Abstract
Nucleic acid and protein were assayed in the hypothalamo-hypophysial system of adult Rana esculenta during the annual reproductive cycle. Adult frogs, weighing 25–35 g, were used and six to seven monthly determinations were made. For each determination material (pars distalis (PD), hypothalamus and cerebral cortex) was collected from five frogs and each pool of material, homogenized in 4 ml cold acetate buffer at pH 5, was analysed in duplicate for RNA, DNA and protein as described earlier (Rastogi & Chieffi, 1972). In both sexes PD weight, and RNA:DNA and protein:DNA ratios increased during the spawning period (April-June) and thereafter declined (Fig. 1). In fact PD cells accumulated increasing amounts of granules with the approach of spawning and degranulated during July-September (cf. Rastogi & Chieffi, 1970), the latter conforming with decreased PD weight and RNA: DNA and protein: DNA ratios (Fig. 1). The DNA concentration decreased with increasing PD weight and

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