title: Effects of imidazoline and nonimidazoline alpha-adrenergic agents, including xylazine, medetomidine, yohimbine, tolazoline, and atipamezole, on aggregation of bovine and equine platelets.
abstract: OBJECTIVE
  To investigate effects of various imidazoline and nonimidazoline α-adrenergic agents on aggregation and antiaggregation of bovine and equine platelets.
  
  
  METHODS
  Blood samples obtained from 8 healthy adult cattle and 16 healthy adult Thoroughbreds.
  
  
  METHODS
  Aggregation and antiaggregation effects of various imidazoline and nonimidazoline α-adrenergic agents on bovine and equine platelets were determined via a turbidimetric method. Collagen and ADP were used to initiate aggregation.
  
  
  RESULTS
  Adrenaline, noradrenaline, or α-adrenoceptor agents alone did not induce changes in aggregation of bovine or equine platelets or potentiate ADP- or collagen-induced platelet aggregation. Adrenaline and the α(2)-adrenoceptor agonist clonidine had an inhibitory effect on ADP- and collagen-induced aggregation of bovine platelets. The α(2)-adrenoceptor antagonists phentolamine and yohimbine also inhibited collagen-induced aggregation of bovine platelets. Noradrenaline, other α-adrenoceptor agonists (xylazine, oxymetazoline, and medetomidine), and α-adrenoceptor antagonists (atipamezole, idazoxan, tolazoline, and prazosin) were less effective or completely ineffective in inhibiting ADP- and collagen-induced aggregation of bovine platelets. The imidazoline α(2)-adrenoceptor agonist oxymetazoline submaximally inhibited collagen-induced aggregation of equine platelets, and the α(2)-adrenoceptor antagonist idazoxan, along with phentolamine and yohimbine, also inhibited collagen-induced aggregation of equine platelets. The imidazoline compound antazoline inhibited both ADP- and collagen-induced aggregation of equine platelets.
  
  
  CONCLUSIONS
  Several drugs had effects on aggregation of platelets of cattle and horses, and effective doses of ADP and collagen also differed between species. The α(2)-adrenoceptor agonists (xylazine and medetomidine) and antagonists (tolazoline and atipamezole) may be used by bovine and equine practitioners without concern for adverse effects on platelet function and hemostasis.
authors: Department of Veterinary Internal Medicine, Faculty of Agriculture, Tottori University, Koyama-Minami 4-101, Tottori 680-8553, Japan.
authors: Shin-ichi
authors: S
authors: Yokota
authors: Yoshiaki
authors: Y
authors: Hikasa
authors: Itsumi
authors: I
authors: Shimura
authors: Shuei
authors: S
authors: Kusunose
mesh_terms: D018663:Adrenergic Agents / Q000494:pharmacology*; D000818:Animals; D002417:Cattle / Q000097:blood*; D005260:Female; D006736:Horses / Q000097:blood*; D007093:Imidazoles / Q000494:pharmacology; D048288:Imidazolines / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D008297:Male; D020926:Medetomidine / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D014043:Tolazoline / Q000494:pharmacology; D014991:Xylazine / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D018663:Adrenergic Agents; D007093:Imidazoles; D048288:Imidazolines; C050701:atipamezole; D014991:Xylazine; D015016:Yohimbine; D014043:Tolazoline; D020926:Medetomidine