Abnormal responsiveness of nephrogenous cyclic AMP excretion following intravenously administered calcium in normocalcaemic squamous cell cancer patients.

The renal response to calcium infusion was compared in ten normocalcaemic patients with squamous cell cancer and in ten normocalcaemic patients with adenocarcinoma. Both groups were comparable with regard to tumour load, renal function, magnesium and 25-hydroxyvitamin D levels. After injection of 3 mg elementary Ca/kg BW nephrogenous cAMP excretion fell significantly in the group of adenocarcinoma patients (1.74 +/- 1.14 nmol/dl GF vs. 2.81 +/- 1.39 nmol/dl GF; P less than 0.01) and TmPO4/GFR rose significantly at 60 and 120 min. No fall in NcAMP excretion was observed in the group of squamous cell cancer patients (2.18 +/- 0.84 vs. 2.24 +/- 0.84 nmol/dl GF; NS) and TmPO4/GFR remained unchanged. Three of ten patients with squamous cell cancer showed a paradoxical rise in NcAMP excretion following calcium administration. The other seven patients with squamous cell cancer showed a decline in NcAMP excretion (delta NcAMP) which was significantly less than in the ten patients with adenocarcinoma (0.52 +/- 0.16 vs. 1.23 +/- 0.74 nmol/dl GF; P less than 0.05). Increased phosphaturia was observed in three of ten patients with squamous cell cancer after calcium was administered. This also occurred in the presence as well as in the absence of a paradoxical activation of the adenylate cyclase system. It is concluded that the abnormal NcAMP response to calcium-infusion in normocalcaemic squamous cell cancer patients might be due to the presence of a non-suppressible PTH-like substance in these patients.