The occurrence of segmental constrictions classified by branching order in control and diabetic rats. Assessed during administration of ACh (3.0 μg/kg/min), SNP (3.0 μg/kg/min), combined; L-NAME (10 mg/kg iv. bolus) + meclofenamate (2 mg/kg iv. bolus), combined + ACh and combined + fasudil (10 mg/kg iv.). Segmental constrictions predominately occurred in second order vessels in control animals. In diabetic animals constrictions were predominant in second order vessels and to a lesser extent in first order. ACh administration following combined NOS/COX blockade alleviated first order constrictions while fasudil treatment further reduced second order constrictions. Segmental constrictions are expressed as a proportion of total vessels visible. Control, n = 6 and diabetic, n = 8. Values expressed as mean ± SEM.