Early effects of total hepatectomy on haemodynamic state and organ uptake of catecholamines in the pig

α1-Adrenoceptor-dependent vascular hypertrophy and remodeling in murine hypoxic pulmonary hypertension

Excessive proliferation of vascular wall cells underlies the development of elevated vascular resistance in hypoxic pulmonary hypertension (PH), but the responsible mechanisms remain unclear. Growth-promoting effects of catecholamines may contribute. Hypoxemia causes sympathoexcitation, and prolonged stimulation of α1-adrenoceptors (α1-ARs) induces hypertrophy and hyperplasia of arterial smooth muscle cells and adventitial fibroblasts. Catecholamine trophic actions in arteries are enhanced when other conditions favoring growth or remodeling are present, e.g., injury or altered shear stress, in isolated pulmonary arteries from rats with hypoxic PH. The present study examined the hypothesis that catecholamines contribute to pulmonary vascular remodeling in vivo in hypoxic PH. Mice genetically deficient in norepinephrine and epinephrine production [dopamine β-hydroxylase−/− (DBH−/−)] or α1-ARs were examined for alterations in PH, cardiac hypertrophy, and vascular remodeling after 21 days exposure to normobaric 0.1 inspired oxygen fraction (FiO2). A decrease in the lumen area and an increase in the wall thickness of arteries were strongly inhibited in knockout mice (order of extent of inhibition: DBH−/− = α1D-AR−/− > α1B-AR−/−). Distal muscularization of small arterioles was also reduced (DBH−/− > α1D-AR−/− > α1B-AR−/− mice). Despite these reductions, increases in right ventricular pressure and hypertrophy were not attenuated in DBH−/− and α1B-AR−/− mice. However, hematocrit increased more in these mice, possibly as a consequence of impaired cardiovascular activation that occurs during reduction of FiO2. In contrast, in α1D-AR−/− mice, where hematocrit increased the same as in wild-type mice, right ventricular pressure was reduced. These data suggest that catecholamine stimulation of α1B- and α1D-ARs contributes significantly to vascular remodeling in hypoxic PH.

Enhanced α1-adrenergic trophic activity in pulmonary artery of hypoxic pulmonary hypertensive rats

Mechanisms that induce the excessive proliferation of vascular wall cells in hypoxic pulmonary hypertension (PH) are not fully understood. Alveolar hypoxia causes sympathoexcitation, and norepinephrine can stimulate α1-adrenoceptor (α1-AR)-dependent hypertrophy/hyperplasia of smooth muscle cells and adventitial fibroblasts. Adrenergic trophic activity is augmented in systemic arteries by injury and altered shear stress, which are key pathogenic stimuli in hypoxic PH, and contributes to neointimal formation and flow-mediated hypertrophic remodeling. Here we examined whether norepinephrine stimulates growth of the pulmonary artery (PA) and whether this is augmented in PH. PA from normoxic and hypoxic rats [9 days of 0.1 fraction of inspired O2 (FiO2)] was studied in organ culture, where wall tension, Po2, and Pco2 were maintained at values present in normal and hypoxic PH rats. Norepinephrine treatment for 72 h increased DNA and protein content modestly in normoxic PA (+10%, P < 0.05). In hypoxic PA, these effects were augmented threefold ( P < 0.05), and protein synthesis was increased 34-fold ( P < 0.05). Inferior thoracic vena cava from normoxic or hypoxic rats was unaffected. Norepinephrine-induced growth in hypoxic PA was dose dependent, had efficacy greater than or equal to endothelin-1, required the presence of wall tension, and was inhibited by α1A-AR antagonist. In hypoxic pulmonary vasculature, α1A-AR was downregulated the least among α1-AR subtypes. These data demonstrate that norepinephrine has trophic activity in the PA that is augmented by PH. If evident in vivo in the pulmonary vasculature, adrenergic-induced growth may contribute to the vascular hyperplasia that participates in hypoxic PH.

Alpha(1)-adrenoceptor stimulation directly induces growth of vascular wall in vivo

Previous studies suggesting that norepinephrine is directly trophic for the vascular wall have been confounded by concomitant hemodynamic disturbances. Herein, a microcatheter connected to an osmotic minipump was implanted adjacent to the rat carotid for 2-wk perivascular suffusion of agents at systemic levels ~1,000 times below the threshold for altering arterial pressure. Norepinephrine decreased lumen and adventitial areas and circumference by 10, 14, and 5%, respectively (all P < 0.05); a nonsubtype-specific alpha(1)-adrenoceptor (AR) antagonist had no effect. When begun at the time of balloon injury, 2-wk norepinephrine increased lumen loss by 45%, increased neointimal area by 64% and collagen content by 33%, and reduced vessel circumference by 5% (all P < 0.05). alpha(1)-AR antagonists decreased neointimal area by 33% (all P < 0.05). alpha(1)A-AR antagonist reduced lumen loss by 70%, neointimal area by 54%, circumference decline by 84%, and adventitial thickening by 87% (all P < 0.05), whereas alpha(1B)-, alpha(1D)-, alpha(2)- and beta-AR antagonists were without effect. These are the first in vivo studies demonstrating that norepinephrine is directly trophic for the vascular wall and augments injury-induced intimal lesion growth.

Different alpha-adrenoceptors mediate migration of vascular smooth muscle cells and adventitial fibroblasts in vitro

Norepinephrine directly induces growth of the vascular wall, which may involve not only proliferation of smooth muscle cells (SMCs) and adventitial fibroblasts (AFBs) but also augmentation of their migration. To test this hypothesis, growth-arrested SMCs and AFBs from rat aorta were exposed to norepinephrine. Norepinephrine caused dose-dependent migration of both cell types that was dependent on chemotaxis. In contrast, platelet-derived growth factor (PDGF)-BB, used as a positive control, stimulated both chemotaxis and chemokinesis. Only alpha(1D)-adrenoceptors (AR) and alpha(2)-AR antagonists inhibited norepinephrine migration of SMCs, whereas norepinephrine migration of AFBs was only inhibited by alpha(1A)-AR and alpha(1B)-AR antagonists; beta-AR blockade was without effect. Norepinephrine and PDGF-BB were additive for AFB, but not SMC, migration. Stimulation of migration was reversed at high norepinephrine concentrations (10 microM); this inhibition was mediated by alpha(2)- and beta-ARs in AFBs but not in SMCs. Thus norepinephrine induces migration of SMCs and AFBs via different alpha-ARs. This action may participate in wall remodeling and norepinephrine potentiation of injury-induced intimal lesion growth.

Trophic effect of norepinephrine on arterial intima-media and adventitia is augmented by injury and mediated by different alpha1-adrenoceptor subtypes

In vivo studies have suggested that norepinephrine (NE) directly contributes to normal vascular wall growth and worsening of hypertrophy, atherosclerosis, and restenosis. However, it is unknown whether these effects are secondary to hemodynamic changes caused by systemic NE or alpha-adrenoceptor (AR) antagonists. Herein, we determined if NE directly stimulates growth of medial smooth muscle cells (SMCs) and adventitial fibroblasts (AFBs) that we have shown express alpha1-ARs in similar abundance. The rat aorta was isolated before injury, 4 days after, or 12 days after balloon injury, and maintained under circumferential tension in organ culture for 48 hours with 1 micromol/L NE. Intima-media and adventitia were separated and DNA content, protein synthesis, and protein content measured. In uninjured aorta, NE increased DNA and protein content similarly in adventitia, and increased only protein content in intima-media, suggesting AFB proliferation and SMC hypertrophy. In vessels isolated 4 or 12 days after injury, NE increased all 3 endpoints in both layers by up to 20-fold greater than in uninjured vessels. These effects were dose-dependent and were unaffected by alpha2- or beta-AR blockade (except increased DNA content in adventitia that was also inhibited by alpha2-AR blockade). Intima-media growth was blocked by KMD3213 (alpha1A-AR antagonist) and adventitial growth by AH11110A (alpha1B-AR antagonist), whereas BMY7378 (alpha1D-AR antagonist) had no effect. NE decreased SMC marker proteins (eg, alpha-smooth muscle actin and desmin) and augmented the changes induced by injury. These data suggest that prolonged stimulation of alpha1A- and alpha1B-ARs induces growth of SMCs and AFBs, respectively, that is significantly augmented by injury.

A possible increase in plasma norepinephrine by removal of the liver

BACKGROUND

It has recently been suggested that the human liver plays an important role in clearing plasma norepinephrine, especially in restricting most of the norepinephrine to reach the systemic circulation from the gut.

METHODS

We examined the changes in plasma catecholamine levels in a patient undergoing extracorporeal hepatic resection and 4 patients undergoing living-related orthotopic liver transplantation.

RESULTS

While the changes in plasma epinephrine levels were not necessarily consistent with the proposal that plasma catecholamine levels increase during the anhepatic period, plasma norepinephrine did show a transient increase in accordance with the anhepatic period in all cases. Although we could not rule out the increase in the inflow rate of norepinephrine into plasma, the interrupted hepatic elimination of norepinephrine, especially released from the gut, seemed to be partly responsible for the anhepatic period-associated increase in plasma norepinephrine.

CONCLUSION

The present finding might have the potential to improve perioperative management of patients undergoing extracorporeal hepatic resection and orthotopic liver transplantation.