Assay of urinary 4-hdyroxy-3-methoxymandelic (vanillylmandelic) acid by liquid chromatography with electrochemical detection.

We describe a method for the assay of urinary 4-hydroxy-3-methoxymandelic acid (vanillylmandelic acid) based on separation on a microparticulate reversed-phase column and direct electrochemical detection. The method can be used after extraction from urine or by direct urine injection after 100-fold dilution.

Assay of 4-hydroxy-3-methoxyphenylacetic (homovanillic) acid by liquid chromatography with electrochemical detection.

We describe a method for the assay of urinary 4-hydroxy-3-methoxyphenylacetic acid (homovanillic acid), based on its separation on a microparticulate reversed-phase column and direct electrochemical detection. Patients with neuroblastoma, pheochromocytoma, and Parkinson's disease have increased amounts of this compound in their urine.

Guanosine 3',5'-cyclic monophosphate and the in vitro physiology of frog photoreceptor membranes.

Frog rod outer segments freshly detached from dark-adapted retinas contain approximately 1-2 molecules of guanosine 3',5'-cyclic monophosphate (cyclic GMP) for every 100 molecules of visual pigment present. This cyclic GMP decays to 5'-GMP, and the conversion is accelerated upon illumination of the outer segments. Bleaching one rhodopsin molecule can lead to the hydrolysis of 1,000-2,000 molecules of cyclic GMP within 100-300 ms. The decline in cyclic GMP concentration becomes larger as illumination increases, and varies with the logarithm of light intensity at levels which bleach between 5 X 10(2) and 5 X 10(5) rhodopsin molecules per outer segment-second. Light suppression of plasma membrane permeability, assayed in vitro as light suppression of outer segment swelling in a modified Ringer's solution, occurs over this same range of light intensity. The correlation between cyclic GMP and permeability or swelling is maintained in the presence of two pharmacological perturbations: papaverine, a phosphodiesterase inhibitor, increases both cyclic GMP levels and the dark permeability of the plasma membrane; and beta,gamma-methylene ATP increases the effectiveness of light in suppressing both permeability and cyclic GMP levels.