David T. Armstrong

Increased Cholesterol Biosynthesis Following Phenobarbital Induced Hypertrophy of Agranular Endoplasmic Reticulum in Liver.

Summary Previous workers have correlated hypertrophy of the agranular reticulum in the liver with increase in drug-metabolizing enzymes following repeated injections of phenobarbital. Our investigation confirms their morphological observation and adds additional biochemical data which suggest that the enzyme systems responsible for cholesterol biosynthesis are associated with the smooth reticulum and are also increased following phenobarbital stimulation.

Action of luteinizing hormone on conversion of ovarian chlolesterol stores to steroids secreted in vitro and synthesized in vitro by the pseudopregnant rabiit ovary

Abstract The stimulatory action of luteinizing hormone (LH) upon ovarian steroidogenesis in vivo and in vitro has been investigated in pseudopregnant rabbits in which labelling of ovarian cholesterol has been accomplished by prior intravenous injection of cholesterol-7-3H or cholesterol-4-14C. Intravenous administration of LH was followed within minutes by 4 to 20-fold increases in secrtion rate of 20α-hydroxy-pregn-4-en-3-one, accompanied by 4 to 13-fold increases in rate of appearance of the radioactivity in this steroid isolated from ovarian venous plasma. Rates of in vitro synthesis of 20α hydroxy-pregn-4-en-3-one and of 20α-hydroxy-pregn-4-en-3-one-3H or 20α-hydroxy-pregn-4-en-3-one-14C by slices of ovarian interstitial tissue were similarly increased by intravenous injection of LH 30–70 minutes before removal of ovaries for incubation, or by addition of LH directly to the incubation medium. Addition of NADP plus glucose-6-phosphate or NADPH to the incubation medium produced less marked stimulation of steroidogenesis, as compared by both mass and incorporated of radioactivity. It is concluded that LH stimulates synthesis and secretion of 2ga-hydroxy-pregn-4-en-3-one in ovarian interstitial tissue of rabbits primarily by accelerating the conversion of pre-formed cholesterol to steroid secretory products.

Stimulation of testosterone biosynthesis by luteinizing hormone in transplantable mouse leydig cell tumors.

Abstract Leydig cell tumors having large amounts of esterified sterols are capable of synthesizing testosterone when incubated in vitro . Addition of Luteinizing Hormone (LH) to the incubation medium in concentrations above 0.1 μg/ml greatly enhances the synthesis of progesterone and testosterone by these tumors. This response occurs within 15 minutes and lasts at least one hour in the continued presence of LH. In a two-hour incubation, LH also increases acetate incorporation into steroids and decreases its incorporation into sterol esters. The response of the tumor to LH is similar to that of ovarian and testicular tissue.

Localization of Radioactivity in Immature Rat Ovaries Following Physiological Doses of 125I-Labeled Bovine LH

Summary Bovine LH was labeled with 125I by chloramine T oxidation and gel filtration. Immunological characterization of iodinated LH, using either gel filtration on Sephadex G-200 or double antibody precipitation to separate free and antibody-bound 125I-LH, indicated that 71 and 64%, respectively, of total radioactivity was reactable with antibody to bovine LH. A dose of 125I-LH within the physiological range (51 ng/100 g of body wt) was administered intravenously to immature female rats. Serum samples, ovaries, adrenals, thyroids, and portions of liver were taken for radioassay at times ranging from 5 min to 12 hr following injection. Disappearance of radioactivity from blood approximated a hyperbolic function with a half-life of 19.6 min. Radioactivity in liver at its 15-min maximum represented 43% of the total injected dose per whole organ. Radioactivity in ovary and adrenal appeared at similar low levels (0.05-0.07% of injected dose per pair of glands). Disappearance curves from the two organs, however, were significantly different, with radioactivity in ovary, but not in adrenal, being retained up to 30 min following injection.