THE HYPERCALCAEMIC RESPONSE TO PARATHYROID HORMONE IN JAPANESE QUAIL

Abstract

SUMMARY The nature of the rapid hypercalcaemic response in birds to intravenously administered parathyroid hormone (PTH) has been studied using the Japanese quail and, to a lesser extent, the chicken. The response has been examined in acutely 45 Ca-labelled birds. Parathyroid hormone, synthetic (Beckman 1–34 peptide) bovine PTH, was given with or without the simultaneous administration of a calcium load of 51 m m -CaC l2 . It is concluded that the hypercalcaemic response in birds is complex involving two or more underlying mechanisms. The initial phase (30 min or less) is characterized by an increase in plasma 45 Ca levels; interpretation of this response in terms solely of bone resorption is difficult. It is suggested that inhibition of bone accretion is the basis for the initial phase. The later phase (30 min or longer) can be interpreted as being largely due to bone resorption. In calciumloaded birds, which were used in recently described avian bioassay methods for PTH, similar results, and therefore interpretations, pertain. No immediate hypocalcaemic response to PTH was found in immature Japanese quail or chickens.