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Radioimmunoassays were used to estimate luteinizing hormone (LH) and progesterone in samples of blood taken from individual hens at frequent intervals throughout their respective ovulatory cycles. A consistent pattern in the plasma levels of both hormones was observed. Significantly more LH and progesterone was present in plasma 4\p=n-\7h before ovulation than at other times during the cycle. An increase in the level of progesterone either preceded that of LH or the two hormones increased simultaneously. At no time did an increase in the level of LH occur before the rise in progesterone.In those birds which did not ovulate during the experimental period the levels of both hormones remained low. The significance of these findings in relation to the neuroendocrine control of ovulation in the hen is discussed.

Pure antiandrogens, like flutamide, antagonize androgen action both peripherally and centrally at the hypothalamic-pituitary axis, which leads to an increase in LH and testosterone secretion. A new non-steroidal antiandrogen ICI 176,334 [2RS)-4'-cyano-3-(4-fluorophenylsulphonyl)-2-hydroxy-2-methyl-3'- trifluoromethyl)propion-anilide) has now been discovered which causes regression of the accessory sex organs but does not increase serum concentrations of LH and androgens. ICI 176,334 binds to rat prostate androgen receptors with an affinity around fourfold that of hydroxyflutamide. When administered s.c. concurrently with testosterone propionate (200 micrograms/kg) for 7 days to immature castrated rats, ICI 176,334 (10 mg/kg) significantly (P less than 0.001) inhibited growth of the seminal vesicles and ventral prostate gland. Oral administration of ICI 176,334 at doses of 1, 5 and 25 mg/kg for 14 days to adult rats caused a dose-related reduction in accessory sex organ weights but had no effect on the testes. None of these doses caused a significant increase in serum LH and testosterone. Flutamide was around fourfold less potent and significantly increased serum LH and testosterone at the higher doses. ICI 176,334 was well tolerated. ICI 176,334 should, therefore, prove useful for the treatment of androgen-responsive benign and malignant diseases.

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A radioimmunoassay for the estimation of progesterone in plasma from the domestic fowl is described. Antibodies were raised in goats to progesterone conjugated at the 11 position of the steroid nucleus to bovine serum albumin. An antiserum of high specificity was obtained which allowed the estimation of progesterone in extracts of plasma without purification. The sensitivity of the assay, which was 25 pg using an antiserum dilution of 1:8000, allows the determination of progesterone in 200 μl plasma. The accuracy and precision of the method were highly satisfactory. Plasma progesterone levels in laying hens ranged from 0.67–9.60 ng ml−1 with a mean value of 3.13 ± 0.37 ng ml−1 but were low (< 0.10–0.67 ng ml−1) in plasma from moulting, ovariectomised and hypophysectomised hens and in plasma of intact and castrated cockerels. Progesterone concentrations in blood obtained from a follicular vein ranged from 12.8–133.1 ng ml−1; these values were 8–50 times higher than in peripheral blood collected concurrently. The results suggest that high concentrations of progesterone found in the blood of laying hens are associated with the ovulatory cycle and that the preovulatory follicle secretes significant amounts of progesterone.

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