EXPRESSION OF TRANSFORMING GROWTH-FACTOR-ALPHA AND GROWTH-FACTOR-BETA-1 MESSENGER-RNA IN THE BOVINE MAMMARY-GLAND DURING DIFFERENT STAGES OF DEVELOPMENT AND LACTATION

It is now widely accepted that the mammary gland is under interconnect ed hormonal and local control. Growth factors are involved in the inte rcellular signalling of the gland. Our aim was the detection of transf orming growth factors alpha (TGF-alpha) and beta 1 (TGF-beta 1) messen ger RNA during mammogenesis, lactogenesis, galactopoiesis and involuti on in the bovine mammary gland (total n=27). During these stages the R NA was assessed by means of ribonuclease protection assay and reverse transcription-polymerase chain reaction (RT-PCR). To study possible in fluences of oestrogen, progesterone and prolactin on growth factor exp ression, mammary RNA was obtained from heifers after induced mammogene sis and lactogenesis, with and without additional prolactin inhibition (total n=20). Very low levels of TGF-alpha and TGF-beta 1 expression were detected during lactogenesis and galactopoiesis, increasing level s during mammogenesis of primigravid heifers, and highest levels durin g mammo-genesis of virgin heifers and during involution. TGF-alpha exp ression after induced mammogenesis was greater than after induced lact ogenesis or physiological mammogenesis during pregnancy. Furthermore, TGF-alpha mRNA contents increased after prolactin inhibition. TGF-beta 1 expression was almost equal after induced mammogenesis and lactogen esis, but greater than during the physiological mammogenesis and lacto genesis. In conclusion, it can be assumed that growth promoting TGF-al pha and growth inhibiting TGF-beta 1 are co-expressed in the bovine ma mmary gland. Higher mRNA contents of both factors during mammogenesis and involution may indicate autocrine or paracrine functions for these growth factors during proliferation and reorganisation of the mammary tissue.