Prolactin (PRL) is a pituitary hormone whose molecular weight is approximately 23000 Daltons. It is a single polypeptide chain composed of about 200 amino acid residues with three disulphide bonds. In mammals prolactin has been claimed to exert a wide range of different physiological effects. These include stimulation of mammary gland development and lactation, hair maturation, synergism with androgen in male sex accessory growth and maintenance and secretion of corpus luteum. PRL is predominantly under inhibitory control by the hypothalamus. Stimulation of prolactin release can be mediated by dopamine and thyrotrophin-releasing hormone(TRH).