Nucleic acid metabolism in adult tissues of Gromphadorhina in response to ecdysterone: Quantitative effects

Abstract

Tissues of two species of adult Madagascar cockroaches, Gromphadorhina portentosa and G. bruneri, were examined to determine their competence to respond to ecdysterone at the transcriptional level. The tissues surveyed were fat body, testes, and male accessory glands. Hormone treatment was carried out either in vivo, by injection, or in vitro using the isolated tissues. The tissues were then exposed to radioactive adenine to label newly formed nucleic acids. In quantitative experiments, nucleic acids and ATP were extracted by acid precipitation of the tissue homogenate. ATP was assayed using crude firefly luciferase, whereas RNA and DNA were quantitated colorimetrically. Radioactivity was determined by liquid scintillation spectrometry. Differences in specific activity between experimental and control groups were expressed as percentages of control values. In vivo experiments with both male and female fat body showed an increase in ATP and decrease in RNA and DNA specific activities following 1 hr of treatment, and a decrease in ATP and increase in RNA and DNA specific activities after 8 hr of treatment. Sequential injections over an 8 hr period yielded the same pattern of incorporation as that described for 1 hr. Hydrocortisone treatment was ineffective, as was in vitro treatment with either hormone. Experiments with testes, both in vivo and in vitro, were largely negative, although some changes in specific activities were noted. With male accessory glands, there was an increase in ATP, RNA, and DNA specific activities at 1 hr of treatment as well as following sequential administration of hormone over 8 hr. It is concluded that adult Gromphadorhina fat body is competent to respond to ecdysterone on the level of nucleic acid metabolism in vivo, but that in vitro conditions for optimal response remain to be defined. Male adult accessory glands are competent to respond on this level both in vivo and in vitro. In general, it appears that an early effect of the hormone is to bring about an increase in the ATP pool, whereas a later effect is to stimulate the synthesis of nucleic acids.