Cholinergic innervation of the human pulmonary circulation

Cholinesterase activity in human pulmonary arteries and veins: correlation with mRNA levels

Isolated intact human pulmonary arteries and veins were used to determine the acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) activities in the absence or presence of two selective cholinesterase (ChE) inhibitors, iso-OMPA or BW284c51, respectively. These results were compared with the mRNA levels for each enzyme in human pulmonary vessels. Total ChE activities measured in presence of acetylthiocholine (ACTI, 1 mM) in intact vascular preparations were 45+/-04 and 114+/-07 mU/g tissue in human pulmonary arteries (n=14) and veins (n=14), respectively. These activities were completely abolished in presence of 10 microM neostigmine. In both types of vessels AChE and BChE activities were observed. These activities were at least 2-fold higher in human pulmonary veins when compared with arteries and were correlated with the accumulation of the corresponding transcripts (n=8). In each type of vessel, similar total ChE activities were detected in homogenized and intact preparations, while in human bronchial preparations this activity was 5-fold higher in homogenates than in intact preparations. Together these results provide evidence that the ChE activities in human pulmonary vessels may be extracellular and that the higher activity measured in veins as compared to arteries was associated with the differential accumulation of the corresponding transcripts.

Cholinergic staining of bronchus- associated lymphoid tissue

The cholinergic staining of human bronchus-associated lymphoid tissue (BALT) was studied in humans. Morsels of the human lung (containing BALT) were harvested, after having obtained the appropriate approvals, during autopsies in 24 human subjects. The samples were stained by means of the enzymatic technique of acetylcholinesterase (AChE) and/or the monoclonal immunohistochemical method of choline acetyltransferase (ChAT). A morphometrical analysis was performed by means of quantitative analysis of images and statistical analyses of the data. AChE and proteins were also measured by biochemical assay. Our results demonstrate that both AChE and ChAT are localized in the BALT of young and old humans. These enzymes undergo age-related changes. The biochemical values of AChE are as follows: 22.3 +/- 2.5 international units in young subjects and 78.5 +/- 1.9 international units in old ones. The morphometrical values of AChE confirm the biochemical ones. The morphometrical data for ChAT are 31.6 +/- 1.4 conventional units in young subjects and 71.2 +/- 1.5 conventional units in old ones. Further results are needed to draw definite conclusions concerning the location and the distribution of these two enzymatic activities in BALT. In our opinion, the presence of AChE and ChAT in BALT can be both 'non-neuronal', with a role in general metabolism, and/or 'neuronal' with a role in neuroimmunomodulation.

Cholinergic innervation of BALT (bronchus associated lymphoid tissue) in rat

The presence and distribution of acetylcholinesterase (AChE) and cholineacetyl transferase activities (Chat) were examined in the bronchus-associated lymphoid tissue (BALT) of juvenile, adult and old rats. Histoenzymatic and immunochemical methods were used in association with quantitative analysis of images and statistical analysis of the data. Our results showed that both AChE and Chat activities were primarily confined to the BALT lymphoid cells. Only a low level of activity was observed in the sub-pleural parenchyma of the lung and in the wall of the bronchus. Moreover, both AChE and Chat activities in the BALT are specifically located in the lymphoid cells. Histoenzymatic staining and corresponding values of quantitative analysis of images confirmed morphological and immunochemical results. Finally, the intensity of histoenzymatic staining for AChE and of immunochemical staining for Chat in BALT of rats strongly decreases with age. On the basis of our results we hypothesize that both AChE and Chat activities may play an important role in BALT and both these enzymes undergo specific age-related changes.

Cholinesterase activity in human pulmonary arteries and veins

1. Human isolated pulmonary vessels were treated with cholinesterase (ChE) inhibitors to determine the role of these enzymes in regulating vascular muscle tone. In addition, kinetic parameters were determined for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in human pulmonary vessel homogenates. 2. Carbachol (CCh) and acetylcholine (ACh) were equipotent contractile agonists in human pulmonary arteries (pD2 values, 5.28 +/- 0.05 and 5.65 +/- 0.16; Emax, 0.91 +/- 0.26 and 0.98 +/- 0.30 g wt. for CCh and ACh, respectively; n = 7). In venous preparations, ACh was ineffective and CCh induced small contractions (Emax, 0.08 +/- 0.04 g wt; n = 13). 3. In human pulmonary arteries following pretreatment with tetraisopropylpyrophosphoramide (iso-OMPA, 100 microM), an increased sensitivity to the contractile agonist ACh was observed (pD2 values, 5.80 +/- 0.13 and 6.37 +/- 0.19 for control and treated preparations, respectively; n = 5). This pretreatment had no effect on the CCh concentration response curve. In contrast, human pulmonary veins pretreated with iso-OMPA failed to elicit a contractile response to ACh. 4. Neither Iso-OMPA nor neostigmine elicited concentration-dependent contractions in human isolated pulmonary arteries or veins. These results suggest the absence of sufficient spontaneous release of ACh to modulate human pulmonary vessel basal tone. 5. CCh was less potent than ACh in relaxing precontracted human isolated pulmonary arteries (pD2 value, CCh: 6.55 +/- 0.15 and ACh: 7.16 +/- 0.13, n = 4) and veins (pD2 value, CCh: 4.95 +/- 0.13; n = 5 and ACh: 5.56 +/- 0.17; n = 6). Pretreatment of vessels with either iso-OMPA or neostigmine did not modify ACh relaxant responses in either type of preparation. 6. In human pulmonary veins, the ChE activity was two fold greater than in arteries (n = 6). Vmax for AChE was 1.73 +/- 0.24 and 3.36 +/- 0.26 miu mg-1 protein in arteries and veins, respectively, whereas Vss for BChE was 1.83 +/- 0.22 and 4.71 +/- 0.17 miu mg-1 protein, in these respectively. 7. In human pulmonary arteries, BChE activity may play a role in the smooth muscle contraction but not on the smooth muscle endothelium-dependent relaxation induced by ACh. A role for ChE activity in the control of venous tone is presently difficult to observe, even though this tissue contains a greater amount of enzyme than the artery.

Autoradiographic localization of muscarinic acetylcholine receptors in the rat pulmonary vascular tree

The pharmacological characteristics and the anatomical localization of muscarinic receptors in the pulmonary vascular tree were investigated in lung sections of Wister-Kyoto (WKY) and spontaneously hypertensive rats (SHR). [3H]Quinuclidinyl benzylate [( 3H]QNB) was bound by sections of rat lung in a manner consistent with the labeling of muscarinic acetylcholine receptors, with a dissociation constant value (Kd) of 0.41 +/- 0.3 nM in WKY rats and of 0.37 +/- 0.2 nM in SHR. The density of muscarinic acetylcholine receptors was higher in sections of lung of WKY rats than of SHR. In the pulmonary vasculature these sites were associated with the smooth muscle of the medial layer of different size branches of the pulmonary artery and vein. No [3H]QNB binding sites were found within the endothelium in the blood vessels of either WKY rats or SHR. The density of [3H]QNB binding sites was significantly lower in the smooth muscle of pulmonary vein and its branches in SHR. There were no significant hypertension-dependent changes in the density and pattern of muscarinic receptors of pulmonary artery smooth muscle.

A study of nerves containing peptides in the pulmonary vasculature of healthy infants and children and of those with pulmonary hypertension

Nerves containing peptides that supply the human intrapulmonary vasculature were studied in 21 controls aged one month to 24 years and in 13 patients with pulmonary hypertension aged 11 days to eight years. An indirect immunofluorescence technique was used to study the distribution and relative density of nerve fibres containing the general neuronal marker, protein gene product 9.5; tyrosine hydroxylase; synaptophysin; neuropeptide tyrosine; vasoactive intestinal polypeptide; substance P, somatostatin; and calcitonin gene related peptide. At all ages in normal and hypertensive lungs neuropeptide tyrosine was the predominant neuropeptide associated with the pulmonary vascular nerves. In normal lungs the relative density of nerve fibres increased during childhood only in the arteries of the respiratory unit. Pulmonary hypertension was associated with the premature innervation of these arteries during the first year of life. Innervation of small, abnormally thick-walled pre-capillary vessels by predominantly vasoconstrictor nerves may help to explain the susceptibility of infants to pulmonary hypertensive crises.