Robert L. Ney

CORRELATION OF PLASMA ACTH CONCENTRATION WITH ADRENOCORTICAL RESPONSE IN NORMAL HUMAN SUBJECTS, SURGICAL PATIENTS, AND PATIENTS WITH CUSHING'S DISEASE.

The role of ACTH in various clinical disorders has been difficult to ascertain because the available assay methods have lacked the sensitivity necessary for valid quantitation of the hormone in the plasma of normal subjects (1-4). Even the method of Lipscomb and Nelson (5), the most sensitive practical bioassay procedure now available, usually requires the injection of at least 0.05 mUof ACTHper rat, if responses are to be elicited that will be statistically significant without the use of a prohibitive number of animals. It is usually impractical to inject more than 5 ml of crude human plasma into a single rat. Therefore, in order to be accurately measurable by this procedure, the concentration of ACTH in the plasma must be at least 0.05 mUper 5 ml, or 1 mUper 100 ml. Numerous studies indicate that normal plasma levels of ACTHare well below this concentration. Byr the adrenal ascorbic acid depletion assay method, Sydnor, Sayers, Brown, and Tyler (1) were unable to detect ACTH in plasma of normal subjects, even after attempting to extract the hormone with oxvcellulose in preparation for the bioassay. These workers concluded that blood ACTH concentrations of normal human subjects were less than 0.5 mUper 100 ml. Using a similar procedure, Fujita (3) estimated the normal level of ACTHto be about 1 mUper L, i.e., 0.1 mUper 100 ml. Cooper and Nelson (6) were able to detect ACTH in the plasma of only 3 of 10 patients before surgery, by a method that they

Abnormal hormone responses of an adrenocortical cancer adenyl cyclase

Properties of adenyl cyclase of normal adrenals and of a corticosterone-producing adrenal cancer of the rat have been compared. Enzyme activity was found in all particulate fractions of both tissues. The cyclase of the tumor as well as of the adrenals was stimulated by adrenocorticotropic hormone (ACTH) over similar concentration ranges. Unexpectedly, the tumor enzyme was also stimulated by epinephrine, norepinephrine, and thyroid-stimulating hormone (TSH). These hormones produced a dose-related effect over a concentration span that was comparable with that for ACTH. The tumor cyclase was not responsive to angiotensin Il, vasopressin, glucagon, insulin, growth hormone, parathyroid hormone, and thyrocalcitonin. ACTH was the only hormonal preparation that stimulated normal adrenal cyclase. These findings are compatible either with the possibility that the adenyl cyclase receptor of the tumor has undergone structural alteration with a consequent loss of specificity for ACTH or with the possibility that the tumor possesses several cyclase regulatory receptors.

Puromycin analogs: action of adrenocorticotropic hormone and the role of glycogen.

The effect of the injection into rats of analogs of puromycin, 6-dimethylaminopurine, and the aminonucleoside of puromycin on the stimullation of steroidogenesis by adrenocorticotropic hormone was coin pared with that of puromycin and cycloheximide. This stimulation was blocked only by the antibiotics, which also inhibited adrenal protein synthesis. Glycogenolysis is not associated with the primary mechanism of the adrenocorticotropic hormone stimnulation of steroid hormone biosynthesis in rats.

Heterogeneity of Template RNA in Adrenal Glands

Template RNA in adrenal glands appears to be heterogeneous in stability. The RNA that regulates synthesis of a large fraction of adrenal protein has a turnover time of 4 hours or less. The remainder of adrenal-protein synthesis, including synthesis of protein that mediates the rapid steroidogenic response to ACTH, depends on RNA with considerably greater stability.

A Study of the Mechanisms by Which Adrenocorticotropic Hormone Maintains Adrenal Steroidogenic Responsiveness

Following hypophysectomy in the rat, there was a progressive decline in the rate of adrenal protein synthesis in vivo during the ensuing 24-48 hr, and an accompanying decrease in the acute corticosterone secretory response to an intravenous injection of ACTH. There was a similar decrease in the in vitro conversion of Delta(5)-pregnenolone, progesterone, and deoxycorticosterone to corticosterone. These in vivo and in vitro effects of hypophysectomy could be reversed by the administration of depot ACTH for an additional 7 hr period. However, if cycloheximide, an inhibitor of protein synthesis, was administered concomitantly with the depot ACTH, then the restorative actions of ACTH on the steroid biosynthetic pathway were prevented. These experiments suggest that ACTH maintains not only the general structure of the adrenal cortex, but also the level of the steroid biosynthetic mechanism, through its effects on adrenal protein synthesis.