Endothelial defect mediates attenuated vasorelaxant response to isoproterenol after lung transplantation

Elevated glucose impairs cAMP-mediated dilation by reducing Kv channel activity in rat small coronary smooth muscle cells

Hyperglycemia impairs endothelium-dependent vasodilation. In this study, we examined the effect of high glucose (HG) on vascular smooth muscle function. Rat small coronary arteries were freshly isolated or incubated for 24 h with normal glucose (NG; 5.5 mmol/l) or HG (23 mmol/l). In freshly isolated arteries, dilation to isoproterenol (Iso) was reduced by 3 mmol/l 4-aminopyridine (4-AP; 44 +/- 10% vs. 77 +/- 4%; P < 0.05) and further reduced by 4-AP + iberiotoxin (IbTX; 100 nmol/l; 17 +/- 2%). Dilation to forskolin was abolished by 4-AP (-3 +/- 17 vs. 73 +/- 9%). cAMP production was similar in NG and HG vessels. Dilations to Iso and forskolin were significantly reduced in HG arteries (Iso, 41 +/- 5% vs. 70 +/- 6%; forskolin, 40 +/- 4% vs. 75 +/- 4%) compared with NG arteries. A similar reduction was also observed to the dilation to papaverine. Endothelial denudation had no effect on Iso-induced dilation. In HG vessels, the reduced 4-AP-sensitive component of Iso-induced dilation was greater compared with the IbTX-sensitive component. Iso increased whole cell K+ current in NG cells but had little effect in HG cells. Similarly, 4-AP-, but not IbTX-sensitive, K+ currents were reduced in HG cells. These results suggest that HG impairs cAMP-mediated dilation primarily by reducing Kv channel function. We speculate that in addition to the endothelial dysfunction, altered smooth muscle function may also contribute to the reduced coronary vasodilation in diabetes.

Postnatal changes in beta-adrenoceptors in the lung and the effect of hypoxia induced pulmonary hypertension of the newborn

1. beta-adrenoceptor activation leads to pulmonary vasodilatation. The increase in circulating catecholamines at birth may assist the postnatal fall in vascular resistance by their activation. To study beta(1)- and beta(2)-adrenoceptors during postnatal adaptation, we used [(125)I]-iodocyanopindolol (ICYP) binding to lung membranes and sections to quantify and locate the binding sites in piglets from birth to 14 days of age and compared them with those in adult pigs. In addition, pulmonary hypertension was induced in newborn piglets by hypobaric hypoxia. 2. In lung membranes the equilibrium dissociation constant (K(d)) did not change with age for total beta-adrenoceptors or for beta(2)-adrenoceptors, but there was a significant increase in maximum binding sites (B(max)) between birth and 3 days of age. On tissue sections, B(max) increased between 3 days and adulthood with no change in K(d). 3. Binding sites of beta(1)- and beta(2)-adrenoceptors were localized to the bronchial epithelium, to endothelium of extra- and intra-pulmonary arteries and to lung parenchyma. Total beta-adrenoceptor density increased with age at all locations (P<0.05 - 0.01). At birth intrapulmonary arteries showed no binding, beta(2)-adrenoceptors appeared on day 1 and increased up to 14 days of age. beta(1)-adrenoceptors appeared by 3 days of age and increased with age. 4. Hypobaric hypoxia from birth led to attenuation in the normal postnatal increase in receptor number, but hypoxia from 3 - 6 days did not decrease receptor density. 5. The normal postnatal increase in beta-adrenoceptors suggests a potential for catecholamine induced dilatation in the lung during adaptation which is attenuated in pulmonary hypertension.

Pulmonary vasoregulation by endothelin in conscious dogs after left lung transplantation

We tested the hypothesis that regulation of the pulmonary circulation by endogenous endothelin (ET) during normoxia and hypoxia was altered in conscious dogs 1 mo after left lung autotransplantation (LLA). Sham-operated control and post-LLA dogs were chronically instrumented to measure the left pulmonary vascular pressure-flow (LP-Q) relationship. LP-Q plots were generated on separate days during normoxia and hypoxia (arterial PO(2) approximately 50 Torr) in the intact condition, after selective ET(A)-receptor inhibition (BQ-485), and after combined ET(A+B)-receptor inhibition (bosentan). Although LLA resulted in a chronic increase in pulmonary vascular resistance, the ET-receptor antagonists had no effect on the LP-Q relationship during normoxia in either group. The magnitude of hypoxic pulmonary vasoconstriction (HPV) was flow dependent in both groups, and the HPV response was potentiated post-LLA compared with control. ET(A)-receptor inhibition attenuated the HPV response to the same extent in both groups. ET(A+B)-receptor inhibition attenuated the HPV response to a greater extent than did ET(A)-receptor inhibition alone, and this effect was greater post-LLA compared with control. Plasma ET-1 concentration only increased during hypoxia in the LLA group. These results indicate that ET does not regulate the baseline LP-Q relationship in either group. Both ET(A)- and ET(B)-receptor activation mediate a component of HPV in conscious dogs, and the vasoconstrictor influence of ET(B)-receptor activation is enhanced post-LLA.