Estrogen Levels in Peripheral Plasma of Immature Female Chickens as Determined by Radioimmunoassay

Abstract

The levels of estrogen in the plasma of the immature female chicken {Gallus domesticus) were estimated by a radioimmunoassay procedure. Determinations on 16 consecutive blood samples withdrawn over a period of 5 days from each of four 6-wk old birds, which were housed under continuous light, indicated that there were 4 to 5 estrogen peaks over this period. The peaks appeared every 14-34 hr. The lowest and highest levels for each bird during the S-day period averaged 188 (range 101-294) and 1190 (range 1136-1276) pg/ml plasma, respectively. (Endocrinology 94: 1168(Endocrinology 94: , 1974 T7ARLY attempts to measure quantitatively •*-^ the plasma estrogens of birds during various reproductive stages met. with little success. O'Grady and Heald (1) and O'Grady (2) were able to estimate the estrogens in laying-hen plasma by using double-labeling and triplelabeling techniques, respectively. However, the sensitivity of the methods was relatively low and the values tended to be overestimated (3). Peterson and Common (4), using a highly sensitive and specific radioimmunoassay, have recently reported estrogen (estradiol and estrone) levels in laying-hen plasma.In vitro studies (5-7) indicated that estrogenesis begins early in the embryonic gonads of both male and female birds. No data, however, are available on the plasma estrogen levels in the immature female chicken. The present paper reports the patterns of plasma estrogen concentration as determined by radioimmunoassay over a period of 5 days in immature female chickens. Materials and Methods Animals and sample collectionA preliminary study and a subsequent experiment were conducted. Immature female chickens (Cobb X Cornish Cross) were obtained from a commercial hatchery. All birds were kept under continuous light from the time of birth until the termination of the experiment.Blood samples were obtained from the wing veinReceived November 20, 1972.with a heparinized syringe. Samples were centrifuged immediately and the plasma was stored at -20 C.Estrogen determinations were carried out within a few days of sampling. The birds were killed after the last blood samples were withdrawn and the ovary and oviduct were removed and weighed. Assay of estrogenThe radioimmunoassay procedure for estrogen was a modification of Abraham (8) and similar to that of Hendricks et al (9). The procedure quantitated total estrogen, since a chromatographic separation of the estrogens was omitted. Briefly, 0.5 ml of plasma was extracted once with 8 ml diethyl ether (anaesthetic grade, Squibb) from a freshly opened can and allowed to slow freeze at -20 C. The ethereal layer was decanted into another tube and dried under a gentle stream of filtered nitrogen at 39 C. The dried residue was dissolved in 0.8 ml of 0.1M phosphate buffer, containing 0.15M NaCl, 0.1% NaN :{ and 0.1% gelatin (Knox, unflavored) and incubated overnight at 4 C with estradiol antiserum (1:100,000 dilution) and 2,000 dpm of estradiol-17p-6,7 3 H (SA 46.6 Ci/mM, New England Nuclear). Dextran-coated charcoal was employed to...