Recent studies indicate that circulating peptides or plasma proteins, such as insulin or transferrin, or modified proteins, such as cationized albumin, undergo receptor-mediated or absorptive-mediated transport through the brain capillary wall, i.e., the blood-brain barrier (BBB). Although morphologic studies such as autoradiography or immunoperoxidase labeling can demonstrate transport of blood-borne protein into brain, there is a need for a rapid, sensitive, and quantifiable physiology-based technique for comparing the relative rates of transport of several different blood-borne peptides or proteins into brain. Therefore, the present investigations describe a carotid arterial infusion technique coupled with a capillary depletion method for quantifying transport of blood-borne cationized albumin, cationized IgG, and acetylated low-density lipoprotein (LDL). Because differentiation of true transcytosis into the postcapillary compartment of brain parenchyma from binding and/or endocytosis to the brain microvasculature is important, the present studies use a dextran density centrifugation step to deplete brain homogenate of the vasculature. In addition, 3H-labeled native albumin is used as a vascular space marker to account for release of capillary contents into the postcapillary supernatant following homogenization of brain. This study demonstrates rapid transport of cationized IgG or cationized albumin into brain, as these compounds achieve a volume of distribution of 20-30 microliters/g within 10 min of arterial perfusion. Conversely, acetylated LDL, although rapidly bound by cerebral microvasculature, is shown not to undergo transport into the post-capillary compartment of brain parenchyma. These studies provide the basis for a sensitive, quantifiable technique for studying transport of radiolabeled blood-borne peptides and proteins across the BBB of anesthetized animals.

IgG molecules are potential neuropharmaceuticals that may be used for therapeutic or diagnostic purposes. However, IgG molecules are excluded from entering brain, owing to a lack of transport of these plasma proteins through the brain capillary wall, or blood-brain barrier (BBB). The Cationization of bovine immunoglobulin (Cohn fraction II) was performed as described for bovine albumin (9, 18). The isoelectric point (pI) of the native and cationized IgG was determined by polyacrylamide slab gel isoelectric focusing (IEF) by methods described previously (19). Samples (10 Al) containing 2 ug of either native or cationized IgG and 2% Nonidet P40 and 2% Pharmalyte 3-10 were applied to the middle of the gel. IEF was performed at 30 W, at a maximum voltage of 3000 V, and was performed for a duration of 4000 V-hr at 10°C. The IEF gels were fixed with 10% trichloroacetic acid (TCA) and 5% sulfosalicylic acid at room temperature for 60 min, washed in 30%o methanol/10%6 acetic acid for 30 min at 37°C and then overnight at room temperature, and the gels were stained with 0.2% Coomassie blue R-250 in 30% methanol/10%o acetic acid at room temperature for 60 min. The gels were destained with 30% methanol/10% acetic acid overnight and then photographed.To 4761The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

While interstitial cells of Cajal (ICC) in the urethra respond to nitric oxide (NO) donors by increasing cGMP, it remains unclear whether urethral ICC are functionally innervated by nitrergic nerves. We have addressed this issue in the rat and sheep urethra, where cGMP production and relaxation were compared in preparations subjected to electrical field stimulation (EFS; 2 Hz, 4 min) of nitrergic nerves or to exogenous S-nitroso-L-cysteine (SNC; 0.1 mM, 4 min). Upon EFS, cGMP immunoreactivity (cGMP-ir) was observed in both smooth muscle cells (SMC) and in spindle-shaped cells that contained c-kit and vimentin, features of ICC. Similarly, cGMP-ir was preferentially, but inconsistently, found in ICC of the outer muscle layer on exposure to SNC. We found separate functional groups of ICC within the urethra. Thus only ICC present in the muscle layers (ICC-M) but not those in the serosa (ICC-SR) and lamina propia (ICC-LP) seem to be specifically influenced by activation of neuronal NO synthase (nNOS). Thus the increase in cGMP-ir in the ICC-M induced by EFS was prevented by Nomega-nitro-L-arginine and ODQ. Urethral ICC did not express nNOS, although they were closely associated with nitrergic nerves. cGMP-ir was also present in the urothelium (in the rat but not in the sheep) and the vascular endothelium but not in neural structures, such as the nerve trunks and nerve terminals. Together, these results suggest a model of parallel innervation in which both SMC and ICC-M are effectors of nerve-released NO in the urethra.

Previous studies showing downregulation of blood-brain barrier (BBB) glucose-transporter activity in vivo in experimental diabetes have recently been questioned. Therefore, our investigations examined both the BBB glucose-transporter activity in experimental diabetes in vivo, with the use of the in situ internal carotid artery perfusion technique, and the microvessel glucose-transporter concentration, with quantitative Western immunoblots. These studies show that BBB glucose-transporter activity in vivo is decreased 44% in experimental diabetes (blood glucose concn 443 +/- 12 mg/dl), parallel with a 44% decrease in cerebral blood flow, a normal brain blood volume, and a 75% prolongation of capillary transit time. The glucose-transporter concentration is decreased 77 +/- 9% in microvessels isolated from diabetic rat brain compared with controls, as measured by quantitative Western blotting. These studies confirm the original observations that the BBB glucose transporter is downregulated in experimental diabetes, in association with a parallel decrease in cerebral blood flow. In addition, these studies, in conjunction with other recent experiments from this laboratory showing elevated glucose-transporter mRNA in diabetic rat brain capillaries, suggest the primary mechanism underlying the downregulation is a posttranscriptional inhibition of glucose-transporter mRNA translation.

1. Isolated transverse and longitudinally oriented preparations of sheep urethra precontracted with noradrenaline responded to electrical field stimulation (EFS) with stimulus-dependent non-adrenergic, non-cholinergic (NANC) relaxations. 2. Exogenous nitric oxide (NO) (acidified NaNO2), S-nitroso-L-cysteine (NC), sodium nitroprusside (SNP), 8-Br-cGMP, dibutyryl-cAMP, forskolin and isoprenaline each relaxed precontracted transverse urethral preparations in a concentration-dependent manner in order of potency: NC > forskolin > isoprenaline = SNP > NO > 8-Br-cGMP = dibutyryl-cAMP. Longitudinally oriented preparations responded to NO and NC with concentration-dependent relaxation, no different from that observed in transverse strips. 3. Methylene blue (MB) and oxyhaemoglobin (HbO2) mechanism independent of NO generation. 9. A dense network of NADPH diaphorase-positive fibres associated with both the circular and longitudinal smooth muscle layers of sheep urethra was found. 10. The possibility that a nitrosyl compound which releases NO in the target tissue is the NANC transmitter in sheep urethra is discussed. The data also suggest a role for increased cGMP levels in the relaxation mechanisms, whereas changes in cAMP levels, phosphoinositide hydrolysis or K+ channel activation do not seem to be involved.