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Summary
Bovine placental lactogen is secreted by the fetus during pregnancy. Its circulating levels in cows are significantly lower compared to other species, detected only when prolactin is high.
Area of Science:
- Reproductive biology
- Endocrinology
- Comparative physiology
Background:
- Placental lactogen (PL) is a key hormone in mammalian pregnancy, influencing fetal and maternal adaptations.
- Previous studies have established PL secretion in various species, but its role and levels in cattle remain less defined.
Purpose of the Study:
- To investigate the secretion and circulating levels of bovine placental lactogen (bPL) during pregnancy.
- To compare bPL levels with those of prolactin and growth hormone and to assess its lactogenic activity in vivo.
Main Methods:
- Co-culture of bovine cotyledonary tissue with mouse mammary gland explants to detect PL secretion.
- Radioimmunoassay (RIA) of peripheral plasma for prolactin concentrations in heifers.
- Bioassay of plasma for lactogenic activity using rabbit mammary gland organ culture.
Main Results:
- Bovine placental lactogen was detected at various stages of pregnancy (days 36, 178, 182, 270) and originated from the foetal cotyledon.
- No cross-reactivity of bPL with antibodies for bovine prolactin or growth hormone was observed.
- Seasonal variation in heifer prolactin levels was noted, with peaks in summer.
- Significant lactogenic activity in plasma was detected only when prolactin levels exceeded 70 ng/ml, suggesting low circulating bPL.
Conclusions:
- Bovine placental lactogen is secreted during pregnancy, likely from the foetal cotyledon.
- Circulating levels of bovine placental lactogen are considerably lower than in sheep, goats, or humans.
- The detection of lactogenic activity is dependent on high prolactin concentrations, indicating a limited contribution of bPL to overall lactogenic activity in cows.