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Levels of F prostaglandin (PGF) in uterine tissue during the estrous cycle of hamster: Effects of estradiol and progesterone
LEVELS OF F PROSTAGLANDIN
(PGF) IN UTERINE TISSUE
DURING THE ESTROUS CYCLE OF HAMSTER:
EFFECTS OF
ESTRADIOL AND PROGESTERONE
S. K. Saksena and M. J. K. Harper Worcester Foundation for Experimental Biology Shrewsbur~y~ Massachusetts 01545 U,S.A.
ADSTRACT The uterine content and concentration of PGF varied throughout the estrous cycle of the hamster. The content was highest between 2400 hr of day 4 and 0030 hr of day i~ and lowest between 1045 to 1145 hr of day i. The concentration was highest between 1045 to 1145 hr of day 2 and between 2400 hr of day 4 and 0030 br of day i~ and lowest between 1045 to 1145 hr of day i. The changes did n o t correlate well with the times of maximum and minimum secretion of PGF in uterine vein blood of the hamster reported by Shaikh and Saksena (19).
ACKNOWLEDGMENTS We are grateful to Dr. W. Stylos for PGF antiserum and to the Upjohn Co. for generous donations of prostaglandins. This study was supported by the Ford Foundation Training Program in Reproductive Physiology and a Career Development Award (K4-HD-42369) (MJKH) from N.I.C.H.D.
*Present address (for correspondence and reprint requests): W.H.0.~ Human Reproduction Unit~ 1211 Geneva 27~ Switzerland
Accepted October l l ,
N O V E M B E R 1972
1972,
VOL. 2 NO. 5
405
PROSTAGLANDINS
It has been found that unilateral hystereetomy in guinea pigs prolongs the life span of corpora lutea (i). Similar findings in sheep (2) hamsters (3) pseudopregnant rats (~ and in sheep with autotransplanted ovaries (5) have been reported. The evidence indicates that the uterus produces a luteolytic substance which acts locally (6-8); it has been postulated (9) that this luteolytie substance may be prostaglandin F2^ (PGF2~). An aqueous extract of ovine (i~ or bovine endometrium ~ii) when collected on days 14 to 15 of the estrous cycle caused luteolysis when injected into hystereetomized pseudopregnant hamsters. Recent reports indicate that levels of PGF2~ or F2~ like material in uterine vein blood (5~12) and endometrium (13) increased sharply at the end of estrous cycle and are associated with regression of the corpus luteum. Furthermore, administration of estrsdiol benzoate on days 4 to 6 of the estrous cycle of the guinea pig caused elevated levels of prostaglandin F (14). It has been postulated (15) that the rising levels of estrogen on day 13 of the estrous cycle of the ewe are responsible for the production of prostaglandin F in the endometrium. In the present study~ the levels of prostaglandin F (PGF) have been measured by radioimmunoassay in uterine tissue of intact hamsters throughout the estrous cycle and around the time of ovulation. Experiments were also done to test whether pretreatment with estrogen and/or progesterone could affect the synthesis of F prostaglandin by the uterine tissue of hamsters. MATERIALS AND METHODS
Golden hamsters weighing between 140-150 g purchased from a local breeder were maintained on a 14 hr light:iO hr dark schedule with the lights coming on at 0600 hr. Animals, that had experienced at least 2 consecutive 4 day estrous cycles were used. The day of conspicuous post ovulatory vaginal discharge was designated day i of the cycle. Hamsters were decapitated on different days of the estrous cycle. Both uterine horns from the utero-tubal junction to the cervix were removed, cleaned of adhering tissues and blotted in two folds of filter paper. They were then frozen on dry ice, and stored at -20oc until required. Estrogen 4 ~g and progesterone 4 mg (Sigma Chemical Co.) were injected (so) in two equally divided doses at 2000 hr on day 3 and 0800 hr of day 4 subcutaneously in a volume of 0.4 ml of cotton seed oil. Control animals were given 0.2 ml per injection of cotton seed oil only. Animals in the treated groups were killed between 2000-2090 hr on the day of proestrous. Uterine tissues were obtained as described above.
406
NOVEMBER 1972 VOL. 2 NO. 5
PROSTAGLANDINS
For measurement of prostaglandin F (PGF) content, the tissues were homogenized in cold acetate buffer (0.6 M, pH 4.5) to which was added (3H) PGF2~ (~ 1600 dpm - New England Nuclear). The extraction was performed by a method described earlier (16). The samples were fractionated on silieie acid columns (17) and fractions containing F prostaglandins (average recovery 76%) were assayed in duplicate by radioimmunoassay (18). All samples were analyzed in a single assay. RESULTS Table I shows the uterine content and coneentration of PGF during the estrous cycle of hamsters. The lowest value for content (2.1 ± 0.2 ng) was seen on day 1 between 1045-1145 hr. The content and concentration first showed a significant rise on day 2. On day 3 the PGF content levels were not significantly different either from day 1 or day 2 values~ however~ there was a significant drop in eoneentration. On the morning of day 4 the content of PGF had returned to the value observed on day 2, but the concentration remained unehanged. There were minor fluctuations in both content and concentration of PGF throughout day % until a small drop in both values occurred in animals killed between 2000 and 2030 hr. This was followed by a sharp and highly significant increase in content to 7.4 ! 0.5 ng and in coneentration to 19.6 • 1.5 ng of PGF in animals killed only 4 hr later. By 1045 hr of day l, the values had decreased to their lowest levels. The uterine content and concentration levels of PGF in hamsters treated with estrogen or progesterone on day 3 at 2000 hr and day 4 at 0800 hr, and killed between 2000-2030 hr on day 4 are shown in Table II. The content and concentration levels of PGF in estrogen treated animals rose significantly compared to the values obtained in control animals. Similarly, progesterone treatment significantly increased PGF levels, although to a lesser extent than obtained with estradiol. DISCUSSION Shaikh and Saksena (19) have recently determined the levels of PGF in uterine venous plasma of hamsters eannulated at similar times during the estrous cycle. On days i to 4 in animals killed at 1000-1200 hr the PGF values were 2.5, 5.0~ 8.0 and 1.0 ng/ml respectively. Comparison with Table I shows that although PGF eoneentrations in uterine tissue rose from day 1 to day 2~ they were signifieantly smaller on day 3 than on day 2: yet on day 3 secretion was maximal. Similarly, uterine PGF (per ml of plasma) was low on day 4 at 2000-2030 hr and high at 2400-0300 hr~ and
N O V E M B E R 1972
VOL. 2 NO. 5
407
PROSTAGLANDINS
Table I Prostaglandin F (PGF) levels in uterine tissue of cyclic hamsters Day of Estrous Cycle
Time of Sample Collection
Day 1
1045-1145 hr
2.1 ± 0.2
(5) e
Day 2
1045-1145 hr
3.8 • 0.2
(5) bed
Day 3
1045-1145 hr
2.7 ± 0.3
(6) de
i045-i145 hr
4.0 • 0.3
(6) be
1800-1830 hr
4.8 ~ 0.5 (5) b
2000-2030 hr
3.2 ± 0.3
(6) ode
2400-0030 hr
7.4 ~ 0.5
(5) a
Day 4
Uterine Content (ng/organ) Mean i SE
Uterine Concentration (ng/g) Mean • SE 6.8 ~ 0.7 16.3
~ 1.3
(5) d (6) a
9.6 ~ i. 3 (6) bed 10.7 ~ 0.8 (6) be 11.9 ~ 0.9 (5) b 7.6 i 0.9
(6) ed
19.6 ~ 1.5 (5) a
Figures in parentheses indicate the number of animals. Figures in columns with different superscript (a,b...) differ significantly at P < 0.05. (eg ~ is significantly different from ~ but not from a ~ . Dunean's test.
yet in the work of Shaikh and Saksena (19) the concentration of PGF in uterine vein blood was maximal at 1900-2100 hr (7.1 ng/ml) and low at 2300 of day 4 to 0100 hr of day 1 (2.1 ng/ml). Both synthesis and release of PGF were occurring on the mornings of day 2 and 3~ since the content per ml of PGF in uterine vein blood was higher than the total uterine content. Both processes must also be occurring at 1900-2100 hr of day % since the blood eoneentration of PGF is similar to the uterine coneentration and almost twiee the uterine content. Since the luteal function appears to be regulated by PGF produced by the endometrium and released into the uterine vein~ then changes of PGF in blood are more meaningful in terms of physiological response than those in the endometrium. Although there are differences in uterine content of PGF throughout the cycle, these differences are not very large and may be of questionable importance. The greater fluctuations observed in uterine concentrations of PGF may be merely a reflection of uterine weight changes.
408
N O V E M B E R 1972
VOL. 2 NO. 5
PROSTAGLANDINS
Table II Levels of prostaglandin F (PGF) in uterine tissue of hamsters injected with steroids on day 3 and day 4 of cycle and killed on day 4 between 2000-2030 hr Uterine Content (ng/tissue) Mean ~ SE
Treatment Control +
3.0 • 0.3 (4)
Estrogen a Progesterone
13.3 b
~ 3.6 (4) x
6.0 + 0.9
(4) x
Uterine Concentration (ng/g) Mean i SE 8.6 ~ 0.9
(4)
32.5 ~ 3.6 (4) x 22.1 ± 1.6
(4) x
Figures in parentheses indicate the number of animals. + Controls injected with 0.2 ml of cotton seed oil - sc. a Estradiol-17$~ at 2000 hr on day 3 and 0800 hr on day 4 (2 ~g/injection so). b Progesterone, a t 2000 hr on day 3 and 0800 on day 4 (2 mg/injection se). x Signifieantly different from control animals at P < 0.05.
The results of the experiments with the ovarian hormone treatments show that estrogen in partieular~ can significantly increase uterine levels of PGF. Whether in these animals release of PGF into uterine vein blood also occurred is not known~ but Blatehley et al. (14) reported that utero-ovarian vein content of PGF_z~ was increased in guinea pigs pretreated wi'th estrogen. The faet that in the present study progesterone also increased PGF in the uterus is interesting. It is~ however~ known that PGF in endometrium and uterine vein blood increases sharply at the end of the estrous cycle in sheep (5~12~13) at a time when the uterus has been exposed to high progesterone levels for several days. Thus the action of ovarian hormones on endometrial synthesis of PGF may depend not only on the dose administered but on the preexisting hormonal environment. REFERENCES i.
Fischer, T.V. Local pathway eontrolling luteal function in the guinea pig. Biol. Reprod. ~, 26 (1971).
2.
Inskeep, E.K. and Butcher, R.L. Local component of uteroovarian relationships in the ewe. J. Anim. Sei. 25, 1164 (1966).
3.
Orsini~ M.W., Discussion VIII. Biennial Symposium on Animal Reproduction. Ed. A. V. Nalbandov and D. E. Beeker. J. Anita. Sei. 2__7_7~(Suppl I) 131 (1968).
N O V E M B E R 1972
VOL. 2 NO. 5
409
PROSTAGLANDINS
4.
Barley~ D.A., Butcher~ R.L and Inskeep~ E.K. Local nature of utero-ovarian relationship in the pseudopregnant rat. Endocrinology 79~ 119 (1968).
5.
McCracken~ J.A.~Baird~ D.T. and Goding~ J.R. Faetors affecting the secretion of steroids from the transplanted ovary of the sheep. Recent Progr. Hormone Res. 27~ 537 (1971).
6.
Ginther~ O.J.~ Woody~ C.O.~ Mahajan~ S.~ Janakiraman~ K. and Casid% L.E. Effect of oxytocin administration on the oestrous cycle of unilaterally hysterectomized heifers. J. Reprod. Fertil. i_~% 225 (1966).
7.
Ginther~ O.J.~ Pope, A.L. and Casid% L.E. Local effect of an intrauterine plastic coil on the corpus luteum of the ewe. J. Anim. Set. 2~5~ 472 (1966).
8.
Gintherj O.J.~ Woody~ C.O.j Janakiraman~ K. and Casid% L.E. Effect of an intrauterine plastic coil on the oestrous cycle of the heifer. J, Reprod. Fertil. 12~ 193 (1966).
9.
Pharriss~ B.B. The possible vascular regulation of luteal function. Persp. Biol. Med. i_~ 434 (1970).
i0.
Caldwell, B.V., Moor~ R.M. and Lawson, R.A.S. Effects of sheep endometrial grafts and extracts on the length of pseudopregnancy in the hystereetomized hamster. J. Reprod. Fertil. 17; 567 (1968).
ii.
Duby~ R.T., McDanielj J.W.~ Spilman~ C.H. and Blaek~ D.L. Utero-ovarian relationships in the golden hamster III. Influence of uterine transplants and extracts on ovarian function following hysterectomy. Aeta Endocrinol. (Kbh) 60~ 611 (1969).
12.
Shaikh~ A.A. and Saksena, S.K. Periovulatory levels of F prostaglsndins (PGF) in the uterine venous plasma of the cyclic hamster. Abstr: International Conf. Prostaglandin~ Vienna~ Austria (1972)~ p. 105.
13.
Wilson~ L. Jr.~ Cenedell% R.J.~ Butcher~ R.L. and Inskeep, E.K. Levels of prostaglandins in the uterine endometrium during the ovine estrous cycle. J. Anim. Set. 3 % 93
(1972). 14.
410
Blatehley~ F.R.~ Donovan~ B.T.~ Horton~ E.W. and Poyser~ N.L. The release of prostaglandins and progestins into the utero-ovarian venous blood of guinea pigs during the oestrous cycle and following oestrogen treatment. J. Physiol. Lond. 223 ~ 69 (1972).
NOVEMBER 1972 VOL. 2 NO. 5
PROSTAGLANDINS
15.
Caldwell; B.V.~ Tillson~ S.A.~ Brock~ W.A. and Speroff~ L. The effects of exogenous progesterone and estradiol on prostaglandin F levels in ovarieetomized ewes. Prostaglandins !~ 217 (1972).
16.
Skarnes~ R.C. and Harper~ M.J.K. Relationship between endotoxin-induced abortion and the synthesis of prostaglandin F. Prostaglandins l; 191 (1972).
17.
Caldwell~ B.V.~ Burstein~ S.~ Brock; W.A. and Speroff~ L. Radioimmunoassay of the F prostaglandins. J. Clin. Endocr. 3_~3~171 (1971).
18.
Stylos~ W.~ Burstein~ S.~ Rivetz~ B., Gunsalus~ P. and Skarnes~ R.C. The production of anti F prostaglandin serum and its use in radioimmunoassay. Intrascience Chem. Rept. VI (#i) (in press).
19.
Shaikh~ A,A. and Saksena; S.K. Cyclic chanzes in uterine venous and peripheral plasma levels of F prostaglandins correlated with peripheral progesterone levels in the golden hamster. Adv. Bioscienees ~ Perzamon Press/ Vieweg (1972) (in press).
NOVEMBER 1972
VOL. 2 NO. 5
411
(PGF) IN UTERINE TISSUE
DURING THE ESTROUS CYCLE OF HAMSTER:
EFFECTS OF
ESTRADIOL AND PROGESTERONE
S. K. Saksena and M. J. K. Harper Worcester Foundation for Experimental Biology Shrewsbur~y~ Massachusetts 01545 U,S.A.
ADSTRACT The uterine content and concentration of PGF varied throughout the estrous cycle of the hamster. The content was highest between 2400 hr of day 4 and 0030 hr of day i~ and lowest between 1045 to 1145 hr of day i. The concentration was highest between 1045 to 1145 hr of day 2 and between 2400 hr of day 4 and 0030 br of day i~ and lowest between 1045 to 1145 hr of day i. The changes did n o t correlate well with the times of maximum and minimum secretion of PGF in uterine vein blood of the hamster reported by Shaikh and Saksena (19).
ACKNOWLEDGMENTS We are grateful to Dr. W. Stylos for PGF antiserum and to the Upjohn Co. for generous donations of prostaglandins. This study was supported by the Ford Foundation Training Program in Reproductive Physiology and a Career Development Award (K4-HD-42369) (MJKH) from N.I.C.H.D.
*Present address (for correspondence and reprint requests): W.H.0.~ Human Reproduction Unit~ 1211 Geneva 27~ Switzerland
Accepted October l l ,
N O V E M B E R 1972
1972,
VOL. 2 NO. 5
405
PROSTAGLANDINS
It has been found that unilateral hystereetomy in guinea pigs prolongs the life span of corpora lutea (i). Similar findings in sheep (2) hamsters (3) pseudopregnant rats (~ and in sheep with autotransplanted ovaries (5) have been reported. The evidence indicates that the uterus produces a luteolytic substance which acts locally (6-8); it has been postulated (9) that this luteolytie substance may be prostaglandin F2^ (PGF2~). An aqueous extract of ovine (i~ or bovine endometrium ~ii) when collected on days 14 to 15 of the estrous cycle caused luteolysis when injected into hystereetomized pseudopregnant hamsters. Recent reports indicate that levels of PGF2~ or F2~ like material in uterine vein blood (5~12) and endometrium (13) increased sharply at the end of estrous cycle and are associated with regression of the corpus luteum. Furthermore, administration of estrsdiol benzoate on days 4 to 6 of the estrous cycle of the guinea pig caused elevated levels of prostaglandin F (14). It has been postulated (15) that the rising levels of estrogen on day 13 of the estrous cycle of the ewe are responsible for the production of prostaglandin F in the endometrium. In the present study~ the levels of prostaglandin F (PGF) have been measured by radioimmunoassay in uterine tissue of intact hamsters throughout the estrous cycle and around the time of ovulation. Experiments were also done to test whether pretreatment with estrogen and/or progesterone could affect the synthesis of F prostaglandin by the uterine tissue of hamsters. MATERIALS AND METHODS
Golden hamsters weighing between 140-150 g purchased from a local breeder were maintained on a 14 hr light:iO hr dark schedule with the lights coming on at 0600 hr. Animals, that had experienced at least 2 consecutive 4 day estrous cycles were used. The day of conspicuous post ovulatory vaginal discharge was designated day i of the cycle. Hamsters were decapitated on different days of the estrous cycle. Both uterine horns from the utero-tubal junction to the cervix were removed, cleaned of adhering tissues and blotted in two folds of filter paper. They were then frozen on dry ice, and stored at -20oc until required. Estrogen 4 ~g and progesterone 4 mg (Sigma Chemical Co.) were injected (so) in two equally divided doses at 2000 hr on day 3 and 0800 hr of day 4 subcutaneously in a volume of 0.4 ml of cotton seed oil. Control animals were given 0.2 ml per injection of cotton seed oil only. Animals in the treated groups were killed between 2000-2090 hr on the day of proestrous. Uterine tissues were obtained as described above.
406
NOVEMBER 1972 VOL. 2 NO. 5
PROSTAGLANDINS
For measurement of prostaglandin F (PGF) content, the tissues were homogenized in cold acetate buffer (0.6 M, pH 4.5) to which was added (3H) PGF2~ (~ 1600 dpm - New England Nuclear). The extraction was performed by a method described earlier (16). The samples were fractionated on silieie acid columns (17) and fractions containing F prostaglandins (average recovery 76%) were assayed in duplicate by radioimmunoassay (18). All samples were analyzed in a single assay. RESULTS Table I shows the uterine content and coneentration of PGF during the estrous cycle of hamsters. The lowest value for content (2.1 ± 0.2 ng) was seen on day 1 between 1045-1145 hr. The content and concentration first showed a significant rise on day 2. On day 3 the PGF content levels were not significantly different either from day 1 or day 2 values~ however~ there was a significant drop in eoneentration. On the morning of day 4 the content of PGF had returned to the value observed on day 2, but the concentration remained unehanged. There were minor fluctuations in both content and concentration of PGF throughout day % until a small drop in both values occurred in animals killed between 2000 and 2030 hr. This was followed by a sharp and highly significant increase in content to 7.4 ! 0.5 ng and in coneentration to 19.6 • 1.5 ng of PGF in animals killed only 4 hr later. By 1045 hr of day l, the values had decreased to their lowest levels. The uterine content and concentration levels of PGF in hamsters treated with estrogen or progesterone on day 3 at 2000 hr and day 4 at 0800 hr, and killed between 2000-2030 hr on day 4 are shown in Table II. The content and concentration levels of PGF in estrogen treated animals rose significantly compared to the values obtained in control animals. Similarly, progesterone treatment significantly increased PGF levels, although to a lesser extent than obtained with estradiol. DISCUSSION Shaikh and Saksena (19) have recently determined the levels of PGF in uterine venous plasma of hamsters eannulated at similar times during the estrous cycle. On days i to 4 in animals killed at 1000-1200 hr the PGF values were 2.5, 5.0~ 8.0 and 1.0 ng/ml respectively. Comparison with Table I shows that although PGF eoneentrations in uterine tissue rose from day 1 to day 2~ they were signifieantly smaller on day 3 than on day 2: yet on day 3 secretion was maximal. Similarly, uterine PGF (per ml of plasma) was low on day 4 at 2000-2030 hr and high at 2400-0300 hr~ and
N O V E M B E R 1972
VOL. 2 NO. 5
407
PROSTAGLANDINS
Table I Prostaglandin F (PGF) levels in uterine tissue of cyclic hamsters Day of Estrous Cycle
Time of Sample Collection
Day 1
1045-1145 hr
2.1 ± 0.2
(5) e
Day 2
1045-1145 hr
3.8 • 0.2
(5) bed
Day 3
1045-1145 hr
2.7 ± 0.3
(6) de
i045-i145 hr
4.0 • 0.3
(6) be
1800-1830 hr
4.8 ~ 0.5 (5) b
2000-2030 hr
3.2 ± 0.3
(6) ode
2400-0030 hr
7.4 ~ 0.5
(5) a
Day 4
Uterine Content (ng/organ) Mean i SE
Uterine Concentration (ng/g) Mean • SE 6.8 ~ 0.7 16.3
~ 1.3
(5) d (6) a
9.6 ~ i. 3 (6) bed 10.7 ~ 0.8 (6) be 11.9 ~ 0.9 (5) b 7.6 i 0.9
(6) ed
19.6 ~ 1.5 (5) a
Figures in parentheses indicate the number of animals. Figures in columns with different superscript (a,b...) differ significantly at P < 0.05. (eg ~ is significantly different from ~ but not from a ~ . Dunean's test.
yet in the work of Shaikh and Saksena (19) the concentration of PGF in uterine vein blood was maximal at 1900-2100 hr (7.1 ng/ml) and low at 2300 of day 4 to 0100 hr of day 1 (2.1 ng/ml). Both synthesis and release of PGF were occurring on the mornings of day 2 and 3~ since the content per ml of PGF in uterine vein blood was higher than the total uterine content. Both processes must also be occurring at 1900-2100 hr of day % since the blood eoneentration of PGF is similar to the uterine coneentration and almost twiee the uterine content. Since the luteal function appears to be regulated by PGF produced by the endometrium and released into the uterine vein~ then changes of PGF in blood are more meaningful in terms of physiological response than those in the endometrium. Although there are differences in uterine content of PGF throughout the cycle, these differences are not very large and may be of questionable importance. The greater fluctuations observed in uterine concentrations of PGF may be merely a reflection of uterine weight changes.
408
N O V E M B E R 1972
VOL. 2 NO. 5
PROSTAGLANDINS
Table II Levels of prostaglandin F (PGF) in uterine tissue of hamsters injected with steroids on day 3 and day 4 of cycle and killed on day 4 between 2000-2030 hr Uterine Content (ng/tissue) Mean ~ SE
Treatment Control +
3.0 • 0.3 (4)
Estrogen a Progesterone
13.3 b
~ 3.6 (4) x
6.0 + 0.9
(4) x
Uterine Concentration (ng/g) Mean i SE 8.6 ~ 0.9
(4)
32.5 ~ 3.6 (4) x 22.1 ± 1.6
(4) x
Figures in parentheses indicate the number of animals. + Controls injected with 0.2 ml of cotton seed oil - sc. a Estradiol-17$~ at 2000 hr on day 3 and 0800 hr on day 4 (2 ~g/injection so). b Progesterone, a t 2000 hr on day 3 and 0800 on day 4 (2 mg/injection se). x Signifieantly different from control animals at P < 0.05.
The results of the experiments with the ovarian hormone treatments show that estrogen in partieular~ can significantly increase uterine levels of PGF. Whether in these animals release of PGF into uterine vein blood also occurred is not known~ but Blatehley et al. (14) reported that utero-ovarian vein content of PGF_z~ was increased in guinea pigs pretreated wi'th estrogen. The faet that in the present study progesterone also increased PGF in the uterus is interesting. It is~ however~ known that PGF in endometrium and uterine vein blood increases sharply at the end of the estrous cycle in sheep (5~12~13) at a time when the uterus has been exposed to high progesterone levels for several days. Thus the action of ovarian hormones on endometrial synthesis of PGF may depend not only on the dose administered but on the preexisting hormonal environment. REFERENCES i.
Fischer, T.V. Local pathway eontrolling luteal function in the guinea pig. Biol. Reprod. ~, 26 (1971).
2.
Inskeep, E.K. and Butcher, R.L. Local component of uteroovarian relationships in the ewe. J. Anim. Sei. 25, 1164 (1966).
3.
Orsini~ M.W., Discussion VIII. Biennial Symposium on Animal Reproduction. Ed. A. V. Nalbandov and D. E. Beeker. J. Anita. Sei. 2__7_7~(Suppl I) 131 (1968).
N O V E M B E R 1972
VOL. 2 NO. 5
409
PROSTAGLANDINS
4.
Barley~ D.A., Butcher~ R.L and Inskeep~ E.K. Local nature of utero-ovarian relationship in the pseudopregnant rat. Endocrinology 79~ 119 (1968).
5.
McCracken~ J.A.~Baird~ D.T. and Goding~ J.R. Faetors affecting the secretion of steroids from the transplanted ovary of the sheep. Recent Progr. Hormone Res. 27~ 537 (1971).
6.
Ginther~ O.J.~ Woody~ C.O.~ Mahajan~ S.~ Janakiraman~ K. and Casid% L.E. Effect of oxytocin administration on the oestrous cycle of unilaterally hysterectomized heifers. J. Reprod. Fertil. i_~% 225 (1966).
7.
Ginther~ O.J.~ Pope, A.L. and Casid% L.E. Local effect of an intrauterine plastic coil on the corpus luteum of the ewe. J. Anim. Set. 2~5~ 472 (1966).
8.
Gintherj O.J.~ Woody~ C.O.j Janakiraman~ K. and Casid% L.E. Effect of an intrauterine plastic coil on the oestrous cycle of the heifer. J, Reprod. Fertil. 12~ 193 (1966).
9.
Pharriss~ B.B. The possible vascular regulation of luteal function. Persp. Biol. Med. i_~ 434 (1970).
i0.
Caldwell, B.V., Moor~ R.M. and Lawson, R.A.S. Effects of sheep endometrial grafts and extracts on the length of pseudopregnancy in the hystereetomized hamster. J. Reprod. Fertil. 17; 567 (1968).
ii.
Duby~ R.T., McDanielj J.W.~ Spilman~ C.H. and Blaek~ D.L. Utero-ovarian relationships in the golden hamster III. Influence of uterine transplants and extracts on ovarian function following hysterectomy. Aeta Endocrinol. (Kbh) 60~ 611 (1969).
12.
Shaikh~ A.A. and Saksena, S.K. Periovulatory levels of F prostaglsndins (PGF) in the uterine venous plasma of the cyclic hamster. Abstr: International Conf. Prostaglandin~ Vienna~ Austria (1972)~ p. 105.
13.
Wilson~ L. Jr.~ Cenedell% R.J.~ Butcher~ R.L. and Inskeep, E.K. Levels of prostaglandins in the uterine endometrium during the ovine estrous cycle. J. Anim. Set. 3 % 93
(1972). 14.
410
Blatehley~ F.R.~ Donovan~ B.T.~ Horton~ E.W. and Poyser~ N.L. The release of prostaglandins and progestins into the utero-ovarian venous blood of guinea pigs during the oestrous cycle and following oestrogen treatment. J. Physiol. Lond. 223 ~ 69 (1972).
NOVEMBER 1972 VOL. 2 NO. 5
PROSTAGLANDINS
15.
Caldwell; B.V.~ Tillson~ S.A.~ Brock~ W.A. and Speroff~ L. The effects of exogenous progesterone and estradiol on prostaglandin F levels in ovarieetomized ewes. Prostaglandins !~ 217 (1972).
16.
Skarnes~ R.C. and Harper~ M.J.K. Relationship between endotoxin-induced abortion and the synthesis of prostaglandin F. Prostaglandins l; 191 (1972).
17.
Caldwell~ B.V.~ Burstein~ S.~ Brock; W.A. and Speroff~ L. Radioimmunoassay of the F prostaglandins. J. Clin. Endocr. 3_~3~171 (1971).
18.
Stylos~ W.~ Burstein~ S.~ Rivetz~ B., Gunsalus~ P. and Skarnes~ R.C. The production of anti F prostaglandin serum and its use in radioimmunoassay. Intrascience Chem. Rept. VI (#i) (in press).
19.
Shaikh~ A,A. and Saksena; S.K. Cyclic chanzes in uterine venous and peripheral plasma levels of F prostaglandins correlated with peripheral progesterone levels in the golden hamster. Adv. Bioscienees ~ Perzamon Press/ Vieweg (1972) (in press).
NOVEMBER 1972
VOL. 2 NO. 5
411