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Effect of parathyroid hormone, calcitonin and growth hormone on cAMP content of growth cartilage in experimental uraemia

Abstract. The response of proximal tibial growth cartilage cAMP content to different hormonal stimuli, i.e. parathyroid hormone, calcitonin and somatotropic hormone was evaluated in rats with bilateral or subtotal nephrectomy. In uraemic rats, basal cAMP content of growth cartilage was unchanged. Administration of 1–34 PTH in vivo or incubation of growth cartilage with 1–34 PTH in vitro caused a significantly smaller increment of cAMP in uraemic rats (40 IU PTH in vivo: 11·4±1·01 pmol cAMP/mg protein; controls 24·0±2·55; P<0·001). This finding implies PTH resistance. Diminished cAMP response in uraemic animals was not changed by pretreatment with 1,25(OH)2D3 or parathyroidectomy. The increment of cAMP content of growth cartilage of uraemic animals was significantly (P<0·01) greater after in vivo administration of 10 IU calcitonin (46·1±4·89 pmol/mg protein; control: 29·0±3·99) or incubation of cartilage with calcitonin in vitro. This finding implies overresponsiveness to calcitonin. Neither in acute nor in chronic uraemia, STH caused a significant change of cartilage cAMP or cGMP content, but STH stimulated 3H‐thymidine incorporation into chondrocytes of rats with 5 days uraemia (solvent 2·98±0·51 times 103 cpm per cartilage; STH 5·08±0·34; P<0·05) and caused significant improvement of longitudinal growth of rats with 20 days uraemia.