium diet were again practically normal. The maximum plasma calcium and phosphate response for the 5.00% calcium diet was more than twice as large as for the 2.26% calcium diet, while the stage in the egg cycle had no effect on the response curves. During the period of hypercalcemia the increases in plasma calcium and phosphate were closely correlated (r = 0.733, p < 0.001), suggesting that the release of these two ions into blood was caused by a common mechanism. The rapid decay of the PTH response and its dependence on dietary calcium may explain the results of some investigators who found little or no response to parathyroid hormone in laying hens. (Endocrinology 92: 853, 1973) D URING the formation of each egg shell laying hens fed a diet containing 1.95% calcium mobilize about 4% of their skeletal calcium (1). Although it is likely that parathyroid hormone (PTH) plays a role in synchronizing egg formation and the concomitant changes in skeletal metabolism (2) surprisingly little is known about the effects of PTH in laying hens. One reason may be that a number of early investigators, cited by Polin et al. (3), were unable to detect any effect of PTH on blood calcium in birds. More recent studies have shown that these negative results were probably due to failure to examine calcium levels early enough (3, 4). It has been reported (4) that laying hens exhibit significant hypercalcemia 8 min after iv injection of 20 U/kg PTH and a similarly rapid response has been reported for chicks and Japanese quail (5).Information of the phosphatemic response

Effect of Dietary Calcium and Phosphorus Levels on Ultra-Filterable Calcium and Dialyzable Phosphorus in the Laying Hen

“…Oviposition times in this experiment were in the morning so the change in total calcium level during this period corresponds to the oviposition time and that of calcium intake. At 2400 h, total calcium level had increased to 24.7 mg/dL, which corresponds to the reports in the literature of the effect of parathyroid hormone for the resorption of bone and for active formation of egg shell (Mueller et al, 1973). These results are similar to those observed by Deobald et al (1938), Winget and Smith (1958), Hertelendy and Taylor (1961), and Parsons and Combs (1981) who reported cyclic fluctuation of blood calcium during the egg cycle.…”

The Hypercalcaemic Response to Parathyroid Hormone in Japanese Quail

“…This experiment, and others in which blood samples were withdrawn 1, 5, 15 and 30 min after PTH injec¬ tion, showed no evidence of a hypocalcaemic response (Table 1). Such a response has been observed in dogs and rats (Parsons, Neer & Potts, 1971 ;) and in laying hens (Mueller et al 1973) during the first minutes after i.v. injection of PTH.…”

“…Others have observed such a response in dogs ) and in rats ). In laying hens, on the other hand, an immediate hypocalcaemic response to PTH has been reported to occur only under conditions of very high calcium (5 %) in the diet; it was not observed in hens on diets lower (2-26%) in calcium (Mueller et al 1973). Our results therefore do not conflict with these findings; the Japanese quail were maintained on diets containing less than 2-26 % calcium.…”

Avian Physiology

“…in chickens. Mueller et al (1973b) injected 31 U of PTH per kilogram into hens fed either 5.00% or 2.26% calcium in the diet and measured changes in plasma calcium or phosphate from 2.5 to 180 min. After 2 hr this trend was reversed, with a return to the basal state.…”