Prolactin levels in ovariectomized Brahman, Brahman × Hereford and Hereford cows following a 20 mg dose of estradiol-17β

THERIOCENOLOGY

PROLACTIN LEVELS IN OVARIECTOMIZEO BRAHMAN, BRAHMAN X HEREFORD AND HEREFORD CO!IS FOLLOWING A 20 MG DOSE OF ESTRADIOL-1761,2'3 R. C. Rhodes

III,

R. D. Randel and P. G. Harms

Texas A&M University Agricultural Research and Extension Center, Overton 75684, and Department of Animal Science, College Station 77843 Received

for Publication:

April 25, 1979

ABSTRACT Six Brahman (B), six Brahman x Hereford (BxH) and six Hereford (H) chronically ovariectomized cows were injected intramuscularly with 20 mg of estradiol-176 (EZ). The cows were bled via coccygeal vessel puncture immediately before E2 injection, every 2 hr from 0 to 8 hr post-injection, every hr from 9 to 24 hr post-injection and every 2 hr from 26 to 36 hr post-injection. Serum prolactin (PRL) concentrations were quantitated by a validated radioimnunoassay. All cows exhibited a PRL surge following the E2 injection. A PRL surge was defined as a sustained elevation in PRL of at least one standard deviation above the level of PRL before the rise. Nadir levels of PRL prior to the surge did not differ significantly between breeds. Time (hr) to the onset of the E2-induced PRL surge was 5.0, 5.0 and 6.2 in B, BxH and H, respectively (P>.lO). Elapsed time (hr) from E2 injection to the PRL peak level varied (Pc.01) between B (10.8) and H (17.8) and BxH (11.8) and H. Peak PRL levels (ng/ml) varied (Pc.10) between breeds (B, 70.6; BxH, 123.9; H, 49.4). Area under the PRL curve (sq cm) varied (Pc.05) between BxH (45.2) and H (24.7) but not between BxH and B (34.3; P>.lO) or B and H (Pb.10). Duration (hr) of the PRL surge did not differ significantly between breeds (B, 19.3; BxH, 20.5; H, 21.2). Overall, bleeding period effects (P<.OI), breed effects (Pc.lO), and breed x period interactions (Pc.01) were found.

'Journal paper TA

15097

, Texas Agricultural

Experiment

Station.

2The authors gratefully acknowledge Mrs. Martha Wright for technical assistance and the American Brahman Breeders Association for partial funding. 3This study was a contribution to Western Reproductive Performance in Beef Cattle.

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1979 VOL. 12 NO.2

Regional

Research

Project W-112,

85

THERIOGENOLOGY INTRDDUCTION It is well established that elevated endogenous levels of estrogen (1) or exogenous estrogen (1) can increase serum prolactin levels in the rat. In the bovine, however, the effects of endogenous or exogenous estrogen on serum prolactin is not well established. Swanson and Hafs (2) reported no increase in serum prolactin in Holstein heifers around estrus. Marked increases in relative prolactin values during estrus have been reported in the rat (3) and in the ewe (4). Shams and Karg (5) reported elevated levels of prolactin following infusion of 2-6 mg However, in one cow a 12 mg infusion of estradiol-17B for 1 to 3 hours. of estradiol-170 over 3 hr resulted in a small change in prolactin comDuring all infusion periods prolactin levels pared to the 2-6 mg level. appeared depressed. Differences in the reproductive capabilities of Brahman, Brahman x Hereford and Hereford cattle have been reported by various investigators (6, 7, 8). Further, it is apparent that a portion of the reproductive differences between the Bos indicus and Bos taurus species is due to a genetic dissimilarity inthehypothalami~y~eal axis. Randel (9) and Randel and Moseley (10) have shown that Brahman heifers have significantly lower LH levels during the preovulatory surge of LH, have an earlier LH surge and a shorter interval from estrus to ovulation than do Brahman x Hereford or Hereford heifers. Rhodes and Randel (11) observed fewer behavioral responses of ovariectomized Brahman x Hereford or Hereford cows following varying doses of estradiol-170. The ovariectomized Brahman cow has also been shown to secrete less LH upon a maximal gonadotropin releasing hormone (GnRH) (500 ug) or estradiol-176 (20 mg) challenge than either spayed Brahman x Hereford or Hereford cows (12, 13), respectively.

MATERIALS

AND METHODS

Eighteen mature chronically ovariectomized cows were divided into three groups of six animals by breed (Brahman, Brahman x Hereford and Hereford). All animals were injected intramuscularly with 20 mg of estradiol-17B suspended in corn oil. Ten ml blood samples were collected from each cow via coccygeal vessel puncture at 0 hr (sample prior to injection) and subsequently at 2, 4, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 26, 28, 30, 32, 34 and 36 hr post estradiol-176 administration. The blood was allowed to clot and was centrifuged for 30 minutes at 2,500 g at a temperature of 0 C and stored at -20 c. Serum concentration of PRL was quantitated by the double antibody radioimunoassay (RIA) developed for ovine PRL (14). Antibody DJB 7-0330 obtained from a rabbit immunized with ovine PRL (NIH-P-S8) was used as the first antibod A 1:160,000 dilution of the antibody which bound 30 to 40% of the r-251 bovine PRL with nonspecific binding less than 3% was used. Purified PRL (NIH-P-B4) was used for iodination and the antibody-hormone complex was precipitated with antirabbit gamma globulin (DJB5X2). Bovine PRL (NIH-P-B4) was used as the reference standard and results were expressed in terms of this preparation.

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1979 VOL. 12 NO. 2

THERIOGENOLOGY Performance of the assay was evaluated by the following parameters. Dose response curves for bovine serum were parallel to the reference standard. Bovine follicle stimulating hormone (FSH) (NIH-FSH-B), luteinizing hormone (LH) (NIH-LH-B) or thyroid stimulating hormone (TSH) (NIHTSH-B) failed to inhibit binding of 251 bovine PRL at a level of 500 Pg. Growth hormone (GH) (NIH-GH-B) inhibited binding in proportion with the PRL contanimation of the preparation. Sensitivity of the assay was such that Recovery could be distinguished from zero. of NIH-P-B4 added to bovine plasma of known Inter and 115, 110 and 102X, respectively. variation were 8.6 and 4.1, respectively.

.2 ng of the PRL NIH-P-B4 of .5, 1.0, 2.0 and 4.0 ng PRL concentration was 120, intra assay coefficients of

The parameters of the prolactin measurements made were: (1) prolactin surge exhibition, (2) time to the onset of the prolactin surge, (3) elapsed time from estradiol-17B injection to prolactin peak, (4) the area under the prolactin surge curve, and (5) the duration of the prolactin surge. A prolactin surge was defined as a sustained rise of prolactin at least one standard deviation above the first point of the rise. Analysis of variance was used to determine breed, period and breed mean separation test x period interactions (15). A Student-Neuman-Keuls for discriminating breed differences was also utilized (16).

RESULTS AND DISCUSSION Prolactin levels prior to the estrogen-induced-prolactin surges did not differ between breeds (Table I). The ore-suroe orolactin levels of this trial were similar to‘prolactin values reported'in Holstein heifers (range: 12 to 18 ng/ml; 2) pregnant Holstein heifers (range: 12 to 15 ng/ml; 17) and levels reported in Brown Swiss bulls (range: 8 to 20 ng/ml; 18). Prolactin concentrations reported in lactating cows were similar to the pre-surge prolactin values reported in this trial (17). The lactating cows used by Schams and Karg (5), in contrast, had a tendency to have higher basal prolactin levels than either the castrated cows used in this trial or the heifers, pregnant heifers, lactating cows or bulls utilized in the previous studies. All Brahman, Brahman x Hereford and Hereford cows exhibited a prolactin surge following the 20 mg dose of E2. Profiles of the mean-estroqen-induced-prolactin surges are shown by breed for each bleeding period in Figure 1. Standard error of the means for each bleeding period by breed type to correspond with Figure 1 are depicted in Table II. It should be noted that there is a slight disparity between values in This is due to the fact that the values Figure 1 and Table I, III and IV. in Figure 1 are the means of each discrete bleeding period, whereas, the means depicted in each of the tables are the means for each discrete parameter. Period effects (P<.Ol), breed effects (Pc.10) and breed x period interactions (Pc.01) were detected. These results agree with the reported effect of estrogen on pituitary PRL secretion in rabbits (18), ovariectomized rats (19) and cattle (20).

AUGUST 1979 VOL. 12 NO. 2

87

THERIOGENOLOGY The elapsed time (hr) from E2 administration until the onset of the prolactin surge did not vary (.P>.lO) between the three groups of ovariectomized animals (Table II), However, the elapsed time from E2 injection to the peak prolactin value varied between Brahman and Hereford cows and Brahman x Hereford and Hereford cows (Table II; Pc.05). These data differ from that reported by Schams and Karg (5) who found peak values of prolactin 2 to 6 hr post-E2 infusion and Beck et al. (22) who reported no -7 prolactin response following removal of estradlol-176 implants. Karg and Schams (20) also reported that infusion of 2 to 6 mg of estradiol stimulated prolactin release while higher dosages of E2 (i.e., 12 mg) The depressing effect of E2 at appeared to depress prolactin secretion. a higher dose level is in contrast to the prolactin stimulating effect Although a 20 mg dose of estradiol-176 of 20 mg E2 reported in this study. probably exceeded physiological levels, the large dosage of E2 utilized in the present study was due to the marginal effect of 8 mg of E2 on observed sexual behavior in the ovariectomized Brahman cow (11). The discrepancies between levels reported in this trial and levels reported in the other studies might be explained by the different animal model, E2 dosage and mode of estrogen administration. Mean peak prolactin values varied significantly between each breed (Table I; Pc.10). The magnitude of the mean peak prolactin values (49.4 to 123.9 ng/ml) are similar to prolactin levels found in estrogeninfused lactating cows (100 to 110 ng/ml; 2). In this trial, a genetic difference was observed with the general tendency being that the Brahman and Brahman x Hereford cows secreted a greater amount of prolactin upon the estrogen challenge than the Hereford cows. The Brahman and Brahman cross bred cow have been shown to have a strong lactational drive (23). Brahman cows also appear to be more susceptible to stress situations and prolactin has been shown to be stress related (24, 25). These facets of the Zebu-type cow may partially explain the capability of the Brahman cow to secrete more prolactin upon a very large estrogen challenge. The area under the prolactin curve did not vary between Brahman and Hereford cows (P>.lO), Brahman and Brahman x Hereford cows (P>.lO), but did vary between Brahman x Hereford and Hereford cows (Table III; Pc.05). This statistic might be anticipated due to the fact that the Brahman x Hereford cows had a significantly greater prolactin peak versus the Hereford cows while the duration of the prolactin surges were similar. The tendency for the Hereford cows to have a slightly longer prolactin surge (Table II) resulted in the time to the end of the surge varying between Brahman and Hereford cows (P<.O5) but not between Brahman and Brahman x Hereford cows (P>.lO) or Brahman x Hereford and Hereford cows (Table I; P>.lO). The mode of action of E2 in inducing the prolactin surge is not clear. It has been reported that addition of estrogen to the incubation medium of rat pituitary cell cultures enhances prolactin secretion in vitro (26, 27, 28). Estrogen inhibition of a hypothalamic prolactin inKb_ factor (PIF) has been postulated by Minaguchi and Meites (29). These investigators found administration of norethynodrel (Enovid) to rats reduces hypothalamic PIF, thus increasing prolactin release, apparently due to the metabolism of the Enovid to an estrogenic compound.'. It is well established that an inhibitory dopaminergic mechanism is responsible for the inhibitory effect of the central nervous system on prolactin re-

88

AUGUST

1979 VOL. 12 NO. 2

THERIOGENOLOGY

has also shown that the increased dopamay be reversed by estrogen treatment (31). Consequently, it is quite possible that both hypothalamic and hypophyseal sites of action may exist.

lease (1, 30).

Recent evidence

mine content of the median eminence after long term ovariectomy

In summary, these results demonstrate that a high dosage of estradiol178 can elicit a prolactin response in the bovine. Further, these results show that a genetic difference is evidenced in both the timing of the E2 induced prolactin surge and peak prolactin values between the ovariectomized Brahman and Brahman crossbred cow versus the ovariectomized Hereford cow. These findings may also suggest that steroidal secretion from Finally, an intact gonad in the bovine may affect prolactin secretion. the data strengthens the concept that a functional difference in the hypothalamic-hypophyseal (and perhaps gonadal) axis does exist between the -____ Bos indicus and -Bos taurus species. REFERENCES 1.

Meites, J., K. H. Lu, W. Wuttke, C. W. Welsch, H. Nagasawa and S. K. Quadri. Recent studies on functions and control of prolactin secretion in rats, Rec. Prog. Horm. Res. 28:471. (1972)

2.

Swanson, L. V. and H. Il. Hafs. LH and prolactin in blood serum from estrus to ovulation in Holstein heifers. J. Anim. Sci. 33:1038. (1971)

3.

Niswender, G. D., C. L. Chen, A. R. Midgley, Jr., J. Meites and S. Ellis. Radioimmunoassay for rat prolactin. Proc. Sot. Exp. Biol. Med. 130:793. (1969)

4.

Reeves, J. J., A. Arimora and A. V. Schally. Serum levels of prolactin and luteinizing hormone (LH) in the ewe at various stages of the estrous cycle. Proc. Sot. Exp. Biol. Med. 134:938. (1970)

5.

Schams, D. and H. Karg. The immediate response of plasma prolactin level to oestrogen infusion in dairy cows. Acta Endocrinologica 69:47. (1972)

6.

Warnick, A. C., W. C. Burns, M. Koger and M. W. Hazen. Puberty in English, Brahman and crossbred breeds of beef heifers. Proc. Assoc. of Southern Agr. Workers. (1956)

7.

Luktuke, S. N. and P. Subramanian. Studies on certain aspects of the oestrous phenomenon in Hariana cattle. J. Reprod. Fertil. 2:199. (1961)

8.

Plasse, D., M. Koger and A. C. Warnick. Reproductive behavior of Bos indicus females in a subtropical environment. In. Calving intervals from first exposure to conception and intervalFfrom parturition to conception. J. Anim. Sci. 27:105. (1968)

9.

Randel, R. 0. LH and ovulation in Brahman, Brahman x Hereford and Hereford heifers. J. Anim. Sci. 43:300 (Abstr.). (1976)

AUGUST

1979 VOL. 12 NO. 2

89

THERIOGENOLOGY 10.

Serum luteinizing hormone surge Randel, R. D. and W. M. Moseley. and progesterone near estrus in Brahman compared to Brahman x J. Anim, Sci, 45 (Suppl. 1):199 Hereford and Hereford heifers. (Abstr.). (1977)

11.

Reproductive studies of Brahman Rhodes, R. C. III and R. D. Randel. cattle. I. Behavioral effect of various dose levels of Estradiol178 upon ovariectomized Brahman, Brahman x Hereford and Hereford Theriogenology 9:429. (1978) cows.

12.

Reproductive studies of Brahman Griffin, J. L. and R. D. Randel. cattle. II. Luteinizing Hormone patterns in ovariectomized Brahman and Hereford cows before and after injection of Gonadotropin Releasing Hormone. Theriogenology 9:437. (1978)

13.

Rhodes, R. C. III, R. D. Randel and P. G. Harms. Reproductive studies of Brahman cattle. IV. Luteinizing Hormone levels in ovariectomized Brahman, Brahman x Hereford and Hereford cows following a 20 mg dose of Estradiol-178. Theriogenology 10:429. (1978)

14.

Etchernkamp, hormones 42:893.

15.

Steele, R. D. G. and J. H. Torrie. Principles and Procedures Statistics. McGraw-Hill, New York. (1960)

16.

Hicks, C. R. Fundamental concepts in the design of experiments. Holt, Rinehart and Winston, Dallas. (1973)

17.

Vines, D. T., E. M. Convey and H. A. Tucker. Serum prolactin growth hormone responses to thyrotropin releasing hormone postpubertal cattle. J. Dairy Sci. 60:1949. (1977)

18.

Schams, D., V. Reinhardt and H. Karg. The immediate response of the plasma prolactin level to oestrogen and progesterone infusions in bulls. Acta Endocrinologica 76:242. (1974)

19.

Tindal, J. S. and G. S. Knaggs. An ascending pathway for release of prolactin in the brain of the rabbit. J. Endocrinol. 45:lll. (1969)

20.

Chen, C. L. and J. Meites. Effects of thyroxine and thiouracil on hypothalamic PIF and pituitary prolactin levels. Proc. Sot. Exp. Biol. Med. 131:576. (1970)

21.

Karg, H. and D. Schams. Prolactin Fertil. 39:463. (1974)

22.

Beck, Thomas W., Valdin G. Smith, Brad E. Sequin and E. M. Convey. Bovine serum LH, GH and prolactin following chronic implantation of ovarian steroids and subsequent ovariectomy. J. Anim. Sci. 42:461. (1976)

90

S. E., D. J. Bolt and H. W. Hawk. Ovarian and pituitary in blood of progestogen-treated ewes. J. Anim. Sci. (1976)

release

in cattle.

AUGUST

of

and in

J. Reprod.

1979 VOL. 12 NO. 2

THERIOGENOLOGY 23.

Crossbreeding Beef Cattle. Koger, M., T. J, Cunha and A. C. Warnick. (1973) Series 2. Univ. of Florida Press, Gainesville,

24.

Factors affecting the plasma prolactin level in the Johke, Tetsu. cow and the goat as determined by radioinxnunoassay. Endocrinol. Japonica 17:393. (1970)

25.

Tucker, H. A. Hormonal response Suppl. 1, 137. (1971)

26.

Prolactin secretion in vitro. Nicoll, C. S. and J. Meites. of gonadal and adrenal cortical steroids. ProczExp. Biol. Med. 117:579. (1964)

27.

Ben-David, M., S. Dikstein and F. G. Solman. Effects of different steroids on prolactin secretion in pituitary-hypothalamus Proc. Sot. Exp. Biol. Med. 117:511. organ co-culture. (1964)

28.

Tashjian, A. H. and R. F. Loyt, Jr. Transient controls of organspecific functions in pituitary cells in culture. In. Molecular Genetics and Developmental Biology. Prentice-Hall, Englewood Cliffs, N.J. p. 353. (1972)

29.

Effects of suckling on hypothalamic LHMinaguchi, H. and J. Meites. releasing factor and prolactin inhibiting factor, and on pituitary LH and prolactin. Endocrinol. 80:603. (1967)

30.

Ojeda, S. R., P. G. Harms and S. M. McCann. Effect of blockade of dopaminergic receptors on prolactin and LH release: Median eminence and pituitary sites of action. Endocrinol. 94:1650. (1974)

31.

Increase in dopamine Gudelesky, G., L. Annunziato and K. E. Moore. content of the rat median eminence after long-term ovariectomy and its reversal by estrogen treatment. Endocrinol. 101:1894. (1977).

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1979 VOL. 12 NO. 2

to milking.

J. Anim. Sci. 32,

Effects

91

I.

0

;‘;

2

4

a:

6

Figure 1.

*.

k

.

*

lb

*

.

1’2

.

:

14

*

:

16

:

18

4.

HOURS

*

2’0

:

22

8

FROM

*

‘..*‘..*

---_

“;a

2a E2

26

‘.

;.

30 INJECTION

2’8

32

;.

34

:’

COWS X HEREFORD COWS

(E2) administration and Hereford COWS.

BRAHMAN BRAHMAN HEREFORD

Mean prolactin levels following Estradiol-17B in ovariectomized Brahman, Brahman x Hereford

;

36

COWS

"c'dMeans

within

the same rows followed

error of the mean. by different

superscripts

31.3

123.gc

70.6b 11.1

Peak PRL value (ng/ml)

aSE = standard

1.2

9.Bb

SE

differ

x Hereford

5.4

Mean --

10.4b

level parameters

SEa

Breed type Brahman

PRL value at onset of surge (rig/ml)

Prolactin

Mean __-

Brahman

8.0

49.4d

significantly

1.1

SE

14.4b

--Mean

Hereford

(Pc.10).

TABLE I. PROLACTIN (PRL) LEVELS (NG/ML) AT SEVERAL DIFFERENT STAGES OF THE PROLACTIN SURGE FOLLOWING ESTRADIOL-778 ADMINISTRATION IN OVARIECTOMIZED BRAHMAN, BRAHMAN X HEREFORD AND HEREFORD COWS.

THERIOGENOLOGY

STANDARD TABLE II. BREED TYPE.

ERROR OF THE MEAN FOR EACH BLEEDING

PERIOD BY

Breed type Hours post estradiol injection 0 2 4 : 1; 11 12 13 14 15 16 17

22 23 24 26 28 30 32 34 36

94

Brahman

11.1 7.1 9.5 10.1 10.5 5.8

10:7 1Z 10.4

Brahman x Hereford

2.4 2.9 1.2 3.1 3"';

Hereford

2713

:-: 1:o 3.5 3.9 4.3 4.1

:-; 30:1

5.1 7.0 3.7

11.1 8.2 6.9 6.7 5.7

8.6 42:; t-z

:-; 5:9 3.9 3.3

?"9 5:2 2:;

217 3.9 5.3 4.0 3.1

2.9 5.6 6.2 6.0 5.0

:::

;*:

4.1 5.1

;::

2:o 2.8

1.3

1.3

:-E:

2.4 1.6

2:4 3.5

4:2 43.;

AUGUST

1979 VOL. 12 NO. 2

the same rows followed

.4 1.2 1.0

10.Bb 19.3b 24.3b

superscripts

.7

5.0b

bycMeans

by different

superscripts

error of the mean.

followed

aSE = standard

differ significantly

34.3b'C 8.5

(sq cm)

Area under the PRL curve

SEa

Mean --

Area parameter

Brahman

.7 .7

20.5b 25.5byC

significantly

.7

ll.Bb

4.4

45.2'

(Pc.05).

SE

x Hereford Mean --

Brahman

Breed type

ESTRADIOL-176

differ

.9

SE

.7

27.4'

1

24.7b

Mean -_

6.4

SE

Hereford

IN

1.6

21.2b

(Pc.05

1.7

17.8'

-

1.5

SE

6.2b

Mean --

ADMINISTRATION

x Hereford

5.0b

Mean --

Brahman

IN

Hereford

E2) ADMINISTRATION

Breed types

ESTRAOIOL-17~

TABLE IV. THE AREA (SQ CM) UNDER THE PROLACTIN (PRL) CURVE FOLLOWING OVARIECTOMIZED BRAHMAN, BRAHMAN X HEREFORD AND HEREFORD COWS.

bycMeans within

by different

to end of PRL surge

(hr)

aSE = standard error of the mean.

Hours from E2 injection

Duration of the PRL surge

to peak PRL value

Hours from E2 injection

surge

to onset of PRL surge

of the prolactin

Hours from E2 injection

Time parameters

SEa

Mean --

Brahman

TIMING OF PROLACTIN(PRL) SURGE PARAMETERS FOLLOWING TABLE III. OVARIECTOMIZED BRAHMAN, BRAHMAN X HEREFORD AND HEREFORD COWS.