EFFECTS OF CLOSE-ARTERIAL (EXTERNAL PUDIC) INFUSION OF INSULIN-LIKE GROWTH FACTOR-II ON MILK-YIELD AND MAMMARY BLOOD-FLOW IN LACTATING GOATS

Five lactating goats were infused, via an external pudic arterial cath eter, directly into the mammary gland with 0.9% (w/v) NaCl (20 ml/h), recombinant human insulin like growth factor-I (IGF-I; 80 nmol/h), rec ombinant human IGF-II (133 nmol/h) or IGF-I and IGF-II combined. The i nfusion was for 6 h and milk yield was determined every 2 h. The ratio of milk yield in the infused relative to the non-infused gland was ch anged only slightly by saline (2%), but increased to 9% (P<0.05) in re sponse to IGF-I and 8% (P<0.05) in response to IGF-II. When combined, both peptides increased this ratio by 6%. These effects were elicited within 2-4 h of the beginning of infusion. Mammary blood flow increase d 50-80% (P<0.05) during all IGF infusions, but only 28% during saline treatment. Plasma insulin decreased 50% (P<0.01) during the infusion of IGF-I alone or in combination with IGF-II and 25% in response to IG F-II alone. Whereas plasma glucose increased by approximately 10% duri ng infusion of IGF-I alone or with IGF-II, it was not altered by infus ion of IGF-II only. The rapidity and unilateral nature of the milk-yie ld response to IGF-I and IGF-II is consistent with their acting direct ly on mammary tissue itself. Thus, the present results demonstrate sim ilar local and systemic actions induced by intramammary infusion of IG F-II and IGF-I, although the magnitude of the response to IGF-II tends to be less than that to IGF-I.