Summary. Jugular vein blood was collected daily from four mature ewes throughout anoestrus and the first oestrous cycle of the breeding season until 4 days after the second oestrus. The levels of oestrogen, progesterone and LH were determined by radioimmunoassay. There were fluctuations in the LH level throughout most of the observed anoestrous period with a mean \ m=+-\ S.E. value of 2\m=.\3\ m=+-\ 0\m=.\9 ng/ml. High LH values of 20\m=.\0, 41\m=.\2and 137\m=.\5 ng/ml were observed in three ewes on Day \m=-\24of anoestrus. A brief minor rise in progesterone level was also observed around this period. Progesterone levels were consistently low (0\m=.\11 \ m=+-\ 0 \ m= . \ 0 1 ng/ml) before Day \m=-\25of anoestrus. A major rise occurred on Day \m=-\12 of anoestrus and this was followed by patterns similar to those that have been previously reported for the oestrous cycle of the ewe. Random fluctuations of oestrogens deviating from a mean level of 4\m=.\40 \ m=+-\ 0\m=.\1 pg/ml were observed during anoestrus and the mean level during the period from the first to the second oestrus was 5\m=.\2\ m=+-\ 0\m=.\3 pg/ml. A wel l \x=req-\ defined peak of 13\m=.\3\ m=+-\ 0\m=.\7 pg/ml was seen in all ewes on the day of the second oestrus. Results of the present study suggest that episodic releases of LH occur during anoestrus and periods of low luteal activity. The fluctuations in LH levels, as observed during the period of low luteal activity, i.e. before Day \m=-\25 of anoestrus, were less pronounced during the periods of high luteal activity. The view that luteal activity precedes the first behavioural oestrus of the breeding season is supported.

No abstract

Yurneslsrurosor, P., Howr.rNo, B. E., Srlren-lrs, S. AND PeI-uEn, W. M. 1974. Estrogen-induced LH release in progesterone-treated ovariectomized ewes.Can. J. Anim. Sci For personal use only.

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 Determinations on 16 consecutive blood samples withdrawn over a period of 5 days from each of four 6-wk old birds, which were housed under continuous light, indicated that there were 4 to 5 estrogen peaks over this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...