Plasma Prolactin Measured by Radioimmunoassay and Bioassay in Pregnant and Lactating Goats and the Occurrence of a Placental Lactogen

Abstract

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.

The Relationship Between Lactation and the Release of Prolactin and Growth Hormone in the Goat

“…A. Jones, personal communication). In view of the low levels of prolactin found in the goat during pregnancy and the presence of a placental lactogen (Buttle et al, 1972) . In the cow, at least, it seems that the elevated level of prolactin before parturition, and its regular release at milking or suckling after parturition, is concerned in further increasing milk secretion in the already well developed mammary gland.…”

The Effect of Anterior Cervical Ganglionectomy on the Seasonal Variation in Prolactin Concentration in Goats

“…Blood samples were taken by venipuncture and were added to heparin (25 IU/ml blood) and centrifuged; the plasma was stored at -2 0°C until assay for Prl concentration by radioimmunoassay [Buttle et al, 1972] using NIH PS6 as standard. For statistical analysis, the obtained values were pooled by month or time group and the treatments were compared by analysis of variance.…”

Prolactin Release in the Sheep

“…Once labour started and uterine contractions were frequent, sequential samples were taken at intervals between 1 min and 5 min and continued until after the first suckling period Knaggs, 1972;Gautvik, Weintraub, Graeber, Maloof, Zuckerman & Tashjian, 1973 (Text-figs 7b, c and d).…”