Substance P release in response to cardiac ischemia from rat thoracic spinal dorsal horn is mediated by TRPV1.

Spinal cord stimulation (SCS) inhibits substance P (SP) release and decreases the expression of the transient receptor potential vanilloid 1 (TRPV1) in the spinal cord at thoracic 4 (T4) during cardiac ischemia in rat models (Ding et al., 2007). We hypothesized that activation of TRPV1 in the T4 spinal cord segment by intermittent occlusion of the left anterior descending coronary artery (CoAO) mediates spinal cord SP release. Experiments were conducted in urethane-anesthetized Sprague-Dawley male rats using SP antibody-coated microprobes to measure SP release at the central terminal endings of cardiac ischemic-sensitive afferent neurons (CISAN) in the spinal T4 dorsal horns. Vehicle, capsaicin (CAP; TRPV1 agonist) and capsazepine (CZP; TRPV1 antagonist) were injected into the left T4 prior to stimulation of CISAN by intermittent CoAO (with or without upper cervical SCS). CAP induced endogenous SP release from laminae I and II in the T4 spinal cord above baseline. Conversely, CZP injections significantly inhibited SP release from laminae I-VII in the T4 spinal cord segment below baseline. CZP also attenuated CoAO-induced SP release, while T4 injections of CZP with SCS completely restored SP release to basal levels during CoAO activation. CAP increased the number of c-Fos (a marker for CISAN activation) positive T4 dorsal horn neurons compared to sham-operated animals, while CZP (alone or during CoAO and SCS+CoAO) significantly reduced the number of c-Fos positive neurons. These results suggest that spinal release of the putative nociceptive transmitter SP occurs, at least in part, via a TRPV1 mechanism.

Oral use of interferon-alpha stimulates ISG-15 transcription and production by human buccal epithelial cells.

ISG-15 is a 15-kDa protein encoded by an interferon (IFN)-stimulated gene (ISG), which is transcriptionally regulated by IFN-alpha and IFN-beta. Considered as part of the cytokine network, ISG-15 has the potential to amplify the immunomodulatory effects of these IFNs by enhancing IFN-gamma production, natural killer cell proliferation, and lymphokine-alphactivated killer cell cytotoxicity. To understand better the mechanism(s) of action of orally administered IFN-alpha, we have studied the effect of IFN-alpha on ISG-15 gene expression by human buccal epithelial cells (BEC). For in vitro studies, ISG-15 mRNA and protein levels were measured in BEC incubated for 0.5, 2, and 9 h with 100 or 1,000 IU/ml of human lymphoblastoid IFN-alpha. For in vivo studies, ISG-15 mRNA was measured in BEC samples collected at baseline, and 0.5, 2, and 9 h after 5-20 min of oral rinsing with 10 ml of IFN-alpha (1,000 IU/ml). ISG-15 mRNA was measured by reverse transcriptase polymerase chain reaction (RT-PCR), and ISG-15 protein production by Western Blot analysis. IFN-alpha augmented BEC ISG-15 gene expression in a concentration dependent manner both in vivo and in vitro. We conclude that orally administered IFN-alpha exerts its immunomodulatory effects in humans in part by upregulating the production of ISG-15 by BEC, thereby enhancing the immune reactivity of mucosa-associated lymphocytes.

Multifunctional cytokine expression by human coronary endothelium and regulation by monokines and glucocorticoids.

Human endothelium is capable of expressing a variety of molecules, including cytokines and growth factors, critical to inflammation. This aspect of coronary endothelium has not been studied in detail. In this study, we report, for the first time, expression of multifunctional cytokines by human coronary artery endothelial cells (HCAEC) and their regulation by inflammatory cytokines and glucocorticoids. We also compared expression of cytokine transcripts in two additional cell lines derived from pulmonary artery (HPAEC) and umbilical vein (HUVEC) endothelium. HCAEC expressed transcripts for interleukin 5 (IL-5), IL-6, IL-8, and monocyte chemotactic protein-1 (MCP-1) constitutively. Induction of IL-1alpha, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), and MCP-1 was seen following treatment with TNFalpha. We found no expression of IL-1RA, IL-2, IL-4, IL-13, TNF-alpha, or IFN-gamma in HCAEC. IL-1beta and TNF-alpha synergistically induced IL-6 and GM-CSF and additively induced IL-8 and MCP-1 production, while IL-2, IL-10, IFN-alpha, and IFN-gamma had little or no additional effects. Interestingly, no IL-1alpha or IL-5 protein product was found even after maximal stimulation of HCAEC. No significant differences were seen in the profile of cytokine genes expressed by HCAEC, HPAEC, or HUVEC. Glucocorticoids inhibited IL-8 production from all three cell lines. This study demonstrates that human coronary endothelial cells are capable of expressing a wide variety of multifunctional cytokines which may be of relevance to vascular inflammation.

Resting distribution and stimulated translocation of protein kinase C isoforms alpha, epsilon and zeta in response to bradykinin and TNF in human endothelial cells.

Protein kinase C (PKC) has been linked to functional and morphological changes in endothelial cells involved in increased microvessel permeability. Bradykinin and TNF are potent inflammatory mediators which translocate PKC from the cytosol to the membrane of various cell types, including endothelial cells. The PKC isoforms alpha, epsilon and zeta have been demonstrated as the most prominent in human umbilical vein endothelial cells (HUVEC). We propose that bradykinin and TNF cause increased microvascular permeability via a PKC-dependent endothelial cell signalling pathway. HUVEC were incubated at 37 degrees C and 5% CO2 for 1 min, 15 min and 3 h with either bradykinin (1 microM) or TNF (100 U/ml). PMA incubation served as a positive control (100 nM, 15 min). Cytosolic and membrane-bound extracts were obtained by incubation in digitonin (0.5%) and Triton X100 (1%). PKC isoforms were assayed by Western blot and membrane fractions calculated. These experiments revealed that: HUVEC clearly displayed a non-uniform basal membrane fraction distribution of PKC isoforms, with zeta (35.4%) greater than epsilon (30.6%) and both much greater than alpha (8.6%); Bradykinin caused significant translocation of PKC alpha with 15 min and 3 h of treatment but not 1 min; TNF caused dramatic translocation of PKC alpha at 1 min treatment which subsided at 15 min and 3 h but remained significantly elevated; and PMA caused dramatic translocation of alpha and epsilon but not zeta. Treatments of bradykinin and TNF that translocated PKC also showed cytoskeletal rearrangement of rhodamine-phalloidin stained actin, causing it to become more prevalent near cell membranes and concentrated at focal points between cells. These results suggest that PKC alpha may contribute to long term low grade increases in microvessel permeability in response to bradykinin, and that PKC alpha could be involved in both transient and sustained microvessel permeability changes induced by TNF. Also, cytoskeletal actin organization appears to be a downstream pathway in the activation process, possibly leading to alteration in endothelial cell shape and contact points.

Bradykinin and tumor necrosis factor-alpha alter albumin transport in vivo: a comparative study.

These studies indicate that tumor necrosis factor-alpha (TNF alpha) alters albumin permeability and unlike bradykinin (BK) the increased albumin permeability lasts for the duration of the application. Neither agonist requires the presence of white blood cells or other blood-borne substances to produce this inflammatory response. These experiments were completed in the in situ, microcannulated, perfused venules of the mesentery in the anesthetized hamster. Albumin transport was measured using intravital fluorescence microscopy, TRITC-labeled albumin, and densitometric tracking. Further, by varying the intravascular pressure, the hydraulic (Lp(1 sigma)) and diffusive permeability (P0) coefficients of these microvessels were determined. Both BK and TNF alpha produced an increase in albumin flux, which was dependent upon the dose and time domains. This response was present when the agonists were given by either intra- or extravascular presentation. Both hydraulic coupling and microvascular permeability were increased by BK and TNF alpha. TNF alpha increased albumin permeability rapidly and its effect lasted as long as TNF alpha was present, whereas the increased albumin transport by BK was biphasic. The results implicate a dynamic modification in the microvascular wall to these inflammatory agonists and the mechanism(s) for transduction in the endothelium are quite different.

Heterogeneity of endothelial cell function for angiotensin conversion in serial-arranged arterioles.

The involvement of the endothelial cell in the vasoconstriction induced by angiotensin I and II (AI, AII), and norepinephrine (NE) was studied in microvessels of the hamster cheek pouch before and after the following procedures: endothelial impairment by light-dye treatment, inhibition of angiotensin-converting enzyme (ACE), blockade of endothelium-derived relaxing factor (EDRF) and inhibiting prostaglandin (PG) synthesis. The results showed that in large 2nd-order arterioles, endothelial impairment did not affect the vasoconstrictor activity of AII and NE, nor did it alter ACE activity. However, in small 4th-order arterioles, endothelial impairment significantly reduced angiotensin conversion without altering the vasoconstrictor responses to either AII or NE. Thus, the endothelium plays differential roles in the modulation of local angiotensin conversion in these distinct segments of serial-arranged arterioles. Furthermore, it is unlikely that the vasoconstrictor response to AII in these arterioles is modulated by the endothelium through a pathway involving the release of EDRF or PGs.

Contributions of K+, Na+, and Cl- to the membrane potential of intact hamster vascular endothelial cells.

The transmembrane potential (Vm) of vascular endothelial cells (EC) is an important property that may be involved in intra- and intercellular signal transduction for various vascular functions. In this study, Vm of intact aortic and vena caval EC from hamsters were measured using conventional microelectrodes. Vascular strips with the luminal surface upwards were suffused in a tissue chamber with Krebs solution in physiological conditions. The resting Vm of aortic and vena caval EC was found to be -40 +/- 1 mV (n = 55) and -43 +/- 1 mV (n = 15), respectively. The Vm recordings were confirmed to have originated from EC by scanning and transmission electron microscopy combined with the comparison of electrical recordings between normal and endothelium-denuded aortic strips. The input resistance varied from 10-240 M omega, which implied the presence of electrical coupling between vascular EC. Elevating the K+ level in the suffusate from 4.7 mM to 50 and 100 mM depolarized aortic EC by 19% and 29% and vena caval EC by 18% and 29%, respectively. These low percentages indicated a relatively small contribution of [K+] to the resting Vm of vascular EC. A positive correlation (r > 0.69) between the resting Vm and the magnitude of depolarization by the high [K+]o may be related to the involvement of voltage-dependent K+ channels. The hyperpolarization caused by lowering both [Na+]o and [Cl-]o suggested the disengagement of some electrogenic transport systems in the membrane, such as a Na(+)-K(+)-Cl- cotransporter. The transference number (t(ion)), as an index of membrane conductance for specific ions, was calculated for K+ (15-20%), Na+ (16%), and Cl- (9-15%), demonstrating that both Na+ and Cl- as well as K+ contribute to the overall resting Vm. Our study documented some basic electrophysiology of the vascular EC when both structural and functional properties of the cell were maintained, thus furthering the understanding of the essential role of endothelial cells in mediating vascular functions.

Angiotensin II binding sites in the hamster brain: localization and subtype distribution.

This study was designed to characterize the distribution of angiotensin II (AII) binding sites in the hamster brain. Brain sections were incubated with [125I][sar1,ile8]-angiotensin II in the absence and presence of angiotensin II receptor subtype selective compounds, losartan (AT1 subtype) and PD123177 (AT2 subtype). Binding was quantified by densitometric analysis of autoradiograms and localized by comparison with adjacent thionein stained sections. The distribution of AII binding sites was similar to that found in the rat, with some exceptions. [125I][sar1,ile8]-angiotensin II binding was not evident in the subthalamic nucleus and thalamic regions, inferior olive, suprachiasmatic nucleus, and piriform cortex of the hamster, regions of prominent binding in the rat brain. However, intense binding was observed in the interpeduncular nucleus and the medial habenula of the hamster, nuclei void of binding in the rat brain. Competition with receptor subtype selective compounds revealed a similar AII receptor subtype profile in brain regions where binding is evident in both species. One notable exception is the medial geniculate nucleus, predominately AT1 binding sites in the hamster but AT2 in the rat. Generally, the AII binding site distribution in the hamster brain parallels that of the other species studied, particularly in brain regions associated with cardiovascular and dipsogenic functions. Functional correlates for AII binding sites have not been elucidated in the majority of brain regions and species mismatches might provide clues in this regard.

In vivo responses of allografted cerebral parenchymal arterioles to ethanol and angiotensin II: effect of calcium channel blockade.

The goals of these studies were to determine: 1) the effect of ethanol and angiotensin II on the diameter of allografted cerebral parenchymal arterioles in vivo, and 2) the effect of the calcium antagonist, verapamil, in modulating the responses of allografted cerebral parenchymal arterioles to ethanol and angiotensin II. Using a chamber technique, neonatal (< 24 hours old) cortical tissue was transplanted onto the cheek pouch of adult hamsters. Eight to thirteen days after allografting, hamsters were anesthetized with sodium pentobarbital (6.0 mg/100 grams i.p.), and allografted cerebral parenchymal arterioles were viewed using intravital microscopy. Diameter of allografted cerebral parenchymal arterioles was measured before (control), during and after topical application of ethanol (0.1%, 0.25%, 0.5%, 1.0%, and 2.0%) and angiotensin II (0.1 and 1.0 ng/ml). Application of ethanol and angiotensin II was repeated after changing the suffusion fluid to one containing verapamil (50 mg/L). We found that ethanol and angiotensin II produced dose-related constriction of allografted cerebral parenchymal arterioles. In addition, verapamil significantly attenuated vasoconstriction produced by ethanol and angiotensin II. Thus, our findings suggest that ethanol and angiotensin II cause constriction of allografted cerebral parenchymal arterioles through a calcium-dependent mechanism.

Differential role of endothelial function on vasodilator responses in series-arranged arterioles.

Both in vitro and in vivo studies have revealed that removal of vascular endothelial cells abolishes the vasodilation to acetylcholine (Ach) but not sodium nitroprusside (SNP). Differential properties of endothelial cells in the series-arranged arterioles to vasodilator responses have not been studied. In this study, the cheek pouch microcirculation from the golden syrian hamster anesthetized with sodium pentobarbital (6 mg/100 g body wt, ip) was prepared for intravital microscopy. Measurements of lumen diameters of small series-arranged arterioles (2nd- and 4th-order) were made before, during, and after topical microapplication of different doses of either Ach or SNP. After control measurements, a light-dye (L-D) technique utilizing sodium fluorescein (FITC-dextran(150K), 50 mg/100 g body wt, iv) and illuminating a discrete area of the arteriole with 490-nm-wavelength light for 3 (4th) or 10 (2nd) min was used to impair endothelial cell function without damaging vascular smooth muscle cells. Responses to vasoactive substances for both 4th-order (10-20 microns) and second-order (30-50 microns) arterioles were retested. Vasodilatory responses to 10(-7) M Ach and SNP also were tested with and without the presence of NG-monomethyl L-arginine (L-NMMA), an inhibitor of EDRF/NO formation. In the control state, Ach and SNP produced a focal, dose-dependent increase in diameter in all arterioles tested. Endothelial impairment by L-D treatment significantly suppressed the vasodilator response to Ach in 4th- but not 2nd-order arterioles, whereas the SNP response was not significantly affected. Consistent with these observations, L-NMMA treatment significantly attenuated Ach-induced vasodilation in 4th-order arterioles, but it had no effect on 2nd-order arterioles. These studies document further the role of the endothelium in local modulation of arteriolar diameter in response to acetylcholine and demonstrate a differential effect for this response in series-arranged microvessels. Thus, there may be a heterogeneous distribution of endothelial cell functions for modulating vasodilator activity in microvessels.

Morphological study of bovine lung grafted into the hamster cheek pouch.

The hamster cheek pouch has been used extensively to study the modulation of microvascular responsiveness of native and transplanted tissues, because it is immunologically privileged. The purpose of this study was to determine the structural changes that occur over time in bovine lung tissue (donor) that was grafted into the hamster cheek pouch (recipient). Lungs from adult cows were cut into 1-mm-thick slices and grafted into the cheek pouch of adult Syrian golden hamsters (n = 60). After induction of anesthesia, bovine lung tissue was placed under the avascular tissue covering the cheek pouch, and the overlying skin was sutured. Intravital microscopy (IM) and transmission electron microscopy (TEM) of the cheek pouch and grafted tissue were performed 1, 7, 14, and 28 days after grafting. By using IM, we found blood flow throughout the grafted bovine lung tissue between days 7 and 14 post-transplantation. Both IM and TEM showed that the grafted tissue contained patent microvessels anastomosing with cheek pouch microvessels, alveolar structures, and interstitial tissue. Mast cell infiltration around microvessels of the grafted tissue was evident in all animals between days 14 and 28 post-grafting. No other inflammatory cells were identified throughout the observation period. By day 28 post-grafting, the entire lung tissue became fibrotic. We conclude that bovine lung tissue can be successfully transplanted into the hamster cheek pouch, that blood flow is established throughout the graft, and that prominent mast cell infiltration is associated with fibrosis of the graft 28 days after transplantation. We suggest that this model can be useful in studying pulmonary microvascular responses in situ.

Role of neutrophils in endotoxin-mediated microvascular injury in hamsters.

The purpose of this study was to examine the role of circulating neutrophils in endotoxin-induced increase in microvascular permeability in vivo. Fifteen hamsters were anesthetized, and a plastic chamber was placed in each cheek pouch to observe the microvasculature. Fluorescein-labeled dextran (FITC-D, 150 kDa) was injected intravenously, and changes in leaky sites and FITC-D clearance were measured in three groups: control (saline, n = 4), endotoxin suffusion (n = 6), and endotoxin suffusion after neutropenia induction (n = 5). We found a significant increase in leaky sites and FITC-D clearance with endotoxin (45 +/- 18/cm2 and 20 +/- 6 x 10(-6) ml/min, respectively; mean +/- SD, P less than 0.05) in comparison to control (7 +/- 6/cm2 and 7 +/- 5 x 10(-6) ml/min) and endotoxin suffusion in neutropenic animals (19 +/- 11/cm2 and 12 +/- 4 x 10(-6) ml/min). There was a significant correlation between the number of leaky sites and FITC-D clearance (r = 0.91, P less than 0.01) and between the number of circulating neutrophils and FITC-D clearance (r = 0.87, P less than 0.01). We conclude that endotoxin-mediated increase in microvascular permeability in the peripheral circulation is dependent in part on circulating neutrophils.

Antioxidants attenuate endotoxin-induced microvascular leakage of macromolecules in vivo.

The purpose of this study was to examine whether antioxidants attenuate endotoxin-induced microvascular hyper-permeability for macromolecules in the hamster cheek pouch. Twenty-two adult male Syrian hamsters were anesthetized, and a removable plastic chamber was placed in the cheek pouch to observe and collect suffusate from the microvasculature. Fluorescent-labeled dextran (FITC-D; mol wt 150,000) was injected intravenously, and changes in the number of microvascular leaky sites and microvascular clearance of FITC-D were measured in five groups: saline control (group 1, n = 4), endotoxin (0.1 mg/ml) suffusion for 120 min (group 2, n = 6), endotoxin plus dimethyl sulfoxide (1.0 g/kg iv; group 3, n = 4), endotoxin plus allopurinol (30 mg/kg ip; group 4, n = 4), and endotoxin plus dimethyl sulfoxide and allopurinol (group 5, n = 4). The number of leaky sites and the FITC-D clearance were significantly higher in group 2 [45 +/- 18 (SD) sites/cm2 and 20 +/- 6 X 10(-6) ml/min, respectively; P less than 0.01] than in group 1 (7 +/- 6 sites/cm2 and 7 +/- 5 X 10(-6) ml/min), group 3 (9 +/- 5 sites/cm2 and 8 +/- 2 X 10(-6) ml/min), group 4 (11 +/- 7 sites/cm2 and 9 +/- 4 X 10(-6) ml/min), and group 5 (11 +/- 6 sites/cm2 and 7 +/- 1 x 10(-6) ml/min). The leaky sites appeared predominantly in postcapillary venules. There was a positive and significant correlation between the number of leaky sites and FITC-D clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Graded modulation of frog microvessel permeability to albumin using ionophore A23187.

We investigated the exchange of water and macromolecules across venular microvessels after permeability was increased. Quantitative fluorescence microscopy was used to measure albumin permeability coefficients in individually perfused microvessels of decerebrate frogs. Control permeability coefficient was 2.3 +/- 0.25 X 10(-7) cm/s. Solvent drag increased the apparent solute permeability coefficient (Ps) by 0.57 +/- 0.05 X 10(-7) cm/s for each cmH2O increase in microvessel pressure. The divalent cation ionophore A23187 (0.1-5 microM) produced a transient increase in Ps to a peak value (within 1-3 min), followed (after 4-8 min) by a sustained increase in permeability (16-34% of peak values). Peak values of Ps were 13 and 80 times control for 0.1 and 5 microM A23187, respectively. Both diffusion and solvent drag contributed to the sustained increase in Ps. The equivalent pore radius of the structures determining diffusion and solvent drag was less than or equal to 25 nm during the sustained increase in permeability, smaller than observed gaps between adjacent endothelial cells. The basement membrane and a fibrous matrix secreted by endothelial cells into the gaps may offer resistance to exchange in the high permeability state.

Albumin extravasation rates in tissues of anesthetized and unanesthetized rats.

Bovine serum albumin (BSA) labeled with 131I was injected intravenously in chronically prepared, unanesthetized rats and into pentobarbital-anesthetized rats that had received 2 ml 5% BSA to help sustain plasma volume. Initial uptake rates (clearances) in skin, skeletal muscles, diaphragm, and heart (left ventricle) were measured over 1 h. BSA labeled with 125I was injected terminally to correct for intravascular 131I-BSA. Observed clearances were in the following order in both groups of animals: heart much greater than diaphragm approximately equal to skin greater than resting skeletal muscles. Differences between unanesthetized and anesthetized animals were small and inconsistently directed. Our results suggest that the lower albumin clearances reported in the literature for anesthetized rats are not the result of their immobility or any direct effect of anesthesia on albumin transport in these tissues. The lower transport rates appear to result indirectly from changes produced by anesthesia and/or surgery in controllable parameters such as plasma volume and intravascular protein mass.

In vivo microscopy of the cerebral microcirculation using neonatal allografts in hamsters.

Studies were performed to characterize the morphology and vascular reactivity of the allografted cerebral microcirculation. Cerebral cortical tissue was allografted into the cheek pouch of the hamster so that cerebral parenchymal vessels could be studied. The vascular morphology was characterized by a large number of looping vessels. The ultrastructural examination indicated viable cerebral tissue containing typical vessels, that is, "tight" junctions, not like those of the cheek pouch. Also, the microvasculature was impermeable to 150, 70, and 20 kDa fluorescein isothiocyanate dextrans. Angiotensin II and norepinephrine caused constriction of the cerebral vessels whereas adenosine caused dilation. Isoproterenol did not affect cerebral arterioles; however, it dilated cheek pouch arterioles. Thus, this preparation provides a satisfactory model for studying the living cerebral microcirculation.

Angiotensin reactivity in the cheek pouch of the renovascular hypertensive hamster.

Increased reactivity to vasoconstrictor agents and decreased arteriolar luminal diameter have been implicated in the maintenance of hypertension. The same hamster cheek pouch microvessels were tested for angiotensin I (Ang I) and angiotensin II (Ang II) reactivity before and 10 to 14 days after Grollman (two-kidney, one figure-8) or sham operation. Microvascular geometric parameters were measured before and after a maximal vasodilator dose of adenosine. Then maximal vasoconstrictions to Ang I or Ang II were measured: Ang I and Ang II were applied adjacent to arterioles (10(-2)-10(0) pmol) and venules (10(-1) pmol) in 10-microliter aliquots for 1 minute. Blood pressure (178 +/- 11/133 +/- 8 mm Hg) of renovascular hypertensive hamsters was elevated significantly over blood pressure of sham-operated hamsters (120 +/- 11/97 +/- 10 mm Hg). No change was observed in venular geometry or reactivity in renovascular hypertensive hamsters. Arteriolar luminal diameter, wall thickness, wall/lumen ratio, and wall area were not altered in hypertensive hamsters in the normal or vasodilated state; vasodilator capacity was the same in all groups. Conversion of Ang I to Ang II (response to Ang I divided by response to Ang II) for first-order and Third-order arterioles and third-order venules was 74 +/- 5, 79 +/- 3, and 72 +/- 6%, respectively, and was unaltered in renovascular hypertensive hamsters. Although vessel geometry was not altered, there was a significant shift to the left of the Ang I and Ang II dose-response curves of first-order and third-order arterioles, indicating increased sensitivity to these vasoconstrictors.(ABSTRACT TRUNCATED AT 250 WORDS)

Extravasation of macromolecules and vascular reactivity of microvessels in response to nicotine in the hamster.

The effects of nicotine on the microvasculature were assessed in the hamster cheek pouch and in fetal tissue grafted into the cheek pouch. Transvascular exchange of FITC-dextran (70-150 K) was measured in the cheek pouch of normal hamsters challenged with either intravenous or suffused nicotine, and in streptozotocin-induced, diabetic hamsters challenged for one week with nicotine delivered by a mini-osmotic pump. The effects of nicotine on microvascular diameter were measured in cheek pouch vessels and in grafts 9-12 days after transplantation. Suffused nicotine did not cause leaky site formation or alter dextran clearance from the pouch. Intravenous nicotine had no effect on either of these parameters but potentiated histamine-induced leaky site formation (40%) and clearance (20%); clearance but not leaky site formation was normalized after cessation of nicotine infusion. Chronic nicotine treatment of diabetic hamsters had no effect on either basal or histamine-induced extravasation as monitored by leaky site or clearance measurements. Suffused nicotine had no effect on arteriolar diameter in the cheek pouch, or in renal, pulmonary or atrial allografts. These results indicate that nicotine can modulate histamine-induced extravasation of macromolecules but has no effect on diameter of arterioles in the non-adrenergically innervated vascular beds studied.