Periovulatory enhancement of spontaneous prolactin secretion in normal women

Periovulatory

Enhancement ofSpon.ta.neous Secretion in Normal Women

Maire T. Buckman,

Glenn T. Peake, and Laxmi S. Srivastava

The role of endogenous estrogen in the regulation of prolactin secretion in man is controversial. To study this question further. spontaneous prolactin patterns were determined over 5 hr in 10 normal women during the early follicular and again during the periovulatory phases of the menstrual cycle. Steroid determinations revealed significant elevations in mean +I SE E, (I 13 + 20 versus 55 + 5 pg/mlL E, (144 + 47 versus 46 + 9 pg/mlL and 17-OHP (I ,301 f 266 versus 639 k 46 pg/ml) during the periovulatory compared to the early follicular phase period. Each subject demonstrated increased mean plasma prolactin concentration during the higher estrogen state. Mean prolactin concentration (calculated from the individual mean values of samples obtained at 15 min intervals for 5 hr) during the midcycle study period was 10.7 + 1.0 ng/ml compared to the early fellicular phase period of 6.1 + 1.0 ng/ml (p < 0.0005). The mean percent increment in plasma prolactin during the periovulatory period was 39% with a range of 9 to 117%. There was no correlation between mean prolactin and serum E,, E,, P, or 17-OHP levels during either study period. However. the incremental change in prolactin showed a positive correlation with the incremental increase in E, (correlation coefficient, c = 0.66, p -c 0.05). In contrast, no significant correlation was present between mean incremental change in prolactin and E,. P, or 17-OHP. These data suggest that enhanced cyclic estrogen secretion during the periovulatory phase of the menstrual cycle is associated with significantly increased serum prolactin concentrations.

correlation with pharmacologically induced prolactin has yielded variable results.“-‘6 Thus, neither the the menstrual nor correlation the presumed endogenous estrogen with pharmacologically has yielded consistent confirmation endogenous esrole in modulation man. Because was attempted the present the possible role of cyctic endogenous estrogen the possible effects of diurnal variation, spontaneous and stress the study was over a prolonged time period hr) during low and high endogenous estrogen states. MATERIALS

of pharmacologic results in eIevation in serum prolactin concentrations in man.14 The role of endogenous estrogen in the regulation of prolactin secretion, in contrast, has been controversial. One approach to this question has been to evaluate the effect of physiologic fluctuations in endogenous estrogen on serum prolactin levels during normal menstrual cycles. Single random prolactin levels and pharmacologically stimulated prolactin responses have been determined throughout normal menstrual cycles. Serum prolactin concentrations measured in single blood specimens throughout normal menstrual cycles have been reported to parallel serum estrogen levelss,6 or to show no relationship to the cyclic estrogen changes throughout the menstrual cycle.‘-” Likewise,

Metabolism, Vol. 29, No. 8 (August).

AND

METHODS

Ten normal women between the ages of 18 and 41 yr on no medication volunteered by informed consent to participate the studies (Table cycles with

A DMINISTRATION doses of estrogens

Prolactin

cycle

1). All interval

women had regular ranging

from

in

menstrual

25 to 32 days.

Subjects came to the Clinical Research Center between 0830 and 1000 hr. The paired studies on the same individual were begun within 30 min of each other to minimize any effect of diurnal

variation

on prolactin

placed in an antecubital

secretion. An intracath

was

vein and kept open with a heparin-

saline

mixture.

during

which the patients

Following

a

30-min

stabilization

were given a breakfast

period of their

From the Veterans Administration Hospital, and the University of New Mexico School of Medicine. Albuquerque, New Mexico; and The University of Cincinnati School of Medicine, Cincinnati, Ohio. Received for publication November 2, 1979. Supported in part by the Veterans Administraiion (Clinical Investigator Award to Dr. Buckman) and by NIH Grants HD 05794-08 and RR 00997-04. Address reprint requests to Maire T. Buckman. M.D., Research Service (I 51). Veterans Administration Hospital, 2100 Ridgecrest Drive S.E.. Albuquerque, N. Mex. 87108. 0 1980 by Grune & Stratton, Inc. 0026%0495/80/2908-XW09$0I .00/O

753

754

BUCKMAN,

Table 1. Serum Estrone /E,). Estradiol (E,). Progesterone Levels Measured

Subpcect

of

Age

Da”

LPI

CVCk

(PI. 17-Hydroxyprogesterone

Over a 5-hr Period During the Early and Periovulatory

E,

E,

bg/ml)

bglmll

P (pglmll

170HP Ip9lmll

Mean PRL lng/mll

Day Of

I1 7-OHP). and Mean Prolactin (PRL)

Phases of the Menstrual

El

Cycle

PEAKE, AND SRIVASTAVA

P

E*

1 ,-OHP

(Pg/mll

Lpdmll

lpaimll

Cycle

Mea”

(pslmll

PRL

inaIm

1

28

4

61

38

286

645

4.7

14

21,

426

1.268

2 514

IO 2

2

27

2

62

117

433

787

9.5

11

241

396

726

2.67,

12 6

3

26

3

58

56

500

526

46

14

111

113

1.942

2.273

53

4

18

3

33

18

253

831

4.3

12

79

42

328

1.091

72

5

19

4

61

45

429

736

13.9

12

1,

49

32,

660

16.9 11 1

6

18

3

49

3,

224

502

83

12

89

45

232

888

7

20

4

84

43

368

668

8.7

11

66

51

333

773

11 1

8

24

3

4,

23

322

408

10.2

11

79

42

295

753

13 1

8

41

3

66

4,

272

780

12

111

260

930

10

24

6

38

57

347

506

12

59

235

459

25 t 2

3 f 0.3

56 f 5

x* lp

ISE

48

f 9

343

r 28

639

t 46

5.7 106 8.1

I

1 0

12 z 0.3

113

r 20’

17, 95 144 i

47,

595

-

182

1 ,301

i 266,

80 ,I 10,

6 * to*

< 0.01 compared to early follicular phase.

tp < 0.025 $p < 0.0005

compared to early folllcular phase. compared to early follicular phase.

choice, which was identical during the 2-study periods, 5 cc of blood was collected in chilled heparinized tubes at 15min intervals for 5 hr. In addition, 20 cc of blood was collected at the beginning of the study for steroid determination. The study was performed twice on each patient: between days 224 (early follicular phase) and again between days 1 I-14 (periovulatory phase) of the menstrual cycle (Table 1). Normal activity, primarily of a sedentary nature, but no vigorous exercise, was allowed during the study periods. Blood for steroid determinations was allowed to clot at room temperature for l-2 hr. centrifuged at 4°C. serum separated and frozen at -2OOC. until assayed. Blood for prolactin was stored in ice, centrifuged at 4°C plasma separated and frozen at -20°C until assayed. Plasma prolactin was determined by a homologous human prolactin radioimmunoassay similar to the one previously reported by Sinha et al.” Interassay coefficient of variation was 15.7% at the low end, 13.0% in the middle, and 12.2% at the high end of the standard curve. The average intrassay variation was 4.5%. Sensitivity of the assay was I ng/mI. All samples from the two studies on the same subject were run in duplicate in the same assay to minimize interassay variation. In order to confirm differences in serum estrogen levels during the two study periods, steroid determinations were performed on the baseline blood samples. Serum for steroid determinations was extracted and fractionated according to the method described by Abraham et al.” Radioimmunoassays for estrone (E,), estradiol (E,), progesterone (P). and 17-hydroxyprogesterone ( 17-OHP) were performed as previously described.” Mean prolactin concentration was determined for each subject over the 5-hr study period. The means of the individual mean prolactin levels and baseline steroid levels were compared during the early and periovulatory phases of the menstrual cycle utilizing the paired one-tailed Student’s t test. The correlation coefficients (r) for the individual mean prolactin versus baseline steroid concentrations and incremental changes in individual mean prolactin versus baseline steroids during the 2-study periods were determined by standard formula utilizing a Hewlett Packard 9815A desk top computer.

RESULTS

Steroids

(Table

I)

Serum steroid determinations at time 0 revealed significantly higher mean E, (113 +r 20 versus 55 + 5 pg/ml, ISE), Ez (144 * 47 versus 48 t 9 pg/ml) and 17-OHP ( 1,301 t 266 versus 639 t 46 pg/ml) concentrations during the periovulatory compared to the early follicular phase of the cycle. Thus, this data provided confirmation for classification of the second study period into the periovulatory phase. Mean serum P levels were similar during the 2-study periods; 2 patients (No. 1 and 3), however, had serum P levels in the luteal phase range indicating that the studies in these 2 individuals were performed in the postovulatory period. Prolactin

Examination of individual plasma prolactin concentrations over 5 hr during the 2-study periods revealed that prolactin patterns varied from fairly stable prolactin concentration (No. 3) to episodic prolactin spike activity (No. 7) to progressively decreasing levels suggestive of diurnal periodicity (No. 10) (Fig. 1). Individual prolactin levels were generally higher during the periovulatory compared to the early follicular phase study period. Mean plasma prolactin concentrations over 5 hr for the individual subjects were significantly higher during the periovulatory phase at 10.7 1?1 1.0 compared to the early follicular phase at 8.1 * 1.0 (p < 0.0005) (Table 1). Mean prolac-

755

SPONTANEOUS PROLACTIN SECRETION IN WOMEN

correlation was found between the incremental changes in prolactin and E,, P, or 17-OHP. DISCUSSION

I

I

I

1

,

4

1

/ 0

60

I

L

I

(

I20 I@0 240 300

MINUTES Fig. 1. Plasma prolactin levels measured at 15-min intervals for 5 hr in 10 normal woman during the early follicular (-1 and periovulatory (O---O) phases of the menstrual CYCl8.

tin increased by 39% (range 9-l 17%) during the period of higher versus lower endogenous estrogen concentration. In individual subjects there was no positive correlation during the early follicular or periovulatory phases of the menstrual cycle between mean plasma prolactin concentration over the 5-hr study period and the baseline serum E,, EZ, P, or 17-OHP levels. However, the incremental change in mean prolactin (APRL) showed significant positive correlation with the incremental change in E, (AE,) during the 2-study periods (correlation coefficient, r = 0.66, p < 0.05). No significant

The role of endogenous estrogen in the regulation of prolactin secretion in man has been a subject of controversy. Three types of studies have been performed to study this relationship: (1) Studies comparing prolactin levels in groups of individuals with different but stable levels of circulating estrogen such as prepubertal children, adult men, and postmenopausal women; (2) longitudinal studies correlating physiologic alterations of endogenous estrogen with serum prolactin concentrations in pubertal children and pregnant women; and (3) studies correlating cyclic alterations in endogenous estrogen with serum prolactin concentrations in women throughout normal menstrual cycles. The contradictory data resulting from the first 2 types of studies have been reviewed elsewhere.‘-** The present discussion will focus on the third type of study: evaluation of the effect of physiologic cyclic estrogen secretion on prolactin levels during the menstrual cycle. This model was further examined in the current studies. The normal menstrual cycle affords a unique opportunity to evaluate the effects of cyclic estrogen secretion on serum prolactin concentrations. Prolactin levels determined on single blood samples obtained from normally cycling women throughout the menstrual cycle, however, have yielded contradictory results. Early studies revealed random daily fluctuations in serum prolactin but failed to show consistent correlation of ovarian estrogen secretion with serum prolactin concentrations.7m’0 Time of day of blood sampling was not specified in three of the studies7*9”0 and in the remaining one blood was withdrawn between 0800 and 1200 hr.’ Vekemans et al6 examined a larger population of women and performed daily prolactin determinations using 2 separate radioimmunoassay systems during 51 menstrual cycles. Blood samples for this study were collected between 1000 and 1600 hr each day. A progressive and significant increase in serum prolactin was observed during the late follicular phase with maximal values occurring concomitantly with the luteinizing hormone (LH) peak. In addition,

756

serum prolactin levels were significantly higher during the luteal compared to the early follicular phase. The midcycle prolactin peak was 50% higher than the early follicular phase levels. Franchimont et al.’ obtained single blood samples daily between 0800 and 1000 hr from 14 normal women throughout an entire ovulatory cycle. Serum prolactin concentrations showed marked day to day fluctuations but were highest during periovulatory and luteal phases of the cycle. Mean prolactin concentrations were significantly higher in all cases during the ovulatory period compared to the follicular phase study period. In the majority of subjects mean prolactin levels were also higher during the luteal compared to the follicular period. In addition, a significant correlation between the percent increase in E, and prolactin during ovulatory and luteal compared to follicular phases was found. Elevations in prolactin showed a mean increase of 32% above follicular phase levels during the ovulatory phase and a mean increase of 19% during the luteal phase. Thus, although the majority of these studies failed to demonstrate cyclic prolactin secretion throughout the menstrual cycle, two studies suggested parallel cyclicity between serum estrogen and prolactin concentrations. The reason for the divergent observations regarding the effect of physiologic alterations of estrogen during the menstrual cycle on serum prolactin concentrations measured on single daily blood samples may be multifactorial. Serum prolactin concentrations are known to be subject to diurnal variation.23.24 Neither the studies failing to show parallelism between serum estrogen and prolactin concentrations’-” nor those that were able to demonstrate such an effect5*6 specified that the time of day of blood withdrawal was closely monitored for each individual subject. However, the study in which time of blood withdrawal was most closely monitored with samples obtained between 0800 and 1000 hr showed a relationship between estrogen and prolactin concentrations.’ In addition, serum prolactin concentrations may be unstable with spontaneous fluctuations throughout the day, potentially yielding imprecise comparisons of single determinations during various estrogen states.* Other factors such as stress resulting from a hospital or clinic visit and/or the veni-

BUCKMAN,

PEAKE, AND SRIVASTAVA

puncture procedureZS may also contribute to unpredictable elevations in prolactin levels determined on single random blood specimens. The relative contribution of the stress factor in the routine clinical setting is difficult to assess but may contribute to the variable results reported. Thus, the lability of serum prolactin levels related to diurnal variations, spontaneous fluctuations and stress may have contributed to the variable results observed in the different studies evaluating endogenous estrogen effect on serum prolactin concentrations. Another approach to the evaluation of endogenous estrogen effect on prolactin has been the determination of prolactin responsiveness to administration of pharmacologic prolactin secretagogues during different phases of the menstrual cycle. Pharmacologic stimulation of prolactin secretion has been performed utilizing TRH and the phenothiazine, perphenazine. Prolactin responses to TRH administration have been reported to be similar during the early follicular. periovulatory, and luteal phases of the menstrual cycle.‘1.‘2,‘6 These studies suggest that early follicular phase TRH-induced prolactin responses do not differ significantly from those observed during the higher endogenous estrogen states of the periovulatory or luteal phase periods. In contrast, TRH-induced prolactin responses have been reported to be significantly enhanced during the periovulatory’3 and luteall compared to the early follicular phases of the menstrual cycle. Similarly , Buckman et al.” demonstrated that perphenazine-induced prolactin responses were facilitated during the midcycle high estrogen phase of the cycle (37% above early follicular phase responses). Thus, results from studies using pharmacologic secretagogues have also resulted in divergent interpretations regarding the possible modulatory effects of endogenous estrogen on prolactin secretion. The present study determined spontaneous prolactin secretion over a 5-hr period during the early follicular and periovulatory phases of the menstrual cycle controlling for diurnal variation, spontaneous fluctuations and stress factors. In each subject mean prolactin levels were higher during the periovulatory compared to the early follicular phase study period. These differences were variable with a range of 9%117% and a mean increase of 39%. Clearly, in some individu-

SPONTANEOUS

757

PROLACTIN SECRETION IN WOMEN

als the differences were modest in amplitude. No correlation could be found between the absolute estrogen and mean prolactin concentrations, but a positive correlation was seen between incremental changes in estradiol and mean prolactin levels. This data suggests that the dynamic changes in estrogen levels during the menstrual cycle may be more important than the absolute estrogen concentration in modulating serum prolactin levels. Thus, endogenous estrogen may play a role in the enhancement of prolactin

secretion during the periovulatory period of the menstrual cycle. ACKNOWLEDGMENT We wish to acknowledge the assistance of the staff of the University of New Mexico Clinical Research Center in performing the studies, the technical expertise of Barry David and Bharat Shah, and the expert secretarial assistance of Maxine Payne. We thank Drs. Vanderlaan, Lewis, and Sinha and the National Pituitary Agency, NIAMDD, for giving us the materials for the homologous human prolactin radioimmunoassay.

REFERENCES I. Frantz AC, Kleinberg DL, Noel GL: Studies on prolactin in man. Recent Prog Horm Res 28527-573, 1972 2. Robyn C, Delvoye P, Nokin J, et al: Prolactin and human reproduction, in Pasteels JL, Robyn C (eds): Human Prolactin. Amsterdam, Excerpta Medica, 1973, p 167 3. Yen SSC, Ehara Y, Siler TM: Augmentation of prolactin secretion by estrogen in hypogonadal women. J Clin Invest 53:652-655, 1974 4. Vekemans M, Robyn C: The influence of exogenous estrogen on the circadian periodicity of circulating prolactin in women. J Clin Endocrinol Metab 40:886-889, 1975 5. Franchimont P, Dourcy C, Legros J, et al: Prolactin levels during the menstrual cycle. Clin Endocrinol (Oxf) 5:643650,1976 6. Vekemans P, Delvoye M, L’Hermite M, et al: Serum prolactin levels during the menstrual cycle. J Clin Endocrinol Metab 44:989-993, 1977 7. Hwang P, Guyda H, Friesen H: A radioimmunoassay for human prolactin. Proc Natl Acad Sci USA 68:19021906. 1971 8. Ehara Y, Siler T, Vandenberg G, et al: Circulating prolactin levels during the menstrual cycle: Episodic release and diurnal variation. Am J Obstet Gynecol ll7:962-970, 1973 9. McNeilly A, Evans G, Chard T: Observations of prolactin levels during the menstrual cycle, in Pastcels JL, Robyn C (eds): Human Prolactin. Amsterdam, Excerpta Medica, 1973, pp 23 l-232 10. Jaffe R, Yuen B, Keye W, et al: Physiologic and pathologic profiles in circulating human prolactin. Am J Obstet Gynecol ll7:757-773, 1973 I I. Tyson J, Friesen H: Factors influencing the secretion of human prolactin and growth hormone in menstrual and gestational women. Am J Obstet Gynecol 116:377-387. 1973 12. McNeilly A, Hagen C: Prolactin, TSH, LH and FSH responses to a combined‘ LHRH/TRH test at different stages of the menstrual cycle. Clin Endocrinol (Oxf) 3:427, 1974 13. Reymond M, Lemarchand-Beraud T: Effects of oestrogens on prolactin and thyrotropin responses to TRH in women during the menstrual cycle and under oral contraceptive treatment. Clin Endocrinol (Oxf) 5:429-437, 1976

14. Boyd A III, Sanchez-Franc0 F: Changes in the prolactin response to thyrotropin-releasing hormone (TRH) during the menstrual cycle of normal women. J Clin Endocrinol Metab 44:985-989, 1977 15. Buckman M, Peake G, Srivastava L: Endogenous estrogen modulates phenothiazine stimulated prolactin secretion. J Clin Endocrinol Metab 43:901-906, 1976 16. Sawin CT, Hershman JM, Boyd AE III, et al: The relationship of changes in serum estradiol and progesterone during the menstrual cycle to the thyrotropin and prolactin responses to thyrotropin-releasing hormone. J Clin Endocrinol Metab 47: 1296-l 302.1978 17. Sinha YN, Selby F, Lewis UJ, et al: A homologous radioimmunoassay for human prolactin. J Clin Endocrinol Metab 36~509-5 16, 1973 18. Abraham GE, Hopper K, Tulchinky D, et al: Simultaneous measurement of plasma progesterone, 17-hydroxyprogesterone and estradiol-17B by radioimmunoassay. Anal Lett 4:325, 197 I 19. Sinha KN, Srivastava LS, Wulsin JH, et al: Gyneco mastia hormonal evaluation by radioimmunoassay, in Rastogi GK (ed): the Proceedings of the Fifth Asia and Oceania Congress of Endocrinology. Chandigarh, India, 1974, p 163 20. Lee PA, Xenakis T, Winer J, et al: Puberty in girls: Correlation of serum levels of gonadotropins, prolactin, androgens, estrogens, and progestins with physical changes. J Clin Endocrinol Metab 43:775-784, 1976 21. Thorner MO, Round J, Jones A, et al: Serum prolactin and oestradiol levels at different stages of puberty. Clin Endocrinol (Oxf) 7:463468, 1977 22. Hertz J, Andersen AN, Larsen JF: Correlation between prolactin and progesterone, oestradiol I7-beta and oestriol during early human pregnancy. Clin Endocrinol (Gxf) 9:97-100, 1978 23. Sassin JF, Frantz AG, Weitzaman ED, et al: Human prolactin:24 hour pattern with increased release during sleep. Science 177: 1205-I 207,1972 24. Sassin JF, Frantz AG, Kapen S, et al: The nocturnal rise of human prolactin is dependent on sleep. J Clin Endocrinol Metab 36:436440, 1973 25. Koninckx P: Stress hyperprolactinemia in clinical practice. Lancet I :273, 1978.