A STUDY OF THE FINE STRUCTURE OF THE EPIDERMIS OF RANA PIPIENS

The epidermis of adult Rana pipiens has been studied by electron microscopy and histological and histochemical methods. It was found that the epidermis is engaged in the production of both keratin and mucus. The basal cells are mainly filled with tonofilaments, whereas the cells located in the mid-portion of the epidermis contain both tonofilaments and mucous granules. Golgi vesicles and endoplasmic reticulum are found in relative abundance in the mucus-producing cells and seem to be involved in the production of mucous granules. The mucus seen was partly retained within the cells and partly secreted into the intercellular spaces. The outermost keratinized cells contain mainly filaments and a few remnants of cell constituents.

OBSERVATIONS ON THE SIGNIFICANCE OF 5-HYDROXYTRYPTAMINE IN RELATION TO THE PERISTALTIC REFLEX OF THE RAT

Peristalsis of normal rats, and of rats fed either on a control diet or on a tryptophan-free diet (5-hydroxytryptamine-depleted rats), was studied in vitro and in situ to test the hypothesis that 5-hydroxytryptamine functions as a local hormone in the intestine and may be essential for initiation of the peristaltic reflex. A tryptophan-free diet depleted intestinal 5-hydroxytryptamine by a mean value of 90%; in some rats, the depletion appeared to be complete. Peristaltic responses, even of rats with complete depletion, were qualitatively similar to, and quantitatively not statistically different from those of normal or of pair-fed control animals whose intestinal mucosa contained high concentrations of 5-hydroxytryptamine. Intraluminal and serosal 5-hydroxytryptamine produced effects in 5-hydroxytryptamine-depleted rats similar to those in the normal and in the control animals. Furthermore, the maximal stimulatory effects of 5-hydroxytryptamine on peristaltic performance were not greater than spontaneous variations in performance in any group of animals, except with tryptophan-fed control rats, when the effects of the amine on peristalsis in situ were greater than spontaneous variation. It was therefore concluded that 5-hydroxytryptamine is not essential for peristalsis in the rat.

BIOSYNTHESIS OF VITAMIN A WITH RAT INTESTINAL ENZYMES

Vitamin A is synthesized from beta-carotene in cell-free homogenates of rat intestinal mucosa, the biosynthetic enzymatic activity being present in the soluble protein fraction of the homogenate. Also required are a heat-stable factor in the particulate fraction, molecular oxygen, and bile salts. The reaction is stimulated by glutathione. The product, obtained in yields of up to 50 percent, has been identified as vitamin A aldehyde (retinal) by way of its semicarbazone derivative. The reaction mechanism involves the central cleavage of beta-carotene into two molecules of retinal.