Endocrine Activity of the Mammary Gland: Oestrogen and Prostaglandin Secretion by the Cow and Sheep Mammary Glands During Lactogenesis

Abstract

SUMMARY Mammary venous and carotid arterial plasma concentrations of oestradiol-17β and prostaglandin Fα (PGFα), and mammary secretion concentrations of lactose were determined in three Jersey cows and four Friesland sheep from seven days pre-partum until two days post partum. Significant mammary secretion of oestradiol-17β and PGFα into the venous drainage was observed in both cows and sheep pre-partum, supporting the hypothesis postulated for the goat that the mammary gland is an endocrine organ. The timing of the onset of copious milk secretion, coincident with an increased mammary secretion concentration of lactose (lactogenesis), differed between cows and sheep in relation to parturition. However, the temporal pattern of changes in the mammary secretion of oestradiol-17β and PGFα, in relation to lactogenesis, was similar in the two species; a cessation of mammary secretion of PGFα and a transient peak in the mammary secretion of oestradiol-17β occurring immediately prior to the onset of copious milk secretion. This relationship is similar to that observed previously in the goat, and indicates common mechanisms for the control of lactogenesis in these three ruminants which have differing endocrinological profiles associated with the maintenance of pregnancy and control of parturition.