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Blunted prolactin response to hypoglycemia in patients with hypothalamic-pituitary disease and in subjects receiving estrogen
Blunted Prolactin Response to Hypoglycemia in Patients With Hypothalamic-Pituitary Disease and in Subjects Receiving Estrogen Philip May, Stephen The prolactin ated
in 22
response control
to hypoglycemia
subjects
and
hypothalamic-pituitary
disease
serum
Eighteen
prolactin
subjects
levels.
demonstrated
rise in response subjects,
strated
a prolactin
blunted
prolactin
only endocrine In an attempt the prolactin of
early
course
response
response
response
of its known mitosis
pituitary
tumor
diethylstilbestrol
8 patients
to the demonThis
was the
in 3 of these 8 patients. the sensitivity
to hypoglycemia the
of
a short
response
to
Estrogen was selected
acute
stimulatory
chronic
formation
of
as an index
effect
prolactin
was examined.
because
prolactin
In contrast
determine
on the
pituitary
basal
to hypoglycemia.
disease,
and
normal
to hypoglycemia
abnormality to better
estrogen
hypoglycemia
of the
with
of the 22 control
at least a twofold
none
pituitary of
was evalu-
8 patients
but
to hypoglycemia.
control
Proper, Jana Ourednik,
effects
effect
that
in rodents.
on
lead to
Accordingly,
(DES) 5 mg t.i.d. was administered
orally to 8 normal men for 3 days, a period known to stimulate
pituitary
Diethylstilbestrol
vation of the zcseiine ng/ml,
mitotic
treatment
prolactin
p < 0.05): however.
hypoglycemia
activity caused
was blunted
response prolactin
hypoglycemia
response
to
ele-
18 + 3
the prolactin response
hypoglycemia
p
after DES,
blunted
resembled
patients with hypothalamic-pituitary
to
c 10 ng/ml.
+ 5 ng/ml
This estrogen-induced to
rodents.
(8 * 2 versus
(8 ? 2-30
< 0.05, before DES; 18 ‘_ 3-20 p > 0.05).
in
significant
prolactin
the
blunted
found
in
disease.
PROLACTIN is frequently elevated SERUM in patients with pituitary and parapituitary neoplasms;‘32 however, because some patients with documented pituitary tumors have normal serum prolactin levels,24 the basal serum prolactin level is not a reliable indicator of the presence of a pituitary lesion in all instances. In an effort to improve the diagnostic sensitivity of the serum prolactin determination, several investigators have examined the usefulness of various stimulation and suppression tests of prolactin se-
From the Department of Medicine, VA Medical Center, East Orange, NJ., and the CMDNJ/NJ Medical School. Newark, N.J. Receivedfor publication July 23, 1979. Address reprint requests to Dr. P. May, Endocrinology Section, Department of Medicine, VA Medical Center, Tremont Avenue. East Orange, N.J., 07019. o 1980 by Grune & Stratton, Inc. 0026-0495/80/2904/0007$01.00/0
340
George Schneider,
and Norman
Ertel
cretion.3Vs-8 In general, the results of these studies have been disappointing and there appears to be no diagnostic advantage of the various dynamic tests (e.g., TRH, phenothiazine, Ldopa) over the basal prolactin level. When the prolactin level is elevated, dynamic tests tend to be abnormal; when the prolactin level is normal, dynamic tests are usually normal. It has been previously shown that the prolactin response to hypoglycemia may be blunted in patients with pituitary-hypothalamic disease’-” even when the basal prolactin level is normal,’ and it has been suggested that a blunted prolactin response to hypoglycemia may represent an early manifestation of a developing pituitary tumor. The purpose of this study was to investigate the prolactin response to hypoglycemia in patients with a variety of diseases of the hypothalamic-pituitary axis but with normal basal serum prolactin levels and in subjects who had received a short course of estrogen. Estrogen was given because several days of estrogen administration are known to stimulate prolactin secretion and pituitary mitotic activity in rodents,12 suggesting that estrogen-induced hyperprolactinemia might be a marker for pituitary hyperplasia. The results of this study demonstrate that the prolactin response to hypoglycemia is usually blunted in patients with known pituitary disease, even when the basal prolactin level and other tests of pituitary function are normal. Since a normal prolactin response to hypoglycemia is not commonly seen in patients with pituitary lesions, the documentation of a normal prolactin response to hypoglycemia would be one bit of evidence against hypothalamic-pituitary disease. The results with estrogen further suggest that a blunted insulin-response to hypoglycemia may be a laboratory correlate of pituitary hyperplasia. MATERIALS
AND
METHODS
Twenty-two male subjects, 43-60 yr of age, who were free of hypothalamic-pituitary disorders, and 8 patients with
Metabolism, Vol. 29, No. 4 (April). 1980
341
ESTROGEN BLUNTS PROLACTIN RESPONSE
various types of hypothalamic-pituitary disease but normal basal prolactin, were selected for this study after giving informed written consent. There were 5 patients with nonsecretory pituitary adenomas (one of which was calcified), one patient with acromegaly, one patient with a suprasellar meningioma, and one patient with a nasopharyngeal carcinoma invading the pituitary. Studies were begun between 0800 and 0900 hr after an overnight fast. To facilitate drawing of blood, an indwelling i.v. catheter was placed in the antecubital fossa and kept open with a slow saline infusion. After a basal period of 30-60 min. hypoglycemia was induced in all subjects with 0.1 U regular insulin/kg body weight injected intravenously at time 0 with blood samples collected at - 15, 0, 15, 30, 45, 60, 90, and 120 min for measurement of serum glucose, growth hormone (GH). ACTH, cortisol, and prolactin. Thyrotropin-releasing hormone (TRH) (Abbott Laboratories, Chicago. Illinois) 500 pg was administered to four of the individuals with pituitary disease and blood was drawn at standard times for prolactin measurement. In six of the above control individuals who were free of endocrine disease, 5 mg diethylstilbestrol was administered orally t.i.d. for 3 days. Following this period of estrogen administration, hypoglycemia was again induced and blood samples were collected as before. Glucose was measured by a glucose oxidase method using the Beckman glucose analyzer. Serum GH, prolactin. cortisol, and plasma ACTH were measured by radioimmunoassay. Reagents for GH assay were obtained from Kallestad Laboratories (Chaska. Minn.). Reagents for serum prolactin
o--Q -
IS
IO
5
Pltullory Dlrrosr Control
WI ,’
OL -1s
d‘1
-k _
_
radioimmunoassay were obtained from Serono
Laboratories (Boston, Mass.). The normal range for prolactin in males, as determined in 41 male control patients in our laboratory. is 0.6-14.2 ng/ml. The sensitivity of the prolactin assay is I .6 ng/ml with an intraassay variation of 8% and an interassay coefficient of variation of 16%. Cortisol reagents were obtained from Corning Laboratories (Medfield, Mass.). The normal range in our laboratory for morning cortisol is 5-25 pg/lOO ml. Plasma ACTH was determined by kits obtained from C.I.S. Radiopharmaceuticals (Bedford. Mass.) The limit of sensitivity of this ACTH assay in our laboratory is 5 pg/ml. Each number in the figures represents the mean r SE. Statistical analysis was accomplished by using Student’s t test for either unpaired (Fig. 1) or paired (Figs. 3 and 4) observations. RESULTS
The glucose and prolactin responses to i.v. insulin of 22 male subjects who were free of pituitary disorders is shown in Fig. 1. As can be seen in the figure, a greater than 50% drop in blood glucose was associated with a rise in prolactin from a mean baseline of 7 ng/ml to 24 ng/ml at 90 min. A positive response, as defined by at least a twofold rise over baseline, was observed in 18 of the 22 subjects. All 8 patients with hypothalamic-pituitary disease but with normal basal proiactin levels had a blunted prolactin response to hypoglycemia as compared to the control subjects (Fig. 1). In addition, three of these patients with a blunted prolactin response had a normal GH response to hypoglycemia. The GH response to hypoglycemia is generally regarded as the most sensitive endocrine index of pituitary disease.‘j
- ---_ T
’
I
I
I
I
0
IS
30
46
60
- ___-i
I
I
90
I
-_I 120
TIME (mlnl Fig. 1. The glucose and prolactin responses to i.v. insulin in 22 control subjects (--I and 8 patients with hypothalamic-pituitary disease but with normal basal prolactin levels (-_). Note the blunted response to hypoglycemia in the patients. Each value represents the mean f SE.
Fig. 2. Relationship of the prolactin response to hypoglycemia with the prolactin response to TRH in control subjects (0) and in patients with hypothalamic-pituitary disease but with normal basal prolactin (0). Note the relative intact response to TRH as compared to insulin hypoglycemia in the patients.
342
MAY ET AL.
Four of the 8 patients with active pituitary disease but normal basal prolactin and a blunted prolactin response to hypoglycemia underwent testing with TRH. Figure 2 compares the increase of prolactin over baseline in response to TRH versus the increase of prolactin over baseline in response to hypoglycemia. Except for one control individual, there was a general correspondence of the prolactin response to TRH with the prolactin response to hypoglycemia in the control subjects. In contrast to the control group, there was a dissociation of the prolactin response to TRH from the prolactin response to hypogly-
EUrogIn
-15 35
I
I
I
I
I
0
I3
30
45
60
1
I 90
I
I
120
TIME (mid t
Fig. 4. The ACTH and cortisol responses to insulininduced hypoglycemia before (--_) and after (-_) the administration of estrogen. *
25 t
Bar?linr
1
20 -
Estrogen
,
TIME
(min)
The glucose, prolactin. and GH response to i.v. Fig. 3. insulin in 6 control subjects before (-_) and after (-- -_) the administration of estrogen. Estrogen caused a blunting of the prolactin response to hypoglycemia. Each value represents the mean + SE.
cemia in the patients with pituitary disease but with normal basal prolactin. The effect of the administration of estrogen on the glucose and hormonal response to insulin in six of the control subjects is shown in Figs. 3 and 4. Glucose reached a nadir at 30-45 min and was not significantly affected by the administration of estrogen. Basal prolactin rose significantly following treatment with estrogen, but there was no further increase in the prolactin following insulin-hypoglycemia in any of the six subjects. The GH response was not significantly altered by estrogen. The basal cortisol and peak cortisol response were significantly greater following estrogen, however, the percent rise of cortisol following estrogen was diminished, in keeping with a somewhat, although not significantly, blunted ACTH response following estrogen (Fig. 4). DISCUSSION
While some investigators have not found the prolactin response to hypoglycemia to be a useful
ESTROGEN BLUNTS
PROLACTIN
RESPONSE
pituitary function test,14 the results of this study support previous reports demonstrating that the prolactin response to hypoglycemia is a reliable index of hypothalamic-pituitary function.‘-““‘-‘9 Furthermore, the results confirm prior investigations showing that the prolactin response to hypoglycemia is blunted in patients with pituitary disease.‘-” In addition, the results of this study might suggest the potential value of the prolactin response to hypoglycemia in patients with normal basal prolactin levels but suspected pituitary disease since this was the only pituitary abnormality in several patients tested in this study and in a previous study.’ Supporting this notion is a recent report demonstrating that while only 7% of patients with suspected or functional pituitary disease had a blunted prolactin response to insulin-hypoglycemia, the prolactin response to hypoglycemia was blunted in 60% of patients with a definite pituitary lesion but normal basal prolactin.” A normal prolactin response to hypoglycemia is evidence against hypothalamic-pituitary disease in our experience; however, when the prolactin response to hypoglycemia is blunted, this may be less helpful because of the relatively high frequency (18% in our series and 30% in others”) of blunted prolactin responses in normals. In our series, none of the patients with hypothalamic-pituitary disease had a normal prolactin response to hypoglycemia. Improved discrimination between patients with or without hypothalamic disease may be obtained by comparing the prolactin response to TRH with the prolactin response to hypoglycemia, since the prolactin response to TRH was normal in our patients with normal basal prolactin levels, even in the presence of a definite pituitary abnormality. When the basal prolactin is elevated from any cause, the percent rise over baseline in response to stimulating agents (i.e., hypoglycemia, TRH, thorazine) tends to be blunted,3.6 whereas suppression with L-dopa may be normal even when a pituitary tumor is obviously present.3*s.8 However, the results of this study suggest that when the basal prolactin is normal, a blunted prolactin response to hypoglycemia may give additional differential diagnostic information. These studies were performed in men; however, a previous study’ suggests that the results might also apply to women.
343
In order to obtain some indication of the sensitivity of the prolactin response to hypoglycemia in the diagnosis of lesions of the hypothalamic-pituitary axis, 6 control subjects underwent insulin-hypoglycemic stimulation of prolactin secretion before and after a 3-day course of estrogen. Estrogen was selected because we (May et al., unpublished) and others” have demonstrated an acute effect of estrogen on pituitary DNA synthesis and pituitary growth in rats. In addition, we and others have shown that estrogen given acutely to rats also causes a marked increase in prolactin secretion and that this increase correlates well with increased DNA synthesis,” suggesting that prolactin secretion and pituitary DNA synthesis are closely linked. In humans, the pituitary gland is known to enlarge during pregnancy,” presumably as the result of the stimulative effects of estrogen. We reasoned that if we could show a rise in serum prolactin following a short course of estrogen, this might reflect stimulation of growth of lactotrophs. If the prolactin response to hypoglycemia were found to be blunted even after only a short course of estrogen, it might indicate that the prolactin response to hypoglycemia would be a sensitive index of growth of prolactin-producing cells. The blunting effect of estrogen on the prolactin response to hypoglycemia is at variance with the stimulative effect of estrogen on prolactin response to phenothiazines” and Thyrotropin releasing hormone (TRH).‘” This difference might be explained by the different sites of action of the stimulating agents. Thus, whereas the site of action for TRH is predominantly the pituitary,24 phenbthiazines probably act both at the hypothalamic” and pituitary levels.“~3” and hypoglycemic stimulation of pituitary hormone release is probably mediated exclusively by intracellular hypothalamic glucopenia.‘“. ” One might speculate that the potentiating effect of estrogen on prolactin response to TRH and phenothiazines results from a direct effect of estrogen on the pituitary lactotrophs,-“,3’ whereas the blunting effect of estrogen on the prolactin response to hypoglycemia results from the prolactin inhibitory factor (PIF) depleting action of estrogen on the hypothalamus.34 If this were true, the prolactin response to hypoglycemia would be mediated through PI F depletion during hypoglycemia, rather than by stimulation
344
MAY
of a prolactin-releasing factor. Alternatively, estrogen might be acting through a catechol estrogen mechanism. It has recently been shown that catechol estrogens are able to directly interact with dopamine receptors;35 it is generally believed that dopamine is the major PIF. (see Raymond et al.33) Since the pattern of prolactin response to hypoglycemia after estrogen resembles that seen with pituitary tumors, the results might also suggest a role for estrogen or its receptors in the hypothalamus or pituitary in the growth of some types of pituitary tumors in humans. This has been previously postulated to occur in cirrhotic men with signs of estrogenization, hyperprolactinemia, and blunted prolactin response to TRH,36 and in women receiving oral contraceptives.37
ET AL.
Finally, the potentiating effect of estrogen on the cortisol response to hypoglycemia was consistent with previous observations3* and is presumably secondary to the stimulative effect of estrogen on cortisol-binding protein$’ rather than to potentiation of the ACTH response to hypoglycemia. This is further supported by the ACTH data in Fig. 4 which show, if anything, a blunted ACTH response to hypoglycemia following estrogen. The GH response to hypoglycemia was not affected by estrogen in our study. Whereas pretreatment with estrogen appears to potentiate the GH response to hypoglycemia in children,‘* there is little data on adults. In fact, one study has shown that adult men have somewhat greater GH responses to hypoglycemia than adult women.”
REFERENCES 1. Frantz AG: Prolactin. N Engl J Med 298:201-207, 1978 2. May PB: Initial evaluation and management of patients with suspected pituitary tumors, Primary Care 4:89-125, 1977 3. Kleinberg DL, Noel CL, Frantz AG: Galactorrhea: A study of 235 cases, including 48 with pituitary tumors. N Engl Med 296:589-600, 1977 4. Tolis G, Somma M, Van Campenhout J, et al: Prolactin secretion in sixty-five patients with galactorrhea. Am J Obstet Gynecol 118:91-101, 1974 5. Boyd AE, Reichlin S, Turksoy RN: Galactorrheaamenorrhea syndrome: Diagnosis and therapy. Ann Intern Med 87:164-175, 1977 6. Healy DL, Pepperell RJ, Stockdale J, et al: Pituitary autonomy in hyperprolactinemic secondary amenorrhea: Results of hypothalamic-pituitary testing. J Clin Endocrinol Metab 44:809-8 19, 1977 7. Tolis G, Goldstein M. Friesen HG: Functional evaluation of prolactin secretion in patients with hypothalamicpituitary disorders. J Clin Invest 52:783-788, 1973 8. Friesen H, Guyda H, Hwang P, et al: Functional evaluation of prolactin secretion: A guide to therapy. J Clin Invest 51:706-709, 1972 9. May PB, Burrow GN, Kayne RD, et al: Hypoglycemia-induced prolactin release. Arch Intern Med 138:918920, 1978 10. Woolf PD, Lee LA, Leebow WF: Hypoglycemia as a provocative test of prolactin release. Metabolism 27:869877, 1978 11. Buckman MT, Peake GT: Concordance of insulininduced hypoglycemia and phenothiazine-induced prolactin secretion in man. J Clin Endocrinol Metab 48:213-216, 1979 12. Lloyd H, Meares J, Jacobi J, et al: Effects of stilbestrol on growth hormone secretion and pituitary cell proliferation in the male rat. J Endocrinol 5 1:473-48 1, 197 1
13. Nieman E, Landon J, Wynn V: Endocrine function in patients with untreated chromophobe adenomas. Q J Med 143:357-392,1967 14. Cohen MP, Gala RR: Failure of insulin hypoglycemia to produce rise in serum prolactin. Am J Obstet Gynecol 121:1103-1106, 1975 15. Woolf PD, Lee LA, Leebaw W, et al: Intracellular glucopenia causes prolactin release in man. J Clin Endocrinol Metab 45:377-383, 1977 16. Copinschi G, L’Hermite M, Leclercq R, et al: Effects of glucocorticoids on pituitary hormonal responses to hypoglycemia. Inhibition of prolactin release. J Clin Endocrinol Metab 40:442-449, 1975 17. Noel GL, Suh HK, Stone JG, et al: Human prolactin and growth hormone release during surgery and other conditions of stress. J Clin Endocrinol Metab 35:840-851, 1972 18. Wilson RG, Percy-Robb I, Singhal VK, et al: Response of plasma prolactin and growth hormone to insulin hypoglycemia. Lancet 2:1283-1285,1972 19. Osterman, PO, Fagius J, Wide L: Prolactin levels in the insulin tolerance test with and without pre-treatment with dexamethasone. Acta Endocrinol 84:237-245, 1977 20. Davies C, Jacobi J, Lloyd H, et al: DNA synthesis and the secretion of prolactin and growth hormone by the pituitary gland of the male rat: Effects of diethylstilbestrol and 2-bromo-a-ergocriptine methanesulphonate. J Endocrinol 61:411417, 1974 21. Rasmussen A: The weight of the principal components of the normal hypophysis cerebri of the adult human female. Am J Anat 55:253-257, 1934 22. Buckman MT, Peake GT: Estrogen potentiation of phenothiazine-induced prolactin secretion in man. J Clin Endocrinol Metab 37:977-980, 1973 23. Carlson HE, Jacobs LS, Daughaday WH: Growth hormone, thyrotropin and prolactin responses to thyrotropinreleasing hormone following diethylstilbestrol pretreatment. J Clin Endocrinol Metab 37:488-490, 1973
ESTROGEN BLUNTS
PROLACTIN
RESPONSE
24. Tashjian AH, Barowsky NJ, Jensen DK: Thyrotropin releasing hormone: Direct evidence for stimulation of prolactin production by pituitary cells in culture. Biochem Biophys Res Commun 43:516-523.1971 25. DeWied D: Chlorpromazine and endocrine function. Pharmacol Rev 19:251-288, 1967 26. Shani J, Givant Y, Sulman FG, et al: Competition of phenothiazines with oestradiol for oestradiol receptors in rat brain. Neuroendocrinology 8:307-3 16, 197 I 27. MacLeod RM, Lehmeyer JE: Studies on the mechanism of the dopamine-mediated inhibition of prolactin secretion. Endocrinology 94:1077-1085, 1974 28. Dennison AM, Ferin M, Frantz AG: Evidence that two dopamine antagonists act directly on the pituitary to release prolactin in vivo. Endocrine Society Abstracts, 59th Annual Meeting, Chicago, 1977, abstract 9 29. Lawson DM, Gala RR: Influence of anaesthetics on basal, perphenazine-induced and thyrotrophin releasing hormone-induced prolactin secretion in ovariectomized, oestrogen-treated rats. J Endocrinol 66:151-157, 1975 30. Langer G, Ferin M, Sachar EJ: Effect of haloperidol and r-dopa on plasma prolactin in stalk-sectioned and intact monkeys. Endocrinology 102:367-370, 1978 31. Roth J, Click SM. Yalow RS, et al: Secretion of human growth hormone: Physiologic and experimental modification. Metabolism 12:577-579, 1963 32. Ramirez VD, McCann SM: Induction of prolactin secretion by implants of estrogen into the hypothalamo-
hypophyseal 213, 1964
region
of female
rats.
Endocrinology
75:206-
33. Raymond V, Beaulieu M, Labrie F: Potent antidopaminergic activity of estradiol at the pituitary level on prolactin release. Science 2OO:l 173-I 175, 1978 34. Ratner A, Meites J: Depletion of prolactin-inhibiting activity of rat hypothalamus by estradiol or suckling stimulus. Endocrinology 75:377-382, 1964 35. Schaeffer J: Dopamine receptors in rat anterior pituitary: Inhibition of ‘H-spiroperiodol binding by 2-hydroxyestradiol. Endocrine Society Abstracts, 6lst Annual Meeting, Anaheim, Calif., 1979 36. Van Thiel D, McClain CJ, Elson MK, et al: Evidence for autonomous secretion of prolactin in some alcoholic men with cirrhosis and gynecomastia. Metabolism 27: 1778-l 784, 1978 37. Sherman B, Schlechte J, Halmi N. et al: Pathogenesis of prolactin-secreting pituitary adenomas. Lancet 2:10191021, 1978 38. Lippe B, Wong SLR, Kaplan SA: Simultaneous assessment of growth hormone and ACTH reserve in children pretreated with diethylstilbestrol. J Clin Endocrinol 331949-956, 1971 39. Mills IH, Schedl HP, Chen PS. et al: The effect of estrogen administration on the metabolism and protein binding of hydrocortisone. J Clin Endocrinol Metab 2O:Sl S-518. 1960
in 22
response control
to hypoglycemia
subjects
and
hypothalamic-pituitary
disease
serum
Eighteen
prolactin
subjects
levels.
demonstrated
rise in response subjects,
strated
a prolactin
blunted
prolactin
only endocrine In an attempt the prolactin of
early
course
response
response
response
of its known mitosis
pituitary
tumor
diethylstilbestrol
8 patients
to the demonThis
was the
in 3 of these 8 patients. the sensitivity
to hypoglycemia the
of
a short
response
to
Estrogen was selected
acute
stimulatory
chronic
formation
of
as an index
effect
prolactin
was examined.
because
prolactin
In contrast
determine
on the
pituitary
basal
to hypoglycemia.
disease,
and
normal
to hypoglycemia
abnormality to better
estrogen
hypoglycemia
of the
with
of the 22 control
at least a twofold
none
pituitary of
was evalu-
8 patients
but
to hypoglycemia.
control
Proper, Jana Ourednik,
effects
effect
that
in rodents.
on
lead to
Accordingly,
(DES) 5 mg t.i.d. was administered
orally to 8 normal men for 3 days, a period known to stimulate
pituitary
Diethylstilbestrol
vation of the zcseiine ng/ml,
mitotic
treatment
prolactin
p < 0.05): however.
hypoglycemia
activity caused
was blunted
response prolactin
hypoglycemia
response
to
ele-
18 + 3
the prolactin response
hypoglycemia
p
after DES,
blunted
resembled
patients with hypothalamic-pituitary
to
c 10 ng/ml.
+ 5 ng/ml
This estrogen-induced to
rodents.
(8 * 2 versus
(8 ? 2-30
< 0.05, before DES; 18 ‘_ 3-20 p > 0.05).
in
significant
prolactin
the
blunted
found
in
disease.
PROLACTIN is frequently elevated SERUM in patients with pituitary and parapituitary neoplasms;‘32 however, because some patients with documented pituitary tumors have normal serum prolactin levels,24 the basal serum prolactin level is not a reliable indicator of the presence of a pituitary lesion in all instances. In an effort to improve the diagnostic sensitivity of the serum prolactin determination, several investigators have examined the usefulness of various stimulation and suppression tests of prolactin se-
From the Department of Medicine, VA Medical Center, East Orange, NJ., and the CMDNJ/NJ Medical School. Newark, N.J. Receivedfor publication July 23, 1979. Address reprint requests to Dr. P. May, Endocrinology Section, Department of Medicine, VA Medical Center, Tremont Avenue. East Orange, N.J., 07019. o 1980 by Grune & Stratton, Inc. 0026-0495/80/2904/0007$01.00/0
340
George Schneider,
and Norman
Ertel
cretion.3Vs-8 In general, the results of these studies have been disappointing and there appears to be no diagnostic advantage of the various dynamic tests (e.g., TRH, phenothiazine, Ldopa) over the basal prolactin level. When the prolactin level is elevated, dynamic tests tend to be abnormal; when the prolactin level is normal, dynamic tests are usually normal. It has been previously shown that the prolactin response to hypoglycemia may be blunted in patients with pituitary-hypothalamic disease’-” even when the basal prolactin level is normal,’ and it has been suggested that a blunted prolactin response to hypoglycemia may represent an early manifestation of a developing pituitary tumor. The purpose of this study was to investigate the prolactin response to hypoglycemia in patients with a variety of diseases of the hypothalamic-pituitary axis but with normal basal serum prolactin levels and in subjects who had received a short course of estrogen. Estrogen was given because several days of estrogen administration are known to stimulate prolactin secretion and pituitary mitotic activity in rodents,12 suggesting that estrogen-induced hyperprolactinemia might be a marker for pituitary hyperplasia. The results of this study demonstrate that the prolactin response to hypoglycemia is usually blunted in patients with known pituitary disease, even when the basal prolactin level and other tests of pituitary function are normal. Since a normal prolactin response to hypoglycemia is not commonly seen in patients with pituitary lesions, the documentation of a normal prolactin response to hypoglycemia would be one bit of evidence against hypothalamic-pituitary disease. The results with estrogen further suggest that a blunted insulin-response to hypoglycemia may be a laboratory correlate of pituitary hyperplasia. MATERIALS
AND
METHODS
Twenty-two male subjects, 43-60 yr of age, who were free of hypothalamic-pituitary disorders, and 8 patients with
Metabolism, Vol. 29, No. 4 (April). 1980
341
ESTROGEN BLUNTS PROLACTIN RESPONSE
various types of hypothalamic-pituitary disease but normal basal prolactin, were selected for this study after giving informed written consent. There were 5 patients with nonsecretory pituitary adenomas (one of which was calcified), one patient with acromegaly, one patient with a suprasellar meningioma, and one patient with a nasopharyngeal carcinoma invading the pituitary. Studies were begun between 0800 and 0900 hr after an overnight fast. To facilitate drawing of blood, an indwelling i.v. catheter was placed in the antecubital fossa and kept open with a slow saline infusion. After a basal period of 30-60 min. hypoglycemia was induced in all subjects with 0.1 U regular insulin/kg body weight injected intravenously at time 0 with blood samples collected at - 15, 0, 15, 30, 45, 60, 90, and 120 min for measurement of serum glucose, growth hormone (GH). ACTH, cortisol, and prolactin. Thyrotropin-releasing hormone (TRH) (Abbott Laboratories, Chicago. Illinois) 500 pg was administered to four of the individuals with pituitary disease and blood was drawn at standard times for prolactin measurement. In six of the above control individuals who were free of endocrine disease, 5 mg diethylstilbestrol was administered orally t.i.d. for 3 days. Following this period of estrogen administration, hypoglycemia was again induced and blood samples were collected as before. Glucose was measured by a glucose oxidase method using the Beckman glucose analyzer. Serum GH, prolactin. cortisol, and plasma ACTH were measured by radioimmunoassay. Reagents for GH assay were obtained from Kallestad Laboratories (Chaska. Minn.). Reagents for serum prolactin
o--Q -
IS
IO
5
Pltullory Dlrrosr Control
WI ,’
OL -1s
d‘1
-k _
_
radioimmunoassay were obtained from Serono
Laboratories (Boston, Mass.). The normal range for prolactin in males, as determined in 41 male control patients in our laboratory. is 0.6-14.2 ng/ml. The sensitivity of the prolactin assay is I .6 ng/ml with an intraassay variation of 8% and an interassay coefficient of variation of 16%. Cortisol reagents were obtained from Corning Laboratories (Medfield, Mass.). The normal range in our laboratory for morning cortisol is 5-25 pg/lOO ml. Plasma ACTH was determined by kits obtained from C.I.S. Radiopharmaceuticals (Bedford. Mass.) The limit of sensitivity of this ACTH assay in our laboratory is 5 pg/ml. Each number in the figures represents the mean r SE. Statistical analysis was accomplished by using Student’s t test for either unpaired (Fig. 1) or paired (Figs. 3 and 4) observations. RESULTS
The glucose and prolactin responses to i.v. insulin of 22 male subjects who were free of pituitary disorders is shown in Fig. 1. As can be seen in the figure, a greater than 50% drop in blood glucose was associated with a rise in prolactin from a mean baseline of 7 ng/ml to 24 ng/ml at 90 min. A positive response, as defined by at least a twofold rise over baseline, was observed in 18 of the 22 subjects. All 8 patients with hypothalamic-pituitary disease but with normal basal proiactin levels had a blunted prolactin response to hypoglycemia as compared to the control subjects (Fig. 1). In addition, three of these patients with a blunted prolactin response had a normal GH response to hypoglycemia. The GH response to hypoglycemia is generally regarded as the most sensitive endocrine index of pituitary disease.‘j
- ---_ T
’
I
I
I
I
0
IS
30
46
60
- ___-i
I
I
90
I
-_I 120
TIME (mlnl Fig. 1. The glucose and prolactin responses to i.v. insulin in 22 control subjects (--I and 8 patients with hypothalamic-pituitary disease but with normal basal prolactin levels (-_). Note the blunted response to hypoglycemia in the patients. Each value represents the mean f SE.
Fig. 2. Relationship of the prolactin response to hypoglycemia with the prolactin response to TRH in control subjects (0) and in patients with hypothalamic-pituitary disease but with normal basal prolactin (0). Note the relative intact response to TRH as compared to insulin hypoglycemia in the patients.
342
MAY ET AL.
Four of the 8 patients with active pituitary disease but normal basal prolactin and a blunted prolactin response to hypoglycemia underwent testing with TRH. Figure 2 compares the increase of prolactin over baseline in response to TRH versus the increase of prolactin over baseline in response to hypoglycemia. Except for one control individual, there was a general correspondence of the prolactin response to TRH with the prolactin response to hypoglycemia in the control subjects. In contrast to the control group, there was a dissociation of the prolactin response to TRH from the prolactin response to hypogly-
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The glucose, prolactin. and GH response to i.v. Fig. 3. insulin in 6 control subjects before (-_) and after (-- -_) the administration of estrogen. Estrogen caused a blunting of the prolactin response to hypoglycemia. Each value represents the mean + SE.
cemia in the patients with pituitary disease but with normal basal prolactin. The effect of the administration of estrogen on the glucose and hormonal response to insulin in six of the control subjects is shown in Figs. 3 and 4. Glucose reached a nadir at 30-45 min and was not significantly affected by the administration of estrogen. Basal prolactin rose significantly following treatment with estrogen, but there was no further increase in the prolactin following insulin-hypoglycemia in any of the six subjects. The GH response was not significantly altered by estrogen. The basal cortisol and peak cortisol response were significantly greater following estrogen, however, the percent rise of cortisol following estrogen was diminished, in keeping with a somewhat, although not significantly, blunted ACTH response following estrogen (Fig. 4). DISCUSSION
While some investigators have not found the prolactin response to hypoglycemia to be a useful
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pituitary function test,14 the results of this study support previous reports demonstrating that the prolactin response to hypoglycemia is a reliable index of hypothalamic-pituitary function.‘-““‘-‘9 Furthermore, the results confirm prior investigations showing that the prolactin response to hypoglycemia is blunted in patients with pituitary disease.‘-” In addition, the results of this study might suggest the potential value of the prolactin response to hypoglycemia in patients with normal basal prolactin levels but suspected pituitary disease since this was the only pituitary abnormality in several patients tested in this study and in a previous study.’ Supporting this notion is a recent report demonstrating that while only 7% of patients with suspected or functional pituitary disease had a blunted prolactin response to insulin-hypoglycemia, the prolactin response to hypoglycemia was blunted in 60% of patients with a definite pituitary lesion but normal basal prolactin.” A normal prolactin response to hypoglycemia is evidence against hypothalamic-pituitary disease in our experience; however, when the prolactin response to hypoglycemia is blunted, this may be less helpful because of the relatively high frequency (18% in our series and 30% in others”) of blunted prolactin responses in normals. In our series, none of the patients with hypothalamic-pituitary disease had a normal prolactin response to hypoglycemia. Improved discrimination between patients with or without hypothalamic disease may be obtained by comparing the prolactin response to TRH with the prolactin response to hypoglycemia, since the prolactin response to TRH was normal in our patients with normal basal prolactin levels, even in the presence of a definite pituitary abnormality. When the basal prolactin is elevated from any cause, the percent rise over baseline in response to stimulating agents (i.e., hypoglycemia, TRH, thorazine) tends to be blunted,3.6 whereas suppression with L-dopa may be normal even when a pituitary tumor is obviously present.3*s.8 However, the results of this study suggest that when the basal prolactin is normal, a blunted prolactin response to hypoglycemia may give additional differential diagnostic information. These studies were performed in men; however, a previous study’ suggests that the results might also apply to women.
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In order to obtain some indication of the sensitivity of the prolactin response to hypoglycemia in the diagnosis of lesions of the hypothalamic-pituitary axis, 6 control subjects underwent insulin-hypoglycemic stimulation of prolactin secretion before and after a 3-day course of estrogen. Estrogen was selected because we (May et al., unpublished) and others” have demonstrated an acute effect of estrogen on pituitary DNA synthesis and pituitary growth in rats. In addition, we and others have shown that estrogen given acutely to rats also causes a marked increase in prolactin secretion and that this increase correlates well with increased DNA synthesis,” suggesting that prolactin secretion and pituitary DNA synthesis are closely linked. In humans, the pituitary gland is known to enlarge during pregnancy,” presumably as the result of the stimulative effects of estrogen. We reasoned that if we could show a rise in serum prolactin following a short course of estrogen, this might reflect stimulation of growth of lactotrophs. If the prolactin response to hypoglycemia were found to be blunted even after only a short course of estrogen, it might indicate that the prolactin response to hypoglycemia would be a sensitive index of growth of prolactin-producing cells. The blunting effect of estrogen on the prolactin response to hypoglycemia is at variance with the stimulative effect of estrogen on prolactin response to phenothiazines” and Thyrotropin releasing hormone (TRH).‘” This difference might be explained by the different sites of action of the stimulating agents. Thus, whereas the site of action for TRH is predominantly the pituitary,24 phenbthiazines probably act both at the hypothalamic” and pituitary levels.“~3” and hypoglycemic stimulation of pituitary hormone release is probably mediated exclusively by intracellular hypothalamic glucopenia.‘“. ” One might speculate that the potentiating effect of estrogen on prolactin response to TRH and phenothiazines results from a direct effect of estrogen on the pituitary lactotrophs,-“,3’ whereas the blunting effect of estrogen on the prolactin response to hypoglycemia results from the prolactin inhibitory factor (PIF) depleting action of estrogen on the hypothalamus.34 If this were true, the prolactin response to hypoglycemia would be mediated through PI F depletion during hypoglycemia, rather than by stimulation
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of a prolactin-releasing factor. Alternatively, estrogen might be acting through a catechol estrogen mechanism. It has recently been shown that catechol estrogens are able to directly interact with dopamine receptors;35 it is generally believed that dopamine is the major PIF. (see Raymond et al.33) Since the pattern of prolactin response to hypoglycemia after estrogen resembles that seen with pituitary tumors, the results might also suggest a role for estrogen or its receptors in the hypothalamus or pituitary in the growth of some types of pituitary tumors in humans. This has been previously postulated to occur in cirrhotic men with signs of estrogenization, hyperprolactinemia, and blunted prolactin response to TRH,36 and in women receiving oral contraceptives.37
ET AL.
Finally, the potentiating effect of estrogen on the cortisol response to hypoglycemia was consistent with previous observations3* and is presumably secondary to the stimulative effect of estrogen on cortisol-binding protein$’ rather than to potentiation of the ACTH response to hypoglycemia. This is further supported by the ACTH data in Fig. 4 which show, if anything, a blunted ACTH response to hypoglycemia following estrogen. The GH response to hypoglycemia was not affected by estrogen in our study. Whereas pretreatment with estrogen appears to potentiate the GH response to hypoglycemia in children,‘* there is little data on adults. In fact, one study has shown that adult men have somewhat greater GH responses to hypoglycemia than adult women.”
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13. Nieman E, Landon J, Wynn V: Endocrine function in patients with untreated chromophobe adenomas. Q J Med 143:357-392,1967 14. Cohen MP, Gala RR: Failure of insulin hypoglycemia to produce rise in serum prolactin. Am J Obstet Gynecol 121:1103-1106, 1975 15. Woolf PD, Lee LA, Leebaw W, et al: Intracellular glucopenia causes prolactin release in man. J Clin Endocrinol Metab 45:377-383, 1977 16. Copinschi G, L’Hermite M, Leclercq R, et al: Effects of glucocorticoids on pituitary hormonal responses to hypoglycemia. Inhibition of prolactin release. J Clin Endocrinol Metab 40:442-449, 1975 17. Noel GL, Suh HK, Stone JG, et al: Human prolactin and growth hormone release during surgery and other conditions of stress. J Clin Endocrinol Metab 35:840-851, 1972 18. Wilson RG, Percy-Robb I, Singhal VK, et al: Response of plasma prolactin and growth hormone to insulin hypoglycemia. Lancet 2:1283-1285,1972 19. Osterman, PO, Fagius J, Wide L: Prolactin levels in the insulin tolerance test with and without pre-treatment with dexamethasone. Acta Endocrinol 84:237-245, 1977 20. Davies C, Jacobi J, Lloyd H, et al: DNA synthesis and the secretion of prolactin and growth hormone by the pituitary gland of the male rat: Effects of diethylstilbestrol and 2-bromo-a-ergocriptine methanesulphonate. J Endocrinol 61:411417, 1974 21. Rasmussen A: The weight of the principal components of the normal hypophysis cerebri of the adult human female. Am J Anat 55:253-257, 1934 22. Buckman MT, Peake GT: Estrogen potentiation of phenothiazine-induced prolactin secretion in man. J Clin Endocrinol Metab 37:977-980, 1973 23. Carlson HE, Jacobs LS, Daughaday WH: Growth hormone, thyrotropin and prolactin responses to thyrotropinreleasing hormone following diethylstilbestrol pretreatment. J Clin Endocrinol Metab 37:488-490, 1973
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24. Tashjian AH, Barowsky NJ, Jensen DK: Thyrotropin releasing hormone: Direct evidence for stimulation of prolactin production by pituitary cells in culture. Biochem Biophys Res Commun 43:516-523.1971 25. DeWied D: Chlorpromazine and endocrine function. Pharmacol Rev 19:251-288, 1967 26. Shani J, Givant Y, Sulman FG, et al: Competition of phenothiazines with oestradiol for oestradiol receptors in rat brain. Neuroendocrinology 8:307-3 16, 197 I 27. MacLeod RM, Lehmeyer JE: Studies on the mechanism of the dopamine-mediated inhibition of prolactin secretion. Endocrinology 94:1077-1085, 1974 28. Dennison AM, Ferin M, Frantz AG: Evidence that two dopamine antagonists act directly on the pituitary to release prolactin in vivo. Endocrine Society Abstracts, 59th Annual Meeting, Chicago, 1977, abstract 9 29. Lawson DM, Gala RR: Influence of anaesthetics on basal, perphenazine-induced and thyrotrophin releasing hormone-induced prolactin secretion in ovariectomized, oestrogen-treated rats. J Endocrinol 66:151-157, 1975 30. Langer G, Ferin M, Sachar EJ: Effect of haloperidol and r-dopa on plasma prolactin in stalk-sectioned and intact monkeys. Endocrinology 102:367-370, 1978 31. Roth J, Click SM. Yalow RS, et al: Secretion of human growth hormone: Physiologic and experimental modification. Metabolism 12:577-579, 1963 32. Ramirez VD, McCann SM: Induction of prolactin secretion by implants of estrogen into the hypothalamo-
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33. Raymond V, Beaulieu M, Labrie F: Potent antidopaminergic activity of estradiol at the pituitary level on prolactin release. Science 2OO:l 173-I 175, 1978 34. Ratner A, Meites J: Depletion of prolactin-inhibiting activity of rat hypothalamus by estradiol or suckling stimulus. Endocrinology 75:377-382, 1964 35. Schaeffer J: Dopamine receptors in rat anterior pituitary: Inhibition of ‘H-spiroperiodol binding by 2-hydroxyestradiol. Endocrine Society Abstracts, 6lst Annual Meeting, Anaheim, Calif., 1979 36. Van Thiel D, McClain CJ, Elson MK, et al: Evidence for autonomous secretion of prolactin in some alcoholic men with cirrhosis and gynecomastia. Metabolism 27: 1778-l 784, 1978 37. Sherman B, Schlechte J, Halmi N. et al: Pathogenesis of prolactin-secreting pituitary adenomas. Lancet 2:10191021, 1978 38. Lippe B, Wong SLR, Kaplan SA: Simultaneous assessment of growth hormone and ACTH reserve in children pretreated with diethylstilbestrol. J Clin Endocrinol 331949-956, 1971 39. Mills IH, Schedl HP, Chen PS. et al: The effect of estrogen administration on the metabolism and protein binding of hydrocortisone. J Clin Endocrinol Metab 2O:Sl S-518. 1960