<prompt> Which of these mediate the precapillary sphincter relaxation:Local hormonesSympathetic stimulationsCatcholaminesCapillary filling  <response>: A i.e. Local hormonesPrecapillary sphincters are layer of smooth muscle fibres present just at the point where a metaeriole.There is no innervation on precapillary sphincter.Q- Their dilatation or constriction to control the blood flow depends on local hormones.Q , product of metabolism, hydrogen ions etc.Catecholamines causes sphincter constriction.Factors affecting the caliber of aeriole- Decreased local temperature - Autoregulation- Endothelin-1- Platelet serotonin- Thromboxane A2Epinephrin except in skeletal muscle liver- Norepinephrin- AVP- Angiotensin II- Neuropeptide YDilatationIncreased K, adenosine.- Increased CO2- Decreased 02- Decreased local pH- Decreased local temperature- NO- Prostacyclin- Kinins- Epinephrin in skeletal muscle liver Q- Substance P Q- Histamine Q- ANP- VIP 