Effect of polyadenylic acid on the functional half-life of encephalomyocarditis virus RNA during translation

Direct inhibitory actions of GnRH on accessory reproductive organs of rat

Recently gonadotropin releasing hormone (GnRH) and its agonistic analogs were demonstrated to have some direct actions in accessory reproductive organs. In our study the effects of GnRH and its analogs on some steroid hormone induced responses were investigated. GnRH and its analogs inhibited estradiol induced ornithine decarboxylase (ODC) and glucosamine-6-phosphate synthase activities in the uterus of rat. These enzymes which are markers for cell proliferation are regulatory enzymes in the biosynthetic pathways of polyamines and glycoproteins, respectively. Similarly, GnRH and its analogs also inhibited testosterone stimulated ODC activity in ventral prostate of rat. In addition, GnRH analog inhibited incorporation of radioactive precursors into RNA and protein induced by estradiol in uterus or dihydrotestosterone (DHT) in ventral prostate. In an effort to elucidate the mechanism of action of GnRH in uterus, it was found that GnRH analog treatment does not alter the estradiol receptor content in vivo. Also, GnRH does not show any effect on radioactive estradiol binding to its receptor in vitro. Hence, the inhibitory actions of GnRH in uterus may not involve estradiol receptors. However, GnRH analogs were found to have post-transcriptional effects. It was observed that DHT induced poly(A) polymerase activity in ventral prostate and estradiol induced poly(A) polymerase activity in uterus were inhibited by GnRH analog treatment. It was further observed that GnRH inhibited incorporation of [3H]uridine into poly(A)+ RNA of ventral prostate. This indicates that the inhibitory effects of GnRH involve post-transcriptional mechanisms.

Inhibition of sex-steroid hormone induced ornithine decarboxylase and poly(A)-polymerase activities by a GnRH agonist in the rat kidney

Recently GnRH and its synthetic agonists were shown to exert extrapituitary actions and inhibit the growth-promoting effects of testosterone and estradiol. In the present study, the long-term effect of GnRH agonist [des-Gly10, D-Ala6-GnRH ethylamide GnRHa] on the steroid-induced renotropic effect was investigated. Gonadectomy of 30-day old male and female rats resulted in the drastic reduction of kidney ornithine decarboxylase (ODC) activity. Injection of testosterone (75 micrograms/rat) or estradiol (1 microgram/rat) to castrated rats significantly increased the enzyme activity at 24 h. Treatment with the GnRH agonist, two doses of 100 micrograms each, caused significant inhibition of the hormone induced ODC activity. Similarly injection of dihydrotestosterone to castrated adult male rats significantly increased poly(A)-polymerase activity at 24 h. Two doses of 100 micrograms of GnRHa caused significant inhibition of DHT induced poly(A)-polymerase activity. These results show that chronic exposure to potent GnRH analogs may have anti-steroidal activity in the kidney.

Androgen regulation of poly(A) polymerase in the ventral prostate of rat

The effect of various hormones on the levels of poly(A) polymerase in the ventral prostate of castrated rats was investigated. It was observed that this enzyme is specifically induced by androgens; progesterone and estradiol-17 beta did not cause stimulation of poly(A) polymerase activity. Dihydrotestosterone-induced poly(A) polymerase was inhibited by cordycepin, actinomycin-D and cycloheximide, which indicates that the genetic transcription leading to the enzyme poly(A) polymerase is regulated by androgens in the ventral prostate.

Inhibition of polyadenylation of mRNA by gonadotropin releasing hormone

The mechanism of extra pituitary inhibitory action of gonadotropin releasing hormone (GnRH) was investigated. Simultaneous injection of GnRH caused dose dependent inhibition of dihydrotestosterone (DHT) induced poly(A) polymerase in the ventral prostate of rat. In addition injection of GnRH to DHT treated animals caused reduced incorporation of 3H-uridine into poly(A)+ mRNA. Since poly(A) segment is known to help in translation of mRNA, it is possible that the inhibitory effect of GnRH is due to the inhibition of polyadenylation of mRNA.

A comparative study of tick-borne encephalitis virus RNA synthesis in acutely and persistently infected cells

Rate zonal and buoyant density gradient centrifugation did not reveal any difference between tick-borne encephalitis virus virions released from acutely or persistently infected cells. All three RNA species characteristic for flavivirus replication were found both in acutely or persistently infected cells, but increased levels of intracellular 42S RNA polyadenylation was observed in persistently infected cells.