Flock, Eunice V.

Dogs excreted the same compounds in the urine after injections of radioactive thyroxine whether they were normal or had a biliary fistula or biliary obstruction. Dogs with biliary fistulas excreted more of the conjugate in the urine than did normal dogs. Dogs with biliary obstruction excreted the largest amounts of the conjugate and also showed increased levels of the conjugate in the blood. All the changes were minor, however, compared to those found after hepatectomy. No evidence was found for conversion of thyroxine to triiodothyronine or tetraiodothyroacetic acid, but the present studies would not exclude the possibility that these substances are rapidly transformed intermediates in the metabolism of thyroxine.

The pharmacological and biochemical tests available for the diagnosis of pheochromocytoma were evaluated among 28 patients with proved tumors and 148 other patients in whom the diagnosis was suspected. Of the biochemical tests on urine, determinations of total metanephrines (MN) and of vanilmandelic acid (VMA) were much less subject to false-positive results than was determination of catecholamines (CA). Since urinary MN values changed the most in tumor patients, MN determination is preferred as the current screening test. Of the pharmacological tests, the histamine test continues to be the most valuable, especially when combined with determination of plasma CA concentration. The phentolamine (Regitine) test has not proved to be of any distinct value as a primary diagnostic aid. Any of the chemical or pharmacological tests occasionally may give a false-positive result. The urinary output of excessive amounts of homovanillic acid (HVA) was an indication of the presence of pheochromocytoma with some features histologically similar to other neural crest tumors but was not an indication of malignancy. Reliable diagnosis of pheochromocytoma still must be based on multiple studies in an appropriate clinical setting.

Today pharmacologic and chemical tests are helpful in screening a relatively large number of patients for pheochromocytoma and are a definite aid to a correct diagnosis. No one test is infallible, and knowledge concerning the drugs used or the manner in which the blood and urine are collected, or both, is necessary to avoid a false-positive or false-negative result from the tests.

Fluorescent quantitation of epinephrine and norepinephrine in plasma of patients suspected of having pheochromocytomas is of considerable diagnostic value. The concentrations of these pressor amines in normal subjects, patients with various diseases with and without hypertension, and 13 patients with pheochromocytomas are reported. In all patients with pheochromocytomas and sustained hypertension the concentrations of pressor amines were significantly elevated. However, in patients with paroxysmal hypertension secondary to pheochromocytomas the pressor amine concentrations may be unelevated when the blood pressures are normal. In this latter group provocative tests with intravenous histamine are indicated to induce hypertension prior to quantitating pressor amines.