β-Carotene이 비타민 A로의 전환효율에 관한 실험적 연구

Abstract

[한글]

Experimental Studies on the Efficiency of Conversion of β-carotene to Vitamin A

Kei Young Choi, M.D.

Department of Biochemistry Graduate School, Yonsei University

(Directed by Professor Chung Suk Song, M.D. M.S.)

It is well known that in animals Vitamin A is formed from its

precursors(provitamin) which originally are obtained only from plants. These

precursors exsist as carotenoid pigments, the most important of which is

β-carotene.

Moore(1931) reported that β-carotene was converted to Vitamin A in rat's body.

Since then many investigators have studied the metabolism and absorption of

carotenoids. Davis and Moore(1937) observed that Vitamin A was stored in the rat

liver after carotene feeding. Goss and Guilbert(1939) calculated the minimal

maintenance level of Vitamin A and carotene in the rat, and Lewis et al.(1942)

reported the relationship of Vitamin A intake to growth and to the concentration of

Vitamin A in rat blood, liver and retinal. when the carotene was injected

intravenously into the rat, Sexton et al.(1946) found that the hepatic storage of

carotene(but not of Vitamin A). Bieri and Pollard(1955) and Zachman and Olson(1963)

reported that β-carotene was converted to Vitamin A in rat's liver or in other

tissues.

Previously it had been postulated that carotene was taken up by the Kupffer cells

and converted to Vitamin A in the liver. However, recently many investigators have

reported the intestinal metabolism of β-carotene in mammals differs from that of

rats. Carotene does not convert efficiently to retinol in the human intestine as

does occur in the rats and pigs intestine. These animals do not absorb carotene

until it has been metabolized at the intestinal wall to the retinyl ester(Wanger et

al., 1960; Olson, 1961; Hou et al., 1965; Huang and Goodman, 1965).

In view of these findings, the present investigation was undertaken to clarify

the difference of absorption of Vitamin A and β-carotene from the rat intestine;

secondly the degree of conversion of β-carotene to Vitamin A in the rat; and

thirdly to compare the findings in rats with those in human.

Male albino rats weighing an average of 90gms. were used from the first through

the fourth series of experiments. In the fifth series healthy Korean males weighing

an average of 60kgs. were used. The concentrations of Vitamin A and β-carotene in

the plasma and liver were determined by the method of Oser(1943), and the

concentration of plasma Vitamin C was determined by the method of Bessey(1944).

In the first series of experiments, the concentration of Vitamin A in the rat

liver and plasma were increased as the supplement of dietary Vitamin A was

increased. However, the concentration of asocorbic acid in the rats plasma was

decreased as the diet was supplemented with a high concentration of Vitamin A.

In the second series, only a limited amount of β-carotene was absorbed from the

gastrointestinal tract. The ascorbic acid concentration in the plasma was showed no

significant change.

The third series studied the absorption rate of Vitamin a and β-carotene in the

rat after the administration of these Vitamins. In Vitamin A group, the average

concentration of plasma Vitamin.

A was twice the level noted prior to the administration o vitamin A. In the

β-carotene group there were no changes in plasma concentration of vitamin A and

β-carotene.

The fourth series studied the amount of accumulated Vitamin A and β-carotene in

the rat liver following the injection of these Vitamins. Rat liver Vitamin a in the

test group was twice as much as that of control group. In contrast, there was no

increase of Vitamin a in the β-carotene group. No change in the plasma

concentration of Vitamin A and β-carotene was observed in either group.

The fifth series investigated the absorption of Vitamin A and β-carotene from

the human intestine. Four hours after the administration of Vitamin A the

concentration of plasma Vitamin A was increased to 3 times that of the control

group. Four hours following β-carotene administration the concentration of Vitamin

A in the plasma was 1.4 times that of the control group. Ones after the

administration of β-carotene was not significant. However by 8 hours the

β-carotene concentration in the plasma was increased slowly. The plasma Vitamin A

concentration was slightly increased as was the plasma β-carotene concentration.

The results may be briefly summarized as follows:

1. IN the rats, β-carotene is not absorbed as β-carotene from the intestine,

but is absorbed after being converted to the vitamin A ester. The amount of vitamin

A accumulated in liver when β-carotene was administered was only one twenty-fifty

that accumulated when Vitamin A was give.

2. After the intramuscular administration of β-carotene, no increase in Vitamin

A was observed in rat blood and liver.

3. In humans, the efficiency of conversion of β-carotene to vitamin A was higher

than in rats.

This is shown by the increase in plasma Vitamin a concentration after the

administration of β-carotene.

4. Vitamin A is absorbed as rapidly in rats as it is in humans.

5. The ascorbic acid in rat plasma decreased after administration of large amount

of Vitamin A.

[영문]

It is well known that in animals Vitamin A is formed from its

precursors(provitamin) which originally are obtained only from plants. These precursors exsist as carotenoid pigments, the most important of which is β-carotene.

Moore(1931) reported that β-carotene was converted to Vitamin A in rat's body.

Since then many investigators have studied the metabolism and absorption of carotenoids. Davis and Moore(1937) observed that Vitamin A was stored in the rat liver after carotene feeding. Goss and Guilbert(1939) calculated the minimal maintenance level of Vitamin A and carotene in the rat, and Lewis et al.(1942)

reported the relationship of Vitamin A intake to growth and to the concentration of Vitamin A in rat blood, liver and retinal. when the carotene was injected intravenously into the rat, Sexton et al.(1946) found that the hepatic storage of carotene(but not of Vitamin A). Bieri and Pollard(1955) and Zachman and Olson(1963) reported that β-carotene was converted to Vitamin A in rat's liver or in other tissues.

Previously it had been postulated that carotene was taken up by the Kupffer cells and converted to Vitamin A in the liver. However, recently many investigators have reported the intestinal metabolism of β-carotene in mammals differs from that of rats. Carotene does not convert efficiently to retinol in the human intestine as does occur in the rats and pigs intestine. These animals do not absorb carotene until it has been metabolized at the intestinal wall to the retinyl ester(Wanger et al., 1960; Olson, 1961; Hou et al., 1965; Huang and Goodman, 1965).

In view of these findings, the present investigation was undertaken to clarify the difference of absorption of Vitamin A and β-carotene from the rat intestine; secondly the degree of conversion of β-carotene to Vitamin A in the rat; and

thirdly to compare the findings in rats with those in human.

Male albino rats weighing an average of 90gms. were used from the first through the fourth series of experiments. In the fifth series healthy Korean males weighing an average of 60kgs. were used. The concentrations of Vitamin A and β-carotene in

the plasma and liver were determined by the method of Oser(1943), and the concentration of plasma Vitamin C was determined by the method of Bessey(1944).

In the first series of experiments, the concentration of Vitamin A in the rat liver and plasma were increased as the supplement of dietary Vitamin A was increased. However, the concentration of asocorbic acid in the rats plasma was

decreased as the diet was supplemented with a high concentration of Vitamin A.

In the second series, only a limited amount of β-carotene was absorbed from the gastrointestinal tract. The ascorbic acid concentration in the plasma was showed no significant change.

The third series studied the absorption rate of Vitamin a and β-carotene in the rat after the administration of these Vitamins. In Vitamin A group, the average concentration of plasma Vitamin.

A was twice the level noted prior to the administration o vitamin A. In the β-carotene group there were no changes in plasma concentration of vitamin A and β-carotene.

The fourth series studied the amount of accumulated Vitamin A and β-carotene in the rat liver following the injection of these Vitamins. Rat liver Vitamin a in the test group was twice as much as that of control group. In contrast, there was no increase of Vitamin a in the β-carotene group. No change in the plasma

concentration of Vitamin A and β-carotene was observed in either group.

The fifth series investigated the absorption of Vitamin A and β-carotene from the human intestine. Four hours after the administration of Vitamin A the concentration of plasma Vitamin A was increased to 3 times that of the control group. Four hours following β-carotene administration the concentration of Vitamin

A in the plasma was 1.4 times that of the control group. Ones after the administration of β-carotene was not significant. However by 8 hours the β-carotene concentration in the plasma was increased slowly. The plasma Vitamin A concentration was slightly increased as was the plasma β-carotene concentration.

The results may be briefly summarized as follows:

1. IN the rats, β-carotene is not absorbed as β-carotene from the intestine, but is absorbed after being converted to the vitamin A ester. The amount of vitamin A accumulated in liver when β-carotene was administered was only one twenty-fifty

that accumulated when Vitamin A was give.

2. After the intramuscular administration of β-carotene, no increase in Vitamin A was observed in rat blood and liver.

3. In humans, the efficiency of conversion of β-carotene to vitamin A was higher than in rats.

This is shown by the increase in plasma Vitamin a concentration after the administration of β-carotene.

4. Vitamin A is absorbed as rapidly in rats as it is in humans.

5. The ascorbic acid in rat plasma decreased after administration of large amount of Vitamin A.