Exaggerated Prolactin Response to Thyrotropin-Releasing Hormone and Metoclopramide in Primary Testicular Failure*

Vol. 34, No.6, December 1980

FERTILITY AND STERILITY Copyright ' 1980 The American Fertility Society

Printed in U.8A.

EXAGGERATED PROLACTIN RESPONSE TO THYROTROPIN.RELEASING HORMONE AND METOCLOPRAMIDE IN PRIMARY TESTICULAR FAILURE*

NERI LAUFER, M.D·II MOSHE RON, M.D·II ZVI PALTI, M.D·II JOSEF SCHENKER, M.D·II

IRVING M. SPITZ, M.D., M.R.C.P.t:j: DEREK LEROITH, M.D., PH.D., F.C.P.§ YOSEF LIVSHlN, M.D.~ EDIT ZYLBER-HARAN, PH.D.:j: STEFAN TRESTIAN, M.Sc.:j:

Department of Endocrinology and Metabolism, Shaare Zedek Medical Center, Jerusalem, Department of Medicine, Soroka Medical Center, Beer Sheva, Department of Obstetrics and Gynecology, Bikur Cholim Hospital, Jerusalem, and Hadassah University Hospital, Jerusalem, Israel.

Twenty-eight severely oligospermic and azoospermic men aged 20 to 42 years were challenged with luteinizing hormone (LH)-releasing hormone (LHRH), thyrotropin-releasing hormone (TRH), and the dopaminergic antagonist, metoclopramide, given at 30-minute intervals. According to basal gonadotropin levels, the patients were subdivided into three groups: those with severe testicular failure (basal LH >20 mIUlml and FSH >14 mIUlml), those with moderate testicular failure with predominant seminiferous tubule involvement (LH <20 mIUlml and FSH >14 mIUlml) and those with mild testicular failure (LH <20 mIUlml and FSH <14 mIUlml). With one exception, mean basal prolactin (PRL) levels were normal in all patients. In all three groups, however, there was an exaggerated PRL response to TRH, the response in severe and moderate testicular failure being greater than that in mild testicular failure. The response to metoclopramide was increased only in the first two groups, not in the group with mild testicular failure. When individual patients and control subjects were considered together, the peak PRL response to TRH correlated with both basal and peak gonadotropin responses to LHRH. However, the PRL responses did not correlate with 17f3-estradiol, estrone, testosterone, or the estradiol-testosterone ratio. It is concluded that oligospermic and azoospermic subjects with the most severe testicular failure and the highest gonadotropin levels have the greatest PRL increases after TRH and metoclopramide, indicating that the PRL response is related to the degree of testicular failure. Fertil SteriI34:573, 1980

Although it is well-documented and regarded as an important factor in the etiology offemale infertility, hyperprolactinemia is not so common in the oligospermic male. 1 Some have even reported decreased basal prolactin (PRL) levels in this condition. 2 In oligospermia, controversy also surrounds the PRL response to stimulation, and exaggerated, attenuated, or normal responses have been de. scribed. 3 -6 We previously reported an exaggerated PRL response to thyrotropin-releasing hormone (TRH) in six patients with primary testicular failure. 7 We now extend these observations to 28 severely oligospermic and azoospermic men. In addition to

Received May 6, 1980; revised July 21, 1980; accepted August 11, 1980. *Supported by grants to I. M. S. from the Chief Scientist's Office, Israel Ministry of Health, and Center for Absorption in Science, The Ministry for Immigrant Absorption, State of Israel. tReprint requests: Irving M. Spitz, M.D., Department of Endocrinology and Metabolism, Shaare Zedek Medical Center, P.O. Box 293, Jerusalem 91 000, Israel. :j:Department of Endocrinology and Metabolism, Shaare Zedek Medical Center. §Department of Medicine, Soroka Medical Center. ~Department of Obstetrics and Gynecololy, Bikur Cholim Hospital. IIDepartment of Obstetrics and Gynecology, Hadassah University Hospital.

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SPITZ ET AL.

TRH, we have also challenged these patients with metoclopramide (MET). This potent dopaminergic antagonist causes greater PRL responses than does TRH.B Our results have shown that, despite normal basal PRL levels, these patients have an exaggerated PRL response to both TRH and MET. The greatest PRL secretion is seen in those patients with the highest gonadotropin levels. MATERIALS AND METHODS

Subjects. The patient group comprised 28 men aged 20 to 42 years who had been referred to our male infertility clinic. Azoospermia was evident in 16 subjects and the remainder had severe oligospermia with sperm counts below 10 million/ml. The patients were classified only after sexual abstinence for 4 days and after at least three semen analyses. In none of the subjects was there clinical evidence of Leydig cell dysfunction, and all had intact secondary sex characteristics with normal libido and potency. All claimed to have sexual relations with frequent erections and ejaculations. None had any clinically detectable endocrinopathy, and all had chromatin-negative buccal smears. The severe oligospermia was secondary to mumps orchitis in three subjects and bilateral cryptorchidism (surgically corrected) in four. In two subjects there was an associated varicocele. The remaining subjects had idiopathic oligospermia or azoospermia diagnosed on the basis of no previous history of testicular or prostatic disease; irradiation or administration of chemotherapeutic agents; and normal physical examination of epididymis, spermatic cord, and prostate. In all subjects, routine biochemical investigations as well as thyroid function were normal, and no patient had taken any drugs for at least 6 months prior to the time of study. Tomography of the pituitary fossa and visual field examination were normal in the subject with basal hyperprolactinemia (see below). Testicular biopsies were performed in 13 patients and the results were classified according to previously established criteria. 9 The biopsy revealed hypospermatogenesis in one subject. Although all stages of spermatogenesis were seen, there was a quantitative reduction in the number of germ cells. In one subject the picture showed germinal cell arrest with virtual absence of all spermatogenesis beyond the primary spermatocyte stage. In four subjects the appearance was characteristic of germinal cell aplasia (Sertoli cellonly syndrome). Here the seminiferous tubules

December 1980 were lined exclusively by Sertoli cells, there being a total absence of germinal elements. In three subjects there was a mixed picture with the majority of the tubules being lined by Sertoli cells. However, in some tubules there was severe hypospermatogenesis. In three subjects, there was marked seminiferous tubule hyalinization, the tubules being represented by a fibrotic outline consisting of collagen fibers with no seminiferous epithelium. Interstitial cells appeared normal on light microscopy in all instances except in patients with seminiferous tubule hyalinization. Here Leydig cells were relatively prominent owing to their coalescence following skrinkage of the tubules. One subject had normal testes. All relevant clinical data and testicular biopsy findings are shown in Table 1. Experimental Protocol. The test procedure was performed between 8:00 and 8:30 A.M. after an overnight fast. None of the subjects had received any form of medication prior to the study. A needle inserted into an antecubital vein was kept patent by the slow administration of normal saline. Three blood samples were obtained during a 30-minute equilibration period. All subjects then received 100 ,..,g ofluteinizing hormone-releasing hormone (LHRH), 200 ,..,g of thyrotropin-releasing hormone (TRH), and 10 mg of metoclop ramide (MET) in sequence at 30-minute intervals. All agents were administered by rapid intravenous injection. Blood samples were obtained at 10-minute intervals after the administration of each agent and continued for 60 minutes after the MET injection. We have previously shown that, in men, a 10-mg intravenous dose of MET does not influence basal gonadotropin levels nor their response to LHRH.I0 The hormonal response in the patients was compared with that in 28 healthy controls, aged 20 to 40 years, who received the same protocol. Informed consent for the.test procedure was obtained from both patients and controls. Methods. Serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), testosterone (T), and 17~-estradiol (E 2 ) were determined by previously describ~d methods. 7 LH and FSH levels were expressed by reference to the Second International Reference Preparation of human menopausal gonadotropins. The actual standard used in the assay was the International Reference Preparation of pituitary FSH and LH (69/104). This standard and the PRL standard (75/504) were kindly provided by the Division of Biological Standards and Control, Hampstead, London, England. Antisera to LH (final

PROLACTIN RESPONSE IN TESTICULAR FAILURE

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575

TABLE 1. Clinical and Laboratory Details Patient and

Age

groupa

Group I 1 2 3 4 5 6 7 8 9 10

~!:!is

Etiology'

21 31 34 39 29 30 32 30 42 32 27 29 28

D D D D D D D N D D N D N

M

Group II 14 15 16 17 18

31 32 23 30 36

N D D D N

V

Group III 19 20 21 22 23 24 25 26 27 28

39 28 30 41 40 28 36 29 24 31

N D N D N D N D D D

11

12 13

e e e M M

e

V

Az Az Az Az Az Az Az Oli Oli Oli Oli Oli Oli

Hypo Hyal seo seo Hyal

Az Oli Az Az Az

seo, Hypo seo seo

Oli Oli Oli Az Oli Oli Az Az Az Az

MA

seo, Hypo Intact

Hyal seo, Hypo

eontrol Mean SD

Peak response to LHRH

PRL

Biopsy'

~~

Basal

Peak TRH

Peak MET

LH

FSH

nglml

nglml

nglml

mJUlml

mJUlml

11.4 14.2 12.1 12.7 11.8 8.0 8.8 8.0 5.2 22.0 13.0 8.0 7.2

76.6 98.0 80.3 55.6 136.9 110.7 59.8 64.2 52.0 78.0 62.0 41.0 88.3

121 165 150 176 288 193 374 196 239 110 140 75 282

307 292 119 182 217 255 112 400 127 181 165 137 180

114 96 56 63 70 84 61 68 67 94 68 51 108

13.0 15.1 7.5 8.8 6.5

129.4 78.6 96.5 86.5 107.7

199 128 169 109 191

95 95 91 80 89

42. 78 80 42 26

7.4 8.5 7.0 7.0 5.0 9.9 11.1 8.6 10.0 8.1

67.7 55.4 38.1 32.8 60.0 51.0 34.9 46.8 72.7 107.9

156 105 81 48 99 110 57 212

74 113 206 100 168 160 86 96 180 228

9.6 4.1

32.1 10.7

135 75.5 22.3

49.7 14.5

16.8 30.4 18.4 23.8 41.5 30.2 19.2 18.7 23.9 36.1 8.3 2.9

aGroup I, basal FSH levels> 14 mIU/ml; LH > 20 mIU/ml; group II, basal FSH levels> 14 mIU/ml; LH < 20 mIU/ml; group III, basal FSH levels < 14 mIU/ml; LH < 20 mIU/mi. The control group comprised 28 subjects 20 to 0 years of age. bD, Decreased; N, normal. eM, Mumps orchitis; e, bilateral cryptorchidism, surgically corrected; V, varicocele. d Az, Azoospermia; Oli, oligospermia. eHypo, Hypospermatogenesis; Hyal, hyalinized tubules; seo, Sertoli cell-only syndrome; MA, maturation arrest; Intact, normal biopsy.

dilution 1:200,000), FSH (1:400,000), and PRL (1:400,000) were kindly supplied by the National Pituitary Agency, National Institute of Arthritis, Metabolism and Digestive Diseases, Bethesda, Md. 125I-Labeled LH, FSH, and PRL were purchased from CEA-SORIN. Intra- and interassay coefficients of variation were as follows: 5.8% and 19.1 % (LH); 4.3% and 6.9% (FSH); and 6.6% and 12.2% (PRL). Estrone (E I ) was measured by radioimmunoassayll using rabbit anti-estrone-6-thyroglobulin (Miles-Yeda Ltd., Rehovot, Israel), 2,4,6,7- 3 H-Estrone (The Radiochemical Center, Amersham, England), and cold estrone standard (Makor Chemicals Ltd., Jerusalem, Israel). E 2, Eb and T

were determined after pooling equal volumes of the three basal samples. Student's t-test was used to compare responses in patients and controls. RESULTS

Gonadotropins (Table 1; Fig. 1) In the control subjects the mean (± standard deviation [SD)) basal LH level was 11.5 ± 4.2 mIUlml and the mean FSH level was 5.9 ± 2.1 mIU/ml. The term basal refers to mean values of the three samples obtained prior to LHRH administration. The peak gonadotropin responses to

December 1980

SPITZ ET AL.

576

tween 20 and 30 minutes, and in all three groups the maximal responses were greater than those of the control subjects (P < 0.005). However, the peak LH response in group II subjects was significantly less than that in group I (P < 0.005) or group III (P < 0.05). Similarly, basal and peak FSH responses to LHRH were significantly greater in all three patient groups as compared with those of the control subjects (P < 0.005). The maximal FSH responses occurred between 40 and 60 minutes in all groups. There were no significant differences between basal and peak FSH responses in groups I and II. FSH levels were, however, decreased in group III as compared with either group I (P < 0.005) or group II (P < 0.01). PRL (Table 1; Fig. 2) ·20

0

20

40 60 TIME""ifI.)

~

lJO 120

·20

0

20

40

60

~

lJO 120

TIME/min.)

FIG. L LH (left) and FSH (right) response to LHRH (100 /Lg) in testicular failure. -'-'-, Group I (severe testicular failure); - , group II (moderate testicular failure); - - -, group III, (mild testicular failure). Control subjects are represented by . the shaded areas. Values are means ± 1 SEM.

LHRH occurred at 40 minutes and were 49.7 ± 14.5 mlUlml for LH and 8.3 ± 2.9 mlUlml for FSH. The patients were subdivided into three groups according to their individual basal gonadotropin levels. For LH the reference level chosen was 20 mlU/ml (mean + 2 SD of basal value in control subjects); for FSH, 14 mlUlml, which is the mean + 2 SD of the peak FSH response to LHRH in the control subjects. Group I: Severe Testicular Failure. In these 13 patients, basal LH levels exceeded 20 mlU/ml and basal FSH levels exceeded 14 mlUlml. Group II: Moderate Testicular Failure. This group comprised five subjects. Here basal FSH levels were above 14 mlU/ml and LH levels were less than 20 mIU/ml. These subjects had predominant seminiferous tubule failure. Group III: Mild Testicular Failure. This included 10 subjects whose basal FSH levels (with one exception) were below 14 mIU/ml. Six had LH levels below 20 mIU/ml; the remainder had levels which ranged from 21 to 39 mIU/ml. Mean ± SD basal LH levels in groups I and II were 34.3 ± 15.6 mlUlml and 15.9 ± 2.1 mIU/ml, respectively, and were greater than those of the control subjects (P < 0.005). Basal LH levels in group III, however, were not significantly increased relative to those of the control subjects. The peak LH responses to LHRH occurred be-

Mean basal PRL levels in the control subjects were 9.6 ± 4.1 ng/ml. In the three patient groups, mean basal levels ranged from 8.3 to 11.0 ng/ml. These levels were not significantly different from one another. Only one subject (in group I) demonstrated hyperprolactinemia, basal levels ranging from 20.7 to 24.6 ng/ml (Table 1). After TRH administration, maximal PRL responses were 72.9 ± 30.0 ng/ml in group I and 94.5 ± 24.0 ng/ml in group II. In both of these groups, 200

~

~

e. 100

...., ct

Q.. 80

6

40 20 0

, 0

,

20

;

:

60 80 TIME(min.,

FIG. 2. The PRL response to TRH and MET given at 30minute intervals to the three groups of patients with testicular failure and the control subjects. Key as in Figure L

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577

PROLACTIN RESPONSE IN TESTICULAR FAILURE

Vol. 34, No.6

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11

those of the control subjects in group I (P < 0.05) and group III (P < 0.01) but not in group II. The mean T level for the patient group was 4.9 ± 1.8 ng/ml. This was similar to the T level of the control group. There were no differences in T levels between groups I and III, although values were decreased (P < 0.005) in group II. The E2:T ratio was 0.0041 ± 0.0016 in the control subjects and was significantly increased in all three patient groups (P < 0.05 in groups I and II andP < 0.01 in group III). The highest E2:T ratio occurred in group III, which had the least exaggerated PRL response .

••

liT

FIG. 3. E 2 , estrone, testosterone (Test), and estradiol-testos· terone ratio (E2 1T) in control subjects (CONT) and testicular failure subjects-groups I, II, and III. See text for details. Indi· vidual values as well as means ± 1 SEM are shown. 'Y, P < 0.05; n, P < 0.01; 'Yn, P < 0.005.

the peak responses were greater than those in the control subjects (P < 0.005), where the maximal response was 32.1 ± 10.7 ng/ml. In the above three instances, the peak occurred 20 minutes after TRH administration. Levels then decreased transiently prior to MET administration. In group III, the peak response was 53.3 ± 14.6 ng/ml and occurred 30 minutes after TRH. This response was significantly greater than that of the control subjects (P < 0.005) but less than that in groups I (P < 0.05) and II (P < 0.01). Following MET administration, further peaks in PRL response were evident: 75.5 ± 22.3 ng/ml in the control subjects, 172.0 ± 71.0 ng/ml in group I, and 152.1 ± 32.3 ng/ml in group II. The peaks in groups I and II were not different from one another but were higher than that in the control subjects (P < 0.005). In group III, the peak PRL response following MET administration was 107.3 ± 53.2 ng/ml and was not different from that of the control subjects, but it was less than the peak in group I or group II (P < 0.05). In all groups, the maximal response was evident 30 minutes after MET administration.

Steroids (Fig. 3) The mean E2 level in the control subjects was 22.1 ± 6.9 pg/ml; the El level was 52.9 ± 15.5 pg/ml and the T level was 5.9 ± 2.0 ng/ml. When all three patient groups were considered together, there were no significant differences between their E2 levels and that of the control group, although the mean E2 levels were increased (P < 0.01) in group III. El levels were significantly greater than

Correlations (Table 2; Fig. 4) In the individual control subjects, the peak PRL response to TRH correlated inversely with the basal LH and peak LH response to LHRH. However, there was no correlation between the peak PRL response to TRH and FSH. In the subjects with testicular failure, the PRL response to TRH was positively correlated with both basal FSH and LH levels and the peak FSH (but not LH) response to LHRH. When the two groups were considered together, there was a highly significant, positive correlation between peak PRL response to TRH and basal and peak gonadotropin responses to LHRH (Fig. 4). In contrast, when individual control subjects and men with testicular failure were considered together, there was no correlation between the peak PRL response to TRH and T, E 2, Elo or the E2:T ratio. DISCUSSION

Mean FSH and LH responses to LHRH were exaggerated in all three groups of subjects. The high prevalence of abnormal gonadotropin profiles in these subjects is probably a reflection of the TABLE 2. Correlation between Peak PRL Response to TRH and Basal and Peak Gonadotropin Responses to LHRH Peak PRL reo sponse to TRH vs.

Basal FSH r P Basal LH r P Peak. FSH r P Peak LH r p

Testicular failure

Control and tes· ticular failure

0.25 NS

0.42 <0.05

0.69 <0.001

-0.47 <0.05

0.37 <0.05

0.51 <0.001

0.19 NS

0.40 <0.05

0.70 <0.001

-0.47 <0.05

0.15 NS

0.52 <0.001

Control

aNS, Not statistically significant.

SPITZ ET AL.

578

o

0

o

,p

./~

.0

"

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- •

CO

•

a •

r;,;.. n-.' •

., D

o 0

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20

o

0

o

o

10 20 JO FSHmiU/ml.

I,()

50 0 BASAL

10

20 JO I,()' 50 LH m/U/ml.

60

i~

FIG. 4. Correlation between the peak PRL response to TRH on the ordinate and basal FSH (left) and LH (right) in patients with testicular failure (0) and control subjects (e). See text and Table 2 for details.

severity of the testicular disorder and is compatible with previous reports. 9, 12 The subdivision of the patients was based exclusively on gonadotropin levels. Sperm counts and testicular abnormalities were not taken into consideration. Subjects in groups I and II had identical FSH dynamics. However, the maximal LH response in group II was less than that in groups I and III. The pattern in group II suggests predominant seminiferous tubule involvement. Indeed, in the three subjects in group II from whom testicular biopsies were obtained, histology showed intact Leydig cells, the tubules being lined by Sertoli cells. One subject, in addition, had severe hypospermatogenesis in some tubules. The Sertoli cellonly syndrome with intact Leydig cells was also apparent in two subjects in group I. In these instances, LH levels were elevated. This finding confirms recent observations that the Sertoli cellonly syndrome does not compromise FSH levels exclusivelyl3, 14 and suggests that the intertubular tissue of the testis is involved in the pathologic process which by light microscopy appears to be confined only to the seminiferous tubule. 9 Since there was a lack of correlation between the hormonal profile and the pathologic picture, the results were analyzed in terms of gonadotropin levels. In all three groups, mean basal PRL levels were identical to those of the control subjects. These results are similar to data previously reported,l. 6 although other investigators have shown that mean PRL levels in oligospermic men may be increased 15 or even decreased. 2 Only one of our subjects had increased basal PRL levels. In two

December 1980 recent series, significant basal hyperprolactinemia was evident in only 5 of225 cases. 1. 15 It is thus apparent that hyperprolactinemia is not as common in men as it is in women. When challenged with TRH and MET, our patients demonstrated exaggerated PRL responses. Although basal PRL levels had not been attained prior to the MET challenge, we have shown previously that, when MET is given by itself, an exaggerated PRL response occurs.16 When two successive TRH pulses are given at short intervals, the PRL response with the second pulse never exceeds the initial response; moreover, it is often decreased. 17. 18 However, when MET is given after TRH, it induces a far greater PRL response. 17 This indicates that MET and TRH may be acting on different pituitary PRL pools. Alternatively, the PRL profile may also be explained by a TRH-induced alteration in affinity or number of its receptors. 17 Assuming the presence of two pools, it is evident that both are increased in oligospermic patients with high gonadotropin levels. This occurs in the presence of normal basal PRL levels. The finding of an exaggerated PRL response extends our previous observations 7 and confirms the findings of Burman et a1. 3 In contrast, Goldhaber and co-workers,5 found a decreased PRL response to TRH in testicular failure. Their subjects, however, had low levels ofE 2 and T. We have made similar observations in male patients with isolated gonadotropin deficiency. 7 The mechanism of the increased PRL response in severe oligospermia and azoospermia is unknown. In individual patients with testicular failure and in control subjects, the PRL response was directly related to basal and peak gonadotropin responses to LHRH. However, this cannot be the major factor since male castrates with markedly elevated gonadotropin levels have intact PRL responses. 19 Furthermore, in the castrated rat, there is a decreased PRL response to both TRH and MET.20 The high gonadotropin levels in the present series represent a marker of the severity of the testicular disorder. The direct relationship between the PRL response and the gonadotropin levels suggests that greater PRL responses occur in subjects whose testicular function is most severely compromised. In the control subjects, there was an inverse correlation between PRL and the basal as well as the peak LH response to LHRH. The precise mechanism for this is not understood, although in the rat, PRL can suppress LH.21

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PROLACTIN RESPONSE IN TESTICULAR FAILURE

The fact that castrates have PRL responses indistinguishable from normal implies that the exaggerated profile in testicular failure is related to the secretion of a testicular secretory product. The testis can be defective as regards spermatogenesis, but its steroidogenic potential must remain intact. Although E2 is a well-known stimulator of PRL,22, 23 mean E2 levels were increased only in group III subjects who had the least exaggerated PRL response. Moreover, in contrast to the gonadotropins there was no direct relationship between E2 and the PRL response. Although in previous studies7 we found a correlation between the E2:T ratio (indicative of a relative increase in E 2) and the peak PRL response, such a correlation was not confirmed in this large number of patients. Again, the highest E2:T ratio occurred in group III. Although El was increased, this also did not correlate with the PRL response. Estriol is also unlikely to be incriminated directly. 24 The fact that the estrogen antagonist clomiphene citrate has the ability to decrease the exaggerated PRL response nevertheless suggests that estrogens do playa role in this phenomenon. 19 The precise physiologic relevance of this exaggerated PRL response remains to be elucidated, especially since it was evident only after pharmacologic manipulation. Although hyperprolactinemia inhibits testicular function,25, 26 it would appear that the abnormal PRL profile detected in testicular failure with elevated gonadotropin levels is a consequence and not a cause of the gonadal dysfunction. Acknowledgments. We thank Drs. S. Rosen, S. Handwerger, and R. Sobel for their helpful comments. We thank Z. Shemesh, Y. Bidderman, Y. Pur-David, and Y. Cohen for their expert technical help; H. Lapidus for typing the manuscript; and P. Hoffner and the computer department ofShaare Zedek Medical Center for their assistance. We also wish to thank Hoffman La-Roche (Basel, Switzerland) for the generous gift of LHRH and TRH.

REFERENCES 1. Hargreave TB, Kyle KF, Kelly AM, England P: Prolactin and gonadotrophins in 208 men presenting with infertility. Br J Urol 49:747, 1977 2. Pierrepoint CG, John BM, Groom GV, Wilson DW, Gow JG: Prolactin and testosterone levels in the plasma of fertile and infertile men. J Endocrinol 76:171, 1978 3. Burman KD, Dimond RC, Noel GL, Earll JM, Frantz AF, Wartofsky L: Klinefelter's syndrome: examination of thyroid function, and the TSH and PRL responses to thyrotropin-releasing hormone prior to and after testosterone administration. J Clin Endocrinol Metab 41:1161, 1975

579

4. Cheikh I, Hamilton BP, Hsu TH, Wiswell JG: Response of TSH and prolactin to TRH in Klinefelter's syndrome. Presented at the Fifty-Seventh Meeting of The Endocrine Society, New York, 1975, p 153 (abstr 206) 5. Goldhaber G, Zuckerman Z, Shani J, Cohen JJ: Effect of thyrotrophin-releasing hormone on serum prolactin levels in men with azoospermia. J Reprod Fertil49:135, 1977 6. Masala A, Delitala G, Alagna S, Devilla L, Rovasio PR, Lotti G: Dynamic evaluation of prolactin secretion in patients with oligospermia: effects of treatment with metergoline. Fertil Steril 31:63, 1979 7. Spitz 1M, Zylber E, Cohen H, Almaliach U, LeRoith D: Impaired prolactin response to thyrotropin-releasing hormone in isolated gonadotropin deficiency and exaggerated response in primary testicular failure. J Clin Endocrinol Metab 48:941, 1979 8. Sowers JR, McCallum RW, Hershman JM, Carlson HE, Sturdevant RA, Meyer N: Comparison of metoclopramide with other dynamic tests of prolactin secretion. J Clin Endocrinol Metab 43:679, 1976 9. Baker HWG, Bremner WJ, Burger HG, DeKretser DM, Dulmanis A, Eddie LW, Hudson B, Keogh EJ, Lee WK, Rennie GC: Testicular control of follicle-stimulating hormone secretion. Recent Prog Horm Res 32:429, 1976 10. Spitz 1M, Trestian S, Cohen H, Arnon N, LeRoith D: Failure of metoclopramide to influence LH, FSH and TSH secretion or their responses to releasing hormones. Acta Endocrinol (Kbh) 92:640, 1979 11. Emment Y, Collins WP, Sommerville IF: Radioimmunoassay of oestrone and oestradiol in human plasma. Acta Endocrinol (Kbh) 69:567,1972 12. Nankin HR, Castaneda E, Troen P: Endocrine profiles in oligospermic men. In The Testis in Normal and Infertile Men, Edited by P Troen, HR Nankin. New York, Raven Press, 1977, P 529 13. Mecklenburg RS, Sherins RJ: Gonadotropin response to LHRH in men with germinal aplasia. J Clin Endocrinol Metab 38:1005, 1974 14. Guay AT, Tuthill RJ, Wolff PD: Germinal cell aplasia: response ofluteinizing hormone (LH), follicle-stimulating hormone (FSH) , and testosterone to LHIFSH-releasing hormone with histopathologic correlation. Fertil Steril 28:642, 1977 15. Segal S, Polishuk WZ, Ben-David M: Hyperprolactinemic male infertility. Fertil Steril 26:1425, 1976 16. Spitz 1M, Halperin Y, Zylber-Haran E, Shilo S, LeRoith D, Liel Y, Livshin Y, Laufer N, Schenker J: Prolactin response to metoclopramide and chlorpromazine in primary testicular failure and isolated gonadotropin deficiency. Clin Endocrinol. In press 17. Spitz 1M, Gonen G, Luboshitzky R, Rosen E, Shemesh 0: The prolactin response to repeated intravenous stimuli. Horm Metab Res 11:319, 1979 18. Fell LR, Findlay JK, Cumming lA, Goding JR: Effect of synthetic TRF on prolactin release in the sheep. Endocrinology 93:487,1973 19. Spitz 1M, LeRoith D, Potashnik G: Testicular modulation of prolactin secretion in man. Clin Res 28:268A, 1980 20. Zylber E, Gershman H, Shemesh Z, Spitz 1M: Prolactin secretion in the castrated male rat. Isr J Med Sci. In press, 1980 21. Winters SJ, Loriaux DL: Suppression of plasma luteinizing hormone by prolactin in the male rat. Endocrinology 102:864, 1978

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