Subnormal prolactin responsiveness to thyrotropin-releasing hormone (TRH) in women with primary empty sella syndrome

Basal prolactin (PRL) levels and PRL responsiveness to thyrotropin-releasing hormone (TRH) were studied in 10 women with primary empty sella (PES) syndrome (mean age 38.2 yr). Hyperprolactinemia (34 to 72 ng/ml) was found in 5 patients (hyperprolactinemic PES, H-PES), whereas 5 patients showed normal (9.5 to 19 ng/ml) PRL levels (normoprolactinemic PES, N-PES). The results were compared with those obtained in 10 healthy women (mean age 32.8 yr, PRL = 7 to 15 ng/ml) and in 8 women with a PRL-secreting pituitary microadenoma (MA) (mean age 37.5 yr, PRL = 39 to 85 ng/ml). The mean basal levels of PRL were significantly higher in patients with H-PES (50.8 +/- 13.2 ng/ml) or MA (64.0 +/- 18.3 ng/ml) than in the control group (10.9 +/- 2.6 ng/ml, p less than 0.02) and in the patients with N-PES (13.9 +/- 3.7 ng/ml, p less than 0.02). In contrast, the relative maximum response (RMR) of PRL to TRH (peak PRL/basal PRL) was significantly lower in the patients with PES (both H-PES and N-PES) or MA (1.4 +/- 0.4, 2.3 +/- 0.7 and 1.2 +/- 0.2, respectively) than in the control subjects (3.6 +/- 1.1; p less than 0.02, less than 0.05 and less than 0.02, respectively). Our results show that the pituitary responsiveness to the acute stimulation with TRH is significantly decreased both in patients with a PRL-secreting pituitary MA and in those with PES. Therefore, the clinical value of the TRH test in distinguishing the PES syndromes from prolactinomas seems to be questionable.     

Decreased growth hormone (GH) response to oral clonidine in endemic cretinism: effect of L-T3 therapy

As GH secretion is dependent upon thyroid hormone availability, the GH responses to clonidine (150 micrograms/m2) and the TSH and PRL response to TRH were studied in eight endemic (EC) cretins (3 hypothyroid, 5 with a low thyroid reserve) before and after 4 days of 100 micrograms of L-T3. Five normal controls (N) were also treated in similar conditions. Both groups presented a marked increase in serum T3 after therapy (N = 515 +/- 89 ng/dl; EC = 647 +/- 149 ng/dl) followed by a decrease in basal and peak TSH response to TRH. However, in the EC patients an increase in serum T4 levels and in basal PRL and peak PRL response to TRH after L-T3 therapy was observed. One hypothyroid EC had a markedly elevated PRL peak response to TRH (330 ng/dl). There were no significant changes in basal or peak GH values to treatment with L-T3 in normal subjects. In the EC group the mean basal plasma GH (2.3 +/- 1.9 ng/ml) significantly rose to 8.8 +/- 3.2 ng/ml and the mean peak response to clonidine (12.7 +/- 7.7 ng/ml) increased to 36.9 +/- 3.1 ng/ml after L-T3. Plasma SM-C levels significantly increased in N from 1.79 +/- 0.50 U/ml to 2.42 +/- 0.40 U/ml after L-T3 (p less than 0.01) and this latter value was significantly higher (p less than 0.05) than mean Sm-C levels attained after L-T3 in the EC group (respectively: 1.14 +/- 0.59 and 1.78 +/- 0.68 U/ml). These data indicate that in EC the impaired GH response to a central nervous system mediated stimulus, the relatively low plasma Sm-C concentrations, and the presence of clinical or subclinical hypothyroidism may contribute to the severity of growth retardation present in this syndrome.     

INTERACTION OF THYROTROPHIN RELEASING HORMONE AND THE ENKEPHALIN ANALOGUE DAMME ON PITUITARY HORMONE SECRETION

Because TRH counteracts the inhibitory effect of opiate peptides on LH secretion in cultured cells from normal pituitaries, six normal postmenopausal women were studied to determine whether TRH interacts in vivo with opioid peptides in the regulation of pituitary hormone secretion. At two different times a constant 3 h infusion of either saline or TRH (5 micrograms/min) was initiated. At 60 min a 250 micrograms bolus of the opiate agonist peptide D-Ala2-MePhe4-met-enkephalin-0-ol (DAMME) was injected in one of the two saline and TRH infusion tests. The four treatments, i.e. saline infusion alone, saline infusion with a DAMME bolus, TRH infusion alone; and TRH infusion with DAMME bolus were given at random with an interval of at least 7 d. Blood samples were taken every 15 min during the 3 h study. DAMME induced a significant fall (P less than 0.05) in serum LH (from 35 +/- 8.5 to 18.3 +/- 5.1 mIU/ml) (mean +/- SEM) without significantly affecting FSH levels (from 29 +/- 11.2 to 26.9 +/- 12.4 mIU/ml). These changes were not antagonized by the continuous infusion of TRH. PRL had a monophasic response pattern to continuous isolated TRH infusion; the basal levels increased from 4.2 +/- 1.2 to 24.5 +/- 6.8 ng/ml at 30 min and then slowly decreased with a plateau from 90 min until the end of the study. DAMME administration at 60 min induced a significant second peak of PRL secretion (44 +/- 6.5 ng/ml) 30 min later (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Prolactin secretion in acromegalic patients before and after selective adenomectomy

PRL secretion before and after transsphenoidal adenomectomy was studied in 13 patients with acromegaly. Six patient had elevated basal serum PRL levels before surgery, while 7 patients had normal levels. In every patient, the basal serum GH level decreased to less than 5.0 ng/ml after surgery. In the group (group A) with high basal serum PRL levels (mean +/- SD, 41.3 +/- 5.8 ng/ml) before surgery, the PRL levels decreased significantly (P less than 0.0002) to less than 10.0 ng/ml (4.8 +/- 3.6 ng/ml) after the operation. However, in the group (group B) with normal levels (10.8 +/- 4.4 ng/ml) before surgery, PRL levels changed little (7.8 +/- 3.1 ng/ml) after the operation. In group A, the increment of PRL after TRH injection decreased or disappeared (P less than 0.02; 4.1 +/- 2.4 ng/ml) after surgery compared with that before surgery (39.2 +/- 25.9 ng/ml). On the other hand, in group B, the increment of PRL after TRH injection was nearly unchanged (17.1 +/- 7.0 ng/ml) after surgery compared with that before surgery (19.3 +/- 8.0 ng/ml). The results indicate that PRL is secreted from the pituitary adenoma in acromegalic patients with hyperprolactinemia, while PRL secretion from the normal part of the pituitary gland is decreased.     

Effects of bromocriptine on endocrine environment in the polycystic ovary syndrome

In order to investigate the hormone feature and the effect of bromocriptine on endocrine profile in patients with polycystic ovary syndrome (PCO), twenty-four-hour secretion pattern of LH, FSH, PRL and testosterone were assessed in 8 PCO patients and 4 normal women as controls by obtaining serial blood samples, taken through a forearm cannula, at 30 minute intervals for 24 hours. Bromocriptine, 5 mg/day was given and 3 patients were reassessed in the follicular phase of the menstrual cycle after ovulatory periods were established during bromocriptine therapy. There was significant difference in pulse amplitude, but not in pulse frequency of LH and testosterone between PCO and normal women (23.1 +/- 9.49 vs 5.75 +/- 1.28 mIU/ml, p less than 0.01; 27.8 +/- 10.1 vs 10.2 +/- 2.63 ng/dl, p less than 0.01), and the 24 hour mean LH and testosterone levels were higher (p less than 0.01) in PCO (52.3 +/- 20.1 mIU/ml, 105.1 +/- 15.9 ng/dl) than in normal women (13.4 +/- 4.31 mIU/ml, 54.3 +/- 13.3 ng/dl). Though a pulsatility in FSH secretion was identified, no difference between normal women and PCO was observed. Mean PRL level was within the normal range in PCO but with a higher pulse frequency (p less than 0.01) and lower pulse amplitude (p less than 0.01) than those of the normal women. Furthermore, LH and testosterone secretions maintained the circadian changes in PCO patients against the normal women. During bromocriptine therapy, mean level and pulse amplitude of LH and testosterone were significantly suppressed, without changing in pulse frequency, whilst PRL secretory patterns were not reestablished. In conclusion we have found that PCO is associated with high level and pulse amplitude of LH and testosterone, with high frequency and low amplitude of PRL, and bromocriptine administration can blunt LH, PRL and testosterone secretion, suggesting a hypothalamic intervention in gonadotropic regulation in patient with PCO. In addition, the degree of bromocriptine to inhibit LH secretion might be related to the dose or duration of its administration, or to the sensitivity of the patients. The mechanism of bromocriptine for marked LH suppression in PCO patients remains to be elucidated.     

Regulation of prolactin secretion in patients with Cushing's disease. A comparative study on the effects of dexamethasone, lysine vasopressin and ACTH on prolactin secretion by the rat pituitary gland in vitro

In 15 untreated patients with Cushing's disease the regulation of prolactin (PRL) was evaluated. Plasma PRL was 11.5 +/- 4.8 vs. 5.3 +/- 3.6 ng/ml (patients with Cushing's disease vs. control; mean +/- S.D.; p less than 0.001). The maximal increment of plasma PRL in response to TRH was 32.3 +/- 17.3 vs. 27.9 +/- 17.2 ng/ml (NS); the maximal increment of plasma PRL in response to an insulin-induced hypoglycemia was 3.8 +/- 4.6 vs. 22.7 +/- 12.4 ng/ml (p less than 0.001). Additionally the effect of dexamethasone, lysine vasopressin and ACTH on the secretion of PRL by rat pituitary glands in vitro was studied. Dexamethasone (1.25--10 microM) inhibited the secretion of PRL. However, in the presence of dexamethasone modulation of PRL release by TRH and dopamine remained unaltered. Lysine vasopressin (5 nM - 5 microM) and ACTH (0.5--12.5 microM) did not have a direct effect on PRL release by normal rat pituitary glands in vitro and these substances also did not interfere with dopamine-mediated inhibition of PRL release. Conclusions: In Cushing's disease the PRL responses to TRH (normal) and to insulin-induced hypoglycemia (blunted) are differentially affected. Therefore, hypercortisolism probably selectively interferes with the regulation of PRL secretion at a suprahypophyseal level. It is concluded that TRH and dopamine regulate PRL release at sites which are not under corticosteroid regulation, while corticosteroids modulate PRL secretion in response to stress.     

Impaired prolactin secretion in obese patients

To investigate a possible hypothalamic alteration in obesity, we have studied the pattern of PRL secretion in response to insulin hypoglycemia, arginine infusion and TRH injection in 12 grossly obese patients and in 12 normal-weight controls. In the obese patients, PRL secretion was significantly lower than in normal subjects in response to insulin hypoglycemia and arginine infusion, while it was not significantly different from that in controls in response to TRH. The mean +/- SE values of the areas subtended by the PRL curves in the 3 above tests were 54.7 +/- 155.81 vs 3677.3 +/- 520.30 ng/2h, p less than 0,01, 210.3 +/- 148.93 vs 1034.8 +/- 203.15 ng/2h, p less than 0.05 and 1476.8 +/- 275.13 vs 2148.6 +/- 682.06 ng/2h, NS, respectively, in the obese and in controls. These results are compatible with the concept of impaired hypothalamic control of PRL secretion in obesity, although it is still unclear what role this may play in the pathogenesis of this disorder.     

Effect of gestational mastectomy on postpartum gonadotropin releasing hormone and thyrotropin releasing hormone-induced luteinizing hormone and prolactin response in first lactation Holstein cattle

First lactation Holstein cows were divided into two treatment groups to evaluate thyrotropin releasing hormone (TRH, 0.25 microgram/kg body weight) and gonadotropin releasing hormone (GnRH; 200 micrograms) induced secretion of prolactin (PRL) and luteinizing hormone (LH) on days 7 and 16 postpartum. Disregarding treatment, LH response was greater (p less than 0.01) on day 16 than day 7 postpartum (7.5 +/- 0.3 ng/ml on day 7 vs 10.2 +/- 0.3 ng/ml serum on day 16). Mastectomized cattle had similar time for initiation of LH increase, but peak concentrations were achieved later. Peak PRL concentrations were reached 12 to 15 min after injection and returned to baseline within 2.5 h in both groups. However, intact cows had higher (p less than 0.01) mean serum PRL than the mastectomized cows for 1 h following injection. Peak PRL concentration was 83.3 +/- 17.6 ng/ml for mastectomized cows vs 128.0 +/- 24.7 ng/ml for intact cows. It appears that udder removal allows for greater pituitary responsiveness to GnRH but diminishes PRL response to TRH suggesting the mammary gland differentially affects pituitary secretion of LH and PRL.     

The effect of naloxone on endogenous opioid regulation of pituitary gonadotropins and prolactin during the menstrual cycle

To determine the influence of ovarian sex steroid hormones on endogenous opioid regulation of pituitary FSH, LH, and PRL secretion, six women were studied during the follicular phase (days 8-9) and luteal phase (days 21-23) of their menstrual cycles. An iv bolus dose of 10 mg of the opiate antagonist naloxone was given, and plasma FSH, LH, and PRL were measured at -30, -15, 0, 15, 30, 45, 60, 90, 120, and 180 min. During the follicular phase, baseline plasma FSH and LH levels were 10.7 +/- 0.9 and 16.7 n+/- 2.0 mIU/ml (mean +/- SEM), respectively; the plasma PRL level was 11.7 +/- 1.2 ng/ml. Naloxone did not significantly alter plasma FSH, LH, or PRL during the follicular phase. Basal levels of LH were significantly lower during the luteal phase than during the follicular phase (P less than 0.01). During the luteal phase, plasma LH increased significantly from a basal level of 10.0 +/- 1.0 to 20.8 +/- 3.0 mIU at 30 min (P less than 0.001) and remained significantly elevated at 90 min. Similarly, plasma PRL increased significantly from a basal level of 11.0 +/- 0.7 to 16.2 +/- 2.7 ng/ml at 30 min (P less than 0.025), but decreased by 90 min to 12.5 +/- 1.5 ng/ml. Plasma FSH did not change after naloxone treatment. Our results suggest that endogenous opiates have a prominent inhibitory effect on pituitary gonadotropin and PRL secretion only during the luteal phase of the menstrual cycle.     

The dissociation of the exaggerated prolactin and thyrotropin responses in seminiferous tubule failure following the administration of a double-pulse of thyrotropin-releasing hormone

PRL and TSH secretion has been evaluated in 11 patients with seminiferous tubule failure and 9 controls. When compared to the controls, the patients had increased basal FSH, TSH and PRL levels. However, LH, E2, T and thyroid hormone levels were similar to the controls. Both groups were given two pulses of TRH (200 micrograms) at 30 min intervals. Following the initial pulse of TRH, the patients demonstrated exaggerated TSH and PRL responses. The administration of a second pulse of TRH led to a further increment of TSH secretion in the patients. There was, however, no PRL response to the second TRH pulse in either patients or controls although mean PRL levels remained significantly greater in the patients.     

Dynamic evaluation of prolactin secretion in essential hypertension: evidence against hypothalamic-pituitary dopaminergic dysfunction

Hyperprolactinemia has previously been noted in patients with essential hypertension and it has been suggested that the increased PRL levels in this condition may reflect reduced central dopaminergic activity. In the present study, PRL secretion was evaluated in 17 patients with essential hypertension and in 9 normal controls as an indirect index of hypothalamic-pituitary dopaminergic activity. PRL levels were measured basally, at night, and after TRH (200 micrograms, iv), metoclopramide (10 mg, orally), and L-dopa (500 mg, orally). Basal PRL levels were similar in both groups [essential hypertension, 301.2 +/- 176.2 microunits/ml; controls, 334.2 +/- 98.8 microunits/ml (mean +/- SD)]. No differences in PRL levels were found after TRH, L-dopa, and metoclopramide or during sleep between the 2 groups. When the patients were classified according to their PRA, no differences were noticed in either basal levels or the patterns of PRL response. It is concluded that PRL secretion is normal in patients with essential hypertension, which could be indirect evidence against reduced hypothalamic-pituitary dopaminergic activity in this disease. However, minor abnormalities not detected by PRL measurements could be involved in the pathogenesis of essential hypertension.     

Does bromocriptine block thyrotropin-releasing hormone-induced prolactin release during pregnancy?

PRL responses to 200 microgram of iv TRH were measured in 16 healthy women with normal early pregnancy before and at the endo of bromocriptine treatment of 5.0--7.5 mg daily for 1--2 weeks. Before the start of bromocriptine, TRH caused a PRL elevation from 19.1 +/- 2.2 to 95.2 +/- 12.6 ng/ml (mean +/- SE) after 20 min, with a mean maximal PRL increment of 71.7 +/- 11.6 ng/ml. Bromocriptine suppressed basal plasma PRL level to 3.6 +/- 0.8 ng/ml (P less than 0.001). TRH then caused a PRL rise to 18.8 +/- 1.8 ng/ml at 20 min, with a mean maximal PRL increment of 15.7 +/- 1.8 ng/ml. The absolute PRL response was significantly smaller (P less than 0.001) during bromocriptine intake than before, whereas the mean percent increments in PRL levels after TRH administration were similar in the presence and absence of bromocriptine. Fifteen of these women were restudied with TRH stimulation 4--6 weeks after legal abortion, and the PRL responses to TRH were normal. When 7 of these women were once again treated with bromocriptine and retested with TRH, no absolute or relative PRL response to TRH emerged. These results release differs between the pregnant and nonpregnant states.     

THE INTERRELATIONSHIPS BETWEEN PROLACTIN AND THYROTROPHIN SECRETION FOLLOWING DOPAMINERGIC BLOCKAGE IN PATIENTS WITH MILD HYPERPROLACTINAEMIA WITHOUT ANY DEMONSTRABLE PITUITARY TUMOUR

PRL, TSH and gonadotrophin responses to the dopaminergic antagonist, metoclopramide, were studied in mildly hyperprolactinaemic patients with normal sella radiology and CT scan. Eleven female patients with basal PRL levels ranging from 23 to 124 ng/ml were challenged with intravenous metoclopramide (10 mg) and on subsequent occasions with TRH (200 micrograms) and LHRH (100 micrograms). On the basis of the PRL secretory pattern following metoclopramide and TRH stimulation, the patients were divided into two groups. Group I comprised six subjects who were PRL non-responsive to TRH and metoclopramide. Group II (five subjects) demonstrated PRL responses to TRH and metoclopramide indistinguishable from female controls. Mean +/- SD basal PRL levels were 68.5 +/- 29.9 ng/ml in Group I and not different in Group II (40.6 +/- 12.0 ng/ml). Basal LH levels were increased in Group II, whereas FSH was increased in Group I. Basal TSH levels were lower in Group I than the controls. Following metoclopramide, Group I patients had an increase in TSH from a basal of 2.4 +/- 0.7 microU/ml to a peak of 5.9 +/- 2.7 microU/ml (P less than 0.005) which occurred at 30 min. TSH values were increased above basal at all time intervals following metoclopramide. In contrast, TSH levels did not change in Group II patients or the controls after metoclopramide administration. Both patient groups had TSH responses to TRH similar to the controls. Following LHRH, the LH increase was greater in Group II and the FSH in Group I. In neither group nor the controls did gonadotrophin levels change after metoclopramide. In Group II females, PRL responsiveness to metoclopramide was associated with TSH non-responsiveness. In Group I females, PRL levels failed to rise, whereas TSH increased. The PRL and TSH profile in Group I females is typical of a prolactinoma. It is concluded that PRL as well as TSH determinations following metoclopramide are useful indices in the assessment of hyperprolactinaemia and may be of value in differentiating the functional state from that of a pituitary tumour.     

Effect of histamine on basal and TRH/LH-RH-stimulated PRL and LH secretion during different phases of the menstrual cycle in normal women

The neurotransmitter histamine (HA) may participate in the regulation of some pituitary hormones. We, therefore, investigated the effect of HA (50 micrograms/kg body weight/h, infusion 0-240 min) on basal and thyrotropin-releasing hormone (TRH) and luteinizing hormone releasing hormone (LH-RH) stimulated prolactin (PRL) and LH secretion in 5 normal women during the early follicular and the luteal phases of the same menstrual cycle. HA had no effect on the basal secretion of the two hormones. However, the PRL response to 200 micrograms TRH during the HA infusion was significantly increased compared to the response to a saline control infusion during the early follicular phase (peak responses were 1,902 +/- 398 vs. 1,228 +/- 230 microIU/ml, p less than 0.025) and during the luteal phase (peak responses were 2,261 +/- 335 vs. 1,647 +/- 245 microIU/ml, p less than 0.05). HA potentiated the LH response to 100 micrograms LH-RH during the early follicular phase (peak responses were 37.1 +/- 4.9 vs. 26.9 +/- 4.5 mIU/ml, p less than 0.05) and during the luteal phase (peak responses were 79.3 +/- 22.5 vs. 50.7 +/- 11.4 mIU/ml, p less than 0.025). We, therefore, found HA to have a potentiating effect on TRH/LH-RH-stimulated PRL and LH secretion in women. The results are similar to our previous findings in men, although the potentiating effects of HA were higher in women.     

MATERNAL SERUM PROLACTIN AND ITS RESPONSE TO TRH IN NORMAL AND COMPLICATED EARLY PREGNANCY

Maternal serum prolactin levels (PRL) were measured by radioimmunoassay in thirty-four women with either normal or complicated early pregnancy. The basal PRL level (mean +/- S.D.) of 33.4 +/- 16.4 ng/ml in normal pregnancy (n = 15) was similar to the level of 32.7 +/- 18.8 ng/ml in threatened abortion (n = 11) and 32.8 +/- 16.9 ng/ml in hyperemesis gravidarum (n = 8). Two patients, one with blighted ovum and the other with subsequent spontaneous abortion, demonstrated PRL levels lower than the range of 20-63 ng/ml in the control group. The PRL response to 200 microgram of synthetic thyrotropin releasing hormone (TRH) administered intravenously was similar throughout the patient groups. The basal level of PRL in the whole series was more closely related to the level of serum oestradiol (r = 0.778, P less than 0.001) than to that of serum progesterone (r = 0.442, P less than 0.05). However the increments of PRL following TRH administration did not correlate with either oestradiol or progesterone.     

The effects of bromocriptine on anovulatory patients with high LH and euprolactinemia

It is well known that an acute administration of Bromocriptine (dopamine agonist) suppresses the serum LH level either in normal women or in women with polycystic ovary syndrome, in whom the serum LH level is elevated. The present study was carried out to examine the effectiveness of Bromocriptine on anovulatory women with a high LH level (serum LH greater than 30 mIU/ml). Bromocriptine was administered for 3 months, 5 mg daily, to 9 anovulatory women with euprolactinemia (serum PRL less than 25 ng/ml). Ovulation was observed by their BBT charts. Before and after the treatment of Bromocriptine, FSH, LH and PRL secreting capacities were tested by LHRH and TRH injection. Also, estrone, estradiol and testosterone levels were measured before and after the Bromocriptine administration. Resting levels of LH, FSH and PRL were 45.4 +/- 11.0 mIU/ml, 11.4 +/- 3.0 mIU/ml, and 14.3 +/- 4.7 ng/ml (M +/- SD), respectively, before the treatment. As a result of the treatment, the LH level was markedly decreased to 27.3 +/- 14.5 (M +/- SD, P less than 0.05), and PRL decreased to 3.76 +/- 4.2 ng/ml (M +/- SD, P less than 0.005). On the other hand, FSH did not show a marked change. The responsiveness of LH to LHRH before the treatment showed a marked increase, which was suppressed by Bromocriptine. However, FSH showed no change. The responsiveness of PRL to TRH was suppressed by Bromocriptine. Serum estrone, estradiol and testosterone levels before the treatment were 115.5 +/- 76.7 pg/ml, 93.7 +/- 61.0 pg/ml and 0.809 +/- 0.209 ng/ml (M +/- SD), respectively, which showed no significant change after the treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of norepinephrine administration upon pituitary hormone secretion in normal men

This study has investigated the effects of 6.2, 12.5, 25, 50 and 100 ng/kg/min/60 min of NE infused to normal men. Blood samples were obtained every 10 min, before, during and after drug administration for 3 consecutive h. Plasma levels on NE, LH, FSH, PRL, and GH were measured in all samples. The administration of 12.5 ng/kg/min over 60 min of NE induced a significant increase (p less than 0.001) in plasma NE levels (n = 5) from a mean (+/- SE) baseline of 239 +/- 14 ng/L to 706 +/- 54 ng/L which peaked and plateaued at 40 min. The calculated area under the curve was 18562 +/- 3537 ng/L/h of NE and significantly higher (p less than 0.001) than during the h before the infusion (2358 +/- 780 ng/L/h). This increase in plasma NE correlated well with the rise in plasma LH which showed a steady increase from baseline of 7.4 +/- 1.3 mIU/ml to a significant (p less than 0.05) peak of 11 +/- 1.9 mIU/ml at the end of the infusion. Furthermore, analysis of the area under the curve revealed a greater (p less than 0.05) LH release during the NE infusion (180 +/- 18 mIU/ml/h) than before the infusion (92 +/- 17 mIU/ml/h). With the exception of the studies utilizing 12.5 ng/kg/min/60 min, all other doses of NE resulted in no significant and/or consistent changes in plasma concentration of LH, FSH, GH and PRL. Thus, the direct participation of NE in the control of LH secretion in humans seems to occur in a very narrow window.     

Effects of CNS dopamine augmentation on stimulated prolactin secretion.

The site, hypothalamic and/or pituitary, for dopaminergic inhibition of prolactin (PRL) secretion is unknown. Consequently, the effect of central dopamine (DA) augmentation on stimulated PRL release was determined in 5 healthy men. Regular insulin (o.1 U/kg i.v.), a potent central stimulus for PRL secretion, and TRH, a direct hypophyseal stimulus, were given alone or one hour after the third and fourth doses, respectively, of L-dopa plus the peripheral decarboxylase inhibitor, carbidopa (Sinemet 20/200 or 25/250 every 6 hours). PRL increased from 26.6 +/- 5.8 to 48.8 +/- 5.2 ng/ml (p less than 0.01) 40 minutes after insulin administration. In contrast, during Sinemet therapy the hypoglycemia-mediated PRL release did not occur, and the PRL levels were significantly lower than after insulin alone from 40 through 180 minutes. Following TRH, neither the maximal PRL rise (69.3 +/- 3.2, TRH alone vs 48.7 +/- 19.8 ng/ml, TRH + Sinemet) nor the maximal increment (37.5 +/- 5.5 vs 29.9 +/- 20.3 ng/ml) was significantly affected by Sinemet. It is concluded that central DA augmentation abolishes central but not peripherally mediated PRL release.     

Dopamine affects basal and augmented pituitary hormone secretion.

Although the role of the neurotransmitter, dopamine (DA), in the regulation of PRL has been well documented, controversy exists regarding its participation in the regulation of the other pituitary hormones. Consequently, we infused DA into six healthy male subjects (ages 19-32) and studied its effects on both basal pituitary hormone levels and augmented hormonal release induced by insulin hypoglycemia (ITT), TRH, and gonadotropin-releasing hormone (GnRH). DA alone produced a modest though significant increase in GH concentration from 2.2 +/- 0.5 to 11.9 +/- 3.7 ng/ml (P less than 0.05) by 60 min, but the peak incremental GH response to ITT was significantly inhibited by DA (43.5 +/- 5.0 vs. 16.3 +/- 3.3 ng/ml; P less than 0.01). PRL concentrations fell during the DA infusion (20.4 +/- 3.0 to 10.6 +/- 1.5 ng/ml; P less than 0.02) at 235 min, and the PRL responses to both ITT and TRH were completely abolished. Although the basal LH and FSH concentrations were unaffected by DA, the incremental LH response to GnRH was inhibited (45.5 +/- 10.6 to 24.4 +/- 5.4 mIU/ml; P less than 0.05), while the FSH response was unchanged. DA significantly reduced the basal TSH concentration from 3.9 +/- 0.2 to 2.5 +/- 0.2 micro U/ml (P less than 0.01) at 230 min and blunted the peak incremental TSH response to TRH (6.0 +/- 1.5 vs. 2.9 +/- 0.9 microU/ml; P less than 0.01). DA had no effect on basal cortisol levels, the cortisol response to ITT, basal plasma glucose, or the degree of hypoglycemia after ITT. Our data provide new evidence that DA has an inhibitory as well as a stimulatory role in the regulation of GH secretion in normal humans. It inhibits centrally as well as peripherally mediated PRL secretion and blunts the LH response to GnRH. In addition, DA lowers both basal and TRH-mediated TSH release, confirming the reports of other investigators.     

The GH-releasing hormone (GHRH) test in acromegaly before and after adenomectomy

The GHRH test may represent a new tool in the study of GH dynamics in acromegaly. GH responsiveness to GHRH 1-40 (50 micrograms iv) has been studied in 21 acromegalic patients. Nineteen out of 21 had active disease. Five patients were also studied 1-12 months after neurosurgery. Two apparently cured acromegalics were studied 1-2 yr after surgery. GH secretion has been evaluated in all patients by means of TRH, bromocriptine and insulin hypoglycemia tests, too. GH response to GHRH has also been performed in 14 normal subjects. In acromegaly, GH responses after GHRH (p less than 0.01 vs placebo) were variable. The GH peak ranged from 8 to 445 ng/ml in patients with active disease. Maximum GH increase after GHRH (calculated as peak/basal value ratio) was significantly reduced in acromegaly (2.9 +/- 0.5 ng/ml; mean +/- SE) in comparison to controls (34.1 +/- 10.9 ng/ml; p less than 0.01). No significant differences in GH pattern after GHRH were found between untreated and previously treated patients with active disease. A significant correlation was found between GH basal levels and GH incremental area (p less than 0.05) and between GH basal and peak levels (p less than 0.01) after GHRH. A significant increase in PRL secretion was observed in acromegalic patients after GHRH (p less than 0.01 vs placebo). No discernable variation was found in the other pituitary hormones pattern after the peptide administration. A positive correlation was observed between GH increase after GHRH and insulin hypoglycemia (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)