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The effects of vitamin B6 on carbohydrate metabolism in women taking steroid contraceptives: Preliminary report
THE EFFECTS OF VITAMIN Bg ON CARBOHYDRATE METABOLISM IN WOMEN TAKING STEROID CONTRACEPTIVES: PRELIMINARY REPORT
W.N. Spellacy W.C. Buhi S.A. Birk
M.D. M.S. B.S., R.N.
From the Deparhnent of Obstetrics and Gynecology of the University of Miami Medical School, Miami, Florida 33152
Abstract In order to help clarify which mechanisms are responsible for the adverse effects of oral contraceptive steroids on carbohydrate metabolism, the following experiments were undertaken. Twelve women whose glucose tolerance tests had progressively deteriorated while taking steroid contraceptives were given one month of therapy with vitamin Bg with their steroid contraceptive. There was a significant improvement in their glucose tolerance test results after this combined treatment. These data suggest that a relative vitamin Bg deficiency in oral contraceptive users, perhaps acting through an increase in the resulting circulating xanthurenic acid levels, is related in part to the observed carbohydrate metabolism deterioration.
Accepted
for publication
OCTOBER
1972
VOL.
August
2,
6 NO. 4
1972
265
CONTRACEPTION
Introduction It has been clearly established that the use of some of the oral contraceptives results in altered carbohydrate metabolism and this alteration usually consists of elevated blood glucose and plasma insulin levels (1). A still unresolved question relates to the mechanisms causing these metabolic changes. Ovarian-like steroids can also alter vitamin metabolism (2). This report will attempt to investigate the interrelationship between oral contraceptive usage, vitamin B6 metabolism and carbohydrate metabolic abnormalities. Methods Twelve women volunteers from the Jackson Memorial Hospital family planning clinic were studied. Each subject had been followed in the prospective oral contraceptive metabolic studies described previously (3). Accordingly, each had had an oral three hour 100 gram glucose tolerance test performed before starting the steroids and then repeated every six months. The details of the testing procedure have already been described and the blood glucose content was measured in duplicate using the method of Nelson and Somogyi (3). Four different contraceptive steroids were used and they had been taken for six to thirty-six months before the vitamin supplement was added *. The glucose tolerance curve at each testing was summarized by adding the fasting 1, 2, and 3 hour values for the "total glucose" (T ) value and where this exceeded 500, it was considered abnormal $4). Each of the subjects in the present study had a normal control preThey also had progresssteroid treatment tolerance test (T <500). ively increasing blood glucose leveB s while receiving the steroid therapy. Accordingly, it was decided to treat each subject with vitamin B6 plus her steroid for one month before discontinuing the steroid medication in an attempt to investigate the effects of vitamin B6 on the steroid altered glucose tolerance tests. Accordingly, each steroid contraceptive and the tolerance test was repeated after one month of vitamin-steroid treatment. All of the data were placed on punch cards and appropriately analyzed with the aid of a computer. The "total glucose" (Tg) values between two testings were compared by means of the Wilcoxon signed rank test. The probability values were taken from two-tail tables and only values of less than 3.05 were considered significant. * The four steroid preparations used were Ovulen (B) containing 1.0 mgm of eth nodiol diacetate and 0.1 mgm of mestranol (patient l-5); Demulen($) containing 1.0 mgm of ethynodiol diacetate and 0.05 mgm of ethinyl estradiol (patient 6), and ethynodiol diacetate 0.25 mgm (patient 7-8). All of these were kindly supplied by the G.D. Searle and Company of Chicago, Ill. Another steroid used was norgestrel 0.075 mgm (patient 9-12) which was kindly supplied by the Wyeth Laboratories of Philadelphia, Pa.
OCTOBER
1972
VOL.
6 NO. 4
CONTRACEPTION
Results The results of three glucose tolerance tests are shown in Table 1 and the mean Tg values are plotted in Figure 1. The control presteroid treatment test values are not shown but they all had Tg of less than 500 and the median value was 402. The glucose tolerance test results immediately preceding the B6 treatment are shown as "steroid treatment test 2". The glucose tolerance test results six months before this while the subjects were also taking the steroids are shown as "steroid treatment test 1". It can be seen that during this preceding six-month period,there was a significant deterioration of the tolerance test (median Tg change + 127; P <0.02). The difference between the control pre-steroid treatment test and "steroid treatment test 1" was also significant (median Tg change The results of treatment for one month with the + 81; ~(0.05). steroid plus vitamin B6 is shown in the column marked test 3. It can be seen that there is a significant improvement in the glucose tolerance curve during this combined therapy (median Tg change -98; p <0.02). Discussion It is now clear that the synthetic steroids used for contraception can alter both vitamin and carbohydrate metabolism in some women (122). A particular vitamin of interest is pyridoxine (B6) This vitamin is an important cofactor in many metabolic reactions. One of importance here is the pathway of tryptophan to nicotinic acid as shown in Figure 2. Brin has demonstrated that synthetic ovarian steroids can increase liver tryptophan oxygenase activity and thereby shunt more tryptophan into the pathway (5). Pyridoxine is a necessary cofactor with the enzyme,kynureninase,for the conversion of 3-hydroxykynurenine to 3-hydroxyanthranilic acid (6). The 3hydroxykynurenine can also be converted by kynurenine transaminase and pyridoxiue to xanthurenic acid (6). Metabolic studies of these pathways have been done in humans by administering an oral tryptophan load (2 to 5 grams) and measuring the urine metabolites before and afterwards. One particular metabolite of interest is xanthurenic acid (XA). It has been clearly shown that the excretion of XA is increased during pregnancy and also in subjects receiving oral contraceptives (6-13). Although few progestogens have been studied, the results seem to be primarily related to an estrogen effect (6). This is probably due to both the increased shunting of tryptophan into the pathway secondary to the increase in liver tryptophan oxygenase activity as well as a decrease in the kynureninase activity. It has also been demonstrated that the increased XA excretion in subjects receiving synthetic ovarian steroids can be returned towards normal with vitamin B6 supplementation (6-8, 10-12). Luhby and coworkers have calculated that one would need an approximate 30 mgm intake of B6 per day to normalize the XA excretion pattern (12). The average diet contains only 1-2 mgm of vitamin B6 per day. The vitamin B6 used was kindly supplied as Hexa-Betalin CR) (pyridoxine hydrochloride) 25 mgm by the Eli Lilly Company of Indianapolis, Indiana.
OCTOBER
1972
VOL.
6 NO. 4
267
CONTRACEPTION
Table I.
Total blood glucose scores (III@%) during three oral glucose tolerance tests in women receiving steroid contraceptives alone and steroid contraceptives plus vitamin B6 (N=12).
Steroid treatment Test 1
Steroid and vitamin B6 treatment Test 3
1.
440
763
533
2.
465
597
473
3.
604
645
687
4.
580
702
619
5.
597
1664
1200
6.
613
546
539
7.
432
577
464
8.
556
591
531
9.
458
563
591
10.
548
412
425
11.
329
588
414
12.
475
696
549
+ 127
- 98
Median
glucose change
probability
268
Steroid treatment Test 2
<0.02
<0.02
OCTOBER
1972
VOL. 6 NO. 4
CONTRACEPTION
p < 0.02
p < 0.02
Figure 1. Mean total glucose values for oral glucose tolerance tests during contraceptive steroid treatment without and with vitamin Bg supplement (N=12). Statistical comparisons were made on median score changes for the three tests.
OCTOBER
1972
VOL. 6 NO. 4
269
CONTRACEPTION
02
NH2
Tryptophan
oxygenase
CN,-;N-COON
Ii 0 Tryptophan
N-Formylkyaurenine
1
P; ‘tN2 C-CH2-CH-COOH
0 II
‘14
C-CH2-CH-COOH
* NHz
NH2
Kynurenine
OH 3-Hydroxykynurenine Kynurenine
Kynureninase \
/
66
3-Hydroxyanthranilic 4 Nicotinic
OH
Xanthurenic
acid
acid
Figure
270
acid
Bg
transaminase
2.
Metabolic
pathways
for tryptophan.
OCTOBFR
1972 VOL. 6 X0. 4
CONTRACEPTION
Several important studies of XA and carbohydrate metabolism have been made. Murakami has shown that two moles of XA will bind to one dimer of insulin at the histadine imidazole group through a zinc linkage (14). The physiologic effects of this "insulin-gnXA" complex have been studied. There is a significant decrease in the biologic activity of the insulin-complex in both the ratdiaphragm and rat epididymal fat pad bioassays (15). In addition, there is approximately a 50% decrease in the hypoglycemic effect of the insulin-complex when injected into dogs and rabbits (15-16). Thus, when insulin binds to XA,the resultant complex decreases the insulin's biologic activity. Whether the above data are pertinent to human females who are pregnant or taking contraceptive steroids is unknown. The present study was undertaken in order to help clarify this enigma. Subjects were chosen who had already demonstrated a deteriorating carbohydrate tolerance while receiving synthetic steroids. They were then kept on the steroid and, in addition, given a large dose (100 mgm) of vitamin B6 every day for one month. This dose was chosen since it is in excess of that calculated to return XA levels to normal. The results show that the glucose tolerance which was significantly deteriorated before the vitamin treatment improved during the vitamin B6 treatment, although it did not completely return to normal. Many questions remain unanswered, These results suggest that possibly all of the steroids tested, including some of the progestogens, may alter the blood levels of X.A. The XA then could become bound to insulin and decrease the insulin biologic activity finally resulting in elevated blood glucose levels. The progestogens tested may have exerted their actions by "estrogenic-like" metabolites. Whether the vitamin B6 decreased the XA and thereby improved the insulin biologic activity remains unknown, The simultaneous measurements of all of these metabolites were not done however so these remain only speculations. Insulin levels were measured in these subjects with a radioinmmnoassay method but whether the insulin-Zn-XA complex is measurable in this assay system is unknown. Finally, although no data are available, it is possible that some steroid induced carbohydrate abnormalities could be prevented with the addition of supplementary vitamin B6 to the diet of wcmen taking contraceptive drugs. Additional studies are underway to attempt to answer some of these questions. Acknowledgement The authors wish to thank Mrs. R. Cabal and Mrs. S. McCreary for their help in these studies. In addition, they would like to thank Mrs. J. Cassady for her help in analyzing these data. Support These studies were supported in part by grant No. 700-0338 from the Ford Foundation of New York.
OCTOBER
1972
VOL. 6 NO. 4
271
CONTRACEPTION
References 1.
Spellacy, W.N. A review of carbohydrate metabolism and the oral contraceptives. Am. J. Obst. Gynec. 104:448-460 (1969).
2.
Theuer, R.C. Effect of oral contraceptive agents on vitamin and mineral needs. A Review. J. Rep. Med. 8:13-19 (1972).
3.
Spellacy, W.N., Buhi, W.C., Birk, S.A., and McCreary, S.A. Studies of ethynodiol diacetate and mestranol on blood glucose and plasma insulin. II. Twelve month oral glucose tolerance test. Contraception 3:185-194 (1971).
4.
Klimt, C.R., Prout, T.E., Bradley, R.F., Dolger, H., Fisher, G., Gastineau, C.F., Marks, H., Meinert, C.L., and Schumacher, O.P. Standardization of the oral glucose tolerance test. Diabetes 18:299-307 (1969).
5.
Brin, M. Abnormal tryptophan metabolism in pregnancy and with the oral contraceptive pill. I. Specific effects of an oral estrogenic contraceptive steroid on the tryptophan oxygenase and two aminotransferase activities in livers of ovariectomizedadrenalectomized rats. Am. J. Clin. Nut. 24:699-703 (1971).
6.
Wolf, H., Brown, R.R., Price, J.M., and Madsen, P.O. Studies of tryptophan metabolism in male subjects treated with female sex hormones. J. Clin. Endocr. 31:397-408 (1970).
7.
Zartman, E.R., Barnes, A.C., and Hicks, D.J. Observations on pyridoxine metabolism in pregnancy. Am. 3. Obst. Gynec. 70:645649 (1955).
8.
Rose, D.P. Excretion of xanthurenic acid in the urine of women taking progestogen-oestrogen preparations. Nature 210:196-197 (1966).
9.
Price, J.M., Thornton, M.J., and Mueller, L.M. Tryptophan metabolism in women using steroid hormones for ovulation control. Am. J. Clin. Nut. 20:452-456 (1967).
10.
Rose, D.P., Brown, R.R., and Price, J.M. Metabolism of tryptophan to nicotinic acid derivatives by women taking oestrogen-progestogen preparations. Nature 219:1259-1260 (1968).
11.
Heilmann, H.H., Knapp, A., Stolp, A., and Sudhodoletz, O.V. Gber den einfluss von ovulation shemmern auf den tryptophanstoffwechsel in abhsngig-keit von vitamin B6. Klin. Wschr. 46:1059-1060 (1968).
272
OCTOBER 1972
VOL. 6 NO. 4
CONTRACEPTION
12.
Luhby, A.L., Brin, M., Gordon, M., Davis, P., Murphy, M., and Spiegel, H. Vitamin B6 metabolism in users of oral contraceptive agents. I. Abnormal urinary xanthurenic acid excretion and its correction by pyridoxine. Am. J. Clin. Nut. 24:684-693 (1971).
13. Aly, H.E., Donald, E.A., and Simpson, M.H.W. Oral contraceptives and vitamin B6 metabolism. Am. J. Clin. Nut. 24:297-303 (1971). 14. Murakami, E. Studies on the xanthurenic acid-insulin complex. I. Preparation and properties. J. Biochem (Tokyo) 63:573-577 (1968). 15.
Kotake, Y., Sotokawa, T., Murakami, E., Hisatake, A., Abe, M., and Ikeda, Y. Studies on the xanthurenic acid-insulin complex. II. Physiological activities. J. Biochem (Tokyo) 63:578-581 (1968).
16.
Kotake, Y., Sotokawa, Y., Murakami, E., Hisatake, A., Abe, M., and Ikeda, Y. Physiological activities of xanthurenic acid-8 methyl ether-insulin complex. J. Biochem (Tokyo) 64:895-896 (1968).
OCTOBER
1972
VOL.
6 NO. 4
273
W.N. Spellacy W.C. Buhi S.A. Birk
M.D. M.S. B.S., R.N.
From the Deparhnent of Obstetrics and Gynecology of the University of Miami Medical School, Miami, Florida 33152
Abstract In order to help clarify which mechanisms are responsible for the adverse effects of oral contraceptive steroids on carbohydrate metabolism, the following experiments were undertaken. Twelve women whose glucose tolerance tests had progressively deteriorated while taking steroid contraceptives were given one month of therapy with vitamin Bg with their steroid contraceptive. There was a significant improvement in their glucose tolerance test results after this combined treatment. These data suggest that a relative vitamin Bg deficiency in oral contraceptive users, perhaps acting through an increase in the resulting circulating xanthurenic acid levels, is related in part to the observed carbohydrate metabolism deterioration.
Accepted
for publication
OCTOBER
1972
VOL.
August
2,
6 NO. 4
1972
265
CONTRACEPTION
Introduction It has been clearly established that the use of some of the oral contraceptives results in altered carbohydrate metabolism and this alteration usually consists of elevated blood glucose and plasma insulin levels (1). A still unresolved question relates to the mechanisms causing these metabolic changes. Ovarian-like steroids can also alter vitamin metabolism (2). This report will attempt to investigate the interrelationship between oral contraceptive usage, vitamin B6 metabolism and carbohydrate metabolic abnormalities. Methods Twelve women volunteers from the Jackson Memorial Hospital family planning clinic were studied. Each subject had been followed in the prospective oral contraceptive metabolic studies described previously (3). Accordingly, each had had an oral three hour 100 gram glucose tolerance test performed before starting the steroids and then repeated every six months. The details of the testing procedure have already been described and the blood glucose content was measured in duplicate using the method of Nelson and Somogyi (3). Four different contraceptive steroids were used and they had been taken for six to thirty-six months before the vitamin supplement was added *. The glucose tolerance curve at each testing was summarized by adding the fasting 1, 2, and 3 hour values for the "total glucose" (T ) value and where this exceeded 500, it was considered abnormal $4). Each of the subjects in the present study had a normal control preThey also had progresssteroid treatment tolerance test (T <500). ively increasing blood glucose leveB s while receiving the steroid therapy. Accordingly, it was decided to treat each subject with vitamin B6 plus her steroid for one month before discontinuing the steroid medication in an attempt to investigate the effects of vitamin B6 on the steroid altered glucose tolerance tests. Accordingly, each steroid contraceptive and the tolerance test was repeated after one month of vitamin-steroid treatment. All of the data were placed on punch cards and appropriately analyzed with the aid of a computer. The "total glucose" (Tg) values between two testings were compared by means of the Wilcoxon signed rank test. The probability values were taken from two-tail tables and only values of less than 3.05 were considered significant. * The four steroid preparations used were Ovulen (B) containing 1.0 mgm of eth nodiol diacetate and 0.1 mgm of mestranol (patient l-5); Demulen($) containing 1.0 mgm of ethynodiol diacetate and 0.05 mgm of ethinyl estradiol (patient 6), and ethynodiol diacetate 0.25 mgm (patient 7-8). All of these were kindly supplied by the G.D. Searle and Company of Chicago, Ill. Another steroid used was norgestrel 0.075 mgm (patient 9-12) which was kindly supplied by the Wyeth Laboratories of Philadelphia, Pa.
OCTOBER
1972
VOL.
6 NO. 4
CONTRACEPTION
Results The results of three glucose tolerance tests are shown in Table 1 and the mean Tg values are plotted in Figure 1. The control presteroid treatment test values are not shown but they all had Tg of less than 500 and the median value was 402. The glucose tolerance test results immediately preceding the B6 treatment are shown as "steroid treatment test 2". The glucose tolerance test results six months before this while the subjects were also taking the steroids are shown as "steroid treatment test 1". It can be seen that during this preceding six-month period,there was a significant deterioration of the tolerance test (median Tg change + 127; P <0.02). The difference between the control pre-steroid treatment test and "steroid treatment test 1" was also significant (median Tg change The results of treatment for one month with the + 81; ~(0.05). steroid plus vitamin B6 is shown in the column marked test 3. It can be seen that there is a significant improvement in the glucose tolerance curve during this combined therapy (median Tg change -98; p <0.02). Discussion It is now clear that the synthetic steroids used for contraception can alter both vitamin and carbohydrate metabolism in some women (122). A particular vitamin of interest is pyridoxine (B6) This vitamin is an important cofactor in many metabolic reactions. One of importance here is the pathway of tryptophan to nicotinic acid as shown in Figure 2. Brin has demonstrated that synthetic ovarian steroids can increase liver tryptophan oxygenase activity and thereby shunt more tryptophan into the pathway (5). Pyridoxine is a necessary cofactor with the enzyme,kynureninase,for the conversion of 3-hydroxykynurenine to 3-hydroxyanthranilic acid (6). The 3hydroxykynurenine can also be converted by kynurenine transaminase and pyridoxiue to xanthurenic acid (6). Metabolic studies of these pathways have been done in humans by administering an oral tryptophan load (2 to 5 grams) and measuring the urine metabolites before and afterwards. One particular metabolite of interest is xanthurenic acid (XA). It has been clearly shown that the excretion of XA is increased during pregnancy and also in subjects receiving oral contraceptives (6-13). Although few progestogens have been studied, the results seem to be primarily related to an estrogen effect (6). This is probably due to both the increased shunting of tryptophan into the pathway secondary to the increase in liver tryptophan oxygenase activity as well as a decrease in the kynureninase activity. It has also been demonstrated that the increased XA excretion in subjects receiving synthetic ovarian steroids can be returned towards normal with vitamin B6 supplementation (6-8, 10-12). Luhby and coworkers have calculated that one would need an approximate 30 mgm intake of B6 per day to normalize the XA excretion pattern (12). The average diet contains only 1-2 mgm of vitamin B6 per day. The vitamin B6 used was kindly supplied as Hexa-Betalin CR) (pyridoxine hydrochloride) 25 mgm by the Eli Lilly Company of Indianapolis, Indiana.
OCTOBER
1972
VOL.
6 NO. 4
267
CONTRACEPTION
Table I.
Total blood glucose scores (III@%) during three oral glucose tolerance tests in women receiving steroid contraceptives alone and steroid contraceptives plus vitamin B6 (N=12).
Steroid treatment Test 1
Steroid and vitamin B6 treatment Test 3
1.
440
763
533
2.
465
597
473
3.
604
645
687
4.
580
702
619
5.
597
1664
1200
6.
613
546
539
7.
432
577
464
8.
556
591
531
9.
458
563
591
10.
548
412
425
11.
329
588
414
12.
475
696
549
+ 127
- 98
Median
glucose change
probability
268
Steroid treatment Test 2
<0.02
<0.02
OCTOBER
1972
VOL. 6 NO. 4
CONTRACEPTION
p < 0.02
p < 0.02
Figure 1. Mean total glucose values for oral glucose tolerance tests during contraceptive steroid treatment without and with vitamin Bg supplement (N=12). Statistical comparisons were made on median score changes for the three tests.
OCTOBER
1972
VOL. 6 NO. 4
269
CONTRACEPTION
02
NH2
Tryptophan
oxygenase
CN,-;N-COON
Ii 0 Tryptophan
N-Formylkyaurenine
1
P; ‘tN2 C-CH2-CH-COOH
0 II
‘14
C-CH2-CH-COOH
* NHz
NH2
Kynurenine
OH 3-Hydroxykynurenine Kynurenine
Kynureninase \
/
66
3-Hydroxyanthranilic 4 Nicotinic
OH
Xanthurenic
acid
acid
Figure
270
acid
Bg
transaminase
2.
Metabolic
pathways
for tryptophan.
OCTOBFR
1972 VOL. 6 X0. 4
CONTRACEPTION
Several important studies of XA and carbohydrate metabolism have been made. Murakami has shown that two moles of XA will bind to one dimer of insulin at the histadine imidazole group through a zinc linkage (14). The physiologic effects of this "insulin-gnXA" complex have been studied. There is a significant decrease in the biologic activity of the insulin-complex in both the ratdiaphragm and rat epididymal fat pad bioassays (15). In addition, there is approximately a 50% decrease in the hypoglycemic effect of the insulin-complex when injected into dogs and rabbits (15-16). Thus, when insulin binds to XA,the resultant complex decreases the insulin's biologic activity. Whether the above data are pertinent to human females who are pregnant or taking contraceptive steroids is unknown. The present study was undertaken in order to help clarify this enigma. Subjects were chosen who had already demonstrated a deteriorating carbohydrate tolerance while receiving synthetic steroids. They were then kept on the steroid and, in addition, given a large dose (100 mgm) of vitamin B6 every day for one month. This dose was chosen since it is in excess of that calculated to return XA levels to normal. The results show that the glucose tolerance which was significantly deteriorated before the vitamin treatment improved during the vitamin B6 treatment, although it did not completely return to normal. Many questions remain unanswered, These results suggest that possibly all of the steroids tested, including some of the progestogens, may alter the blood levels of X.A. The XA then could become bound to insulin and decrease the insulin biologic activity finally resulting in elevated blood glucose levels. The progestogens tested may have exerted their actions by "estrogenic-like" metabolites. Whether the vitamin B6 decreased the XA and thereby improved the insulin biologic activity remains unknown, The simultaneous measurements of all of these metabolites were not done however so these remain only speculations. Insulin levels were measured in these subjects with a radioinmmnoassay method but whether the insulin-Zn-XA complex is measurable in this assay system is unknown. Finally, although no data are available, it is possible that some steroid induced carbohydrate abnormalities could be prevented with the addition of supplementary vitamin B6 to the diet of wcmen taking contraceptive drugs. Additional studies are underway to attempt to answer some of these questions. Acknowledgement The authors wish to thank Mrs. R. Cabal and Mrs. S. McCreary for their help in these studies. In addition, they would like to thank Mrs. J. Cassady for her help in analyzing these data. Support These studies were supported in part by grant No. 700-0338 from the Ford Foundation of New York.
OCTOBER
1972
VOL. 6 NO. 4
271
CONTRACEPTION
References 1.
Spellacy, W.N. A review of carbohydrate metabolism and the oral contraceptives. Am. J. Obst. Gynec. 104:448-460 (1969).
2.
Theuer, R.C. Effect of oral contraceptive agents on vitamin and mineral needs. A Review. J. Rep. Med. 8:13-19 (1972).
3.
Spellacy, W.N., Buhi, W.C., Birk, S.A., and McCreary, S.A. Studies of ethynodiol diacetate and mestranol on blood glucose and plasma insulin. II. Twelve month oral glucose tolerance test. Contraception 3:185-194 (1971).
4.
Klimt, C.R., Prout, T.E., Bradley, R.F., Dolger, H., Fisher, G., Gastineau, C.F., Marks, H., Meinert, C.L., and Schumacher, O.P. Standardization of the oral glucose tolerance test. Diabetes 18:299-307 (1969).
5.
Brin, M. Abnormal tryptophan metabolism in pregnancy and with the oral contraceptive pill. I. Specific effects of an oral estrogenic contraceptive steroid on the tryptophan oxygenase and two aminotransferase activities in livers of ovariectomizedadrenalectomized rats. Am. J. Clin. Nut. 24:699-703 (1971).
6.
Wolf, H., Brown, R.R., Price, J.M., and Madsen, P.O. Studies of tryptophan metabolism in male subjects treated with female sex hormones. J. Clin. Endocr. 31:397-408 (1970).
7.
Zartman, E.R., Barnes, A.C., and Hicks, D.J. Observations on pyridoxine metabolism in pregnancy. Am. 3. Obst. Gynec. 70:645649 (1955).
8.
Rose, D.P. Excretion of xanthurenic acid in the urine of women taking progestogen-oestrogen preparations. Nature 210:196-197 (1966).
9.
Price, J.M., Thornton, M.J., and Mueller, L.M. Tryptophan metabolism in women using steroid hormones for ovulation control. Am. J. Clin. Nut. 20:452-456 (1967).
10.
Rose, D.P., Brown, R.R., and Price, J.M. Metabolism of tryptophan to nicotinic acid derivatives by women taking oestrogen-progestogen preparations. Nature 219:1259-1260 (1968).
11.
Heilmann, H.H., Knapp, A., Stolp, A., and Sudhodoletz, O.V. Gber den einfluss von ovulation shemmern auf den tryptophanstoffwechsel in abhsngig-keit von vitamin B6. Klin. Wschr. 46:1059-1060 (1968).
272
OCTOBER 1972
VOL. 6 NO. 4
CONTRACEPTION
12.
Luhby, A.L., Brin, M., Gordon, M., Davis, P., Murphy, M., and Spiegel, H. Vitamin B6 metabolism in users of oral contraceptive agents. I. Abnormal urinary xanthurenic acid excretion and its correction by pyridoxine. Am. J. Clin. Nut. 24:684-693 (1971).
13. Aly, H.E., Donald, E.A., and Simpson, M.H.W. Oral contraceptives and vitamin B6 metabolism. Am. J. Clin. Nut. 24:297-303 (1971). 14. Murakami, E. Studies on the xanthurenic acid-insulin complex. I. Preparation and properties. J. Biochem (Tokyo) 63:573-577 (1968). 15.
Kotake, Y., Sotokawa, T., Murakami, E., Hisatake, A., Abe, M., and Ikeda, Y. Studies on the xanthurenic acid-insulin complex. II. Physiological activities. J. Biochem (Tokyo) 63:578-581 (1968).
16.
Kotake, Y., Sotokawa, Y., Murakami, E., Hisatake, A., Abe, M., and Ikeda, Y. Physiological activities of xanthurenic acid-8 methyl ether-insulin complex. J. Biochem (Tokyo) 64:895-896 (1968).
OCTOBER
1972
VOL.
6 NO. 4
273