The goat mammary gland as a target organ for atrial natriuretic peptide

Milk secretion represents a major route for electrolyte and water excretion in the dairy goat. The aims of this study were to investigate whether the mammary gland is a target site for atrial natriuretic peptide (ANP) in the goat and whether ANP affects mammary sodium and water secretion. Receptor autoradiography using I-125-ANP as radioligand revealed specific binding sites in the secretory tissue of the mammary gland. The radioligand was totally displaced by unlabelled ANP, but not by brain natriuretic peptide or the ANP fragment C-ANP(4-23), indicative of ANP-A receptor preference. To elucidate the role of ANP in milk secretion, ANP (30 ng kg(-1)min(-1); 120 min) or 0.15 M NaCl (control) were administered in vivo. The ANP infusions caused haemoconcentration, but did not change milk flow or the concentrations of sodium, potassium, lactose, fat and protein in the milk. The results show that the mammary gland of the goat expresses ANP-specific binding sites, however, a physiological role of ANP in goat mammary gland function remains to be elucidated.