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Uterine motility in the cow during the estrous cycle. II. Comparative effects of prostaglandins F2α, E2, and cloprostenol
THERIOGENOLOGY
U;;RIh!EMOTILITY IN THE COW DURING THE ESTROUS CYCLE. . COMPARATIVE EFFECTS OF PROSTAGLANDINS F2a, E2, AND CLOPROSTENOL H. Rodriguez_Martinez,I,2 J. Ko,2 D. McKenna,2 P.G. Weston,3 H.L. Whitmore, B.K. Gustafsson,2 and W.C. Wagner3 Departments of Veterinary Clinical Medicine2 and Veterinary Biosciences3 College of Veterinary Medicine University of Illinois at Urbana-Champaign Urbana, IL 61801 Received for publication: ~ebrzinr~p ‘:8, 1986 Accepted: Dei't-~i-~~r~ L', I‘Q8/i ABSTRACT Intrauterine pressure (IUP) changes were recorded in nonlactating, cyclic dairy cows using transcervically placed intraluminal pressure microtransducers. Spontaneous activity was recorded for the first 30 min. Prostaglandins (PG) Fp, (5 Pg/kg), E2 (5 kg/kg), or cloprosteno1 (0.1 pg/kg) were then injected intravenously (i.v.1 at diestrus, proestrus, estrus, and metestrus, and their effects were recorded. The drug administrations did not alter the duration of the estrous cycle of the cows. Single doses of PGF2, and E2 significantly increased uterine activity at all stages of the estrous cycle, while cloprostenol had no effect. PGF2, and PGE2 increased IUP, frequency, and amplitude during all stages of the estrous cycle. The spontaneous pattern resumed within 20 min postinjection. Partial uterine refractoriness occurred with both PGs. The results indicate that low doses of natural prostaglandins stimulate uterine activity during the estrous cycle in cattle. Key words:
cow, uterus, pressure, prostaglandins INTRODUCTION
Luteolysis can be effectively induced in the bovine by the use of natural synthetic analogue prostaglandin F2= (PGF2,) or its IPresent address: Department of Anatomy and Histology, College of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala 75007, Sweden. This study was supported by Animal Health Formula funds, Project No. 70-o-976, Agricultural Experiment Station, College of Agriculture, University of Illinois, Urbana-Champaign, and by the Illinois Department of Agriculture.
FEBRUARY
1987 VOL.
27 NO. 2
349
THERIOGENOLOGY
cloprostenol (1,2,3). PGF2, and PGE2 are effective uterotonic agents in humans (4,5,6). PGF a has been reported to stimulate bovine myometrium in vitro (7,85 and in vivo (9). Natural PGF2, induced refractoriness in the bovine rrlyometrium when given i.v. repetitively. Undesirable side effects such as cough, involuntary contractions of the abdomen, intestinal evacuation, and micturition were also observed when 8 to 32 mg of PGF2, were given i.v. (9). Apparently, no information is available in the literature concerning the effect of low doses of natural PGs F2, and E2 or the synthetic analogue cloprostenol on myometrial activity of the cow in vivo throughout the estrous cycle. Recently, a method for recording IUP changes in cyclic cows and mares was reported (10,111. This method records spontaneous IUP and drug-induced responses under controlled conditions. The objective of the present study was to examine the effects of small i.v. doses of PGE2, PGF2=, and cloprostenol (10% of the effective luteolytic dose) on IUP and myometrial activity of the bovine at different stages of the estrous cycle. A newly developed method for recording IUP will be used (10). MATERIALS AND METHODS Four nonlactating Holstein cows were used in this study. The animals were palpated per rectum for determination of cyclic ovarian activity and observed twice daily for signs of estrus. The animals were fitted with silastic indwelling catheters in the jugular vein for collection of blood samples. IUP was recorded using an elastic dacron catheter equipped with two ultraminiature pressure sensor transducers. A description of the transducers and recording procedures has been reported (10). Spontaneous uterine motility was recorded during diestrus for 30 min prior to treatment. Single doses of either PGF2a,a PGE2,b or cloprostenolc were injected i.v. at 30-min intervals, and their effect on IUP was recorded. The dose of PGE2, PGF2,, and cloprosteno1 given was 5 Vg/kg, 5 vg/kg, and 0.1 pg/kg, respectively. Preliminary studies revealed that the action of these hormones on bovine myometrium at this dose lasted for 0 to 20 min, and then spontaneous motility resumed. This dose of PGF2, and cloprostenol is approximatelylD%ofthe normal luteolytic dose. The order of hormone administration was randomized within each stage of the estrous cycle. Following completion of treatment-induced effects on myometrium during diestrus, each cow was given 25 mg of PGF2, intramuscularly to alulatyse, Upjohn Co., Kalamazoo, MI. bSigma Chemical Co., St. Louis, MO. cEstrumate, Baynet Inc., Shawnee, KA.
FEBRUARY
1987 VOL.
27 NO. 2
THERIOGENOLOGY
induce luteolysis and estrus. Cows were classified as being in proestrus, estrus, and metestrus at 48 to 72, 72 to 96, and 120 to 168 h after the luteolytic dose of PGF2,, respectively. Cows were not observed for signs of estrus; however, blood samples were collected each day for progesterone assay and documentation of stage of estrous cycle. The same treatments as described above were repeated during proestrus, estrus, and metestrus, and IUP was recorded. Blood samples were collected daily into heparjnized tubes. Plasma was removed immediately and stored frozen at -20 C for later analysis of progesterone. Planimetry was performed on all IUP recordings using a digitizing pad (Tales, Model 6721 connected to a Data General, Eclipse S/140 computer. Baseline IUP was set at zero, and treatment effects were expressed as + percent change from baseline. This method of measurement includes-any increase in baseline pressure, increase in number of contractions, and increase in amplitude of contractions: relative changes in these variables arenot identified. Data were analyzed for effect of treatment and stage of the estrous cycle. Comparisons among the three hormone treatments refer only to the single dose used. RESULTS The effects of PGF2u, PGE2, and cloprostenol on bovine IUP during the estrous cycle are presented (Table 1). Single doses of PGF2, and PGE2 significantly (P < 0.05) increased uterine motility during all four stages of the estrous cycle. However, cloprostenol did not affect uterine motility. Typical tracings of IUP following PGF2,, PGE2, and cloprosteno1 treatments are likewise presented (Figures 1, 2, and 3, respec-. tivelyl. These tracings reveal an immediate significant increase in baseline tone and in frequency and amplitude of uterine contractions following treatment with PGF2, and PGE2. However, treatment with a low dose of cloprostenol (0.1 vg/kg)did not reveal any change in IUP. Throughout the experiment, normal spontaneous uterine activity patterns occurred or resumed within 20 min after treatment in all cows. Daily plasma progesterone values following induction of estrus are shown (Figure 41. The results confirm luteolysis and subsequent ovulation in all cows. There appeared to be partial uterine refractoriness following treatment with natural prostaglandins. When PGF2, was administered first, the response to PGE2 was reduced. When PGE2 was administered first, the response to PGF2, was reduced. This appeared to reduce the means presented in Table 1 by approximately 20%. Intravenous administration of natural and synthetic prostaglandins at 10% of the normal luteolytic dose did not alter the estrous cycle. The three estrous cycles of all four cows following the experiment
FEBRUARY
1987 VOL. 27 NO. 2
351
THERIUGENOLOGY
ranged from 19 to 21, 20 to 21, and 19 to 22 d, respectively. effects were observed in any of the cows. Table 1. Stage of the Estrous Cycle
No side
Effects of prostaglandin Fe,, Ep, and cloprostenol intrauterine pressure during the estrous cyclea
on
Cloprostenol (0.1 pg/kgl
(nib
Diestrus
5
72.62 2 9.15;
167.47 + 11.26d g
-6.93 + 9.17c f
Proestrus
5
160.38 + 16.25;
144.60 + 18.74d g
2.49 + 1.13c f
4
103.57 +8.50e
g
78.91 + 8.97d f
-2.44 2 9.13c f
67.86 + 8.03d f
60.20 + 9.08d f
5.18 + 2.24c f
Metestrus
7
aMeans + SEM are expressed as percent change from baseline uterine activi-y. bn = number of observations. c,d,efleansin rows with different superscripts are different (P < 0.051. f,g,hMeans in columns with different subscripts are different (P < 0.051. DISCUSSION The uterine response to PGF2, in our experiments was greatest during proestrus. This may be related to higher levels of estrogen present at this stage of the cycle. Estrogen treatment of ovariectomized sheep produced greater uterine activity following prostaglandin treatment than was observed in control animals (12). The effect of estrogen on prostaglandin synthesis, receptor sites, and release has been studied in several species (13,14,15). These effects are not constant, and further studies are needed to determine their interrelationship.
In our study, cloprostenol was given i.v. at 10% of the normal luteolytic dose, and no effect on IU? was detected. However, recent work in mares revealed that cloprostenol produced a significant increase in IUP when given i.v. at 50% of the normal luteolytic dose (161. It was also reported that a clear response to cloprostenol in mares was not seen on every occasion. Luteolytic doses of cloprostenol have also been reported to increase uterine activity in sheep following
352
FEBRUARY
1987 VOL.
27 NO. 2
THERIOGENOLOGY
F oop
100
100
0
EE
P
Figure 1. The effect of prostaglandin F2, on bovine uterine activity in a = Anterior transducer during the estrous cycle. near uterine body. uterine horn. p = Posterior transducer
FEBRUARY
1987 VOL. 27 NO. 2
353
THERIOGENOLOGY
I”0
0
P
FF
Fi,gure2. The ,effect of prostaglandin E2 on bovine uterine activity in a = Anterior transducer during the estrous cycle. near uterine body. uterine horn. p = Posterior transducer
354
FEBRUARY
1987 VOL.
27 NO. 2
THERIOGENOLOGY
Figure 3. The effect of cloprostenol on bovine uterine activity during in uterine the estrous cycle. a = Anterior transducer near uterine body. horn. p = Posterior transducer
FEBRUARY
1987 VOL.
27 NO. 2
355
THERIOGENOLOGY
PGF,,
I I
6-
5-
I = E & c 2 % visl
4-
3
2-
2 a l-
O-
III
I
-6-5-4-3-2-l
1
I,,,,,,,,,
0
1
2
3
4
5
6
7
Time of EstrousCycle(days)
Figure 4.
356
Plasma progesterone concentration of four cows prior to and following estrus (PGF~~ = 25 mg of Lutalyse i.m.1.
FEBRUARY
1987 VOL.
27 NO. 2
THERIOGENOLOGY
priming with exogenous estrogen (12). Further studies in cattle are needed to determine if normal luteolytic doses or even larger doses of cloprostenol affect uterine activity. REFERENCES Synchronization of F2cr analogue (ICI
1.
Tervit, H.R., Rowson, L.E.A. and Brand, A. oestrus in cattle using a prostaglandin 79939). J. Reprod. Fertil. %:179-181 (1973).
2.
Edqvist, L.E., Settergren, I. and Astrom, G. Peripheral plasma levels of fertility after progesterone and prostaglandin F2,-induced estrus in heifers. Cornell Vet. -65:120-131 (1975).
3.
Day, A.M. Cloprostenol for termination of pregnancy in cattle. The induction of abortion. N. Zealand Vet. J. E:139-144 (1977).
4.
Bygdeman M. The effect of different prostaglandins on human myometrium in vivo. Acta Physiol. Stand. -63:Suppl 242:1-78 (1964). -
5.
Beazley, J.M., Dewhurst, C.J. and Gillespie, A. The induction of labour with PGE2. J. Obst. Gyn. Brit. Commonwealth 77: 193-.199 (1970).
6.
Karim, S.Y.M. and Hillier, K. Prostaglandins in the control of animal and human reproduction. Br. Med. Bull. -35:173-180 (1979).
7.
Singh, L.P., Sadiku, A. and Verma, O.P. Prostaglandin F2ainduced response of the bovine ovary, oviduct (uterine tube), and (1979). uterus. Am. J. Vet. Res. %:1789-1791
8.
Patil, R.K., Sinha, S.N., Einarsson, S. and Settergren, I. The effect of prostaglandin F2 and oxytocin on bovine myometrium in vitro. Nord. Vet. Med. -38:474-479 (1980). --
9.
Eiler, H., Oden, J., Schaub, R. and Sims, M. Refractoriness of both uterus and mammary gland of the cow to prostaglandin F2a administration: clinical implication. Am. J. Vet. Res. 42:314317 (1981).
10.
Rodriguez-Martinez, H., McKenna, D., Weston, P.G., Whitmore, H.L. and Gustafsson, B.K. Uterine motility in the cow during the estrous cycle. I. Spontaneous activity. Theriopenology 27~337-348 (1987).
11.
Genital tract Goddard, P.J., Allen, W.E. and Gerring, E.L. Normal pressures and the effect of pressures in mares. I. physiological events. Theriogenology -23:815-827 (1985).
FEBRUARY
1987 VOL. 27 NO. 2
357
THERIOGENOLOGY
12.
Garcia-Villar, R., Marnet, P.G., Laurentie, M.P. and Toutain, P.L. Relative oxytocic properties of fenprostalene compared with cloprostenol, prostaglandin F2a and oxytocin in the ovariectomized ewe. Am. J. Vet. Res. %:841-844 (1985).
13.
Rarcikowski, B.J., Carlson, J., Wilson, L. and McCracken, J.A. The effect of endogenous and exogenous estradiol-176 on the release of prostaglandin F2a from the ovine uterus. Endocrinology -95:1340-1345 (1974).
14.
Blatchley, F.R. and Poyser, N.L. The effect of estrogen and progesterone on the release of prostaglandins from the uterus of the ovariectomized guinea pig. J. Reprod. Fertil. %:205-210 (1974).
15.
Smith, S.K., Abel, M.H. and Baird, O.T. Effects of 17e-estradiol and progesterone on the levels of prostaglandins F2, and E in human endometrium. Prostaglandins 7:591-597 (1984).
16.
Goddard, P.J.
358
and Allen, W.E. Genital tract pressures in mares. by oxytocin and prostaglandin F2,. :i&iogCe?Po?y& -. 2~n~~~~~ (1985).
FEBRUARY
1987 VOL.
27 NO. 2
U;;RIh!EMOTILITY IN THE COW DURING THE ESTROUS CYCLE. . COMPARATIVE EFFECTS OF PROSTAGLANDINS F2a, E2, AND CLOPROSTENOL H. Rodriguez_Martinez,I,2 J. Ko,2 D. McKenna,2 P.G. Weston,3 H.L. Whitmore, B.K. Gustafsson,2 and W.C. Wagner3 Departments of Veterinary Clinical Medicine2 and Veterinary Biosciences3 College of Veterinary Medicine University of Illinois at Urbana-Champaign Urbana, IL 61801 Received for publication: ~ebrzinr~p ‘:8, 1986 Accepted: Dei't-~i-~~r~ L', I‘Q8/i ABSTRACT Intrauterine pressure (IUP) changes were recorded in nonlactating, cyclic dairy cows using transcervically placed intraluminal pressure microtransducers. Spontaneous activity was recorded for the first 30 min. Prostaglandins (PG) Fp, (5 Pg/kg), E2 (5 kg/kg), or cloprosteno1 (0.1 pg/kg) were then injected intravenously (i.v.1 at diestrus, proestrus, estrus, and metestrus, and their effects were recorded. The drug administrations did not alter the duration of the estrous cycle of the cows. Single doses of PGF2, and E2 significantly increased uterine activity at all stages of the estrous cycle, while cloprostenol had no effect. PGF2, and PGE2 increased IUP, frequency, and amplitude during all stages of the estrous cycle. The spontaneous pattern resumed within 20 min postinjection. Partial uterine refractoriness occurred with both PGs. The results indicate that low doses of natural prostaglandins stimulate uterine activity during the estrous cycle in cattle. Key words:
cow, uterus, pressure, prostaglandins INTRODUCTION
Luteolysis can be effectively induced in the bovine by the use of natural synthetic analogue prostaglandin F2= (PGF2,) or its IPresent address: Department of Anatomy and Histology, College of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala 75007, Sweden. This study was supported by Animal Health Formula funds, Project No. 70-o-976, Agricultural Experiment Station, College of Agriculture, University of Illinois, Urbana-Champaign, and by the Illinois Department of Agriculture.
FEBRUARY
1987 VOL.
27 NO. 2
349
THERIOGENOLOGY
cloprostenol (1,2,3). PGF2, and PGE2 are effective uterotonic agents in humans (4,5,6). PGF a has been reported to stimulate bovine myometrium in vitro (7,85 and in vivo (9). Natural PGF2, induced refractoriness in the bovine rrlyometrium when given i.v. repetitively. Undesirable side effects such as cough, involuntary contractions of the abdomen, intestinal evacuation, and micturition were also observed when 8 to 32 mg of PGF2, were given i.v. (9). Apparently, no information is available in the literature concerning the effect of low doses of natural PGs F2, and E2 or the synthetic analogue cloprostenol on myometrial activity of the cow in vivo throughout the estrous cycle. Recently, a method for recording IUP changes in cyclic cows and mares was reported (10,111. This method records spontaneous IUP and drug-induced responses under controlled conditions. The objective of the present study was to examine the effects of small i.v. doses of PGE2, PGF2=, and cloprostenol (10% of the effective luteolytic dose) on IUP and myometrial activity of the bovine at different stages of the estrous cycle. A newly developed method for recording IUP will be used (10). MATERIALS AND METHODS Four nonlactating Holstein cows were used in this study. The animals were palpated per rectum for determination of cyclic ovarian activity and observed twice daily for signs of estrus. The animals were fitted with silastic indwelling catheters in the jugular vein for collection of blood samples. IUP was recorded using an elastic dacron catheter equipped with two ultraminiature pressure sensor transducers. A description of the transducers and recording procedures has been reported (10). Spontaneous uterine motility was recorded during diestrus for 30 min prior to treatment. Single doses of either PGF2a,a PGE2,b or cloprostenolc were injected i.v. at 30-min intervals, and their effect on IUP was recorded. The dose of PGE2, PGF2,, and cloprosteno1 given was 5 Vg/kg, 5 vg/kg, and 0.1 pg/kg, respectively. Preliminary studies revealed that the action of these hormones on bovine myometrium at this dose lasted for 0 to 20 min, and then spontaneous motility resumed. This dose of PGF2, and cloprostenol is approximatelylD%ofthe normal luteolytic dose. The order of hormone administration was randomized within each stage of the estrous cycle. Following completion of treatment-induced effects on myometrium during diestrus, each cow was given 25 mg of PGF2, intramuscularly to alulatyse, Upjohn Co., Kalamazoo, MI. bSigma Chemical Co., St. Louis, MO. cEstrumate, Baynet Inc., Shawnee, KA.
FEBRUARY
1987 VOL.
27 NO. 2
THERIOGENOLOGY
induce luteolysis and estrus. Cows were classified as being in proestrus, estrus, and metestrus at 48 to 72, 72 to 96, and 120 to 168 h after the luteolytic dose of PGF2,, respectively. Cows were not observed for signs of estrus; however, blood samples were collected each day for progesterone assay and documentation of stage of estrous cycle. The same treatments as described above were repeated during proestrus, estrus, and metestrus, and IUP was recorded. Blood samples were collected daily into heparjnized tubes. Plasma was removed immediately and stored frozen at -20 C for later analysis of progesterone. Planimetry was performed on all IUP recordings using a digitizing pad (Tales, Model 6721 connected to a Data General, Eclipse S/140 computer. Baseline IUP was set at zero, and treatment effects were expressed as + percent change from baseline. This method of measurement includes-any increase in baseline pressure, increase in number of contractions, and increase in amplitude of contractions: relative changes in these variables arenot identified. Data were analyzed for effect of treatment and stage of the estrous cycle. Comparisons among the three hormone treatments refer only to the single dose used. RESULTS The effects of PGF2u, PGE2, and cloprostenol on bovine IUP during the estrous cycle are presented (Table 1). Single doses of PGF2, and PGE2 significantly (P < 0.05) increased uterine motility during all four stages of the estrous cycle. However, cloprostenol did not affect uterine motility. Typical tracings of IUP following PGF2,, PGE2, and cloprosteno1 treatments are likewise presented (Figures 1, 2, and 3, respec-. tivelyl. These tracings reveal an immediate significant increase in baseline tone and in frequency and amplitude of uterine contractions following treatment with PGF2, and PGE2. However, treatment with a low dose of cloprostenol (0.1 vg/kg)did not reveal any change in IUP. Throughout the experiment, normal spontaneous uterine activity patterns occurred or resumed within 20 min after treatment in all cows. Daily plasma progesterone values following induction of estrus are shown (Figure 41. The results confirm luteolysis and subsequent ovulation in all cows. There appeared to be partial uterine refractoriness following treatment with natural prostaglandins. When PGF2, was administered first, the response to PGE2 was reduced. When PGE2 was administered first, the response to PGF2, was reduced. This appeared to reduce the means presented in Table 1 by approximately 20%. Intravenous administration of natural and synthetic prostaglandins at 10% of the normal luteolytic dose did not alter the estrous cycle. The three estrous cycles of all four cows following the experiment
FEBRUARY
1987 VOL. 27 NO. 2
351
THERIUGENOLOGY
ranged from 19 to 21, 20 to 21, and 19 to 22 d, respectively. effects were observed in any of the cows. Table 1. Stage of the Estrous Cycle
No side
Effects of prostaglandin Fe,, Ep, and cloprostenol intrauterine pressure during the estrous cyclea
on
Cloprostenol (0.1 pg/kgl
(nib
Diestrus
5
72.62 2 9.15;
167.47 + 11.26d g
-6.93 + 9.17c f
Proestrus
5
160.38 + 16.25;
144.60 + 18.74d g
2.49 + 1.13c f
4
103.57 +8.50e
g
78.91 + 8.97d f
-2.44 2 9.13c f
67.86 + 8.03d f
60.20 + 9.08d f
5.18 + 2.24c f
Metestrus
7
aMeans + SEM are expressed as percent change from baseline uterine activi-y. bn = number of observations. c,d,efleansin rows with different superscripts are different (P < 0.051. f,g,hMeans in columns with different subscripts are different (P < 0.051. DISCUSSION The uterine response to PGF2, in our experiments was greatest during proestrus. This may be related to higher levels of estrogen present at this stage of the cycle. Estrogen treatment of ovariectomized sheep produced greater uterine activity following prostaglandin treatment than was observed in control animals (12). The effect of estrogen on prostaglandin synthesis, receptor sites, and release has been studied in several species (13,14,15). These effects are not constant, and further studies are needed to determine their interrelationship.
In our study, cloprostenol was given i.v. at 10% of the normal luteolytic dose, and no effect on IU? was detected. However, recent work in mares revealed that cloprostenol produced a significant increase in IUP when given i.v. at 50% of the normal luteolytic dose (161. It was also reported that a clear response to cloprostenol in mares was not seen on every occasion. Luteolytic doses of cloprostenol have also been reported to increase uterine activity in sheep following
352
FEBRUARY
1987 VOL.
27 NO. 2
THERIOGENOLOGY
F oop
100
100
0
EE
P
Figure 1. The effect of prostaglandin F2, on bovine uterine activity in a = Anterior transducer during the estrous cycle. near uterine body. uterine horn. p = Posterior transducer
FEBRUARY
1987 VOL. 27 NO. 2
353
THERIOGENOLOGY
I”0
0
P
FF
Fi,gure2. The ,effect of prostaglandin E2 on bovine uterine activity in a = Anterior transducer during the estrous cycle. near uterine body. uterine horn. p = Posterior transducer
354
FEBRUARY
1987 VOL.
27 NO. 2
THERIOGENOLOGY
Figure 3. The effect of cloprostenol on bovine uterine activity during in uterine the estrous cycle. a = Anterior transducer near uterine body. horn. p = Posterior transducer
FEBRUARY
1987 VOL.
27 NO. 2
355
THERIOGENOLOGY
PGF,,
I I
6-
5-
I = E & c 2 % visl
4-
3
2-
2 a l-
O-
III
I
-6-5-4-3-2-l
1
I,,,,,,,,,
0
1
2
3
4
5
6
7
Time of EstrousCycle(days)
Figure 4.
356
Plasma progesterone concentration of four cows prior to and following estrus (PGF~~ = 25 mg of Lutalyse i.m.1.
FEBRUARY
1987 VOL.
27 NO. 2
THERIOGENOLOGY
priming with exogenous estrogen (12). Further studies in cattle are needed to determine if normal luteolytic doses or even larger doses of cloprostenol affect uterine activity. REFERENCES Synchronization of F2cr analogue (ICI
1.
Tervit, H.R., Rowson, L.E.A. and Brand, A. oestrus in cattle using a prostaglandin 79939). J. Reprod. Fertil. %:179-181 (1973).
2.
Edqvist, L.E., Settergren, I. and Astrom, G. Peripheral plasma levels of fertility after progesterone and prostaglandin F2,-induced estrus in heifers. Cornell Vet. -65:120-131 (1975).
3.
Day, A.M. Cloprostenol for termination of pregnancy in cattle. The induction of abortion. N. Zealand Vet. J. E:139-144 (1977).
4.
Bygdeman M. The effect of different prostaglandins on human myometrium in vivo. Acta Physiol. Stand. -63:Suppl 242:1-78 (1964). -
5.
Beazley, J.M., Dewhurst, C.J. and Gillespie, A. The induction of labour with PGE2. J. Obst. Gyn. Brit. Commonwealth 77: 193-.199 (1970).
6.
Karim, S.Y.M. and Hillier, K. Prostaglandins in the control of animal and human reproduction. Br. Med. Bull. -35:173-180 (1979).
7.
Singh, L.P., Sadiku, A. and Verma, O.P. Prostaglandin F2ainduced response of the bovine ovary, oviduct (uterine tube), and (1979). uterus. Am. J. Vet. Res. %:1789-1791
8.
Patil, R.K., Sinha, S.N., Einarsson, S. and Settergren, I. The effect of prostaglandin F2 and oxytocin on bovine myometrium in vitro. Nord. Vet. Med. -38:474-479 (1980). --
9.
Eiler, H., Oden, J., Schaub, R. and Sims, M. Refractoriness of both uterus and mammary gland of the cow to prostaglandin F2a administration: clinical implication. Am. J. Vet. Res. 42:314317 (1981).
10.
Rodriguez-Martinez, H., McKenna, D., Weston, P.G., Whitmore, H.L. and Gustafsson, B.K. Uterine motility in the cow during the estrous cycle. I. Spontaneous activity. Theriopenology 27~337-348 (1987).
11.
Genital tract Goddard, P.J., Allen, W.E. and Gerring, E.L. Normal pressures and the effect of pressures in mares. I. physiological events. Theriogenology -23:815-827 (1985).
FEBRUARY
1987 VOL. 27 NO. 2
357
THERIOGENOLOGY
12.
Garcia-Villar, R., Marnet, P.G., Laurentie, M.P. and Toutain, P.L. Relative oxytocic properties of fenprostalene compared with cloprostenol, prostaglandin F2a and oxytocin in the ovariectomized ewe. Am. J. Vet. Res. %:841-844 (1985).
13.
Rarcikowski, B.J., Carlson, J., Wilson, L. and McCracken, J.A. The effect of endogenous and exogenous estradiol-176 on the release of prostaglandin F2a from the ovine uterus. Endocrinology -95:1340-1345 (1974).
14.
Blatchley, F.R. and Poyser, N.L. The effect of estrogen and progesterone on the release of prostaglandins from the uterus of the ovariectomized guinea pig. J. Reprod. Fertil. %:205-210 (1974).
15.
Smith, S.K., Abel, M.H. and Baird, O.T. Effects of 17e-estradiol and progesterone on the levels of prostaglandins F2, and E in human endometrium. Prostaglandins 7:591-597 (1984).
16.
Goddard, P.J.
358
and Allen, W.E. Genital tract pressures in mares. by oxytocin and prostaglandin F2,. :i&iogCe?Po?y& -. 2~n~~~~~ (1985).
FEBRUARY
1987 VOL.
27 NO. 2