CHANGES IN LABELLING OF RIBONUCLEIC ACID SPECIES FRACTIONATED FROM THE RAT VENTRAL PROSTATE IN RESPONSE TO TESTOSTERONE

Abstract

ABSTRACT The total RNA isolated at various times up to 24 h after testosterone administration from the ventral prostate of castrated rats, was labelled either by injecting 3H-orotic acid directly into the ventral prostate 6 h before the animals were killed, or by incubating prostatic tissue in vitro with 3H-uridine for 20 to 60 min. The isolated RNA was separated into tRNA, ribosomal RNA (Q1 RNA) and two DNA-like RNA fractions (Q2) and TD RNA) by chromatography on methylated albumin kieselguhr (MAK) columns, and the fractions were further analysed by sucrose gradient centrifugation. Testosterone given into castrated animals for 12 h, stimulated the labelling of all main fractions. The radioactivity of TD RNA after a 60-min incubation period in vitro with 3H-uridine was approximately twice that seen in the castrated rat, while there was a 3.1- and 2.2-fold increase in the radioactivity of the Q1 and Q2 RNA fractions respectively. Kinetics of incorporation of 3H-uridine into different RNA fractions revealed that the hormone facilitated the labelling of the TD RNA fraction relatively more than that of the Q2 fraction. The injection of 3H-orotic acid into the ventral prostate labelled the Q1 RNA preferentially. More than 60 % of the recovered radioactivity was found in Q1 RNA (as 18 and 28 S). Testosterone increased markedly (9.4-fold) the labelling of this fraction. It was concluded that testosterone has an activatory effect on the production of ribosomal RNA, and the bulk of the testosterone effect on the total RNA labelling is to be found in this fraction. Furthermore, it seems likely that testosterone also stimulates both the synthesis and processing of DNA-like RNA. When actinomycin D was given 2 h before the hormone administration in a dose of 25 μg per 100 g of body weight, there was no noticeable increase in the labelling of any fraction above the level seen in the untreated castrated rat. There is evidence that testosterone exerts some effects on the labelling of proteins with radioactive amino acids and 14C-glucose metabolism in the absence of that fraction of the total RNA synthesis which is sensitive to a low dose (25 μg per 100 g of body weight) of actinomycin D (Isotalo & Santti 1972). In this way it may be concluded that the major changes of the RNA synthesis after testosterone administration are likely to be secondary to the protein synthesis and glucose metabolism, or the hormone exerts its anabolic effect on prostatic cells at different sites and by different modes of action, each of which can be operated independently.