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This investigation evaluated the microvascular permeability and ultrastructure of skeletal muscle capillaries in the skeletal muscle of diabetic (DIA) rats using two-photon laser scanning microscopy (TPLSM) and transmission electron microscopy (TEM). Microvascular permeability was assessed in the tibialis anterior muscle of control (CON) and DIA (streptozocin) male Wistar rats (n = 20, 10–14 wk) by in vivo imaging using TPLSM after fluorescent dye intravenous infusion. Fluorescent dye leakage was quantified to determine microvascular permeability. The ultrastructure was imaged by TEM ex vivo to calculate the size and number of intercellular clefts between capillary endothelial cells and also intracellular vesicles. Compared with control, the volumetrically determined interstitial fluorescent dye leakage, the endothelial cell thickness, and the number of intercellular clefts per capillary perimeter were significantly higher, and the cleft width was significantly narrower in tibialis anterior (TA) of DIA (interstitial fluorescent dye leakage, 2.88 ± 1.40 vs. 10.95 ± 1.41 µm3 × min × 106; endothelial thickness, 0.28 ± 0.02 vs. 0.45 ± 0.03 µm; number of intercellular clefts per capillary perimeter, 6.3 ± 0.80 vs. 13.6 ± 1.7/100 µm; cleft width, 11.92 ± 0.95 vs. 8.40 ± 1.03 nm, CON vs. DIA, respectively, all P < 0.05). The size of intracellular vesicles in the vascular endothelium showed an increased proportion of large vesicles in the DIA group compared with the CON group (P < 0.05). Diabetes mellitus enhances the microvascular permeability of skeletal muscle microvessels due, in part, to a higher density and narrowing of the endothelial intercellular clefts, and larger intracellular vesicles. NEW & NOTEWORTHY: Microvascular permeability in diabetic muscle was investigated using our original two-photon scanning laser microscopy method. Compared with controls, the leakage volume was increased in diabetic muscle, which was atrophic with smaller capillary diameter, endothelial cell thickening, and the appearance of more endothelial intercellular gaps or clefts, and large vesicles. Hyperpermeability was closely related to ultrafine structural changes of the capillary endothelial cell junctions. [ABSTRACT FROM AUTHOR]

Aging is associated with inspiratory muscle dysfunction; however, the impact of aging on diaphragm blood flow (BF) regulation, and whether sex differences exist, is unknown. We tested the hypotheses in young animals that diaphragm BF and vascular conductance (VC) would be greater in females and that aging would decrease the diaphragm's ability to increase BF with contractions. Young (4–6 mo) and old (22–24 mo) Fischer 344 rats were divided into four groups: young female (YF, n = 7), young male (YM, n = 8), old female (OF, n = 9), and old male (OM, n = 9). Diaphragm BF (mL/min/100 g) and VC (mL/mmHg/min/100 g) were determined, via fluorescent microspheres, at rest and during 1 Hz contractions. In YF versus OF, aging blunted the increase in medial costal diaphragm BF (44 ± 5% vs. 16 ± 12%; P < 0.05) and VC (43 ± 7% vs. 21 ± 12%; P < 0.05). Similarly, in YM versus OM, aging blunted the increase in medial costal diaphragm BF (43 ± 6% vs. 24 ± 12%; P < 0.05) and VC (50 ± 6% vs. 34 ± 10%; P < 0.05). In female rats, age increased dorsal costal diaphragm BF, whereas in male rats, age increased crural diaphragm BF (P < 0.05). Compared with age-matched females, dorsal costal diaphragm BF was lower in YM and OM (P < 0.05). In conclusion, aging results in an inability to augment medial costal diaphragm BF and alters regional diaphragm BF distribution in response to muscular contractions. Furthermore, sex differences in regional diaphragm BF are present in young and old animals. NEW & NOTEWORTHY: This is the first study, to our knowledge, to demonstrate that old age impairs the hyperemic response and alters blood flow distribution in the diaphragm of both female and male rats. In addition, this investigation provides novel evidence of sex differences in regional diaphragm blood flow distribution with contractions. The data presented herein suggest that aging compromises diaphragm vascular function and provides a potential mechanism for the diaphragm contractile dysfunction associated with old age. [ABSTRACT FROM AUTHOR]

Pulmonary hypertension (PH) is characterized by pulmonary vascular remodeling, respiratory muscle and cardiac impairments, and exercise intolerance. Specifically, impaired gas exchange increases work of the diaphragm; however, compromised contractile function precludes the diaphragm from meeting the increased metabolic demand of chronic hyperventilation in PH. Given that muscle contractile function is in part, dependent upon adequate blood flow (Q), diaphragmatic dysfunction may be predicated by an inability to match oxygen delivery with oxygen demand. We hypothesized that PH rats would demonstrate a decreased hyperemic response to contractions compared to healthy controls. Methods: Sprague-Dawley rats were randomized into healthy (HC, n = 7) or PH (n = 7) groups. PH rats were administered monocrotaline (MCT) while HC rats received vehicle. Disease progression was monitored via echocardiography. Regional and total diaphragm blood flow and vascular conductance at baseline and during 3 min of electrically-stimulated contractions were determined using fluorescent microspheres. Results: PH rats displayed morphometric and echocardiographic criteria for disease (i.e., acceleration time/ejection time, right ventricular hypertrophy). In all rats, total costal diaphragm Q increased during contractions and did not differ between groups. In HC rats, there was a greater increase in medial costal Q compared to PH rats (55% ± 3% vs. 44% ± 4%, p < 0.05), who demonstrated a redistribution of Q to the ventral costal region. Conclusion: These findings support a redistribution of regional diaphragm perfusion and an impaired medial costal hyperemic response in PH, suggesting that PH alters diaphragm vascular function and oxygen delivery, providing a potential mechanism for PH-induced diaphragm contractile dysfunction. [ABSTRACT FROM AUTHOR]

Previous work has shown that orthostatic hypotension associated with cardiovascular deconditioning results from inadequate peripheral vasoconstriction. We used the hindlimb-unloaded (HU) rat in this study as a model to induce cardiovascular deconditioning. The purpose of this study was to test the hypothesis that 14 days of HU diminishes vasoconstrictor responsiveness of mesenteric resistance arteries. Mesenteric resistance arteries from control (n = 43) and HU (n = 44) rats were isolated, cannulated, and pressurized to 108 cm [H.sub.2]O for in vitro experimentation. Myogenic (intralumenal pressure ranging from 30 to 180 cm [H.sub.2]O), KCl (2-100 mM), norepinephrine (NE, [10.sup.-9]-[10.sup.-4] M) and caffeine (1-20 mM) induced vasoconstriction, as well as the temporal dynamics of vasoconstriction to NE, were determined. The active myogenic and passive pressure responses were unaltered by HU when pressures remained within physiological range. However, vasoconstrictor responses to KCl, NE, and caffeine were diminished by HU, as well as the rate of constriction to NE (C, 14.8 [+ or -] 3.6 [micro]m/s vs. HU 7.6 [+ or -] 1.8 [micro]m/s). Expression of sarcoplasmic reticulum [Ca.sup.2+] ATPase 2 and ryanodine 3 receptor mRNA was unaffected by HU, while ryanodine 2 receptor mRNA and protein expression were diminished in mesenteric arteries from HU rats. These data suggest that HU-induced and microgravity-associated orthostatic intolerance may be due, in part, to an attenuated vasoconstrictor responsiveness of mesenteric resistance arteries resulting from a diminished ryanodine 2 receptor [Ca.sup.2+] release mechanism. hindlimb unloading; vasoconstrictor responsiveness

Approximately 40% of patients with type 2 diabetes present with concurrent hypertension at the time of diabetes diagnosis. Increases in peripheral vascular resistance and correspondingly enhanced vasoconstrictor capacity could have profound implications for the development of hypertension and the progression of insulin resistance to overt diabetes. The purpose of this study was to determine whether skel[ET.sub.A]l muscle arteriolar vasoconstrictor dysfunction precedes or occurs concurrently with the onset of diabetes and hypertension. Male Zucker diabetic fatty (ZDF) rats were studied at 7, 13, and 20 wk of age to represent prediabetic and short-term and long-term diabetic states, respectively. Conscious mean arterial pressure (MAP), fasted plasma insulin and glucose, vasoconstrictor responses, and passive mechanical properties of isolated skel[ET.sub.A]l muscle arterioles were measured in prediabetic, diabetic, and age-matched control rats. Elevated MAP was manifest in short-term diabetes (control 117 [+ or -] l, diabetic 135 [+ or -] 3 mmHg) and persisted with long-term diabetes (control 113 [+ or -] 2, diabetic 135 [+ or -] 3 mmHg). This higher MAP was preceded by augmented arteriolar vasoconstrictor responses to norepinephrine and endothelin-1 and followed by diminished [b[ET.sub.A]]-adrenergic vasodilation and enhanced myogenic constriction in long-term diabetes. Furthermore, we demonstrate that diminished nitric oxide (NO) signaling underlies the increases in vasoconstrictor responsiveness in arterioles from prediabetic and diabetic rats. Arteriolar stiffness was not different between control and prediabetic or diabetic rats at any time point studied. Collectively, these results indicate that increases in vasoconstrictor responsiveness resulting from diminished NO signaling in skel[ET.sub.A]l muscle arterioles precede the development of diabetes and hypertension in ZDF rats. type 2 diabetes; vasoconstriction; nitric oxide; norepinephrine; endothelin-1

Type I diabetes reduces dramatically the capacity of skeletal muscle to receive oxygen (Q[O.sub.2]). In control (C; n = 6) and streptozotocin-induced diabetic (D: n = 6, plasma glucose = 25.3 [+ or -] 3.9 mmol/l and C: 8.3 [+ or -] 0.5 mmol/l) rats, phosphorescence quenching was used to test the hypothesis that, in D rats, the decline in microvascular P[O.sub.2] [[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], which reflects the dynamic balance between [O.sub.2] utilization (V[O.sub.2]) and Q[O.sub.2]] of the spinotrapezius muscle after the onset of electrical stimulation (1 Hz) would be faster compared with that of C rats. [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] data were fit with a one or two exponential process (contingent on the presence of an undershoot) with independent time delays using least-squares regression analysis. In D rats, [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] at rest was lower (C: 31.2 [+ or -] 3.2 mmHg; D: 24.3 [+ or -] 1.3 mmHg, P < 0.05) and at the onset of contractions decreased after a shorter delay (C: 13.5 [+ or -] 1.8 s; D: 7.6 [+ or -] 2.1 s, P < 0.05) and with a reduced mean response time (C: 31.4 [+ or -] 3.3 s; D: 23.9 [+ or -] 3.1 s, P < 0.05). [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] exhibited a marked undershoot of the end-stimulation response in D muscles (D: 3.3 [+ or -] 1.1 mmHg, P < 0.05), which was absent in C muscles. These results indicate an altered V[O.sub.2]-to-Q[O.sub.2] matching across the rest-exercise transition in muscles of D rats. streptozotocin diabetes; oxygen uptake kinetics; exercise intolerance; muscle oxygen delivery; phosphorescence quenching