Cultured guinea pig epidermal cells were treated with vitamin A acid (VA; 2, 5, 10 μg/ml) and controlled by autoradiography and histochemical methods. Cells attached to the bottom of the plates were counted and their number correlated with the number of cells sloughed off into the medium (A/D ratio). VA reduced the size of multilayered cell colonies, favoured cell spreading and accelerated confluence. It altered the mode of shedding since the cells sloughed off into the medium as isolated cells rather than cell complexes, as in untreated controls. It increased the A/D ratio in early cell cultures and decreased the A/D ratio in late cell cultures. The higher the concentration of VA, the earlier and more prominent was the decrease of the A/D ratio. Low concentration of VA (2 μg/ml) given once at seeding favoured the formation of keratohyalin and cornifíed envelopes whereas high concentrations (5, 10μg/ml) given continuously prevented their formation and caused mucoid vacuolar degeneration of single cells. VA inhibited complete keratinization in all cases, but appeared to allow pre-keratinization, particularly at low concentrations. The results indicate that VA controls epidermal homeostasis in vitro by its influence on both proliferation and shedding. Its effect on the markers of differentiation is heterogeneous since it prevented keratinization in every case, but induced keratohyalin formation under certain conditions.
1. The effect of 15 days' treatment with purified pituitary growth hormone (GH) on the composition of the protein of the quadriceps muscle was studied in adult female rats.2. The muscle protein was divided into three fractions, the sarcoplasmic protein, the myofibrillar protein, and collagen and elastin. No differences were found in the proportions of the three fractions in normal and in GH-treated rats.3. There are two components of muscle with adenosine triphosphatase (ATP-ase) activity: the myofibrils and the sarcoplasmic granules. These two activities and the total ATP-ase activity were assayed in homogenates from GH-treated and control rats. The only alteration observed in the rats receiving GH treatment was a diminution in the amount of myofibrillar ATP-ase per gram of fresh tissue.Although it has been known for many years that there is an increase in the protein content of the body as a result of pituitary growth hormone treatment, the nature of the extra protein laid down has not been investigated. The present research was undertaken to determine whether the composition of muscle of rats treated with growth hormone differs materially from that of control animals. METHODS Treatment of animalsAdult female rats of the hooded Norwegian strain were used throughout. They were given and consumed each day an amount of a full synthetic diet (diet 41 ; Short & Parkes [1949]), which was just sufficient to maintain the weights of the control animals. The experimental group of rats received, during a period of 15 days, daily subcutaneous injections of 0-4 ml. of a solution of purified pituitary growth hormone (GH), containing 1-25 mg/ml., while the control group was given an equal volume of saline. The purified GH was prepared by a modification of the method of Wilhelmi, Fishman & Russell [1948]. In some experiments both GH and testosterone propionate (TP) were administered, the experimental animals receiving daily intra¬ peritoneal injections of 0-4 ml. arachis oil containing 1-25 mg TP per ml. for 15 days, in addition to the injections of GH, while the control animals were given 0-4 ml. arachis oil intraperitoneally and 0-4 ml. sahne subcutaneously.The rats were killed by decapitation and the quadriceps muscles rapidly dissected out. In some experiments the diaphragm also was removed and trimmed.Determination of the fractions of muscle protein The muscle protein was divided into three fractions, the sarcoplasmic protein, the myofibrillar protein, and collagen and elastin. The methods of fractionation were based on those of Robinson [1952].
Adult female rats were treated with purified pituitary growth hormone for 9 days, and the nucleic acid content of the liver and skeletal muscle determined.An increase was observed in the concentration of muscle ribonucleic acid, expressed per gram of nitrogen, as a result of the treatment. There were no changes in the ribonucleic acid concentration of liver.No changes were observed in the concentration of deoxyribonucleic acid in muscle or liver.
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