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SUMMARY Changes in the concentrations of ovarian steroids and pituitary gonadotrophins were measured by radioimmunoassay in the jugular plasma of six Clun Forest ewes throughout the oestrous cycle. The concentration of oestradiol began to rise 12–14 h before the onset of oestrus from values of 11·2 ± 0·36 (s.e.m.) pg/ml during the luteal phase to 21·1 ± 2·01 pg/ml at −8 to 0 h (oestrus). There was no distinct increase during the luteal phase. Circulating progesterone varied in a cyclic manner with the highest values at the mid-luteal phase (3·70 ± 0·28 ng/ml; n = 28). In five out of six ewes the concentration was still quite high (1·86 ± 0·43 ng/ml) at 35 h before the onset of oestrus. The concentration declined rapidly thereafter, reaching minimum values about 12 h before oestrus coincident with the increase in oestradiol concentration. Plasma LH increased from very low values of 2·59 ± 0·09 ng/ml during the luteal phase to 75·3 ± 7·4 ng/ml about 9 h after the onset of oestrus. Two peaks of plasma FSH concentration were detected after the onset of oestrus. The first peak (171·0± 35·5 ng/ml) coincided with the LH peak and the second (133·0 ± 10·7 ng/ml) occurred about 24 h later at a time when LH values were low. The mean FSH concentration at other times during the cycle was 61·9 ± 2·8 ng/ml.

Adult male rats were subjected to local testicular irradiation, plasma hormone levels and testicular histology being quantified at intervals up to 52 days thereafter. LH and FSH increased coincidently with spermatid but not with spermatocyte or spermatogonia depletion. Testosterone levels seemed to decrease but this effect was not significant. Oestradiol levels showed no significant changes. From the correlations between the various parameters it was concluded that the lack of inhibin was the main cause of the increase in both LH and FSH and that spermatids provide the signal for production of this non-steroidal inhibitor. The site of inhibin production was not definitively established but the results would be consistent with production of inhibin by the Sertoli cells in association with spermatids.

Oral testosterone undecanoate (TU) in arachis oil has been evaluated with a view to its possible use as a means of androgen replacement therapy. A single 100 mg dose was found to elevate plasma androgen levels and urinary 17-ketosteroid excretion in 6 normal men. Ninety mg/day and 60 mg/day doses taken by a hypogonadal man resulted in sustained levels of androgen which appeared physiological when measured by radioimmunoassay without chromatography. However, upon separation of the steroids by chromatography it was found that much of the androgen present was in fact dihydrotestosterone not testosterone. Both TU and dihydrotestosterone undecanoate were detected in plasma by gas chromatography and it is suggested that the ester is absorbed as such from the intestine and the unesterified steroid subsequently released by hydrolysis. The convenience of oral administration, the resulting prolonged elevated plasma androgen levels and the probable lack of deleterious effects on the liver may render oral TU of value where androgen replacement therapy is indicated.

were made every 5 min for at least 20 min before the rapid intrajugular injection of LH-RF and then for a further 45 min. Samples were also taken 60 and 90 min after injection and, when 50 \g=m\g LH-RF was administered, the period of frequent sampling was extended. All experiments began at approximately 14.00 hours and at least 3 days were allowed to elapse between experiments. The TP (Koch Light, Colnebrook, Bucks) was administered by intramuscular injection in arachis oil in a 50-mg dose at 09.00 hours and again at 18.00 hours on the first 2 days followed by 100 mg at 09.00 hours on the 3rd day. The res¬ ponse of rams pretreated with TP to a dose of LH-RF was compared with the response to the same dose of LH-RF (7 days earlier) in the same animal pre¬ treated with vehicle only. Plasma LH was assayed by a double antibody method similar in procedure to that of Niswender, Reichert, Midgley & Nalbandov (1969). An equine anti-bovine LH, preabsorbed with bovine TSH (Snook, Saatman & Hansel, 1971) was used at a final dilution of 1 : 200,000. Ovine LH (LER 10 56)

Some properties of enzymes inactivating oxytocin in the rabbit brain have been investigated. Enzymes acting on oxytocin and cystine di β naphthylamide were compared using enzyme inhibitors. The effect of incubation of both whole brain homogenate and supernatant fraction with deamino oxytocin and deamino carba1 oxytocin was also determined. It is concluded that oxytocin is inactivated by enzymes which are neither amino peptidases nor those which require prior reduction of the disulphide bridge. Comparison with data in the literature suggests that the molecule is probably cleaved at a C-terminal position. The effects of the injection of oestradiol monobenzoate and of various endocrine physiological states on hypothalamic oxytocinase levels were compared with the effects produced on the levels of cystine di β naphthylamidase. The effect of dehydration on hypothalamic supernatant oxytocinase was also determined. The results suggest that there is no correlation between hypothalamic enzymes inactivating oxytocin and those hydrolyzing cystine di β naphthylamide, and that hypothalamic supernatant oxytocinase may be concerned specifically with gonadotrophin feedback control.

Evidence for the existence of a low molecular weight (less than 10,000 daltons) factor in human follicular fluid that inhibits binding in vitro of FSH to ovarian granulosa cells is presented.

5α-androstane-3β,17β-diol was measured in human peripheral plasma using a specific antibody generated against a carboxymethyloxime BSA conjugate linked at position 7. Concentrations were significantly higher in normal men than women. Preliminary results suggest that plasma 5α-androstane-3β,17β-diol concentrations might be a useful clinical parameter in cases of hirsutism and male infertility.

Following the earlier demonstration of inhibin-like activity in human ovarian follicular fluid a method for its purification to apparent homogeneity is described. The fluid was converted to acetone powder and subjected sequentially to ammonium sulphate fractionation, gel chromatography on Sephadex G-200, continuous gradient ion-exchange chromatography on DEAE-cellulose, first with a pH gradient from 8.0 to 4.0 and then with a NaCl gradient to 1 m at pH 5.2. The active fraction from this step was subjected to gel filtration on Sephadex G-100 and finally passed through an Amicon Centriflo membrane CF-25 (cut off point: 25 000 m.w.). The ultrafiltrate was homogeneous by SDS-polyacrylamide gel electrophoresis, had a molecular weight of the order of 23 000 and was capable of suppressing serum gonadotrophin levels in the castrated male rats in as low a dose as 25 μg/rat.

Luteinizing hormone-releasing hormone (LH-RH) is known to be inactivated by peptidases in the rat hypothalamus with consequent loss of LH-releasing ability. To make a further study of the peptidases' action on the decapeptide, synthetic LH-RH and its [1–9NH2] analogue were incubated with the supernatant hypothalamic fraction containing the enzyme activity. Using an assay system measuring gonadotrophin release in ovariectomized/steroid-primed rats, both LH-RH and the [1–9NH2] analogue were found to be inactivated to different extents after incubation with the fraction, the analogue completely losing both LH- and FSH-releasing activity, and the releasing hormone almost completely losing its LH- and totally losing its FSH-releasing activity. The findings extend the initial studies by showing that the peptidases can remove both the decapeptide's intrinsic LH- and FSH-releasing activity and that these enzymes act on LH-RH at a site other than the C-terminal glycinamide, since they are able to inactivate the [1–9NH2] analogue lacking this residue.

Aus Follikelflussigkeit menschlicher Ovarien wurde durch Alkohol-Prazipitation ein steroidhormon-freier Proteinextrakt gewonnen. Dieser Rohextrakt hatte Inhibinwirkung und hemmte die Ovargewichtszunahme HCG behandelter infantiler Ratten und unterdruckte den nach Kastration infantiler mannlicher Ratten auftretenden FSH-Anstieg im Serum. Rohextrakt aus Follikelflussigkeit kleiner Follikel von Frauen mit regularen Zyklen enthielt pro mg Protein mehr Inhibin-Aktivitat als Rohextrakt aus der Follikelflussigkeit eines cystischen Follikels einer 53jahrigen Frau in der Pramenopause.