Response of fetal rabbit ductus arteriosus to bradykinin: role of nitric oxide, prostaglandins, and bradykinin receptors.

Nitric oxide plays a major role in vascular tone control. Increased blood levels of bradykinin (BK), which stimulates nitric oxide biosynthesis, occur at birth. BK effects on ductus arteriosus (DA) tone were investigated in fetal rabbit under fetal (2.5% O2 "low PO2") and neonatal (30% O2 "high PO2") conditions using in vitro isometric tension studies. Intact and endothelium-denuded DA, contracted with norepinephrine (ED75-90), showed a biphasic response to BK, with relaxation at 10(-9) to 10(-7) M BK and contraction at 10(-6) to 10(-5) M BK. BK (10(-6) to 10(-5) M) contracted intact DA from baseline tension, with greater contraction under high PO2. The B2-receptor antagonist D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-BK (Hoe-140, 10(-7) M) abolished relaxation, but not contraction, to BK in intact and denuded DA. The B1-receptor antagonist des-Arg9-[Leu5]-BK (10(-7) M) reduced BK-induced contraction but not relaxation in intact DA only. Nitric oxide synthase inhibitors, N(omega)-nitro-L-arginine methyl ester (10(-4) M) and N(omega)-monomethyl-L-arginine (10(-4) M) partially inhibited relaxation to BK in intact DA, with L-arginine (3 x 10(-4) M) reversing N(omega)-monomethyl-L-arginine inhibition. N(omega)-nitro-L-arginine methyl ester (10(-4) M) caused a small but significant inhibition of relaxation to BK in denuded DA. Indomethacin (2.8 x 10(-6) M), a cyclooxygenase inhibitor, abolished relaxation but not contraction to BK in intact and denuded DA. BK-induced relaxation of the DA acts through B2-receptors, releasing both nitric oxide and prostaglandins, whereas endothelial B1-receptors may mediate contraction. BK action on isolated DA changes from relaxation to contraction as its concentration increases, with greater contraction at neonatal PO2. Thus increased BK levels at birth may aid functional closure of the DA.

Fractures in cryopreserved arteries.

The common carotid artery of the rabbit, a typical small elastic artery, can be cryopreserved using dimethyl sulfoxide, slow cooling, storage at less than -160 degrees C, and rapid warming. This technique provides satisfactory preservation of muscle and endothelial cells, but in about 75% of cases, gross circumferential fractures occur in the vessel wall. This paper investigates the influence of vehicle solution composition, cryoprotectant concentration, cooling rate, and storage temperature on the occurrence of cracks. When cooling was halted at -80 degrees C and the arteries were stored at this temperature, fractures no longer occurred. Possible mechanisms are discussed and it is proposed that mechanical stresses develop in the vitreous material that separates the ice crystals and lead to structural failure.

Electrokinetic properties of human cryopreserved platelets.

A method for the cryopreservation of human platelets with glycerol/glucose is described which was a simplified modification of the method of Dayian and Pert (1979). The effect of cryoinjury of the platelet surface membrane was investigated by studying the surface electrokinetic properties of the platelet. A significant increase in platelet electrophoretic mobility was found after cryopreservation. The fresh platelets had a mean electrophoretic mobility of 1.04 +/- 0.05 microns s-1 V-1 cm-1 and cryopreserved platelets 1.18 +/- 0.05 microns s-1 V-1 cm-1, P < 0.05. However, the total platelet sialic acid of fresh platelets was 62.5 +/- 5.6 nmol 10(-9) platelets compared to 47.2 +/- 4.6 nmol 10(-9) platelets after cryopreservation, P < 0.001. Similarly, the neuraminidase-labile sialic acid was 26.4 +/- 4.3 nmol 10(-9) platelets for fresh platelets and 17.6 +/- 4.0 nmol 10(-9) platelets after cryopreservation, P < 0.001. Using polyacrylamide gel electrophoresis with Western blotting, we showed a reduction in the platelet glycoprotein Gp Ib after cryopreservation, this was confirmed by using crossed immunoelectrophoresis. Electron microscopy revealed a significant change in platelet morphology after the cryopreservation procedure with disruption of the platelet membrane and also platelet shape change. These features may explain the changes in platelet electrokinetic properties.

Permeation of rabbit common carotid arteries with dimethyl sulfoxide.

Proton nuclear magnetic resonance has been used to measure the kinetics of permeation of dimethyl sulfoxide in the common carotid artery of the rabbit. The process is described by the following exponential equations, where t = time in minutes: % Unexchanged at 2 degrees C = 70e-0.515t + 30e-0.104t and %Unexchanged at 22 degrees C = 70e-1.790t + 30e-0.146t. The times required for 95% equilibration were 13 min at 22 degrees C and 18 min at 2 degrees C. The corresponding times for 99% equilibration were 24 and 32 min, respectively.