NOTES AND COMMENTS
475
that the animals used in this experiment were related to the fact that rams, unlike bulls, are seatransferred from a natural 9 h illumination sonal breeders. We conclude that in addition to ambient tem(mid-December in Michigan) to the 16 h photoperiod at the beginning of the experiment. perature (4), photoperiod also may account for at Perhaps the 2-week adjustment period was least a part of the seasonal changes (1-3) in insufficient to allow serum prolactin to adapt to serum prolactin in cattle. the 16 h photoperiod. Support for this hypothesis References was found in the second experiment (Fig. 2) where increases in serum prolactin were delayed 1. Koprowski, J. A., and H. A. Tucker, Endocrinology until after week 8. In contrast, as light was de92: 1480, 1973. creased from 16 h (Fig. 1), the decreases in serum 2. Karg, H., and D. SchamsJ Reprod Fertil 39: 463, prolactin followed within about a week of the 1974. 3. Tucker, H. A., J. A. Koprowski, J. H. Britt, and W. D. light changes. Similar discrepancies in speed of OxenderJ Dairy Sci 57: 1092, 1974. the prolactin response to changes in photoperiod 4. Wettemann, R. P., and H. A. Tucker, Proc Soc Exp were observed in rams (7). Biol Med 146: 908, 1974. Pelletier (7) cited evidence that serum LH 5. Koprowski, J. A., and H. A. Tucker, 7 Dairy Sci concentrations were reduced in sexually mature 54: 1675, 1971. rams artificially exposed to a long photoperiod. 6. Oxender, W. D., H. D. Hafs, and L. A. Edgerton, Possibly our failure tofindchanges in serum LH, J An Sci 35: 51, 1972. associated with changes in photoperiod, was 7. Pelletier, ].,] Reprod Fert 35: 143, 1973. because our bulls were sexually immature. 8. Relkin, R., Neuroendocrinology 9: 278, 1972. Another possible cause of the discrepancy may be 9. Reiter, R. J., Endocrine Res Commun 1: 169, 1974.
Relationship of Steroid Structure to Induction of Chymotrypsinogen in Embryonic Chick Pancreas in Vitro AMOS COHEN AND RICHARD G. KULKA Department of Biological Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel ABSTRACT. The effect of steroid structure on induction of chymotrypsinogen in embryonic chick pancreas was examined in vitro. In order of decreasing potency corn'sol, corticosterone, and 21-deoxycortisol are classified as optimal inducers, whereas 11/3hydroxyprogesterone, 11-deoxycortisol, cortisone,
/"^ORTISOL induces precocious accumulation v>< of chymotrypsinogen and other exportable enzymes in the chick embryo pancreas both in vivo (1) and in vitro (2). In the present investigation we evaluated the effect of steroid structure on the induction of chymotrypsinogen in pancreas explants. Samuels and Tomkins (3), who studied the effect of various steroids on tyrosine aminotransferase activity in hepatoma tissue culture (HTC) cells, classified steroids into 4 categories: 1) optimal inducers, which at high concentrations cause maximal enzyme induction, Received September 27, 1974.
11-deoxycorticosterone and 17-a-hydroxyprogesterone are classified as suboptimal inducers. Progesterone was inactive. It is concluded that the relative importance of the steroid hydroxyl groups for activity is ll/3> 21 > 17a, and that their effect is cumulative. (Endocrinology 97: 475, 1975)
2) suboptimal inducers, which even at saturating concentrations do not induce maximal enzyme levels, 3) anti-inducers, which do not induce the enzyme but inhibit induction by other steroids, and 4) inactive compounds. In the work described below, we attempt to classify steroids tested on the chick pancreas according to the same criteria, as well as to evaluate the relative importance of their hydroxyl groups for activity. Materials and Methods Materials. The following steroids were purchased from Sigma: Corticosterone, deoxycorticosterone, progesterone, testosterone, 17o-methyltestosterone (17a-
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Endo • 1975 Vol 97 • No 2
NOTES AND COMMENTS
476
methyl-A4-androsten-17/8 ol-3one), fluoxymesterone (17a-methyl-A 4 -androsten-ll/8, 17/3-diol-9a-fluoro3one) and 17/3-estradiol. Cortisol and cortisone were obtained from Calbiochem. The following steroids were from Ikapharm, Israel: 11-deoxycortisol (A4pregnen-17a, 21-diol-3,20 dione), 21-deoxycortisol (A4-pregnen-ll/3, 17a diol-3,20 dione), 17a hydroxyprogesterone (A4-pregnen-17a-ol-3,20 dione) and 11/3 hydroxyprogesterone (A4-pregnen-ll/3 ol-3,20 dione). N-Benzoyl-L-tyrosine ethyl ester was the product of Yeda, Israel. Enzyme assays. Chymotrypsinogen was activated with trypsin and assayed spectrophotometrically with 0.6 mM N-benzoyl-L-tyrosine ethyl ester in 0.05M Tris-HCl buffer, pH 9.0, containing 2.5% (vol/vol) methanol and 0.05% triton X-100 as described previously (2). Protein was determined by the method of Lowry et al. (4). Organ cultures. Embryonic chick pancreases (from 11to 12-day-old embryos) were cultured in a chemically defined medium for 40 to 44 h as described earlier (2). Each culture dish contained 2 pancreases. At the end of
the incubation the pancreases were homogenized in 1.0 ml of 50 mM Tris-HCl buffer, pH 8.0, containing 0.05% Triton X-100. The homogenate was mixed with the culture medium and the chymotrypsin(ogen) was determined as described above. For further details see reference 2. The data in Fig. 1 and Table 1 are representative of at least 3 experiments.
Results Figure 1 shows dose-response curves for the induction of chymotrypsinogen by several steroids. Cortisol and corticosterone are both optimal inducers but the former compound is more effective at lower concentrations than the latter. The concentrations required for halfmaximal induction were approximately 1 x 10~7M for cortisol and 3 x 10~7M for corticosterone. 11-Deoxycortisol (cortexolone) and cortisone were sub-optimal inducers and both produced half their maximal response at about 5 x 10~7M. Although saturating concentrations were not reached at 2 x 10~5M, 11-deoxycortico-
30
< cr o
XCORTICOSTERONE
LU
OCORTISOL
20
•11-DEOXYCORTISOL
z LU O O
^CORTISONE
0
11-DEOXYCORTICOSTERONE
X
o
6 10,-7 10" STEROID CONCENTRATIO N
10' 5 (M)
10"
FIG. 1. Dose-response curves for the induction of chymotrypsinogen in pancreas by various steroids. Pancreases from 12-day embryos were incubated for 40 h with steroids at the concentrations indicated.
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477
NOTES AND COMMENTS TABLE 1. Effect of steroid structure on induction of chymotrypsinogen in pancreas explants 8 Group in position
OH CH 3 d
xxxxx
OOOOO
I i I i i
OH OH
X
Cortisol Fluoxymesterone
1 1 I I 1 1
3
XOOXO XX X XX
Cortisol 21-Deoxy cortisol 11/3-Hydroxyproge sterone 17a-Hydroxyprogesterone Progesterone
Ratio of chymotrypsin(ogen) activities induced/control
21C
1 1 1 1 xoxoo
2
17a
1 II 1 I I
Cortisol Corticosterone 11-Deoxycortisol Cortisone 11-Deoxycorticosterone
XOXOO XX
1
ll/8 b
o1 x1x1x1x 1
Steroid
XXX oooxx 1 11 1 1
Experiment no.
OH
8.3 10.3 5.4 4.3 2.6 4.4 4.4 3.4 1.6 1.2
4.9 3.8
a Pancreases were from 12-day embryos in experiments 1 and 3 and from 11-day embryos in experiment 2. Pancreas explants were incubated for 40 h in experiments 1 and 3, and for 44 h in experiment 2. Steroid concentrations were 2 x 10"5 M. The activity of chymotrypsin(ogen) in the control was 3 x 10~8 U/pancreas in experiment 1, 1.5 x 10~3 U/pancreas in experiment 2, and 2 x 10~ s U/pancreas in experiment 3. b The group in the l l a position was - H . c Attached to - C H , - . d Fluoxymesterone = 17a methyl-A 4 -androsten-ll/3, 17/8-diol-9a-fluoro-3 one.
sterone is presumably also a weak suboptimal inducer. Table I compares the induction of chymotrypsinogen in pancreas by various steroids. The high concentrations (2 x 10~5M) of steroid used here were probably saturating in most cases. Cortisol, corticosterone and 21-deoxycortisol were optimal inducers. The other compounds, which are listed in order of decreasing effectiveness, namely, 11-deoxycortisol, 11/3-hydroxyprogesterone, cortisone, 11-deoxycorticosterone, and 17ahydroxyprogesterone, did not elicit maximal induction and are presumably suboptimal inducers. Progesterone was virtually inactive. 17a-Methyltesto sterone, progesterone and 17/3-estradiol, which were effective as antiinducers in hepatoma tissue culture cells (3), had no significant inducer or anti-inducer activity in chick embryo pancreas. Fluoxymesterone and cortisone, which were anti-inducers in HTC cells, were suboptimal inducers in the chick pancreas (Table 1).
Discussion The optimal inducers, cortisol, corticosterone, and 21-deoxycortisol all possess an 11/3-hydroxyl group. Cortisol, which has three hydroxyl groups, elicited its maximal response at lower concentrations than did corticosterone and 21-deoxycortisol, which have only two hydroxyl groups.
It should be noted that corticosterone is the principal corticosteroid in the blood of the adult chicken while cortisol is present at much lower concentrations (5). Compounds tested which have one or two hydroxyls at positions other than 11/3 or one hydroxyl at position 11/3, were all suboptimal inducers. The apparent suboptimal activity of cortisone may, however, be due to its partial conversion to cortisol in the pancreas. Our data suggest that the relative importance of the hydroxyl groups is ll/3> 21 > 17a, and that their effect is cumulative. Earlier investigations on the effect of steroid structure on the induction of glutamine synthetase in chick embryo retina stressed the potency of steroids having an 11/3-hydroxyl group whereas steroids lacking this group were considered to have little effect (6-8). In those studies, however, steroids were not tested at saturating concentrations. In more recent experiments Chader and Reif-Lehrer (9) showed that at high concentrations 11-deoxycorticosteroids were effective inducers of glutamine synthetase in the retina. These and previous data support the hypothesis that the relative importance of the hydroxyl groups of corticosteroids for enzyme induction in retina is similar to that proposed above for pancreas. Certain differences in the response of retina and pancreas should be mentioned. Cortico-
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478
NOTES AND COMMENTS
steroids elicit their maximal response in the retina at concentrations about an order of magnitude lower than those required in the pancreas (7-9). Another difference which may be significant is that progesterone is an anti-inducer in the retina (9) but not in the pancreas. This may indicate a difference in the nature of the corticosteroid receptors of pancreas and retina and deserves further investigation. The contribution of the 11/3 and 21 hydroxyl groups to steroid activity is similar in chick embryo pancreas and in HTC cells (10). In hepatoma cells, however, the addition of a 17ahydroxyl group decreases the biological potency of steroids (10), while in chick embryo pancreas it enhances their effect (Table 1). Another difference between the two systems is the lack of activity in chick pancreas of compounds such as progesterone, 17/3-estradiol and 17a-methyltestosterone which are anti-inducers in HTC cells (10,11). The corticosteroid specificity of certain other mammalian systems studied in vitro (12,13) appears to be similar to that of HTC cells. In HeLa cells (14,15), as in chick embryo pancreas and retina, the 17a-hydroxyl group seems to enhance steroid activity. Ackno wl edgment We thank Mrs. Rachel Ampel for her able technical assistance.
Endo i 1975 Vol 97 , No 2
References 1. Cohen, A., H. Heller, and R. G. Kulka, Devel Biol 29: 293, 1972. 2. , and R. G. Kulka, J Biol Chem 249: 4522, 1974. 3. Samuels, H. H., and G. M. Tomkins, J Mol Biol •< 52: 57, 1970. 4. Lowry, O. H., N. J. Rosebrough, A. L. Farr, and R. J. Randall,; Biol Chem 193: 265, 1951. 5. Sturkie, P. D., Avian Physiology, Cornell University Press, Ithaca, 1965, p. 677. 6. Moscona, A. A., and R. Piddington, Science 158: 496, 1967. 4 7. Reif-Lehrer, L., Biochim Biophys Ada 170: 263, 1968. 8. Moscona, A. A., In Hamburgh, M., and E. J. W. Barrington (eds.), Hormones in Development, Appleton-Century-Crofts, New York, 1971, p. 169. 9. Chader, G. J., and L. Reif-Lehrer, Biochim Biophys Ada 264: 186, 1972. 10. Rousseau, G. G., J. D. Baxter, and G. M. Tomkins, / Mol Biol 67: 99, 1972. 11. Baxter, J. D., and G. M. Tomkins, Proc Natl Acad Sci USA 68: 932, 1971. 12. Ballard, P. L., and R. A. Ballard, Proc Natl Acad Sci USA 69: 2668, 1972. 13. Munck, A., and C. Wira, In Raspe, G. (ed.), Advances in the Biosciences 7, Schering Workshop on Steroid Hormone Receptors, Pergamon, Vieweg, 1971, p. 301. 14. Melnykovych, G., and C. F. Bishop, Biochim Biophys Ada 177: 579, 1969. 15. Cox, R. P., Ann NY Acad Sci 179: 596, 1971.
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 20 November 2015. at 03:30 For personal use only. No other uses without permission. . All rights reserved.
475
that the animals used in this experiment were related to the fact that rams, unlike bulls, are seatransferred from a natural 9 h illumination sonal breeders. We conclude that in addition to ambient tem(mid-December in Michigan) to the 16 h photoperiod at the beginning of the experiment. perature (4), photoperiod also may account for at Perhaps the 2-week adjustment period was least a part of the seasonal changes (1-3) in insufficient to allow serum prolactin to adapt to serum prolactin in cattle. the 16 h photoperiod. Support for this hypothesis References was found in the second experiment (Fig. 2) where increases in serum prolactin were delayed 1. Koprowski, J. A., and H. A. Tucker, Endocrinology until after week 8. In contrast, as light was de92: 1480, 1973. creased from 16 h (Fig. 1), the decreases in serum 2. Karg, H., and D. SchamsJ Reprod Fertil 39: 463, prolactin followed within about a week of the 1974. 3. Tucker, H. A., J. A. Koprowski, J. H. Britt, and W. D. light changes. Similar discrepancies in speed of OxenderJ Dairy Sci 57: 1092, 1974. the prolactin response to changes in photoperiod 4. Wettemann, R. P., and H. A. Tucker, Proc Soc Exp were observed in rams (7). Biol Med 146: 908, 1974. Pelletier (7) cited evidence that serum LH 5. Koprowski, J. A., and H. A. Tucker, 7 Dairy Sci concentrations were reduced in sexually mature 54: 1675, 1971. rams artificially exposed to a long photoperiod. 6. Oxender, W. D., H. D. Hafs, and L. A. Edgerton, Possibly our failure tofindchanges in serum LH, J An Sci 35: 51, 1972. associated with changes in photoperiod, was 7. Pelletier, ].,] Reprod Fert 35: 143, 1973. because our bulls were sexually immature. 8. Relkin, R., Neuroendocrinology 9: 278, 1972. Another possible cause of the discrepancy may be 9. Reiter, R. J., Endocrine Res Commun 1: 169, 1974.
Relationship of Steroid Structure to Induction of Chymotrypsinogen in Embryonic Chick Pancreas in Vitro AMOS COHEN AND RICHARD G. KULKA Department of Biological Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel ABSTRACT. The effect of steroid structure on induction of chymotrypsinogen in embryonic chick pancreas was examined in vitro. In order of decreasing potency corn'sol, corticosterone, and 21-deoxycortisol are classified as optimal inducers, whereas 11/3hydroxyprogesterone, 11-deoxycortisol, cortisone,
/"^ORTISOL induces precocious accumulation v>< of chymotrypsinogen and other exportable enzymes in the chick embryo pancreas both in vivo (1) and in vitro (2). In the present investigation we evaluated the effect of steroid structure on the induction of chymotrypsinogen in pancreas explants. Samuels and Tomkins (3), who studied the effect of various steroids on tyrosine aminotransferase activity in hepatoma tissue culture (HTC) cells, classified steroids into 4 categories: 1) optimal inducers, which at high concentrations cause maximal enzyme induction, Received September 27, 1974.
11-deoxycorticosterone and 17-a-hydroxyprogesterone are classified as suboptimal inducers. Progesterone was inactive. It is concluded that the relative importance of the steroid hydroxyl groups for activity is ll/3> 21 > 17a, and that their effect is cumulative. (Endocrinology 97: 475, 1975)
2) suboptimal inducers, which even at saturating concentrations do not induce maximal enzyme levels, 3) anti-inducers, which do not induce the enzyme but inhibit induction by other steroids, and 4) inactive compounds. In the work described below, we attempt to classify steroids tested on the chick pancreas according to the same criteria, as well as to evaluate the relative importance of their hydroxyl groups for activity. Materials and Methods Materials. The following steroids were purchased from Sigma: Corticosterone, deoxycorticosterone, progesterone, testosterone, 17o-methyltestosterone (17a-
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 20 November 2015. at 03:30 For personal use only. No other uses without permission. . All rights reserved.
Endo • 1975 Vol 97 • No 2
NOTES AND COMMENTS
476
methyl-A4-androsten-17/8 ol-3one), fluoxymesterone (17a-methyl-A 4 -androsten-ll/8, 17/3-diol-9a-fluoro3one) and 17/3-estradiol. Cortisol and cortisone were obtained from Calbiochem. The following steroids were from Ikapharm, Israel: 11-deoxycortisol (A4pregnen-17a, 21-diol-3,20 dione), 21-deoxycortisol (A4-pregnen-ll/3, 17a diol-3,20 dione), 17a hydroxyprogesterone (A4-pregnen-17a-ol-3,20 dione) and 11/3 hydroxyprogesterone (A4-pregnen-ll/3 ol-3,20 dione). N-Benzoyl-L-tyrosine ethyl ester was the product of Yeda, Israel. Enzyme assays. Chymotrypsinogen was activated with trypsin and assayed spectrophotometrically with 0.6 mM N-benzoyl-L-tyrosine ethyl ester in 0.05M Tris-HCl buffer, pH 9.0, containing 2.5% (vol/vol) methanol and 0.05% triton X-100 as described previously (2). Protein was determined by the method of Lowry et al. (4). Organ cultures. Embryonic chick pancreases (from 11to 12-day-old embryos) were cultured in a chemically defined medium for 40 to 44 h as described earlier (2). Each culture dish contained 2 pancreases. At the end of
the incubation the pancreases were homogenized in 1.0 ml of 50 mM Tris-HCl buffer, pH 8.0, containing 0.05% Triton X-100. The homogenate was mixed with the culture medium and the chymotrypsin(ogen) was determined as described above. For further details see reference 2. The data in Fig. 1 and Table 1 are representative of at least 3 experiments.
Results Figure 1 shows dose-response curves for the induction of chymotrypsinogen by several steroids. Cortisol and corticosterone are both optimal inducers but the former compound is more effective at lower concentrations than the latter. The concentrations required for halfmaximal induction were approximately 1 x 10~7M for cortisol and 3 x 10~7M for corticosterone. 11-Deoxycortisol (cortexolone) and cortisone were sub-optimal inducers and both produced half their maximal response at about 5 x 10~7M. Although saturating concentrations were not reached at 2 x 10~5M, 11-deoxycortico-
30
< cr o
XCORTICOSTERONE
LU
OCORTISOL
20
•11-DEOXYCORTISOL
z LU O O
^CORTISONE
0
11-DEOXYCORTICOSTERONE
X
o
6 10,-7 10" STEROID CONCENTRATIO N
10' 5 (M)
10"
FIG. 1. Dose-response curves for the induction of chymotrypsinogen in pancreas by various steroids. Pancreases from 12-day embryos were incubated for 40 h with steroids at the concentrations indicated.
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 20 November 2015. at 03:30 For personal use only. No other uses without permission. . All rights reserved.
477
NOTES AND COMMENTS TABLE 1. Effect of steroid structure on induction of chymotrypsinogen in pancreas explants 8 Group in position
OH CH 3 d
xxxxx
OOOOO
I i I i i
OH OH
X
Cortisol Fluoxymesterone
1 1 I I 1 1
3
XOOXO XX X XX
Cortisol 21-Deoxy cortisol 11/3-Hydroxyproge sterone 17a-Hydroxyprogesterone Progesterone
Ratio of chymotrypsin(ogen) activities induced/control
21C
1 1 1 1 xoxoo
2
17a
1 II 1 I I
Cortisol Corticosterone 11-Deoxycortisol Cortisone 11-Deoxycorticosterone
XOXOO XX
1
ll/8 b
o1 x1x1x1x 1
Steroid
XXX oooxx 1 11 1 1
Experiment no.
OH
8.3 10.3 5.4 4.3 2.6 4.4 4.4 3.4 1.6 1.2
4.9 3.8
a Pancreases were from 12-day embryos in experiments 1 and 3 and from 11-day embryos in experiment 2. Pancreas explants were incubated for 40 h in experiments 1 and 3, and for 44 h in experiment 2. Steroid concentrations were 2 x 10"5 M. The activity of chymotrypsin(ogen) in the control was 3 x 10~8 U/pancreas in experiment 1, 1.5 x 10~3 U/pancreas in experiment 2, and 2 x 10~ s U/pancreas in experiment 3. b The group in the l l a position was - H . c Attached to - C H , - . d Fluoxymesterone = 17a methyl-A 4 -androsten-ll/3, 17/8-diol-9a-fluoro-3 one.
sterone is presumably also a weak suboptimal inducer. Table I compares the induction of chymotrypsinogen in pancreas by various steroids. The high concentrations (2 x 10~5M) of steroid used here were probably saturating in most cases. Cortisol, corticosterone and 21-deoxycortisol were optimal inducers. The other compounds, which are listed in order of decreasing effectiveness, namely, 11-deoxycortisol, 11/3-hydroxyprogesterone, cortisone, 11-deoxycorticosterone, and 17ahydroxyprogesterone, did not elicit maximal induction and are presumably suboptimal inducers. Progesterone was virtually inactive. 17a-Methyltesto sterone, progesterone and 17/3-estradiol, which were effective as antiinducers in hepatoma tissue culture cells (3), had no significant inducer or anti-inducer activity in chick embryo pancreas. Fluoxymesterone and cortisone, which were anti-inducers in HTC cells, were suboptimal inducers in the chick pancreas (Table 1).
Discussion The optimal inducers, cortisol, corticosterone, and 21-deoxycortisol all possess an 11/3-hydroxyl group. Cortisol, which has three hydroxyl groups, elicited its maximal response at lower concentrations than did corticosterone and 21-deoxycortisol, which have only two hydroxyl groups.
It should be noted that corticosterone is the principal corticosteroid in the blood of the adult chicken while cortisol is present at much lower concentrations (5). Compounds tested which have one or two hydroxyls at positions other than 11/3 or one hydroxyl at position 11/3, were all suboptimal inducers. The apparent suboptimal activity of cortisone may, however, be due to its partial conversion to cortisol in the pancreas. Our data suggest that the relative importance of the hydroxyl groups is ll/3> 21 > 17a, and that their effect is cumulative. Earlier investigations on the effect of steroid structure on the induction of glutamine synthetase in chick embryo retina stressed the potency of steroids having an 11/3-hydroxyl group whereas steroids lacking this group were considered to have little effect (6-8). In those studies, however, steroids were not tested at saturating concentrations. In more recent experiments Chader and Reif-Lehrer (9) showed that at high concentrations 11-deoxycorticosteroids were effective inducers of glutamine synthetase in the retina. These and previous data support the hypothesis that the relative importance of the hydroxyl groups of corticosteroids for enzyme induction in retina is similar to that proposed above for pancreas. Certain differences in the response of retina and pancreas should be mentioned. Cortico-
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478
NOTES AND COMMENTS
steroids elicit their maximal response in the retina at concentrations about an order of magnitude lower than those required in the pancreas (7-9). Another difference which may be significant is that progesterone is an anti-inducer in the retina (9) but not in the pancreas. This may indicate a difference in the nature of the corticosteroid receptors of pancreas and retina and deserves further investigation. The contribution of the 11/3 and 21 hydroxyl groups to steroid activity is similar in chick embryo pancreas and in HTC cells (10). In hepatoma cells, however, the addition of a 17ahydroxyl group decreases the biological potency of steroids (10), while in chick embryo pancreas it enhances their effect (Table 1). Another difference between the two systems is the lack of activity in chick pancreas of compounds such as progesterone, 17/3-estradiol and 17a-methyltestosterone which are anti-inducers in HTC cells (10,11). The corticosteroid specificity of certain other mammalian systems studied in vitro (12,13) appears to be similar to that of HTC cells. In HeLa cells (14,15), as in chick embryo pancreas and retina, the 17a-hydroxyl group seems to enhance steroid activity. Ackno wl edgment We thank Mrs. Rachel Ampel for her able technical assistance.
Endo i 1975 Vol 97 , No 2
References 1. Cohen, A., H. Heller, and R. G. Kulka, Devel Biol 29: 293, 1972. 2. , and R. G. Kulka, J Biol Chem 249: 4522, 1974. 3. Samuels, H. H., and G. M. Tomkins, J Mol Biol •< 52: 57, 1970. 4. Lowry, O. H., N. J. Rosebrough, A. L. Farr, and R. J. Randall,; Biol Chem 193: 265, 1951. 5. Sturkie, P. D., Avian Physiology, Cornell University Press, Ithaca, 1965, p. 677. 6. Moscona, A. A., and R. Piddington, Science 158: 496, 1967. 4 7. Reif-Lehrer, L., Biochim Biophys Ada 170: 263, 1968. 8. Moscona, A. A., In Hamburgh, M., and E. J. W. Barrington (eds.), Hormones in Development, Appleton-Century-Crofts, New York, 1971, p. 169. 9. Chader, G. J., and L. Reif-Lehrer, Biochim Biophys Ada 264: 186, 1972. 10. Rousseau, G. G., J. D. Baxter, and G. M. Tomkins, / Mol Biol 67: 99, 1972. 11. Baxter, J. D., and G. M. Tomkins, Proc Natl Acad Sci USA 68: 932, 1971. 12. Ballard, P. L., and R. A. Ballard, Proc Natl Acad Sci USA 69: 2668, 1972. 13. Munck, A., and C. Wira, In Raspe, G. (ed.), Advances in the Biosciences 7, Schering Workshop on Steroid Hormone Receptors, Pergamon, Vieweg, 1971, p. 301. 14. Melnykovych, G., and C. F. Bishop, Biochim Biophys Ada 177: 579, 1969. 15. Cox, R. P., Ann NY Acad Sci 179: 596, 1971.
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