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 45Ca-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 mm-CaCl2. 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 45Ca 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.

EFFECTS OF SYNTHETIC BOVINE PARATHYROID HORMONE (1‐34) AND ITS ANALOGUES ON 45Ca UPTAKE AND ADENYLATE CYCLASE ACTIVATION IN BONE AND PLASMA CALCIUM LEVELS IN THE CHICK

“…The responses which we observe could possibly account for the rapid (15 min) hypercalcaemic actions of bPTH(1-34) in chicks and rats (Shaw & Dacke, 1986a). However, native bPTH(I-84) fails to reduce bone 45Ca uptake in chicks (Shaw, 1987) but not rats (Dacke & Shaw, 1987a) at 3-15 min, a finding not entirely consistent with the known hypercalcaemic actions of this molecular species (Kenny & Dacke, 1974). The recent finding that methylxanthine phosphodiesterase inhibitors also reduce 45Ca uptake into chick bone suggests that the similar responses to bPTH(1-34) may be cyclic AMP mediated Present address for both authors: School of Pharmacy and Biomedical Sciences, Portsmouth t9olytechnic, Park…”

“…injection of chicks with bovine parathyroid hormone (1-34) (bPTH-(1-34)), rapidly (3-15 min) inhibits net uptake of an acute 45Ca label into femur and calvarium (Shaw & Dacke, 1985), this response being reflected by reduced plasma 45Ca clearance (Kenny & Dacke, 1974). Using an experimental protocol which utilizes microwave fixation of radioactive calcium levels in bone we find that, in direct contradiction to previous work in which no such fixation method was used (Parsons & Robinson, 1971), this peptide gives a similar response in rat femur (Dacke & Shaw, 1987a).…”

Acute Effects of Parathyroid Extract on Renal Vitamin D Hydroxylases in Japanese Quail

“…In contrast, the two higher doses of PTH in the present study elicited hypercalcemia by 4 h, before any significant changes in l,25-(OH)2D3 and 24,25-(OH)2D3 production were observed. The rapid onset and short duration of the hypercalcemic response to PTH in Japanese quail have been reported before (Dacke and Kenny, 1973;Kenny and Dacke, 1974).…”

Parathyroid and Ultimobranchial Glands

“…Birds respond to administration of PTH by a rapid but transient rise in plasma calcium. Immature birds show a rapid and more sensitive response; 1week-old chickens or 3-week-old Japanese quail respond to 10-20 units of synthetic bPTH( 1-34) within 15 min after intravenous injection (Kenny and Dacke, 1974). units or more of bPTH cause a maximal hypercalcemic response at 3-4 hr after subcutaneous or intramuscular injection in chickens (Polin et ai., 1957) or in Japanese quail (Baksi and Kenny, 1979).…”

“…Kenny and Dacke (1974) followed the plasma 4SCa and total calcium levels in the 2 hr period immediately following intravenous injection of synthetic bPTH(1-34) and 4SCa into Japanese quail and chickens; selected chicken data are presented in Figure 21-2. The response is much more 469 rapid in avian than in mammalian species.…”