Oral microemulsion cyclosporine is an effective drug in the initial management of patients suffering from a steroid-refractory attack of ulcerative and indeterminate colitis. Additional controlled studies with the new oral formulation are required to confirm these results.

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ABSTRACT. We have reported the longitudinal distribution of vascular resistance in the three segments (arteries, microvessels, and veins) of the pulmonary circulation of adult rabbits (J Appl Physiol 60:539-545, 1986). To determine the longitudinal distribution of vascular resistance in lungs of younger animals, we measured microvascular Dressures in the sub~leural microcirculation in nine isolated blood perfused lungs of 3-to 4-wk-old rabbits. We used micropipettes and the servonull pressure measuring system to directly measure pressures in 20-50 pm diameter subpleural arterioles and veuules. We also measured pulmonary arterial and left atrial pressures and lung blood flow. To determine the influence of vascular tone on segmental vascular resistance, in four lungs we measured microvascular pressures both before and after paralyzing the vasculature with papaverine. We found that 51% of the total pressure drop in the pulmonary circulation was in arteries, 24.5% in microvessels, and 24.5% in veins. Vascular tone contributed minimally to baseline arterial resistance. The greater arterial and venous resistance in lungs of 3-to 4-wk-old rabbits as compared to that in adult rabbits is probably due to differences in vessel geometry. (Pediatr Res 20: 1107-11 11, 1986) Various methods have been used to determine the contribution of the three longitudinal segments of the pulmonary vasculature, i.e. the pulmonary arteries, microvessels, and veins to the total vascular resistance in the lung (1-4). Recently, with the development cf the technique of lung micropuncture, it has been possible to measure directly microvascular pressures in the subpleural microcirculation. Using this method, in the isolated dog lung, Bhattacharya and coworkers (5, 6) found that the major site of resistance to blood flow was the middle segment, i.e. microvessels <20 Fm in diameter. Using the same technique in the adult rabbit lung, we found that -60% of the total arteriovenous pressure drop occurs in vessels <20 pm in diameter, -33% occurs in arteries and only -7% occurs in veins (7). In the adult rabbits we had eliminated vascular smooth muscle tone in the lungs by paralyzing the vessels with papaverine.All the estimates of segmental vascular resistance in the lungs have been in lungs from adult animals. There are several reasons why the longitudinal distribution of vascular resistance in the lung is likely to be different in the younger animal. The high pulmonary vascular resistance in the fetus (8,9) falls dramatically at birth (10, 11) but does not reach the low adult value until 3-6 months of age (12). Vascular resistance in the lung is high in early life partly due to a higher basal vasomotor tone (1 3) and in part due to differences in the morphology of the pulmonary vasculature (14).In this study, using an isolated blood perfused lung preparation and the technique of lung micropuncture, we describe the distribution of vascular resistance in the pulmonary arteries, microvessels and veins in 3-to 4-wk old rabbits. METHODS Isolated lung pr...

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