No abstract

We wish to acknowledge the excellent technical assistance of Mrs. Clara Boudreau and Mrs. Constance Self in the preparation of some of these viruses.

Sevemal Armusour and NIH pituitary hormone l)mePalations as well as other homologous serum l)roteimi fractions were labeled with fluorescent tlyes (sulphorhodamsuine B, CI. 45100, and fluoresceims isothiocyanate). Rats were injected intravenously with the different labeled proteins and the animssals killed at various intervals from 3 minutes to 10 days. Sections of the kidneys were studied under ultraviolet light (3,900 A). It was observed that all the labeled proteins passed the glomerular filter they behsave similarly in the kidney.

Rsudioactise isotol)es hunts-c proved to be the most useful tool ins the stu(lv of the distribution and nsietnuhohic turnuos-er of the seruns proteins in differenut t)rgnmns. Sesernul authors has-c densonstrated that rnun hioacti se nulbumusinu leases the circu-Inutiomu i nsunsuedinutt-ly tufter imstravenous injection

Estrogens, as well as other steroid hormones, may exert their stimulatory effect on target tissues by initial activation of RNA synthesis. 1 2 This concept is supported by the observation that estrogen stimulation of the uterus leads quickly to an increase in the rate of incorporation of precursors into RNA,3 4 the initial increase being noted in the nuclear fraction of RNA.5 The uterotrophic action of estradiol-17f3 is prevented by the metabolic inhibitor actinomycin D either administered systemically6 or by injection into the lumen of the uterus.7 The action of estrogen on the vagina can be prevented also by topical application of actinomycin.5 A mechanism for the effect of estradiol on RNA synthesis has been suggested by the identification of a macromolecular fraction of the cell which possesses receptors for the hormone. This fraction, when not combined with the hormone, inhibits the activity of RNA polymerase. When the hormone is present, the inhibition is released.9 The biochemical evidence that the biosynthesis of RNA by rat uteri is immediately accelerated by estrogen suggests that the stimulating hormone may have no further role in causing the transition from the atrophic to the stimulated state. To test this postulate, RNA was extracted from the uteri of estrogen-stimulated rats and administered by local, intraluminal application to estrogen-deprived ovariectomized rats. The resultant morphologic changes in treated uteri are indistinguishable from those that occur following the administration of estrogen.10 Materials and Methods.-Preparation of total RNA extract: Method A: Female rats of the Sprague-Dawley strain weighing 180-200 gm were ovariectomized, and the certainty of anestrus was established by following the vaginal smears for at least two weeks. Each batch of RNA was prepared from the uteri of at least ten ovariectomized females but frequently as many as 100 were used. Each animal was injected intravenously (tail vein) with 10 jsg estradiol-17,3 per 1 ml 1% ethyl alcohol in saline. After 4 hr, the animals were sacrificed by decapitation; the uteri were removed and quickly frozen. In the 4°C cold room, the uteri were homogenized with a Virtis homogenizer in 10 times volume of saline, with or without 0.001 M MgCl2. The tissue brei was filtered through one layer of cheesecloth and mixed with an equal volume of watersaturated phenol. The mixture was stirred vigorously on a magnetic stirrer for 30 min at room temperature, and the stirring was repeated for 30 min in the 4°C cold room. It was centrifuged at 2,000 gravities for 30-60 min at 2-4°C, and the top aqueous layer was saved. The other layers were washed once with an equal volume of saline, centrifugation was repeated, and the saline was combined with the original supernatant with extreme care to avoid carrying over any saline-Downloaded by guest on July 4, 2020