Our objective was to test the hypothesis that bovine growth hormone (bGH) can induce the secretion of vasodilators by the bovine mammary gland. Three adult lactating cows were surgically implanted with catheters in the left costoabdominal artery, in the left subcutaneous abdominal vein (milk vein) and in a lymph duct afferent to the left supramammary lymph node. In addition, a transit time flow probe was implanted on the left pubic artery. Cows were injected s.c. with either saline or 25 mg of bGH according to a crossover design. Samples from arterial and venous blood and from lymph fluid were collected from 2 hours before to 16 hours after the injection. Mammary blood flow was recorded at each sampling. Injection of bGH induced a gradual increase in mammary blood flow in lactating cows while it remained constant after the saline injection. Venous concentrations of 6-keto-prostaglandin F1a, a stable metabolite of the vasodilator prostacyclin I2, were not affected by bGH injection. However, lymphatic concentrations of the prostacyclin I2 metabolite increased when cows were injected with bGH. The time course of the increase in plasma IGF-I concentration was similar to that of mammary blood flow and 6-keto-prostaglandin F1a. In conclusion, a local release of prostacyclin I2 may be responsible for the bGH-induced increase in mammary blood flow. IGF-I might mediate this effect of bGH.

P, Lacasse, E Block, Y Couture, and D Petitclerc

Proceedings of the New Zealand Society of Animal Production, Volume 54, , 111-114, 1994
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