effects of estrogen and progesterone on serum prolactin and luteinizing hormone levels in...

GENERAL AND COMPARATIVE ENDOCRINOLOGY 52, 67-78 (1983)

Effects of Estrogen and Progesterone on Serum Prolactin an Luteinizing Hormone Levels in Ovariectomized Turkeys

(Meleagris gallopavo)l

M. E. EL HALAWANI, J. L. SILSBY, S. C. FEIIRER, AND E. J. BEHNKE

Department of Animal Science, University of Minnesota, St. Paul, Minnesota 55608

Accepted October 13, 1982

Serum prolactin (PRL) and luteinizing hormone (LH) levels from mature female turkeys were determined following ovariectomy and daily subcutaneous injections for 4 or 9 days of 0.002-2.0 mg/kg estradiol benzoate (EB), 0.0.5-2.0 mg/kg progesterone (P), or their combinations. Serum PRL levels were increased (P < 0.05) at the onset of sexual maturity in intact controls, but not in ovariectomized turkeys. Injection of 0.02 mgikg EB into ovariectomized turkeys resulted in elevated (P < 0.05) serum PRL levels after 8 treatment days. Higher doses failed to elicit a response of greater magnitude. EB at doses of 0.02-2.0 mg/ kg reduced LH levels while 0.002 mg/kg EB increased LH levels above (P < 0.05) those of ovariectomized controls. The 1.0-m&g P dose increased (P < 0.05) serum PRL within 24-48 hr of administration while the 0.05, 0.5-, or 2.0-mg/kg P doses failed to elicit a response. When P was injected in doses of 0.5-2.0 mg/kg, LH levels were decreased in a dose-response manner. The injection of EB combined with P had a variable effect on serum PRL levels. The 0.5- or 1 .O-mg/kg dose of P facilitated (advanced in time) the rise in serum PRL level induced by 0.02 mg/kg of EB. In contrast, the positive feedback effect of 0.2 mg/ kg of EB was blocked when administered with 0.5 mg/kg of P. Serum LH levels were dramatically decreased by all steroid combinations used. These results indicate that daily injections of EB and/or P in ovariectomized turkeys have a variable effect on serum PRL and LH levels depending upon the dose, the duration of treatment, or the ratio between EB andP.

Seasonal reproduction in many birds is regulated by the annual cycle in daylength, with 14 hr or longer photoperiods causing increased gonadotropin and prolactin (PRL) release and gonadal development (Nicholls et al., 1974; Follett et al., 1975; Follett, 1976; Godden and Scanes, 1977; Burke and Den- nison, 1980; Goldsmith and Hall, 1980). During the normal breeding cycle it is clear that gonadal steroids attenuate luteinizing hormone (LH) levels in the plasma (Davies, 1976; Williams and Sharp, 1977). Removal of the inhibitory feedback of endogenous gonadal steroids by castration leads to elevated levels of circulating LH and follicle- stimulating hormone (FSH) and administra-

i This paper is Scientific Journal Series paper number 13,199 of the Minnesota Agricultural Experi- ment Station.

tion of gonadal steroids results in an inhi- bition of their release (FoLlett et al., 1972; Hinde et al., 1974; Wilson and Fotiett, 1974; Follett, ‘1976; Wilson and Sharp, 1976; De- viche et al., 1980; Wingfield et ai., 1980). Whereas this relationship is well documented with regard to the inhibitory influence of steroids on LH release in castrate ’ birds, the situation with regard to P relatively unknown. Scanes et al. (1976) showed that gonadectomy had little effect on plasma PRL levels in the chicken, and Hall and Chadwick (1978) reported a stimulatory effect of estradiol on PRL release in vitro.

The dependence on gonadal steroids for PRL release has been established in mam- mals (Franz et al., 1972; Yamamoto et al., 1975). Progesterone or estrogen ~~~~cti~~

67 00166480183 $1.50 Copyright @ 1983 by Academic hess, Inc. All rights of reproduction in any form reserved.

68 EL HALAWANI ET AL.

increased serum PRL levels in ovariectomized rats (Chen and Meites, 1970) and estrogen treatment potentiated the TRH-induced release of PRL in monkeys (Quadri et al., 1979). Ajika et al. (1972) showed an increased PRL release resulting from decreased hypothalamic inhibitory activity in estrogen-treated ovariectomize rats.

It was the purpose of this study to inves- tigate the PRL response to ovariectomy and following injection of estradiol benzoate (EB) and/or progesterone into ovariectomized female turkeys. A reliable and well- documented response to castration is elevated serum LH levels. Therefore serum LH was also determined as a means of char- acterizing the effects of the treatments.

MATERIALS AND METHODS Adult Nicholas strain female turkeys weighing 9.2-

10.4 kg at 30 weeks of age were used in all experiments. Feed and water were constantly available throughout the experiments. The birds were housed in floor pens under a light regimen of 6 hr of light and 18 hr of darkness (6L:18D) daily, with lights on constantly from 0800 to 1400 hr. Ovariectomy and sham surgical procedures were conducted using ke- tamine * HCl-xylazine anesthesia. Two to three weeks after surgery, ovariectomized and sham-operated turkeys were placed into individual wire cages (except birds in Experiment 1) and subjected to a stimulatory photoperiod of 15L:9D, with lights on constantly from 0400 to 1900 hr. The experiments were initiated when the sham-operated turkeys had been in lay for at least 1 week.

P-Estradiol-3-benzoate (EB; Sigma Chemical Co., St. Louis, MO.) and progesterone (P; Sigma,) were dissolved or suspended in 0.5 ml sunflower oil per dose and injected subcutaneously daily between 0900 and 1000 hr just after blood collection for various lengths of time depending upon the experiment. Cas- trated controls and sham-operated turkeys were injected with 0.5 ml oil only.

Experiment 1. Effect of ovariectomy and photostimulation on serum PRL and LH. Ovariectomized and sham-operated turkeys (six birds/treatment) were housed in floor pens and subjected to the stimulatory photoperiod (lSL:9D). Blood samples for subsequent PRL and LH determination were obtained from both groups 7, 5, and 0 days before photostimulation and 1, 2, 7, 11, 12-15, 21, 28, and 35 days after light stimulation.

Experiment 2. Ovariectomized turkeys were ran-

domly divided into experimental groups (5-6 birds/ group). The birds were treated with either EB or P for 4 consecutive days. EB was administered at dose levels of 0.002, 0.008, or 0.02 mg/kg and P was injected at 0.05-, 0.2-, or 0.5-mgikg doses. Serum PRL and LH were determined in blood samples obtained before (1 and 0 days) and during (l-4 days) steroid administration. During steroid treatment blood samples were collected just before the daily steroid injection with the last blood sample being collected 24 hr after the last steroid injection.

Experiment 3. The experimental procedure was the same as described in Exp. 2, except for the steroid dose levels and the duration of treatment. Ovariecto- mized turkeys were treated with 0.02,0.04, or 0.2 mgi kg of EB or 0.5, 1.0, or 2.0 mg/kg of P for 9 consecutive days. Blood samples for PRL and LH determination were taken on Days 2, 1, and 0 before the ini- tiation of treatment and Days 1-9 during treatment.

Experiment 4. Experiment 4 is similar to Exp. 3 except that EB was injected at 1.0 or 2.0 mg/kg. Com- binations of EB and P were administered at the following doses: 0.02 mg/kg EB + 0.5 mg/kg P, 0.02 mg/ kg EB + 1.0 mg/kg P, 0.2 mg/kg EB + 0.5 mg/kg P, or 0.2 m&g EB + 1.0 mgikg P. Blood samples were collected before (2, 1, and 0 days), during (l-9 days), and after (19 days) termination of treatments.

Radioimmunoassay. Blood (4 ml) was obtained from the brachial vein, allowed to clot overnight, and then centrifuged to separate the serum. Serum was de- canted and stored at - 20” until assayed for PRL and LH. PRL and LH radioimmunoassays were conducted according to the methods of Burke and Papkoff (1980) and Burke et al. (1979), respectively. Serum samples for each experiment were run in duplicate in a single assay. The average within-assay coefficients of varia- tion were 5.6% for PRL and 4.5% for LH. Average sensitivities were 0.41 and 0.038 ng for PRL and LH, respectively.

Statistical analysis. Data were analyzed by analysis of variance using the GLM procedure in the Statistical Analysis System (Helwig and Council, 1979). Dun- can’s multiple-range test was used to compare means at the 0.05 level.

RESULTS

Effect of Ovarjectomy and Photostimulation upon Serum PRL and LH Levels

Changes in serum PRL and LH levels fol- lowi,ng ovariectomy and photostimulation are illustrated in Fig. 1. In both sham-operated and ovariectomized birds, there was a significant increase in serum PRL levels

OVARIAN STEROIDS AND THE RELEASE OF PRL AND LH 69

260 t

260

24.0 I

220 t

60

20

0 1 II-

-7 -6 -5 012 7 -21-~ 11 12 13 14 15 28 35

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FIG. 1. Effect of photostimulation on serum levels of PRL and LH of ovariectomized female turkeys and their corresponding intact controls. Each point represents mean values for six birds per group; vertical line on each point represents SEM. -

during the experimental period. Before photostimulation PRL levels were similar in sham-operated (7.4 + 0.6 rig/ml) and ovariectomized turkeys (7.8 +- 0.9 rig/ml). There was an increase (P < 0.05) in serum PRL after 11 days of exposure to the long photoperiod in both the controls (24.8 +- 5.9 rig/ml) and in the ovariectomized (28.0 i 3.0 ngiml) group. After 28 days of photostimulation all sham-operated birds reached se.xual maturity. This was accompanied by a further increase in PRL level to 261.6 + 76.4 rig/ml. The serum PRL in the ovariectomized group remained fairly stable from the I lth day of photostimulation to the end of the experimental period.

The mean serum LH level on the three sampling days prior to photostimulation was lower (P < 0.05) in sham-operated birds than in ovariectomized birds. One day after pho-

tostimulation, an increase in LH was tected in both groups. Subsequently there was a rapid increase in serum LH m ovariectomized turkeys reaching 32.34 & 6.32 &ml whereas the rise was smaller (5.79 + 0.65 ngtml) in sham-operated turkeys

The Effect of Daily Administration of Estradiol Benzoate (EB) OIZ the Levels of Serum -PRL and LH in Ovariectomized Turkeys

The effects of 4 days of EB admiu~~tra- tion on serum PRL levels are shown in Fig. 2A. The injection of 0,002, 0.008, or mgikg EB for 4 consecutive days cause change in serum PRL level. Sequential injections of 0.02 mg/kg EB for 9 days increased the serum PRL level (30.2 + 25 &ml) compared to that in oil-treated controls (19.4 2 1.5 rig/ml; Fig. 2B). The O.O4-


16

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-- 0.002 mg/kg EB -.-. 0.02 mg/kg EB

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DAYS FIG. 2. The effect of estradiol benzoate on serum levels of PRL and LH of ovariectomized female

turkeys. When the F test for data on any treatment day was significant (P < 0.05), treatments significantly different for that day have different letters next to their means. Each point represents mean values for five to six birds per group.

and O.Zmg/kg doses of EB increased (P < No alterations in serum LH levels were 0.05) the mean serum PRL level by Day 4 observed with the 0.008- or O.OZmgkg dose of injection (Fig. 2B). Injection of ovariec- of EB during the 4-day treatment period; tomized turkeys with 1.0 or 2.0 mg/kg EB however, an increase (P < 0.05) in serum (Fig. 2C) yielded a delayed (6 days) in- LH level was noted with the 0.002-mg/kg crease in serum PRL to 35.9 f 2.6 rig/ml dose (19.96 rt 5.97 rig/ml) in comparison and 38.8 +- 4.5 rig/ml, respectively, as com- with the oil-injected controls (9.57 + 0.88 pared to oil-injected controls (22.1 & 1.3 rig/ml; Fig. 2A). In birds receiving 0.02 or rig/ml). The PRL levels remained elevated 0.04 mg/kg EB for 9 days, the LH levels and stable during the remainder of the treat- were reduced (P < 0.05) from ovariectomy ment. levels, and were further suppressed with the

OVARIAN STEROIDS AND THE RELEASE OF PRL AND LH

-B - OIL CONTROL ............ 0.04 mg/kg EB

--0.02 mg/kg EB -.-.- 0.2 mg/kg EB

OL 1 I I I I 1 I I I I 1 -2-l 0 12 3 4 5 6 7 8 9

DAYS FIG. 2-Continued

0.2 mg/kg dose (Fig. 2B). The injection of 1.0 or 2.0 mg/kg EB induced a depression in serum LH levels within 24 hr of injection, These two EB doses were equally effective in depressing serum LH (Fig. 2C).

The Effect of Daily Administration of Progesterone (P) on the Levels of Serum PRL and LH in Qvariectomized Turkeys

The injection of 0.05, 0.2, or 0.5 mg/kg of P on 4 consecutive days did not alter (P > 0.05) serum PRL levels (Fig. 3A). Se- quential administration of 1.0 mg/kg of P,

but not 2.0 mg/kg, induced an increase in serum PRL by the first day of injection, and the peak level (37.5 + 3.2 &ml) was observed on Day 5 (Fig. 3B). Thereafter, the level of PRL declined to 25.0 + 5.1 ngimli by the end of the experimental period.

The administration of 0.05 or 0.2 mg/kg P for 4 days failed to increase or decrease serum LH (Fig. 3A). Daily injection of 0.5 mg/kg P induced only a small decrease in serum LH level compared to the Level in oil-treated controls (Fig. 3B). Serum L levels were further suppressed from the levels in the ovariectomized controls by the


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l.O- and 2.0-mg/kg doses of P. These two doses were equally effective in suppressing LH.

The Effect of Daily Injection of EB plus P on Serum PRL and LH Levels in Ovariectomized Turkeys

The results of the combined treatment with both EB and P are shown in Fig. 4. Sequential administration of 0.2 mg/kg EB together with 0.5 mg/kg P was ineffective in inducing any alterations in serum PRL level, although this dose of EB in combination with 1.0 mg/kg P caused a rise in

serum PRL level on the eighth treatment day (35.5 -+ 4.1 vs 23.5 ? 2.9 rig/ml). In contrast, 0.02 mg/kg EB together with 0.5 or 1 .O mg/kg P induced an elevation in the serum PRL. This rise in serum PRL was observed on the first treatment day and remained throughout the entire treatment period. The elevated PRL levels returned to oil-injected control levels following treatment termination.

Serum LH levels were dramatically decreased by the combined injection of EB + P. The administration of EB + P suppressed LH levels to 37-52% of control


values one day after treatment, where they remained throughout the entire treatment period. Further, the extent of suppression was similar for all the combinations used, When the treatment was discontinued, LH serum values reached control levels.

None of the doses of EB, P, or’ combinations injected into ovariectomized turkeys raised serum PRL levels to those levels found in the sham-operated laying birds. The overall mean PRL levels of intact controls were 40.7 r4: 2.3 r&ml (Experiment 2), 75.6 +- 6.9 rig/ml (Experiment 3), and 67.9 ‘r 2.8 r&ml (Experiment 4). Overall mean LH levels for these groups were 3.94 + 0.26 nglml, 2.00 +- 0.19 rig/ml, and 5.96 +- 0.24 rig/ml, respectively.

DISCUSSION

The results of the present study indicate that estrogen and progesterone have a stimulatory effect on PRL release and a depressing influence on LH release. In un- treated ovariectomized turkeys serum PRL is low and LH is high. The low PRL level is most likely caused by removal of the positive feedback effect of ovarian steroids which was verified by the results of daily injections of EB and/or P. The administration of EB to ovariectomized turkeys caused a delayed increase in the serum PRL level. A delayed pituitary PRL response to EB administration has also been reported in cockerels (Kono et al., 1980). Such a delay is not seen in the ovariectomized rat where serum PRL increases markedly within 24- 48 hr of a single injection of estradiol (Kalra et al., 1970; Ajika et al., 1972; Yamamoto et al., 1975). In humans and rhesus monkeys, as seen in turkeys, estradiol does not cause an immediate PRL rise (Franz et al., 1972; D’Agata and Scapagnini, 1979; Quadri et al., 1979).

Unlike EB, P induced a PRL increase within 24-48 hr (Fig. 3B). The time difference in the serum PRL rise cannot be ex- plained on the basis of dose, since a similar range of doses was used for both. The ob-

servation that only the l.O-mglkg dose of P was effective is perplexing and indicates the need for further work to clarify the role of P in PRL release. The low P doses probably did not yield a high enough circulating hormone level, while the reason for failure of the 2.0-mg/kg P dose is unclear.

The ratio of EB to P appears to have a modifying effect on PRL release. Whew is administered in association with a PRL- releasing dose of EB , it can either facilitate (advance in time) or block PRL release (Fig 4). The indication that P in proper combination with EB can stimulate and faeilitat~ PRL release points to the importance of the presence of and ratio between both steroids,

The stimulatory effect of El3 andior PRL release in ovariectomized female tw- keys is not comparable in magnitude to serum PRL rises observed in intact laying female turkeys. The fact that only certain EB and P combinations were capable of inducing PRL release may explain the failure of the experiments to achieve the layin PRL level, since the optimal EB-to-P ratio might not have been used.

The results once again illustrate the ative feedback effects of estrogen and gesterone on LH release. The elevation of serum LH resulting from the injection of the O.OOZmg/kg dose of EB (Fig. 2A) is an interesting finding. Although data ited to form a firm conclusion, Wilson has found that a low dose of testost increased plasma LH in castrate erels. Further, Bonney and ~~n~in~~arn (1977) have shown an increased pituitary responsiveness to LHRH by a low dose of estrogen.

Photoperiodic induction of gonadal development is associated with a rise in se PRL level in turkeys (Burk nison, 1980) and quail (Goldsmith 1980) and is further supported by this study. Pi- tuitary PRL level has also been shown to increase together with gonadotropin level in the male duck upon exposure to a long


l8 A

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FIG. 3. The effect of progesterone on serum levels of PRL and LH of ovariectomized female turkeys. When the F test for data on any treatment day was significant (P < 0.05), treatments significantly different for that day have different letters next to their means. Each point represents mean values for five to six birds per group.

photoperiod (Assenmacher et al., 1962). However, in ovariectomized turkeys, a smaller increase in PRL level was observed. Investigations of PRL changes following ovariectomy in the rat have indi- cated lower plasma PRL concomitant with an elevation of LH levels (K&a et al., 1970; Ajika et al., 1972).

Serial determinations of serum PRL clearly show that PRL control systems react to photostimulation and ovarian steroids. This relationship is also true for LH, although the pattern of response is different

(Fig. 1). There are two distinct PRL rises following exposure to the stimulatory photoperiod. The initial photoperiodically induced PRL rise occurs after about 7-11 days. There is evidence of a delayed PRL rise in prepubertal bulls following exposure to stimulatory photoperiod (Bourne and Tucker, 1975) and Burke et al. (1981) have reported a delayed decrease in serum PRL in laying turkeys exposed to a short photoperiod. Exactly how the long photoperiod acts to stimulate the early PRL release is open to speculation. The fact that PRL in-


50 - B -OIL CONTROL .-....... 1 .O m&kg P

----0.5 mg/kg P ----2.0 mg/kg P

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creased to the same level in both intact controls and ovariectomized turkeys on stim- ulator-y days suggests that ovarian hormone feedback is not involved in the initial PRL rise, and argues in favor of long photoperiods stimulating PRL release by direct reg- ulation. However, the possibility still re- mains that photoinduction will cause a phase shift in the PRL circadian rhythm, due to a shift in the on and off times of the light. There is evidence for a circadian rhythm in PRL release in the bantam chicken (Sharp, 1980), and a phase shift is observed in the

diurnal rhythm of pituitary PRL Levels in the white-throated sparrow between and August (Meier et al., 1969).

The second rise in serum PRL was observed in the intact group by Day, 28 following photostimulation. At this time a 12- fold difference could be seen between the intact controls and the experiment& group. The agent(s) regulating the second phase of increased PRL release is probably of ovarian origin, since ovariectomy prevents this PRL rise and increases LH levels.

We report data that demonstrate for the


- OIL CONTROL

-- 0.02 mg/kg EB+ 0.5 mg/kg P -.-.- 0.2 mg/kg EB+O.5 mg/kg P ---- 0.02 mg/kg EE+l.O mg/kg P ..(...‘.. 0.2 mg/kg EB +l.O mg/kg P

LAST INJECTION

2 - LAST INJECTION

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-2 -1 0 1 23456789 27

DAYS FIG. 4. The effect of estradiol benzoate together with progesterone on serum levels of PRL and LH

of ovariectomized female turkeys. When the F test for data on any treatment day was significant (P < 0.05), treatments significantly different for that day have different letters next to their means. Each point represents mean values of five to six birds per group.

first time a stimulatory effect of EB on PRL release in the ovariectomized turkey. The indication that P in the proper combination with EB can stimulate and advance PRL release points to the importance of both these steroids. This may partially account for the dramatic rise in serum PRL levels found around the onset of sexual maturity, since alterations in both progesterone and estradiol levels have been reported to occur at this time (Bajpayee and Brown, 1972; Williams and Sharp, 1977).

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OVARIAN STEROIDS AND THE RELEASE OF PRL AND LH

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effects of estrogen and progesterone on serum prolactin and luteinizing hormone levels in...

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