Effect of prazosin on the function of the teat sphincter in lactating cows.
Oxytocin was infused for 60 min into the jugular vein of 8 lactating cows with full udders before milking. Under these circumstances milk loss occurred spontaneously in 3 cows and was evoked in 5 cows by reducing pressure around one teat (-30 cm water) using a plethysmographic chamber. Milk loss was measured continuously. The postsynaptic alpha-blocking agent prazosin ( PRZS ) injected either into the udder artery (2 or 5 mg) or into the jugular vein (200 mg) consistently induced a significant increase in milk leakage. It is suggested that PRZS effectively inhibits alpha-adrenoceptors in the teat sphincter muscles and thus promotes the action of beta-adrenoceptors, in this way inducing relaxation of the teat sphincter.
D000818:Animals; D002417:Cattle / Q000502:physiology*; D005260:Female; D007269:Injections, Intra-Arterial / Q000662:veterinary; D007275:Injections, Intravenous / Q000662:veterinary; D007774:Lactation; D008321:Mammary Glands, Animal / Q000187:drug effects; D008893:Milk Ejection / Q000187:drug effects; D009126:Muscle Relaxation; D009130:Muscle, Smooth / Q000187:drug effects*; D010121:Oxytocin / Q000494:pharmacology; D010991:Plethysmography / Q000662:veterinary; D011224:Prazosin / Q000008:administration & dosage / Q000494:pharmacology*; D011247:Pregnancy; D011799:Quinazolines / Q000494:pharmacology*
D011799:Quinazolines; D010121:Oxytocin; D011224:Prazosin