Adair J. Hotchkiss

Chromogranin A Synthesis and Secretion in Chromaffin Cells

Abstract: A sensitive and selective radioimmunoassay for chromogranin A (Chrg A) has been developed to quantitate content, release, and biosynthesis of this secretory protein in neuroendocrine tissues. An antiserum raised against Chrg A from bovine adrenal medulla was found to detect predominantly only the Mr 70–75 kilodalton Chrg A in its native form, allowing the use of this antiserum as a quantitatively specific probe for Chrg A in cell‐free extracts of the adrenal medulla and chromaffin cells. Chrg A comprises about 10% of the total protein of the chromaffin cell. It is released in parallel with Met‐enkephalin and catechol‐amines from the bovine chromaffin cell in primary culture in response to nicotine and nicotinic cholinergic agonists. From 14 to 22% of total Chrg A is released from the cell during a 15‐min exposure to a maximally stimulatory dose of nicotine (10–100 μM). Chrg A release on nicotinic stimulation is blocked by D‐600 and hexamethonium to the same extent as Met‐enkephalin and catecholamine release. The parallel time course and percent release of Chrg A and Met‐enkephalin indicate that these secretory polypeptides are contained in, and released from, functionally identical cellular compartments. Chrg A and Met‐enkephalin pentapeptide sequences are present in the chromaffin cell at a ratio of about 2:1, although Chrg A is far more abundant on a mass basis. Chrg A and Met‐enkephalin biosynthesis appear to be differentially regulated within the chromaffin cell, since chronic treatment of cells with nicotine and forskolin causes an elevation of Met‐enkephalin pentapeptide without a concomitant elevation of intracellular levels of Chrg A.

Chapter 12. Plasminogen Activators

Publisher Summary Three thrombolytic agents, streptokinase, urokinase, and alteplase (tissue plasminogen activator, recombinant) are approved in the U.S., and in addition a fourth (APSAC) in Europe. Many new thrombolytic agents are currently in preclinical and clinical development. The agents are large proteins and all work by activating the plasma zymogen plasminogen to plasmin that cleaves fibrin. This chapter describes the clinical and preclinical results that include discussion on first and second generations of plasminogen activators and use of plasminogen activators in indications other than MI: preclinical. Treatment of patients with intravenous streptokinase following acute myocardial infarction has been shown to reduce mortality, reduce infarct size, and improve left ventricular function even though intravenous streptokinase has been shown to be relatively ineffective in inducing prompt coronary artery thrombolysis. Preclinical data have shown tissue plasminogen activator (alteplase) and anisoylated plasminogen streptokinase activator complex (APSAC) to be effective thrombolytic agents in vitro and in animal models of myocardial infarction. Single chain urokinase (scu-PA, prourokinase) synthesized in mammalian cells has been shown to be an effective thrombolytic in a rabbit model. Studies in several models of cerebral thromboembolic occlusion have demonstrated a potential role for thrombolytic agents for this indication. Models of retinal vein thrombosis in cat and posterior penetrating eye injuries in rabbit have also been used to test the efficacy of thrombolysis with urokinase. A placebo-controlled pilot study of alteplase in unstable angina showed a favorable angiographic and clinical effect; whereas, a second placebo-controlled study showed a beneficial effect on pacing threshold.