title: Delineating potential control mechanisms of mammary protein synthesis utilizing atropine.
abstract: Amino acids (AA) and/or somatotropin (ST) were infused into a jugular vein of lactating cows receiving atropine to determine the effect on milk protein secretion. Atropine decreased milk protein yield by 35%. Plasma alpha-amino nitrogen, which was decreased by 31% due to atropine, was restored to control levels upon AA infusion. Plasma ST concentration was not affected by atropine and, upon ST infusion, increased by 236% in treated animals. Amino acids, ST, or the combination of the two were unable to return milk protein to control levels in atropine-treated animals. Plasma insulin concentration decreased by 37% in atropine-treated animals and was not significantly different for cows receiving atropine as well as ST, AA, or both ST and AA. Similarly, glucagon decreased by 36% in atropine-treated animals but was partially restored in cows receiving AA. Overall, the insulin-to-glucagon ratio was not significantly affected by treatment. Plasma glucose concentration was not affected by treatment. These data lend support to the importance of the insulin-to-glucagon ratio in terms of whole-body metabolism, with the exception of the mammary glands, which are glucagon-insensitive and, therefore, sensitive to the observed decrease in circulating insulin concentration.
authors.affiliation: Department of Animal Science, McGill University, Ste. Anne-de-Bellevue, QC, Canada.
authors.forename: P H
authors.initials: PH
authors.lastname: Luimes
authors.forename: J P
authors.initials: JP
authors.lastname: Cant
authors.forename: X
authors.initials: X
authors.lastname: Zhao
authors.forename: D
authors.initials: D
authors.lastname: Petitclerc
mesh_terms: D000596:Amino Acids / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism; D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D001786:Blood Glucose / Q000378:metabolism; D002417:Cattle / Q000502:physiology*; D005260:Female; D013006:Growth Hormone / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism; D007263:Infusions, Parenteral / Q000662:veterinary; D007328:Insulin / Q000378:metabolism; D007774:Lactation / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D008894:Milk Proteins / Q000187:drug effects / Q000378:metabolism*; D018727:Muscarinic Antagonists / Q000494:pharmacology*
chemical_list: D000596:Amino Acids; D001786:Blood Glucose; D007328:Insulin; D008894:Milk Proteins; D018727:Muscarinic Antagonists; D001285:Atropine; D013006:Growth Hormone