In the course of studies on the secretion of prolactin by goats in different physiological states, the concentrations of prolactin in the plasma of male goats were measured throughout the year.Three intact male goats aged 5\ m=1/ 2\ (Miljohn), 2\ m=1/ 2\ (Rupert) and 1\ m=1/ 2\ (Minto) years at the beginning of the sampling period were used. The goats were maintained under the usual husbandry conditions, being turned out to pasture in the summer and kept in individual pens in a separate male goat house in winter; supplementary heating from infra-red lamps was used when necessary. During the breeding season, all three males were used to mate with females in the herd and all three were fertile. Samples of blood were withdrawn from a jugular vein once a week, between 14.30 and 15.30 hours for a period of 15 months. The blood samples were taken by venepuncture into heparinized syringes, centrifuged at 4\s=deg\Cfor 20 min at 1800 g and the plasma was stored at \m=-\20\s=deg\C until required for assay.The following year (1972), the same three intact males and another, Ulysses, aged 1 year, and also four castrated males were sampled hourly for 24 hr on 22nd to 23rd June and again on 19th to 20th December. All animals were confined to individual pens for 1 week before sampling started. The day before sampling, polyethylene cannulae were inserted into a jugular vein. Supplemen¬ tary lighting needed to take samples at night was used as little as possible.Prolactin concentration was determined by a radioimmunoassay for ovine prolactin by the technique of Buttle, Forsyth & Knaggs (1972) with the modification that labelled prolactin (NIH-PS-6) was prepared by an enzymatic iodination method adapted from Morrison & Bayse (1970). As far as possible, all samples from one goat were included in one assay. In these circumstances, the smallest significant difference ( =0·05) between any two samples was +0T50 of the log10 concentration.The results for the year for each individual goat are shown in Text- fig. 1. A wide range of values occurred both within and between individuals, ranging from 1 ng prolactin/ml plasma (the lower limit of sensitivity of the assay used) to 256 ng/ml, with fluctuations within individuals from week to week. Concen¬ trations of 8 ng prolactin/ml plasma or less were found only between November and February, whereas the highest concentrations of 60 ng/ml or more in 95

SUMMARY Plasma samples from five goats taken during their first pregnancies and subsequent lactation were examined for prolactin concentration by a radioimmunoassay and for total lactogenic activity by a rabbit mammary gland organ culture assay. Prolactin was released in response to suckling and there was a fair correlation between prolactin concentrations as measured by radioimmunoassay and the levels of total lactogenic activity in the plasma samples from the lactating animals. During pregnancy, however, high levels of lactogenic activity were detected in the second and last thirds of pregnancy when the concentration of immunoreactive prolactin was low or even absent. This discrepancy in the results of the two assays suggests that the blood of pregnant goats contains a second lactogen of placental origin which does not cross-react with prolactin.

Mammogenesis in primiparous hypophysectomized goats has been assessed between days 60 and 120 of gestation and compared with that found in untreated goats and goats treated with 5 mg bromocriptine/day. There were fivefold increases in the weight of lobulo-alveolar tissue in the hypophysectomized and bromocriptine-treated goats and a tenfold increase in the untreated goats. Histological examination of the mammary glands at 120 days showed normal structure, and determinations of lactose, lactose synthetase, cytosol enzymes, protein, DNA and RNA indicated qualitatively normal initiation of milk synthetic capabilities in both the hypophysectomized and bromocriptine-treated goats. Bromocriptine treatment lowered the plasma concentration of placental lactogen as well as that of prolactin. The results indicate that placental lactogen has important mammogenic effects during pregnancy.

Bilateral anterior cervical sympathetic ganglionectomy in castrated male goats had no effect upon the subsequent seasonal variation in the concentration of prolactin (Prl) in plasma when surgery was performed in summer. After ganglionectomy in winter, however, the subsequent rise in Prl concentration associated with season was accelerated.

In the ruminant placenta 15-20% of the trophectodermal epithelium consists of granulated binucleate cells (BNC). In the sheep the granules contain ovine placental lactogen (oPL). These cells migrate from the trophectoderm to form fetomaternal hybrid tissue from implantation to term. The number of BNC, their percentage migration and the potential secretory activity of the syncytium they form were estimated by semiquantitative transmission electron-microscopical techniques after several surgical techniques and hormone or drug infusions. BNC numbers decrease normally just before parturition, and this fall could be eliminated by fetal hypophysectomy or induced early by administration of tetracosactrin to intact or hypophysectomized fetuses. If only one twin was treated with tetracosactrin the placenta of the untreated twin did not show the fall in BNC numbers found in the other unless it died in utero some time before sampling. This indicates fetal control of BNC number and migration. However, fetal catheterization, hypophysectomy, stalk section, adrenalectomy, infusion of mouse epidermal growth factor or bromocriptine had little or no effect on binucleate cell numbers or migration percentages. Maternal carunclectomy, ovariectomy, or epostane or bromocriptine administration also had no consistent significant effect. Previous reports of degeneration of BNC structure plus a decrease in their number (with bromocriptine) or an increase in migration frequency (after adrenalectomy or stalk section) have not been confirmed by this study. The BNC migration delivers the oPL-containing BNC granules close to the maternal circulation but the variation in migration seems only loosely correlated with the reported maternal oPL concentrations. The results indicate that BNC migration is independent of the hormonal milieu, but that BNC production is greatly modified by the hormonal changes just before parturition, with cortisol production by the fetus a possible primary cause.