- Email: [email protected]
Effects of Progesterone on Developing Chick Embryos1,2
RESEARCH NOTES Effects of Progesterone on Developing Chick Embryos1 >2 J. A. RENDEN and P. H. BENOFF Department of Poultry Science, Oregon State University, Corvallis, Oregon 97331 (Received for publication October 1, 1979)
1980 Poultry Science 59:2559-2563 INTRODUCTION
MATERIALS AND METHODS
Steroid hormones play an important role in normal sexual differentiation of birds. It has been suggested that sex hormones produced by the morphologically undifferentiated gonad are sex differentiator substances directing transformation of the indifferent gonad into either ovary or testis (Hafen, 1975). Male embryos treated with estrogens (estrone or estradiol) are transformed into intersexes (Willier et al., 1935; Hamilton, 1961; Narbaitz and Teitelman, 1965; reviewed by Wolf, 1979). Testosterone has little or no effect on female gonads, although the Mullerian ducts undergo partial or complete regression. Androstenedione, an androgen, feminizes male gonads and at the same time masculinizes female ducts.
Fertile chicken eggs from Barred Plymouth Rock females mated to New Hampshire males were stored at 15 C for up to 14 days. All eggs were incubated at 38 C and 55% relative humidity for 4 days prior to hormone injection. Experiment I. To determine the effects of varying levels of progesterone on embryonic development, 153 eggs were randomly assigned to the following treatment groups: 0, .5, 1.0, or 2.0 mg progesterone (A4 Pregnan - 3, 20 dione, US Biochemical Corp.) per egg. The eggs were washed with 70% ethanol, and small holes were made at the blunt and narrow ends of each egg with a fine pointed dental drill. Progesterone was dissolved in .05 ml propylene glycol and injected into the yolk sac through the narrow end of the egg with a No. 22, l'/2-in needle attached to a 1 cc tuberculin syringe. The 0 level treatment served as a control, since preliminary sham injections and control injections of propylene glycol caused neither embryonic malformations nor significant mortality as compared to uninjected eggs. After injection, both ends of the eggs were sealed with melted paraffin wax and returned to the incubator. All eggs were examined at 18 days of incubation. Embryos were sexed by feather color and weighed without the yolk sac. Gross morphology of the body and reproductive system was noted, and weights for the body, right and left gonads, and right shank (metatarsus) were obtained for each embryo. Length of
The effects of progesterone on avian sexual differentiation are unknown. Progesterone is a steroid precursor of androgens, estrogens, and corticosteroids and has important reproductive functions in the mature hen (O'Malley and Means, 1974; Wilson and Sharpe, 1976). The purpose of this study was to examine the effects of progesterone on the developing avian reproductive system and to note alterations in embryonic growth.
1 Oregon Agricultural Experiment Station Technical Paper No. 5292. 2 Presented at the 68th Annual Meeting of the Poultry Science Association, August 1979, University of Florida, Gainesville, FL.
2559
Downloaded from http://ps.oxfordjournals.org/ at Pennsylvania State University on May 27, 2015
ABSTRACT Experiments were conducted to examine the effects of progesterone on the developing chick embryo with particular attention to the reproductive system. Differing levels of progesterone (0, .5, 1.0, or 2.0 mg) were dissolved in propylene glycol and injected at 4 days of incubation into the yolk sac of eggs from Barred Plymouth Rock females mated to New Hampshire males. Progesterone caused significant reductions in body weight and length and shank weight and length in 18-day-old embryos. Aside from reductions in embryonic growth, progesterone did not cause gross alterations in embryonic development. Progesterone modified neither normal morphology nor differentiation of male or female gonads and associated ductal systems. (Key words: progesterone, embryology, chicken)
RENDEN AND BENOFF
2560
RESULTS AND DISCUSSION Experiment 1. Mortality was not significantly different among eggs treated with 0, .5, 1.0, or 2.0 mg progesterone (15.15, 20.51, 27.03, and 33.33%, respectively). However, progesterone did cause significant reductions in body weight and shank weight and length in male and female embryos (Table 1). Shank weight expressed as percent of body weight was not significantly different among the treatment groups for either sex. Testes weights were not affected by progesterone; however, left ovary weight was significantly reduced while right ovary weight was not influenced. Left ovary weight expressed as percent of body weight was not significantly different among the treatment groups. Aside from reductions in body weight, progesterone did not cause gross alterations in embryonic development. Progesterone (.2 to 1.0 mg) was found to be weakly toxic and
teratogenic by Piotrowski (1966) who administered the steroid directly onto the embryo. The bone and joint system, particularly hind limbs, was most frequently affected. Progesterone did not modify normal morphology nor differentiation of male or female gonads and associated ductal systems. The testes of male embryos treated with progesterone showed normal development of the medulla and presumptive seminiferous tubules. The left ovary of treated females displayed normal development of the cortex and secondary sex cords, while the right ovary underwent normal regression. Experiment 2. Mortality was not significantly different between control or .5 mg progesterone treated eggs (12.50% vs. 4.35%, respectively). Body weight and length of embryos injected with .5 mg progesterone on day 4 and examined either at 11 or 14 days incubation were not significantly different from the controls (Table 2). The shank length of progesterone treated embryos at 11 days was significantly decreased; however, there was no significant difference between progesterone and control groups when shank length was expressed as percent of body length. Shank weight or length at 14 days was not significantly different between progesterone and control groups. Body weight and length and shank weight and length were significantly reduced in embryos treated with .5 mg progesterone at 4 days incubation and examined at 18 days as compared to control embryos. Shank weight or length expressed as percent of body weight or length, respectively, was not different between the treated and untreated groups. Ahmad and Zamenhof (1979) reported that 10 fj.g progesterone delivered on the chorioallantoic membrane of 7-day-old chick embryos caused a significant increase in body weight and cerebral hemispheres weight on day 10. It was suggested that progesterone promoted growth of the early embryo, but its effect was dependent upon embryonic age and sex. The action of progesterone on embryonic growth is unknown, although there are several possible reasons for its effects. First, it may be that progesterone was converted to small amounts of corticosterone within the embryo resulting in growth inhibition. Progesterone can be detected in the adrenals of 9-day-old chick embryos and is thought to act as a precursor to other corticosteroids (Kalliecharan and Hall, 1974). Corticosterone is known to cause
Downloaded from http://ps.oxfordjournals.org/ at Pennsylvania State University on May 27, 2015
the right shank was also recorded. Both the right and the left gonads from three embryos in each treatment group were fixed in 10% buffered formalin and processed through standard histological procedures. Tissue samples were sectioned at 5 /J. and stained with hemotoxylin and eosin. Experiment 2. To determine the effects of progesterone on embryonic growth at several ages, 149 eggs were randomly divided between two treatment groups: controls (.05 ml propylene glycol) and .5 mg progesterone. The eggs were injected as described in Experiment 1. A random and equal sample of control and progesterone treated eggs were examined at 11, 14, 18 days of incubation. Weight and length were obtained for the body and right shank of each embryo (shank weights were unavailable for 11-day embryos). Gonad and shank weights were expressed as absolute values and as percent of body weight; shank length was expressed as an absolute value and as percent of body length. Mortality data for Experiments 1 and 2 were analyzed using Chi-squared statistics (Steel and Torrie, 1960). Weight data for Experiment 1 were analyzed within each sex using one-way analyses of variance, and significant means were separated using Duncan's multiple range tests. Percentage data were analyzed using the arcsin % transformed data. Weight data for Experiment 2 were pooled over sexes and analyzed using Student's i-tests.
RESEARCH NOTE
U
,-V
-O 00
•+ -o
rt ^ XI ,~. .O ^ . XI - > O O r j r-* O 00 r-l O r s <3- rf
,-( i n in O
^- o
OOO vOOs
2561
O
m est rrj " ^
\b O
d\
,-<
N 'fo
O
H
6 rr> Oi
00 0 \ 00
00 O O to
N m C-*. t o
rt ^-v t-N.cn Os t o T-H "—'
rt ' —v o\vO \© ^ rH v ~ '
d ^-v OOO Otr, c4 ^
cj .-—-. t>* T—i CO fN *-I s—'
d -—-. d ^-v O 0\ t ^ 00 ^O Cs] O H t o "—' t o ^
d ^—in to i-(fN m -—'
CO m •*$- X ^ O
0 0 ^ r*- ^ fN]"—'
(S t ^ O "^ rri-^-
ml"\Oto r j ^
O O i/i \ 0 o d ^
^-"O l-tro irj"-'
X t~Os ^ ^ *w'
O000 C^ro in"—'
in 00 000 fN ^
O1-1 in<> vO ^
^-O \Q CO t> ^
^O T-t foro rj-' ^ H
m ^ C0\0 ro ^
t^. — i c t ^ m VQ ^
rsito t^.O\ »n ^
cOto t^-O ^"" t-i
(M
rt
,-H
TH •—'
fN
i-H
i-H
i-<
^
TH
\Q 0\ Tf M V
\0 \0 i-l ^O m
O C"-O rH ^
iW oC
•+ -^ rs
—*
f» 00 t^00 •H 00 O H M
to
T-H
ro
vb
00
Os
—
C-)
ON
H
O
t3
£: u;
ca
<
th
6
H ^ -
Downloaded from http://ps.oxfordjournals.org/ at Pennsylvania State University on May 27, 2015
C-J t o ^ 0 0
CO r o \Q tr> r n T-H *H
in r^
^ ^ *© N "
t^
CO [ N 0000
O
Q\ \ 0 rn •* M
CT> Wt
fN to ^O 00
m
0
18
.5
.5
22
21
23
17
48.31 a (.77) 46.99 a (1.29) 356.59 a (16.78) 291.03 b (18.48)
53.14 a (1.08) 93.65 a (1.54) 95.57 a (1.60) 134.57 a (1.34) 125.50 b (3.82)
3.41 a (.15) 10.11 a (.34) 10.43 a (.25) 23.85 a (.75) 19.48 b (.96)
mg
54.33 a (.66)
Body length (mm)
3.47 a (.08) 2
Body weight (g)
2 Standard error. a,b ' Means within the same column for each day examined with the same superscript are not significantly different
'Sexes combined
0
14
21
18
0
11
.5
N
Progesterone (mg)
Day examined
TABLE 2. Effects of progesterone on developing embryos* (injected o
m http://ps.oxfordjournals.org/ at Pennsylvania State University on May 27, 2015
RESEARCH NOTE
ACKNOWLEDGMENTS The authors appreciate the technical assistance provided by Mary Pierson and Janice Fuquay. REFERENCES Ahmad, G., and S. Zamenhof, 1979. The effect of progesterone on brain and body growth of chick embryos. Growth 43:58—61. Enemar, A., 1967. Ontogeny of the hypophysial growth-promoting activity in the chick. J. Endocrinol. 37:9-15. Hafen, K., 1975. Sex differentiation of avian gonads in vitro. Amer. Zool. 15:257-272. Hamilton, T. H., 1961. Studies on the physiology of urogenital differentiation in the chick embryo. I.
Hormonal control of sexual differentiation of Mullerian ducts. J. Exp. Zool. 146:265-274. Kalliecharan, R., and B. K. Hall, 1974. A developmental study of the levels of progesterone, corticosterone, Cortisol, and cortisone circulating in plasma of chick embryos. Gen. Comp. Endocrinol. 24:364-372. Karnofsky, D. A., L. P. Ridgway, and P. A. Patterson, 1951. Growth-inhibiting effect of cortisone acetate on the chick embryo. Endocrinology 48:596-616. Narbaitz, R., and G. Teitelman, 1965. A histochemical study of sex inversion produced by estradiol in chick embryos. J. Embryol. Exp. Morphol. 13:45-50. O'Malley, B. W., and A. R. Means, 1974. Female steroid hormones and target cell nuclei. Science 183:610-620. Piotrowski, J., 1966. Investigations on the progesterone, oestrone and cortisone effect on the embryonal development. I. Experiments on the chicken embryos. Folia Biol. 14:205-225. Silbermann, M., S. Levitan, U. Kleinhaus, and S. Finkelbrand, 1979. Long bone growth during prolonged intermittent corticosteroid treatment and subsequent rehabilitation. Cell Tissue Res. 201:51-62. Steel, R.C.D., and J. H. Torrie, 1960. In Principles and procedures of statistics. McGraw-Hill Book Co., Inc., New York, NY. Willier, B. H., T. F. Gallagher, and F. C. Koch, 1935. Sex modification in the chick embryo resulting from injections of male and female hormones. Proc. Nat. Acad. Sci., 21:625-631. Wilson, S. C , and P. J. Sharpe, 1976. The effects of progesterone on oviposition in the domestic fowl (Gallus Domesticus). Brit. Poultry Sci. 17: 163-173. Wolf, E., 1979. Old experiments and new trends in avian sex differentiation. In Vitro 15:6—10.
Downloaded from http://ps.oxfordjournals.org/ at Pennsylvania State University on May 27, 2015
growth retardation in developing chick embryos (Karnofsky et ah, 1951) and is thought to disrupt normal skeletal growth by interfering with basic metabolic functions of chondrocytes (Silbermann etal, 1979). Second, progesterone may act directly to retard embryonic growth by blocking normal steroid-cell interactions and thus disrupt normal RNA and/or protein synthesis. Third, progesterone may have interfered with the secretion of somatotrophic hormone from the pituitary. The growthpromoting activity of the pituitary is first seen at 15 days of incubation (Enemar, 1967), and in this study progesterone caused growth retardation sometime between 14 to 18 days of embryonic development.
2563
1980 Poultry Science 59:2559-2563 INTRODUCTION
MATERIALS AND METHODS
Steroid hormones play an important role in normal sexual differentiation of birds. It has been suggested that sex hormones produced by the morphologically undifferentiated gonad are sex differentiator substances directing transformation of the indifferent gonad into either ovary or testis (Hafen, 1975). Male embryos treated with estrogens (estrone or estradiol) are transformed into intersexes (Willier et al., 1935; Hamilton, 1961; Narbaitz and Teitelman, 1965; reviewed by Wolf, 1979). Testosterone has little or no effect on female gonads, although the Mullerian ducts undergo partial or complete regression. Androstenedione, an androgen, feminizes male gonads and at the same time masculinizes female ducts.
Fertile chicken eggs from Barred Plymouth Rock females mated to New Hampshire males were stored at 15 C for up to 14 days. All eggs were incubated at 38 C and 55% relative humidity for 4 days prior to hormone injection. Experiment I. To determine the effects of varying levels of progesterone on embryonic development, 153 eggs were randomly assigned to the following treatment groups: 0, .5, 1.0, or 2.0 mg progesterone (A4 Pregnan - 3, 20 dione, US Biochemical Corp.) per egg. The eggs were washed with 70% ethanol, and small holes were made at the blunt and narrow ends of each egg with a fine pointed dental drill. Progesterone was dissolved in .05 ml propylene glycol and injected into the yolk sac through the narrow end of the egg with a No. 22, l'/2-in needle attached to a 1 cc tuberculin syringe. The 0 level treatment served as a control, since preliminary sham injections and control injections of propylene glycol caused neither embryonic malformations nor significant mortality as compared to uninjected eggs. After injection, both ends of the eggs were sealed with melted paraffin wax and returned to the incubator. All eggs were examined at 18 days of incubation. Embryos were sexed by feather color and weighed without the yolk sac. Gross morphology of the body and reproductive system was noted, and weights for the body, right and left gonads, and right shank (metatarsus) were obtained for each embryo. Length of
The effects of progesterone on avian sexual differentiation are unknown. Progesterone is a steroid precursor of androgens, estrogens, and corticosteroids and has important reproductive functions in the mature hen (O'Malley and Means, 1974; Wilson and Sharpe, 1976). The purpose of this study was to examine the effects of progesterone on the developing avian reproductive system and to note alterations in embryonic growth.
1 Oregon Agricultural Experiment Station Technical Paper No. 5292. 2 Presented at the 68th Annual Meeting of the Poultry Science Association, August 1979, University of Florida, Gainesville, FL.
2559
Downloaded from http://ps.oxfordjournals.org/ at Pennsylvania State University on May 27, 2015
ABSTRACT Experiments were conducted to examine the effects of progesterone on the developing chick embryo with particular attention to the reproductive system. Differing levels of progesterone (0, .5, 1.0, or 2.0 mg) were dissolved in propylene glycol and injected at 4 days of incubation into the yolk sac of eggs from Barred Plymouth Rock females mated to New Hampshire males. Progesterone caused significant reductions in body weight and length and shank weight and length in 18-day-old embryos. Aside from reductions in embryonic growth, progesterone did not cause gross alterations in embryonic development. Progesterone modified neither normal morphology nor differentiation of male or female gonads and associated ductal systems. (Key words: progesterone, embryology, chicken)
RENDEN AND BENOFF
2560
RESULTS AND DISCUSSION Experiment 1. Mortality was not significantly different among eggs treated with 0, .5, 1.0, or 2.0 mg progesterone (15.15, 20.51, 27.03, and 33.33%, respectively). However, progesterone did cause significant reductions in body weight and shank weight and length in male and female embryos (Table 1). Shank weight expressed as percent of body weight was not significantly different among the treatment groups for either sex. Testes weights were not affected by progesterone; however, left ovary weight was significantly reduced while right ovary weight was not influenced. Left ovary weight expressed as percent of body weight was not significantly different among the treatment groups. Aside from reductions in body weight, progesterone did not cause gross alterations in embryonic development. Progesterone (.2 to 1.0 mg) was found to be weakly toxic and
teratogenic by Piotrowski (1966) who administered the steroid directly onto the embryo. The bone and joint system, particularly hind limbs, was most frequently affected. Progesterone did not modify normal morphology nor differentiation of male or female gonads and associated ductal systems. The testes of male embryos treated with progesterone showed normal development of the medulla and presumptive seminiferous tubules. The left ovary of treated females displayed normal development of the cortex and secondary sex cords, while the right ovary underwent normal regression. Experiment 2. Mortality was not significantly different between control or .5 mg progesterone treated eggs (12.50% vs. 4.35%, respectively). Body weight and length of embryos injected with .5 mg progesterone on day 4 and examined either at 11 or 14 days incubation were not significantly different from the controls (Table 2). The shank length of progesterone treated embryos at 11 days was significantly decreased; however, there was no significant difference between progesterone and control groups when shank length was expressed as percent of body length. Shank weight or length at 14 days was not significantly different between progesterone and control groups. Body weight and length and shank weight and length were significantly reduced in embryos treated with .5 mg progesterone at 4 days incubation and examined at 18 days as compared to control embryos. Shank weight or length expressed as percent of body weight or length, respectively, was not different between the treated and untreated groups. Ahmad and Zamenhof (1979) reported that 10 fj.g progesterone delivered on the chorioallantoic membrane of 7-day-old chick embryos caused a significant increase in body weight and cerebral hemispheres weight on day 10. It was suggested that progesterone promoted growth of the early embryo, but its effect was dependent upon embryonic age and sex. The action of progesterone on embryonic growth is unknown, although there are several possible reasons for its effects. First, it may be that progesterone was converted to small amounts of corticosterone within the embryo resulting in growth inhibition. Progesterone can be detected in the adrenals of 9-day-old chick embryos and is thought to act as a precursor to other corticosteroids (Kalliecharan and Hall, 1974). Corticosterone is known to cause
Downloaded from http://ps.oxfordjournals.org/ at Pennsylvania State University on May 27, 2015
the right shank was also recorded. Both the right and the left gonads from three embryos in each treatment group were fixed in 10% buffered formalin and processed through standard histological procedures. Tissue samples were sectioned at 5 /J. and stained with hemotoxylin and eosin. Experiment 2. To determine the effects of progesterone on embryonic growth at several ages, 149 eggs were randomly divided between two treatment groups: controls (.05 ml propylene glycol) and .5 mg progesterone. The eggs were injected as described in Experiment 1. A random and equal sample of control and progesterone treated eggs were examined at 11, 14, 18 days of incubation. Weight and length were obtained for the body and right shank of each embryo (shank weights were unavailable for 11-day embryos). Gonad and shank weights were expressed as absolute values and as percent of body weight; shank length was expressed as an absolute value and as percent of body length. Mortality data for Experiments 1 and 2 were analyzed using Chi-squared statistics (Steel and Torrie, 1960). Weight data for Experiment 1 were analyzed within each sex using one-way analyses of variance, and significant means were separated using Duncan's multiple range tests. Percentage data were analyzed using the arcsin % transformed data. Weight data for Experiment 2 were pooled over sexes and analyzed using Student's i-tests.
RESEARCH NOTE
U
,-V
-O 00
•+ -o
rt ^ XI ,~. .O ^ . XI - > O O r j r-* O 00 r-l O r s <3- rf
,-( i n in O
^- o
OOO vOOs
2561
O
m est rrj " ^
\b O
d\
,-<
N 'fo
O
H
6 rr> Oi
00 0 \ 00
00 O O to
N m C-*. t o
rt ^-v t-N.cn Os t o T-H "—'
rt ' —v o\vO \© ^ rH v ~ '
d ^-v OOO Otr, c4 ^
cj .-—-. t>* T—i CO fN *-I s—'
d -—-. d ^-v O 0\ t ^ 00 ^O Cs] O H t o "—' t o ^
d ^—in to i-(fN m -—'
CO m •*$- X ^ O
0 0 ^ r*- ^ fN]"—'
(S t ^ O "^ rri-^-
ml"\Oto r j ^
O O i/i \ 0 o d ^
^-"O l-tro irj"-'
X t~Os ^ ^ *w'
O000 C^ro in"—'
in 00 000 fN ^
O1-1 in<> vO ^
^-O \Q CO t> ^
^O T-t foro rj-' ^ H
m ^ C0\0 ro ^
t^. — i c t ^ m VQ ^
rsito t^.O\ »n ^
cOto t^-O ^"" t-i
(M
rt
,-H
TH •—'
fN
i-H
i-H
i-<
^
TH
\Q 0\ Tf M V
\0 \0 i-l ^O m
O C"-O rH ^
iW oC
•+ -^ rs
—*
f» 00 t^00 •H 00 O H M
to
T-H
ro
vb
00
Os
—
C-)
ON
H
O
t3
£: u;
ca
<
th
6
H ^ -
Downloaded from http://ps.oxfordjournals.org/ at Pennsylvania State University on May 27, 2015
C-J t o ^ 0 0
CO r o \Q tr> r n T-H *H
in r^
^ ^ *© N "
t^
CO [ N 0000
O
Q\ \ 0 rn •* M
CT> Wt
fN to ^O 00
m
0
18
.5
.5
22
21
23
17
48.31 a (.77) 46.99 a (1.29) 356.59 a (16.78) 291.03 b (18.48)
53.14 a (1.08) 93.65 a (1.54) 95.57 a (1.60) 134.57 a (1.34) 125.50 b (3.82)
3.41 a (.15) 10.11 a (.34) 10.43 a (.25) 23.85 a (.75) 19.48 b (.96)
mg
54.33 a (.66)
Body length (mm)
3.47 a (.08) 2
Body weight (g)
2 Standard error. a,b ' Means within the same column for each day examined with the same superscript are not significantly different
'Sexes combined
0
14
21
18
0
11
.5
N
Progesterone (mg)
Day examined
TABLE 2. Effects of progesterone on developing embryos* (injected o
m http://ps.oxfordjournals.org/ at Pennsylvania State University on May 27, 2015
RESEARCH NOTE
ACKNOWLEDGMENTS The authors appreciate the technical assistance provided by Mary Pierson and Janice Fuquay. REFERENCES Ahmad, G., and S. Zamenhof, 1979. The effect of progesterone on brain and body growth of chick embryos. Growth 43:58—61. Enemar, A., 1967. Ontogeny of the hypophysial growth-promoting activity in the chick. J. Endocrinol. 37:9-15. Hafen, K., 1975. Sex differentiation of avian gonads in vitro. Amer. Zool. 15:257-272. Hamilton, T. H., 1961. Studies on the physiology of urogenital differentiation in the chick embryo. I.
Hormonal control of sexual differentiation of Mullerian ducts. J. Exp. Zool. 146:265-274. Kalliecharan, R., and B. K. Hall, 1974. A developmental study of the levels of progesterone, corticosterone, Cortisol, and cortisone circulating in plasma of chick embryos. Gen. Comp. Endocrinol. 24:364-372. Karnofsky, D. A., L. P. Ridgway, and P. A. Patterson, 1951. Growth-inhibiting effect of cortisone acetate on the chick embryo. Endocrinology 48:596-616. Narbaitz, R., and G. Teitelman, 1965. A histochemical study of sex inversion produced by estradiol in chick embryos. J. Embryol. Exp. Morphol. 13:45-50. O'Malley, B. W., and A. R. Means, 1974. Female steroid hormones and target cell nuclei. Science 183:610-620. Piotrowski, J., 1966. Investigations on the progesterone, oestrone and cortisone effect on the embryonal development. I. Experiments on the chicken embryos. Folia Biol. 14:205-225. Silbermann, M., S. Levitan, U. Kleinhaus, and S. Finkelbrand, 1979. Long bone growth during prolonged intermittent corticosteroid treatment and subsequent rehabilitation. Cell Tissue Res. 201:51-62. Steel, R.C.D., and J. H. Torrie, 1960. In Principles and procedures of statistics. McGraw-Hill Book Co., Inc., New York, NY. Willier, B. H., T. F. Gallagher, and F. C. Koch, 1935. Sex modification in the chick embryo resulting from injections of male and female hormones. Proc. Nat. Acad. Sci., 21:625-631. Wilson, S. C , and P. J. Sharpe, 1976. The effects of progesterone on oviposition in the domestic fowl (Gallus Domesticus). Brit. Poultry Sci. 17: 163-173. Wolf, E., 1979. Old experiments and new trends in avian sex differentiation. In Vitro 15:6—10.
Downloaded from http://ps.oxfordjournals.org/ at Pennsylvania State University on May 27, 2015
growth retardation in developing chick embryos (Karnofsky et ah, 1951) and is thought to disrupt normal skeletal growth by interfering with basic metabolic functions of chondrocytes (Silbermann etal, 1979). Second, progesterone may act directly to retard embryonic growth by blocking normal steroid-cell interactions and thus disrupt normal RNA and/or protein synthesis. Third, progesterone may have interfered with the secretion of somatotrophic hormone from the pituitary. The growthpromoting activity of the pituitary is first seen at 15 days of incubation (Enemar, 1967), and in this study progesterone caused growth retardation sometime between 14 to 18 days of embryonic development.
2563