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Uterine luminal prostaglandin F in cycling mares
PROSTAGLANDINS
UTERINE IUMINAL PROSTAGLANDIN F IN CYCLING MARES Michael T. Zavy, Fuller W. Bazer, Dan C. Sharp Marilyn Frank and William W. Thatcher Departments of Animal Science and Dairy Science University of Florida, Gainesville, Florida 52611
ABSTRACT Prostaglandin F was measured by radioimmunoassay in uterine flushings of cycling mares on days 4, 8, 12, 14, 16, 18 and 20 post-ovulation. Prostaglandin F was significantly (P < .05) affected by day of the estrous cycle and reached maximal levels on day 14. Least squares means for days 4, 8, 12, 14, 16, 18 and 20 were: .66, .81, 4.77, 14.31, 5.48, 3.68 and 2.97 ng/ml, respectively. ACKNOWLEDGEMENTS Departments of Animal and Dairy Science, Florida Agricultural Experiment Station, Journal Series No. ]]]6. This research was supported, in part, by N.I.H. Grant HD08560 and the Morris Animal Foundation. The prostaglandin F2~ - Tham salt used in this study was provided by Dr. J. W. Lauderdale of the Upjohn Company, Kalamazo, Michigan.
OCTOBER 1978 VOL. 16 NO. 4
643
PROSTAGLANDINS
INTRODUCTION The uterus has been implicated in controlling ovarian luteal function for over S0 years. It has been shown in guinea pigs (i), cows (2), and mares (3) that hysterectomy in the luteal phase of the estrous cycle results in an extended life span of the corpora lutea (CL). The uterus of many species of mammals produces a luteolysin which causes luteal regression and allows for a new ovarian cycle (4); the possible exception to this being the primate. Prostaglandin F2~ has been shown to induce luteolysis in mares when administered in diestrus (5, 6), luteolysis has been shown to occur after administration by many routes; i.e., systemic (5, 6), intraluteal (7) or intrauterine injection (5, 6). Kooistra and Ginther (8) demonstrated that PGF2~ effectively terminated pseudopregnancy and early pregnancy in the mare by bringing about the demise of the CL. Additionally, it has been demonstrated in the mare that the uterus likely exerts its luteolytic effect through a systemic rather than a local pathway (3). Prostaglandin F has been measured in uterine fluids of the monkey (9) and gilt (i0). A biochemical explanation for the mechanisms of PGF induced luteolysis has been proposed by Henderson and McNatty (II). Recently, it has been demonstrated that immunoreactive prostaglandin F (PGF) reached maximal concentration in the uterine venous plasma of mares on day 14 of the estrous cycle (12); a time coincidental with luteal regression (13). In view of these findings and because PGF is a product of endometrial secretion, a study was conducted to quantitate PGF in uterine flushings of cycling mares on selected days of the estrous cycle. MATERIAL AND METHODS ExpeTimental Animals. Uterine flushings were collected from 14 normally cycling mares of Quarter Horse or Thoroughbred breeding. Days of collection were 4, 8, 12, 14, 16, 18 and 20 post-ovulation. Ovulations were detected by daily rectal palpation of the ovaries. Over the experimental period 32 uterine flushings were collected. Several of the mares were used for the collection of more than one uterine flushing in succeeding estrous cycles with at least one estrous cycle intervening between two collections. Collection Technique. Uterine flushings were obtained by a non=surgical collection technique developed in our laboratory (14). Eighty milliliters of sterile, .33M saline were infused through the inner catheter of the collection device into the uterine lumen. After 5 min the fluid containing uterine secretions was slowly withdrawn from the uterus. Uterine flushings were placed in sterile vials on ice until quantitated. After the volume of each uterine flushing was measured, samples were centrifuged in a refrigerated centrifuge for 20 min at iO,000 rpm. The supernatant was filtered through a .45 micron filter to remove bacteria and/or cellular debris. The filtrate was then transferred into sterile vials and stored at -20°C until analysis were performed. Prostaglandin F Radioimmunoassay. All uterine flushing samples were assayed for PGF concentration by the method described previously for our laboratory
(is).
644
OCTOBER 1978 VOL. 16 NO.'4
PROSTAGLANDINS
Statistical Analysis. Results of this study were analyzed by least squares regression analysis (16) to obtain estimates of day effects of PGF content of mare uterine flushings. RESULTS Least squares analysis of data indicated that PGF in mare uterine flushings was significantly (P< .05) affected by day of the estrous cycle. Prostaglandin F content of mare uterine flushings is expressed as concentration and total recoverable PGF in Table I. When expressed on a concentration basis a third order regression curve (Y = 7378.8 + 923.5X - 137.8X ~ - 16.6X 3 was significant (P< .05), however, data were best described by a non-significant fourth order regression curve (Y = 8940.1 + 454.8X - 348.7X 2 - 1.6X 3 + 3.4X4).
Table I.
Prostaglandin F (PGF) Content of Mare Uterine Flushings
PGF Concentration ng/ml of flushing a
PGF Total ng/flushing a
Day
n
4
5
.66 ± .24
52.19 ± 19.63
8
5
.81 ± .16
65.25 ± 10.34
12
5
4.77 ± 2.41
391.18 ± 190.96
14
4
14.31 ± 4.70
1,133.81 ± 377.36
16
3
5.48 ± 1.80
495.40 ± 165.00
18
3
3.68 ± 1.36
304.39 ± 103.76
20
7
2.97 ± .81
244.06 ± 68.97
aMean + SEM
OCTOBER 1978 VOL 1 6 N O . 4
645
PROSTAGLANDINS
Least squares means for the treatment days appear in histogram form in Figure I. PGF concentration was less than 1 ng/ml on days 4 and 8 of the estrous cycle, increased to 14.3 ng/ml on day 14 and steadily decreased thereafter. When calculated on the basis of total PGF recovered (concentration x recovery volume), an average of 1.13 vg of PGF was recovered from the uterine flushings of mares on day 14.
l-
16.0-
4
o9 14.0; ~.(.9
"1" " "
-r 9.0~
sB
u..l~
T
_z,,, zoQZ
z~.
~5
T
5.o-
Z
7
T
4
8
3
T3
T
1.0-
,~ , ~
i
v
i
18
w
i
20
DAYS POST OVULATION F i g u r e I.
Least squares means histogram of Prostaglandin F (PGF) in ng/ml of mares uterine flushing. Numbers above bars indicate the number of animals per observation group (total = 32), lines above bars represent the standard errors of the least square means. PGF concentration (ng/ml) overall mean ± SEM; 4.67 ~ .77, Coefficient of Variation = 132.15%.
646
OCTOBER 1978 VOL. 16 NO. 4
PROSTAGLANDINS
Data from the present study indicate a distinct peak of PGF in uterine flushings of cycling mares on day 14 of the estrous cycle. This supports work presented by Douglas and Ginther (12) who measured PGF in uterine venous drainage of cycling mares with regard to time trends and magnitude of the PGF peak. An increase in PGF levels in the mid-to-late-luteal phase of the estrous cycle is consistant with the idea that PGF, of uterine origin, may be associated with luteal regression in the mare. This concept is further strengthened by work from Van Niekerk et al. (13), which indicated that equine luteal cells begin to degenerate 12 days after ovulation, a time which is associated with rising uterine luminal PGF levels. Additionally, this rise in PGF is temporally related to declining plasma progesterone levels which have previously been reported by Ganjam et al. (17). Roberts et al. (18) have indicated that mechanical stimulation of the sheep uterus, in situ, resulted in a rapid release of PGF2a into the uterine veins which was sustained for at least the duration of stimulation. It is not known whether the uterine flushing technique in this report acted in a similar stimulatory manner. Regardless of whether the uterine flushing technique was stimulatory or not, the technique was essentially constant at all days of the estrous cycle, thus the time trends and their implied physiological role seem valid. R e c e n t l y , Bazer and T h a t c h e r (19) i n t r o d u c e d t h e c o n c e p t t h a t b o t h PGF and the porcine intrauterine glycoprotein move in an endocrine fashion (toward the vasculature) in cycling gilts whereas, in pregnant gilts, both are accumulated within the uterine lumen (exocrine secretion). The results of such an action would be to prevent secretion toward the vasculature in the pregnant animal, thus PGF would be prevented from reaching the ovary. Many similarities in uterine secretory patterns (total protein, acid phosphatase activity, prostaglandin F) in gilts and mares (Michael T. Zavy, Fuller W. Bazer and Dan C. Sharp, unpublished results) suggest that a similar mechanism may exist in the mare.
OCTOBER 1978 VOL. 16 NO. 4
647
PROSTAGLANDINS REFERENCES
I.
Loeb, L. The effect of extirpation of the uterine horn on the life and function of the corpus luteum in the guinea pig. Proc. Soc. Exp. Biol. Med. 20:441, 1923.
2.
Wiltbank, J. N. and L. E. Casida. Alteration of ovarian activity by hysterectomy. J. Anim. Sci. 15:134, 1956.
3.
Ginther, O. J. and N. L. First. Maintenance of the corpus luteum in hysterectomized mares. Am. J. Vet. Res. 32:1687, 1971.
4.
McCracken, J . A., D. T. B a i r d , J . C. C a r l s o n , J . R. Goding and B. Barcikowski. The r o l e o f p r o s t a g l a n d i n s i n l u t e a l r e g r e s s i o n . J . Reprod. F e r t . Suppl. 18:133, 1973.
5.
Douglas, R. H. and O. J. Ginther. Effect of prostaglandin on length of diestrus in mares. Prostaglandins. 2:265, 1972.
6.
Noden, P. A., H. D. Hafs and W. D. Oxender. o v u l a t i o n a f t e r p r o s t a g l a n d i n F2a in h o r s e s . Med. 145:145, 1973.
P r o g e s t e r o n e , e s t r u s and Proc. Soc. Exp. B i o l .
7. ¸ Douglas, R. H. and O. J . G i n t h e r . Route of p r o s t a g l a n d i n F2 i n j e c t i o n and l u t e o l y s i s in mares. Proc. Soc. Exp. B i o l . Med. 148:263, 1975.
8.
K o o i s t r a , L. H. and O. J . G i n t h e r . T e r m i n a t i o n o f pseudopregnancy by a d m i n i s t r a t i o n of p r o s t a g l a n d i n F2a and t e r m i n a t i o n o f e a r l y p r eg n an cy by a d m i n i s t r a t i o n o f p r o s t a g l a n d i n F2a o r c o l c h i c i n e or by removal o f embryo i n mares. Am. J . Vet. Res. 37:35, 1976.
9.
Demers, L. M., K. Yoshinaga and R. O. Greep. Prostaglandin F in monkey uterine fluid during the menstrual cycle and following steroid treatment. Prostaglandins 5:513, 1974.
10.
Frank, M., F. W. Bazer, W. W. Thatcher and C. J. Wilcox. A study of prostaglandin F2~ as the luteolysin in swine: IV An explanation of the luteotrophlc effect of estradiol. Prostaglandins, In Press.
11.
Henderson, K. M. and K. P. McNatty. A biochemical hypothesis to explain the mechanism of luteal regression. Prostaglandins 9:778, 1975.
12.
Douglas, R. H. and O. J. Ginther. Concentration of prostaglandin F in uterine venous plasma of anesthetized mares during the estrous cycle and early pregnancy. Prostaglandins 11:251, 1976.
13.
Van Nieker~ C. H., J. C. Morgenthal and W. H. Gerneke. Relationship between the morphology of and progesterone production by the corpus luteum of the mare. J. Reprod. Fert. Suppl. 25:171, 1975.
14.
Zavy, M. T . , F. W. Bazer and D. C. Sharp. A non-surgical technique f o r t h e c o l l e c t i o n of u t e r i n e f l u i d from t h e mare. J . Anim. S c i . (In P r e s s ) .
648
ocTOBER : | 9 7 8 VOLi 16 N O . 4
PROSTAGLANDINS
15.
Moeljono, M. P. E., W. W. Thatcher, F. W. Bazer, M. Frank, L. J. Owens and C. J. Wilcox. A study of prostaglandin F2a as the luteolysin in swine: II Characterization and comparison of prostaglandin F, estrogens and progestin concentrations in utero-ovarian vein plasma of nonpregnant and pregnant gilts. Prostaglandins 14:543, 1977.
16.
Harvey, W. R. L e a s t - s q u a r e s a n a l y s i s of d a t a w i t h unequal s u b c l a s s f r e q u e n c i e s . USDA. ARS 20, 1960.
17.
Ganjam, V. K., R. M. Kenney and G. F l i c k i n g e r . Plasma p r o g e s t a g e n s i n c y c l i c , p r e g n a n t and p o s t - p a r t t ~ n m a r e s . J . Reprod. F e r t . Suppl. 23:441, 1975.
18.
R o b e r t s , J . S . , B. B a r c i k o w s k i , L. Wilson, R. C. Skarnes and J . A. McCracken. Hormonal and r e l a t e d f a c t o r s a f f e c t i n g t h e r e l e a s e of p r o s t a g l a n d i n F2a from t h e u t e r u s . J . S t e r o i d Biochem. 6:1091, 1975.
19.
Bazer, F. W. and W. W. Thatcher. Theory of maternal recognition of p r e g n a n c y i n swine b a s e d on e s t r o g e n c o n t r o l l e d e n d o c r i n e v e r s u s exoc r i n e s e c r e t i o n of p r o s t a g l a n d i n F2~ by t h e u t e r i n e endometrium. P r o s t a g l a n d i n s 14:397, 1977.
OCTOBER 1978 VOL. 16 NO. 4
649
PROSTAGLANDINS
FI G U R E
2 e
a J
•
-
Jill
-
'~
I
-
~i
- - -
......
i!0°.m,
We apologise to Higgs et al for the poor reproduction of this figure which appeared in the July issue, page 19, Volume 16, Number i.
650
OCTOBER 1978 VOL. 16 NO. 4
UTERINE IUMINAL PROSTAGLANDIN F IN CYCLING MARES Michael T. Zavy, Fuller W. Bazer, Dan C. Sharp Marilyn Frank and William W. Thatcher Departments of Animal Science and Dairy Science University of Florida, Gainesville, Florida 52611
ABSTRACT Prostaglandin F was measured by radioimmunoassay in uterine flushings of cycling mares on days 4, 8, 12, 14, 16, 18 and 20 post-ovulation. Prostaglandin F was significantly (P < .05) affected by day of the estrous cycle and reached maximal levels on day 14. Least squares means for days 4, 8, 12, 14, 16, 18 and 20 were: .66, .81, 4.77, 14.31, 5.48, 3.68 and 2.97 ng/ml, respectively. ACKNOWLEDGEMENTS Departments of Animal and Dairy Science, Florida Agricultural Experiment Station, Journal Series No. ]]]6. This research was supported, in part, by N.I.H. Grant HD08560 and the Morris Animal Foundation. The prostaglandin F2~ - Tham salt used in this study was provided by Dr. J. W. Lauderdale of the Upjohn Company, Kalamazo, Michigan.
OCTOBER 1978 VOL. 16 NO. 4
643
PROSTAGLANDINS
INTRODUCTION The uterus has been implicated in controlling ovarian luteal function for over S0 years. It has been shown in guinea pigs (i), cows (2), and mares (3) that hysterectomy in the luteal phase of the estrous cycle results in an extended life span of the corpora lutea (CL). The uterus of many species of mammals produces a luteolysin which causes luteal regression and allows for a new ovarian cycle (4); the possible exception to this being the primate. Prostaglandin F2~ has been shown to induce luteolysis in mares when administered in diestrus (5, 6), luteolysis has been shown to occur after administration by many routes; i.e., systemic (5, 6), intraluteal (7) or intrauterine injection (5, 6). Kooistra and Ginther (8) demonstrated that PGF2~ effectively terminated pseudopregnancy and early pregnancy in the mare by bringing about the demise of the CL. Additionally, it has been demonstrated in the mare that the uterus likely exerts its luteolytic effect through a systemic rather than a local pathway (3). Prostaglandin F has been measured in uterine fluids of the monkey (9) and gilt (i0). A biochemical explanation for the mechanisms of PGF induced luteolysis has been proposed by Henderson and McNatty (II). Recently, it has been demonstrated that immunoreactive prostaglandin F (PGF) reached maximal concentration in the uterine venous plasma of mares on day 14 of the estrous cycle (12); a time coincidental with luteal regression (13). In view of these findings and because PGF is a product of endometrial secretion, a study was conducted to quantitate PGF in uterine flushings of cycling mares on selected days of the estrous cycle. MATERIAL AND METHODS ExpeTimental Animals. Uterine flushings were collected from 14 normally cycling mares of Quarter Horse or Thoroughbred breeding. Days of collection were 4, 8, 12, 14, 16, 18 and 20 post-ovulation. Ovulations were detected by daily rectal palpation of the ovaries. Over the experimental period 32 uterine flushings were collected. Several of the mares were used for the collection of more than one uterine flushing in succeeding estrous cycles with at least one estrous cycle intervening between two collections. Collection Technique. Uterine flushings were obtained by a non=surgical collection technique developed in our laboratory (14). Eighty milliliters of sterile, .33M saline were infused through the inner catheter of the collection device into the uterine lumen. After 5 min the fluid containing uterine secretions was slowly withdrawn from the uterus. Uterine flushings were placed in sterile vials on ice until quantitated. After the volume of each uterine flushing was measured, samples were centrifuged in a refrigerated centrifuge for 20 min at iO,000 rpm. The supernatant was filtered through a .45 micron filter to remove bacteria and/or cellular debris. The filtrate was then transferred into sterile vials and stored at -20°C until analysis were performed. Prostaglandin F Radioimmunoassay. All uterine flushing samples were assayed for PGF concentration by the method described previously for our laboratory
(is).
644
OCTOBER 1978 VOL. 16 NO.'4
PROSTAGLANDINS
Statistical Analysis. Results of this study were analyzed by least squares regression analysis (16) to obtain estimates of day effects of PGF content of mare uterine flushings. RESULTS Least squares analysis of data indicated that PGF in mare uterine flushings was significantly (P< .05) affected by day of the estrous cycle. Prostaglandin F content of mare uterine flushings is expressed as concentration and total recoverable PGF in Table I. When expressed on a concentration basis a third order regression curve (Y = 7378.8 + 923.5X - 137.8X ~ - 16.6X 3 was significant (P< .05), however, data were best described by a non-significant fourth order regression curve (Y = 8940.1 + 454.8X - 348.7X 2 - 1.6X 3 + 3.4X4).
Table I.
Prostaglandin F (PGF) Content of Mare Uterine Flushings
PGF Concentration ng/ml of flushing a
PGF Total ng/flushing a
Day
n
4
5
.66 ± .24
52.19 ± 19.63
8
5
.81 ± .16
65.25 ± 10.34
12
5
4.77 ± 2.41
391.18 ± 190.96
14
4
14.31 ± 4.70
1,133.81 ± 377.36
16
3
5.48 ± 1.80
495.40 ± 165.00
18
3
3.68 ± 1.36
304.39 ± 103.76
20
7
2.97 ± .81
244.06 ± 68.97
aMean + SEM
OCTOBER 1978 VOL 1 6 N O . 4
645
PROSTAGLANDINS
Least squares means for the treatment days appear in histogram form in Figure I. PGF concentration was less than 1 ng/ml on days 4 and 8 of the estrous cycle, increased to 14.3 ng/ml on day 14 and steadily decreased thereafter. When calculated on the basis of total PGF recovered (concentration x recovery volume), an average of 1.13 vg of PGF was recovered from the uterine flushings of mares on day 14.
l-
16.0-
4
o9 14.0; ~.(.9
"1" " "
-r 9.0~
sB
u..l~
T
_z,,, zoQZ
z~.
~5
T
5.o-
Z
7
T
4
8
3
T3
T
1.0-
,~ , ~
i
v
i
18
w
i
20
DAYS POST OVULATION F i g u r e I.
Least squares means histogram of Prostaglandin F (PGF) in ng/ml of mares uterine flushing. Numbers above bars indicate the number of animals per observation group (total = 32), lines above bars represent the standard errors of the least square means. PGF concentration (ng/ml) overall mean ± SEM; 4.67 ~ .77, Coefficient of Variation = 132.15%.
646
OCTOBER 1978 VOL. 16 NO. 4
PROSTAGLANDINS
Data from the present study indicate a distinct peak of PGF in uterine flushings of cycling mares on day 14 of the estrous cycle. This supports work presented by Douglas and Ginther (12) who measured PGF in uterine venous drainage of cycling mares with regard to time trends and magnitude of the PGF peak. An increase in PGF levels in the mid-to-late-luteal phase of the estrous cycle is consistant with the idea that PGF, of uterine origin, may be associated with luteal regression in the mare. This concept is further strengthened by work from Van Niekerk et al. (13), which indicated that equine luteal cells begin to degenerate 12 days after ovulation, a time which is associated with rising uterine luminal PGF levels. Additionally, this rise in PGF is temporally related to declining plasma progesterone levels which have previously been reported by Ganjam et al. (17). Roberts et al. (18) have indicated that mechanical stimulation of the sheep uterus, in situ, resulted in a rapid release of PGF2a into the uterine veins which was sustained for at least the duration of stimulation. It is not known whether the uterine flushing technique in this report acted in a similar stimulatory manner. Regardless of whether the uterine flushing technique was stimulatory or not, the technique was essentially constant at all days of the estrous cycle, thus the time trends and their implied physiological role seem valid. R e c e n t l y , Bazer and T h a t c h e r (19) i n t r o d u c e d t h e c o n c e p t t h a t b o t h PGF and the porcine intrauterine glycoprotein move in an endocrine fashion (toward the vasculature) in cycling gilts whereas, in pregnant gilts, both are accumulated within the uterine lumen (exocrine secretion). The results of such an action would be to prevent secretion toward the vasculature in the pregnant animal, thus PGF would be prevented from reaching the ovary. Many similarities in uterine secretory patterns (total protein, acid phosphatase activity, prostaglandin F) in gilts and mares (Michael T. Zavy, Fuller W. Bazer and Dan C. Sharp, unpublished results) suggest that a similar mechanism may exist in the mare.
OCTOBER 1978 VOL. 16 NO. 4
647
PROSTAGLANDINS REFERENCES
I.
Loeb, L. The effect of extirpation of the uterine horn on the life and function of the corpus luteum in the guinea pig. Proc. Soc. Exp. Biol. Med. 20:441, 1923.
2.
Wiltbank, J. N. and L. E. Casida. Alteration of ovarian activity by hysterectomy. J. Anim. Sci. 15:134, 1956.
3.
Ginther, O. J. and N. L. First. Maintenance of the corpus luteum in hysterectomized mares. Am. J. Vet. Res. 32:1687, 1971.
4.
McCracken, J . A., D. T. B a i r d , J . C. C a r l s o n , J . R. Goding and B. Barcikowski. The r o l e o f p r o s t a g l a n d i n s i n l u t e a l r e g r e s s i o n . J . Reprod. F e r t . Suppl. 18:133, 1973.
5.
Douglas, R. H. and O. J. Ginther. Effect of prostaglandin on length of diestrus in mares. Prostaglandins. 2:265, 1972.
6.
Noden, P. A., H. D. Hafs and W. D. Oxender. o v u l a t i o n a f t e r p r o s t a g l a n d i n F2a in h o r s e s . Med. 145:145, 1973.
P r o g e s t e r o n e , e s t r u s and Proc. Soc. Exp. B i o l .
7. ¸ Douglas, R. H. and O. J . G i n t h e r . Route of p r o s t a g l a n d i n F2 i n j e c t i o n and l u t e o l y s i s in mares. Proc. Soc. Exp. B i o l . Med. 148:263, 1975.
8.
K o o i s t r a , L. H. and O. J . G i n t h e r . T e r m i n a t i o n o f pseudopregnancy by a d m i n i s t r a t i o n of p r o s t a g l a n d i n F2a and t e r m i n a t i o n o f e a r l y p r eg n an cy by a d m i n i s t r a t i o n o f p r o s t a g l a n d i n F2a o r c o l c h i c i n e or by removal o f embryo i n mares. Am. J . Vet. Res. 37:35, 1976.
9.
Demers, L. M., K. Yoshinaga and R. O. Greep. Prostaglandin F in monkey uterine fluid during the menstrual cycle and following steroid treatment. Prostaglandins 5:513, 1974.
10.
Frank, M., F. W. Bazer, W. W. Thatcher and C. J. Wilcox. A study of prostaglandin F2~ as the luteolysin in swine: IV An explanation of the luteotrophlc effect of estradiol. Prostaglandins, In Press.
11.
Henderson, K. M. and K. P. McNatty. A biochemical hypothesis to explain the mechanism of luteal regression. Prostaglandins 9:778, 1975.
12.
Douglas, R. H. and O. J. Ginther. Concentration of prostaglandin F in uterine venous plasma of anesthetized mares during the estrous cycle and early pregnancy. Prostaglandins 11:251, 1976.
13.
Van Nieker~ C. H., J. C. Morgenthal and W. H. Gerneke. Relationship between the morphology of and progesterone production by the corpus luteum of the mare. J. Reprod. Fert. Suppl. 25:171, 1975.
14.
Zavy, M. T . , F. W. Bazer and D. C. Sharp. A non-surgical technique f o r t h e c o l l e c t i o n of u t e r i n e f l u i d from t h e mare. J . Anim. S c i . (In P r e s s ) .
648
ocTOBER : | 9 7 8 VOLi 16 N O . 4
PROSTAGLANDINS
15.
Moeljono, M. P. E., W. W. Thatcher, F. W. Bazer, M. Frank, L. J. Owens and C. J. Wilcox. A study of prostaglandin F2a as the luteolysin in swine: II Characterization and comparison of prostaglandin F, estrogens and progestin concentrations in utero-ovarian vein plasma of nonpregnant and pregnant gilts. Prostaglandins 14:543, 1977.
16.
Harvey, W. R. L e a s t - s q u a r e s a n a l y s i s of d a t a w i t h unequal s u b c l a s s f r e q u e n c i e s . USDA. ARS 20, 1960.
17.
Ganjam, V. K., R. M. Kenney and G. F l i c k i n g e r . Plasma p r o g e s t a g e n s i n c y c l i c , p r e g n a n t and p o s t - p a r t t ~ n m a r e s . J . Reprod. F e r t . Suppl. 23:441, 1975.
18.
R o b e r t s , J . S . , B. B a r c i k o w s k i , L. Wilson, R. C. Skarnes and J . A. McCracken. Hormonal and r e l a t e d f a c t o r s a f f e c t i n g t h e r e l e a s e of p r o s t a g l a n d i n F2a from t h e u t e r u s . J . S t e r o i d Biochem. 6:1091, 1975.
19.
Bazer, F. W. and W. W. Thatcher. Theory of maternal recognition of p r e g n a n c y i n swine b a s e d on e s t r o g e n c o n t r o l l e d e n d o c r i n e v e r s u s exoc r i n e s e c r e t i o n of p r o s t a g l a n d i n F2~ by t h e u t e r i n e endometrium. P r o s t a g l a n d i n s 14:397, 1977.
OCTOBER 1978 VOL. 16 NO. 4
649
PROSTAGLANDINS
FI G U R E
2 e
a J
•
-
Jill
-
'~
I
-
~i
- - -
......
i!0°.m,
We apologise to Higgs et al for the poor reproduction of this figure which appeared in the July issue, page 19, Volume 16, Number i.
650
OCTOBER 1978 VOL. 16 NO. 4