Bioactivation of monocrotaline by P-450 3A in rat liver.

Monocrotaline (MCT) is bioactivated in liver cytochrome P-450s to MCT pyrrole (MCTP), which primarily injures the lung endothelium to result in the development of pulmonary hypertension (PH) in rats. However, whether there is a relation between the degree of PH and the activity of liver cytochrome P-450 to convert MCT to MCTP remains unclear. To examine the relation between these physiological and biochemical changes, we first measured the severity of MCT-induced (20 mg/kg) PH in male, female, castrated male, and phenobarbital (PB, liver P-450s inducer)-pretreated male rats. The degree of right ventricular hypertrophy was more severe in PB-pretreated male than in control male rats. It was also more severe in male than in either female or castrated male rats, suggesting that sex-specific P-450s could be involved in the metabolic pathways of MCT in the liver. Further to explore which of the isozymes (2A2, 2C11, and 3A) of P-450s in the liver is responsible for the bioactivation of MCT, we measured the rate of MCTP production in hepatic microsomes by a modified Mattock's method. Treatment of male rats with PB and pregnenolone 16alpha-carbonitrile (PCN), which is the specific inducer of P-450 3A, increased the rate of MCTP production, suggesting that P-450 3A may contribute to the conversion to pyrrole. Therefore we measured the amount of P-450 3A protein by immunoblotting and attempted to inhibit MCT metabolism by using antibodies to P-450 3A. P-450 3A was significantly induced by PCN (6.5-fold) and PB (4.6-fold) treatment and reduced by castration (0.38-fold). The amount of P-450 3A was closely correlated with the production of MCTP, and the conversion of MCT to MCTP was strongly inhibited by antibodies against P-450 3A. These results indicated that P-450 3A was predominantly responsible for the metabolism of MCT to MCTP in rat liver and suggested a tight linkage between the degree of PH and the activity of liver P-450 3A.

[Interleukin-2 activity in monocrotaline-treated rat lungs].

To study the relationship between cytokines and the development of monocrotaline-induced pulmonary hypertension, monocrotaline was given and interleukin-2 was measured. The amount of interleukin-2 produced by pulmonary cells obtained by bronchoalveolar lavage was high only on the 14th day after monocrotaline injection (p < 0.01). This suggests that many kinds of cells in the monocrotaline-treated rat lung were activated by cytokines, and that these interactions play an important role in the development of monocrotaline-induced pulmonary hypertension in rats.

[Changes in smooth muscle cell proliferation in pulmonary arteries of rats given monocrotaline].

To study the relationship between proliferation of smooth muscle cells and structural changes in arteries of rats given monocrotaline, light microscopy with immunohistochemistry for bromodeoxyuridine (BrdU) was done after a single subcutaneous injection of monocrotaline. In increase in DNA synthesis in smooth muscle cells was seen from 3 days until 14 days after administration. Since this increase was seen before pulmonary hypertension and medial thickness developed some mechanisms that induce proliferation of pulmonary atrial smooth muscle may have been triggered soon after monocrotaline injection.

[Relationship between the converting ability of liver microsomes and monocrotaline-induced pulmonary hypertension in male, female and castrated male rats].

It is well known that the initial reaction of monocrotaline-induced pulmonary hypertension in rats (MPH) is injury to the endothelial cells of pulmonary vascular bed by monocrotaline-pyrrole (MP), which is converted from monocrotaline (M) by cytochrome P450 monooxygenase in hepatic microsomes. It is also known that the degree of MPH differs between sexes. The mechanisms of MPH remain, however, to be elucidated. The purpose of this study is to clarify the relationship between the converting ability of hepatic microsomes and the sexual difference in MPH using castrated male rats. A 40 mg/kg dose of M was given to fifteen 6 week-old male, twelve 6 week-old female and fifteen 6 week-old castrated male, Sprague-Dawley, rats. The castration was done at three weeks of age. Four weeks after M administration, the right ventricular systolic pressure (RVSP) and the right ventricular to total ventricular weight ratio (RV/T) were measured as indices of pulmonary hypertension. Livers were taken from six 6 week-old male, six, 6 week-old female and six 6 week-old castrated male, Sprague-Dawley, rats and then homogenized and centrifuged to extract hepatic microsomes. M, at 3.3 mM, was added to concentrated hepatic microsomes (0.25 to 1.5 mg/ml) in order to produce MP. The concentration of the MP was measured using a modification of Mattock's method. The mean value of RVSP was 86.5 mmHg in males, 59.6 mmHg in females and 73.9 mmHg in castrated males. The mean value of RV/T was 0.453 in males, 0.358 in females and 0.403 in castrated males.(ABSTRACT TRUNCATED AT 250 WORDS)

[Three-dimensional CT images of the lung--preliminary study using inflated lung specimens].

Three-dimensional CT images of six inflated lung specimens (4 lung cancer, 1 bronchiectasis, 1 hamartoma) were reconstructed from contiguous serial sections to study some probable problems in the clinical application of the technique. Optimal thickness and space of sections were evaluated, and contiguous 1.5-mm serial sections were found to provide a clear 3-D image with high fidelity. It was difficult to set a proper threshold to create clear images because a wide CT window is inconsistent with low noise. The images of tubular and linear structures such as from bronchi and vessels demonstrated higher resolution when reconstructed from scanning in the more perpendicular cross-sectional direction to their axis. Although 3-D images obtained here were not as clear as expected, technological advances such as helical CT or MRI may provide 3-D images with sufficient resolution to be applied clinically.

[Effects of various doses of monocrotaline administration on the development of pulmonary hypertension and its regression in rats].

We observed the time course of hemodynamic and pathological changes after single injection of various dose of monocrotaline (Mct) to investigate the dose-dependent effects on the induction and regression of pulmonary hypertension in rat: A hundred four-week old male Sprague-Dowley rats were divided into five groups and each group, except the control group, received 10 mg, 20 mg, 30 mg or 40 mg/kg Mct, respectively. The experimental periods were nine weeks after monocrotaline injection. At the third, sixth and ninth week after treatment, the survival rate, cardiac catheterization and pathological changes were evaluated. All rats given 30 mg or 40 mg per kg of Mct died within five weeks. In the third week after the treatment, elevation of the right ventricular systolic pressure (RVSP), the grade of right ventricular hypertrophy (RVH) and histological change showed no significant difference among rats receiving 20, 30 or 40 mg/kg Mct injection. Almost all rats given 10 mg or 20 mg/kg Mct survived through the experimental period of nine weeks. Rats given 10 mg per kg of Mct did not develop pulmonary hypertension or pathological abnormalities in the lungs. Rats receiving 20 mg/kg Mct showed transient elevation of RVSP, RVH and pulmonary histological changes in the early phase, but these findings regressed by the ninth week of the experiment. Namely, rats which received 20 mg pr kg of Mct revealed transient elevation of right ventricular systolic pressure, right ventricular hypertrophy and pulmonary histological changes only in the early phase and these changes regressed gradually thereafter. These results indicate some kind of transient and reversible factor may play a role in the development and regression of Mct-induced pulmonary hypertension in rats.