Abstract
The 10,000 g x 15 minute supernatant from homogenised whole fifth instar Schistocerca gregaria hoppers provided a binding reagent which could be used for the measurement of cyclic GMP without further purification. Preparation of the binding protein was simple and inexpensive, and the assay had a specificity equal to or greater than those reported in previously published protein binding procedures. Cyclic GMP concentrations, measured in urine without preliminary purification, agreed well with those determined by radioimmunoassay. Binding capacity and specificity of the locust reagent were strongly influenced by proteins, phosphodiesterase inhibitors and chelating agents, and by the developmental state of the insect. Cyclic AMP increased the slope of the cyclic GMP standard curve in a dose-related manner over the range 5-100 pmol cyclic AMP per tube. Anti-cyclic GMP antisera were raised against 2'-O-succinyl cyclic GMP conjugated to ovalbumin or keyhole limpet haemocyanin. The high specificity of two rabbit antisera for cyclic GMP permitted the direct analysis of urine and plasma specimens. urinary calcium and cyclic nucleotide excretion after an oral calcium load was not helpful in distinguishing 'absorptive' from 'renal' hypercalciuria in a study of 28 patients. Fasting cyclic AMP output in excess of 4.7 mumol/g creatinine was, however, a useful indicator of inappropriate PTH secretion in hypercalcaemic patients. Cyclic GMP excretion was raised in both PTH-mediated and non-PTH-mediated hypercalcaemia. Eighteen patients with lung, bronchial or oesophageal cancer had no abnormality in pre- and post-operation 24 hour cyclic AMP or cyclic GMP excretion when compared with 11 control patients. Plasma cyclic GMP levels were increased in some patients with cancer of the bladder or the intestine, and in association with cachexia. Urinary cyclic GMP/cyclic AMP ratios fell in three subjects during recovery from asthma attacks, and were decreased in a group of 23 hypertensive patients. Five hyperthyroid women and one woman with a glucagonoma had raised plasma cyclic AMP and normal plasma cyclic GMP concentrations.