The endocrine control of the early stages of oöcyte maturation in Leucophaea maderae (FAB.) Public Deposited

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  • A procedure was developed for the isolation and maintenance of isolated abdomina of the cockroach, Leucophaea maderae. The degree of injury and loss of body fluid was best minimized by ligating the animals immediately following the final molt. The nutritional needs of the isolates were satisfied by filling the animals' crops with a glucose or casamino acid-glucose solution prior to separation of the abdomina. Isolates prepared in this manner quickly recovered from the operation and remained quiescent with normal heart beat and cercal response for periods extending to several months. It was necessary to provide the isolates with an amino acid solution for maximum responsiveness of the reproductive organs to implanted corpora allata. Response was evaluated on the basis of accessory gland activation and oocyte growth. The nymphal diet did not contribute to the responsiveness of the accessory glands or oocytes. Nymphs fed only sucrose prior to the final molt did not provide abdomina responsive to corpora allata unless the newly molted adults were force-fed with amino acids prior to isolation. The amino acid requirement could also be satisfied by injection of the isolates. Abdomina isolated from nymphs fed dog food and force-fed either saline solution or whole casein were not responsive. A time course study of the responsiveness of the oocytes to corpora allata implants showed that the capacity for response coincided with the normal mating time of intact females. Oocytes were unresponsive before the sixth day following ecdysis and thereafter reacted fairly uniformly. Inactive corpora allata obtained from pregnant females returned to activity when implanted in allatectomized intact females. However, such glands produced no response in the reproductive organs of isolated abdomina within the same period of time. It was concluded that reactivation of the corpora allata was due to humoral stimulus present in intact females but absent in the isolates, rather than to an intrinsic cyclic activity as other workers had suggested. Bioassays of materials with known gonadotropic activity were attempted. Farnesol was tested as an external smear on the cuticle of isolated abdomina, and a juvenile hormone extract was tested by injection. Neither of these materials initiated the growth of oocytes, and the maximum accessory gland response observed was very slight. Examination of the evolution of radioactive CO₂ following the injection of isotopically labelled glucose and acetate indicated that the respiratory activity of isolates was reproducible and that abdomina continued to function uniformly for several weeks following isolation. The incorporation of acetate-C¹⁴ into lipids was more variable than its oxidation, but possibly not more so than would be expected with intact animals. The levels of incorporation were similar to those which have been reported for intact roaches. No correlation was observed between the action of the corpora allata on the reproductive organs and the oxidation or incorporation into fatty acids of acetate-C¹⁴. This supports the hypothesis that increases in oxygen utilization which have been observed in the presence of corpora allata are not due to a direct action by the hormone upon respiratory metabolism, but arise indirectly as a result of other events. The incorporation of leucine-C¹⁴ into the proteins of the blood and fat body was examined with respect to the response of the reproductive organs of isolates to implanted corpora allata. In these preliminary experiments it was not possible to detect the presence of corpora allata from measurement of the specific activity of these proteins. Although the highest specific activities were observed in animals with developing oocytes, the proteins of many unresponsive and control animals were labelled nearly as extensively. It is suggested that protein synthesis occurs in all isolates, with some variation, and that when the corpora allata are able to initiate oocyte development, this synthesis is increased due to homeostasis.
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