Bovine growth hormone and its effects on the local production of
prostacyclin I2 and mammary blood flow in dairy cows.
P. Lacasse, E. Block, Y. Couture, D. Petitclerc
Department of Animal Science, McGill University, Sainte-Anne de
Bellevue, PQ, Canada, H9X 1XO.
Proceedings of the New Zealand Society of Animal Production 1994,
54: 111-114
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.
Keywords: NZSAPAB;
Mammary blood flow; prostacyclin I2; growth hormone; cows; 6-keto
prostaglandin F1a.
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Last Updated 25-01-1997
