Inhibition of local blood flow control systems in the mammary glands of lactating cows affects uptakes of energy metabolites from blood.
To test the effect of mammary blood flow on net uptakes of milk precursors by the mammary glands, inhibitors of nitric oxide synthase (NOS) and cyclooxygenase (COX) were infused into the mammary circulation of 4 lactating cows. Inhibitors were infused in a 4×4 Latin square design, where treatments were infusion for 1 h of saline, NOS inhibitor (Nω-nitro-l-arginine methyl ester hydrochloride), COX inhibitor (indomethacin), or both NOS + COX inhibitors into one external iliac artery. Para-aminohippuric acid was also infused to allow for estimation of iliac plasma flow (IPF), of which approximately 80% flows to the mammary glands. Blood samples were collected before, during, and after inhibitor infusion from the contralateral external iliac artery and ipsilateral mammary vein. Inhibition of COX and NOS each produced a decrease in IPF, although the NOS effect was smaller and IPF continued to be depressed throughout the recovery period. The combination of COX and NOS inhibition produced a 50% depression in IPF and there was no carryover into the recovery period. Treatments that depressed IPF also increased arterial concentrations of acetate, β-hydroxybutyrate (BHBA), and glucose. Similarly, arteriovenous differences of acetate, BHBA, and glucose were all increased during IPF depression. To correct for a potential effect of arterial concentration, arteriovenous differences were normalized to arterial concentration, producing an extraction percentage. Inhibition of COX increased glucose extraction and tended to increase acetate and BHBA extraction. Dual inhibition only increased BHBA extraction and had no effect on mammary extraction of other metabolites. These extractions did not increase because clearances of glucose and TAG decreased as IPF decreased, and clearances of acetate and BHBA tended to decrease. Net uptake of TAG was depressed by dual NOS/COX inhibition, whereas uptakes of acetate, BHBA, and glucose were not affected by any of the treatments. To separate effects of flow from effects of arterial concentration, uptakes were regressed against IPF and arterial concentration simultaneously. According to the slopes of the regressions, a 10% decrease in IPF from the mean observed during saline infusion resulted in 3.8, 7.3, and 10.4% decreases in uptakes of acetate, glucose, and triacylglycerol, respectively. These findings indicate that mammary blood flow affects milk precursor uptake, and that clearance should not be assumed constant to predict mammary uptakes of milk precursors in situations where blood flow is changing.
Department of Veterinary Clinical and Animal Science, University of Copenhagen, DK-1870 Frederiksberg C, Denmark.
T G
TG
Madsen
Department of Animal and Poultry Science, University of Guelph, Ontario N1G 2W1, Canada.
S R L
SR
Cieslar
Department of Clinical Studies, University of Guelph, Ontario N1G 2W1, Canada.
D R
DR
Trout
Department of Veterinary Clinical and Animal Science, University of Copenhagen, DK-1870 Frederiksberg C, Denmark.
M O
MO
Nielsen
Department of Animal and Poultry Science, University of Guelph, Ontario N1G 2W1, Canada. Electronic address: jcant@uoguelph.ca.
J P
JP
Cant
D020155:3-Hydroxybutyric Acid / Q000097:blood; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives; D002417:Cattle / Q000502:physiology*; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007774:Lactation / Q000502:physiology; D008321:Mammary Glands, Animal / Q000098:blood supply*; D008892:Milk / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D012039:Regional Blood Flow / Q000502:physiology*; D014280:Triglycerides / Q000378:metabolism; D010130:p-Aminohippuric Acid / Q000097:blood
D016861:Cyclooxygenase Inhibitors; D014280:Triglycerides; C026512:arginine methyl ester; D001120:Arginine; D019001:Nitric Oxide Synthase; D011451:Prostaglandin-Endoperoxide Synthases; D005947:Glucose; D020155:3-Hydroxybutyric Acid; D010130:p-Aminohippuric Acid
dairy cow; mammary blood flow; mammary uptake