Seymour B. Koritz

Studies on the mode of action of glucocorticoids in rats I. Early effects of cortisol on blood glucose and on glucose entry into muscle, liver and adiposèttissue

Abstract 1. Injection of adrenalectomized, fasted rats with cortisol leads to an increase in blood glucose by 80–100 min, and an increase in liver glycogen which begins about 40 min later. 2. On the basis of these and other observations, reasons are given for assuming that the early changes in glucose are probably not due to accelerated gluconeogenesis from proteins or amino acids nor to certain alternative mechanisms, but rather to decreased extra-hepatic utilization of glucose. 3. This assumption has been tested by studying the effect of cortisolin vivo on the extent of incorporation of glucose into gastrocnemius muscle, liver, and epididymal adipose tissue. The evidence obtained suggests that in glucose-fed rats, cortisol does not decrease the uptake of glucose by either muscle or liver within 3.5 h, but may decrease uptake by epididymal adipose tissue.

The effect of calcium ions and freezing on the in vitro synthesis of pregnenolone by rat adrenal preparations

Abstract In the presence of a TPNH-generating system the synthesis of pregnenolone from endogenous precursors by the large particles (pellet 2) of rat adrenals is stimulated by Ca 2+ . Ba 2+ and Sr 2+ at higher concentrations can replace Ca 2+ . The stimulation does not appear to be due to the activation of a proenzyme. At the pH optimum of 6.2, freezing pellet 2 decreases pregnenolone synthesis. However, at pH 7.5 the previously frozen pellet 2 is more active than the normal one. These results are discussed with respect to the Ca 2+ and freezing stimulation of corticoid synthesis in adrenal whole homogenates. In the presence of TPNH and at pH 6.2, Ca 2+ stimulates the formation of pregnenolone from cholesterol but not from 20α-hydroxycholesterol, but at pH 7.5 the latter reaction is stimulated. Also, in whole homogenates at pH 7.5, Ca 2+ stimulates the transformation of 20α-hydroxycholesterol to corticoids. Evidence is presented that the stimulation by freezing of both pregnenolone and corticoid synthesis at pH 7.5 appears to be due to the stimulation of the conversion of cholesterol to 20α-hydroxycholesterol. Several observations also indicate that this step is rate limiting in the transformation of cholesterol to corticoids in adrenal homogenates.

Inhibition of corticoid production in rat-adrenal homogenates by diphosphopyridine nucleotide and its reversal by ascorbate and other substances.

Abstract Diphosphopyridine nucleotides, in the presence of triphosphopyridine nucleotide and glucose 6-phosphate, inhibit the production of corticoids in rat adrenal homogenates. The inhibitory species is DPNH and the inhibition can be reversed by pyruvate, oxaloacetate and ascorbate, all of which bring about the oxidation of DPNH. The inhibition is not due to a transhydrogenase-mediated depletion of TPNH by DPN. The inhibition occurs at the DPN-dependent oxidation of pregnenolone to progesterone and may be due to a product inhibition of the 3β-hydroxysteroid dehydrogenase. The implications of these findings with respect to the role of ascorbic acid in the metabolism of the adrenal cortex are discussed.

The stimulation of pregnenolone synthesis in the large particles from the adrenals of rats administered adrenocorticotropin in vivo

Abstract Pregnenolone synthesis at pH 5.4 and pH 6.2 in the large subcellular particles from adrenals from rats treated with ACTH in vivo is significantly greater than in the large particles from animals which did not receive ACTH. Identical results were obtained when hypophysectomized rats were used in place of normal rats. When adrenal large particles from ACTH-treated rats were incubated in the presence of ATP, and inhibition of pregnenolone synthesis was seen.

The intracellular localization in the rat adrenal of enzymes which degrade 3'-Phosphoadenosine-5'-phosphosulfate.

Summary The degradation of phos-phoadenosinephosphosulfate in a cell free preparation of the rat adrenal is inhibited by inorganic phosphate. The enzymes responsible for this degradation are found to be localized in the lysosomes of this organ.

The response of the microsomal Δ5-3-ketosteroid isomerase from several steroidogenic tissues to nicotinamide-adenine dinucleotides

Abstract The Δ5-3-ketosteroid isomerases (3-ketosteroidΔ4-Δ5-isomerase, EC5.3.1.1) from the microsomal fraction of several mammalian steroidogenic tissues respond to NAD+ and NADH. In three cases, mouse and guinea-pig adrenals and rat testes, these pyridine nucleotides stimulate the isomerase activity in a manner similar to that first noted in the rat-adrenal gland2. The enzymes from beef-adrenal cortex and bovine corpus luteum exhibit only a small stimulation by NAD+ and NADH, but this can be greatly increased under certain conditions. Thus, in an acetone-powder preparation, at elevated temperatures, or in the presence of p- chloromercuriphenylsulfonic acid (PCMS), the activation of the beef-adrenal enzyme is enhanced several fold. The pyridine nucleotides inhibit the rabbit-adrenal isomerase, but a stimulation can be observed at acid pH values. NADP+ and NADPH are less effective by a factor of io 3. Possible mechanisms to account for these observations are discussed.