Changes in nephrogenous cyclic AMP excretion and plasma cyclic AMP following treatment of hyperthyroidism

Plasma cyclic AMP (PcAMP) concentration and the excretion of cyclic AMP dl GF were estimated in 11 thyrotoxic patients before and after medical treatment. PcAMP concentrations were significantly higher during hyperthyroidism (2.30 ± 0.69 vs 1.88 ± 0.71 nmoldl; P < 0.05), and total urinary cyclic AMP (TcAMP) excretion showed no significant changes (3.24 ± 0.64 vs 3.44 ± 1.77 nmol/dl GF). Nephrogenous (NcAMP) excretion rose significantly (1.00 ±0.82 vs 1.68 ±1.31 mmol/dl GF; P < 0.025). The increase in NcAMP excretion correlated significantly with the decrease in serum T3 levels (r = -0.46; P < 0.05). Serum iPTH levels showed no significant change. Both the serum Ca, corrected for serum total protein and TmPO4 GFR declined after treatment (respectively 2.44 ± 0.13 vs 2.33 ± 0.08 mmol l; P <0.05 and 1.18 ± 0.29 vs 1.05 ±0.22 mmol/l; P < 0.05). It is concluded that the rise in NcAMP excretion corroborates the concept of increasing parathyroid activity following the treatment of hyperthyroidism.