Growth hormone and prolactin response to ghrelin during the normal menstrual cycle

Objective  It has been suggested that exogenous oestradiol augments ghrelin-induced growth hormone (GH) secretion in postmenopausal women. Whether endogenous oestrogens exert a similar effect during the normal menstrual cycle is not known. The aim of this study was to test the hypothesis that physiological changes in ovarian steroids during the normal menstrual cycle modulate GH and prolactin (PRL) response to ghrelin.
Design  Healthy women were studied in three phases of the normal menstrual cycle.
Patients  Ten healthy normally cycling women.
Measurements  A single dose of ghrelin (1 µg/kg) was administered intravenously in the early and late follicular phases and in the mid-luteal phase of the cycle. Saline was injected in the preceding cycle. Blood samples were taken before ghrelin or saline injection (time 0) and also at –15, 15, 30, 45, 60, 75, 90 and 120 min. The GH and PRL responses were assessed.
Results  Serum oestradiol and progesterone concentrations showed the variations of a normal menstrual cycle. After ghrelin administration, in the three phases of the cycle, plasma ghrelin and serum GH and PRL levels increased rapidly, peaking at 30 min and declining gradually thereafter ( P <  0·001). There were no significant differences in the hormone levels between the three phases at all time points. No changes in GH and PRL levels were seen after saline injection.
Conclusions  These results demonstrate that GH and PRL responses to ghrelin do not change across the menstrual cycle. It is suggested that the action of ghrelin on the pituitary somatotrophs is modulated differentially by endogenous and exogenous ovarian steroids.     

Changes of pituitary thyrotropin releasing hormone (TRH) receptor level and prolactin response to TRH during the rat estrous cycle.

The plasma PRL and TSH responses to TRH injected iv at different stages of the estrous cycle in normal rats under Surital anesthesia were maximal during the afternoon of proestrus and morning of estrus and lowest on diestrus I. As calculated from the areas under the plasma response curves, a 10-fold difference was found between the maximal and minimal PRL responses while a 2-fold difference was measured for TSH. The plasma PRL and TSH responses to TRH showed a correlation with the binding of [3H]TRH to anterior pituitary gland, a 3-fold difference being observed between the minimal binding measured on the morning of diestrus II and the maximal value found on the evening of proestrus. Contrary to findings with LHRH and LH, repeated injections of a small dose (10 ng) of TRH in the afternoon of proestrus abolished PRL and TSH responses to subsequent injection of the neurohormone.     

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.     

Pulsatile growth hormone release in normal women during the menstrual cycle

OBJECTIVE: We sought to characterize pulsatile growth hormone (GH) release in normal women during the menstrual cycle and to document possible relationships between such characteristics and concentrations of 17 beta-oestradiol and progesterone. SUBJECTS: Fifteen women with ostensibly normal menstrual function were studied during the early follicular phase, 15 during the late follicular phase and 15 during the mid-luteal phase of the menstrual cycle. DESIGN: The phase of the menstrual cycle having been documented, blood samples were obtained from each woman every 10 minutes for 24 hours. MEASUREMENTS: Serum GH was measured in each sample by immunoradiometric assay. Pulsatile GH release was appraised utilizing the objective, statistically-based pulse detection algorithm Cluster. RESULTS: The mean (+/- SEM) integrated serum GH concentration (mU/l min) in late follicular phase women (5335 +/- 848) was higher than that observed in early follicular phase women (3156 +/- 322; P = 0.032). The integrated GH concentration calculated for mid-luteal phase women (3853 +/- 788) was intermediate between but not statistically different from that observed in early follicular (P = 0.48) and late follicular (P = 0.14) phase women. No differences in GH pulse frequency (pulses/24 hours) were found among early follicular (8.27 +/- 0.55), late follicular (7.93 +/- 0.91) or mid-luteal (8.47 +/- 0.66) phase women. Mean maximal GH pulse amplitude (mU/l) was higher in late follicular phase (8.93 +/- 1.00) than early follicular phase (5.74 +/- 0.67; P = 0.008) and mid-luteal phase (5.76 +/- 0.74; P = 0.008) women. Similarly, incremental GH pulse amplitude (mU/l) was higher in late follicular phase (7.33 +/- 0.83) than early follicular phase (4.68 +/- 0.58; P = 0.005) and mid-luteal phase (4.36 +/- 0.39; P = 0.002) women. No differences in mean pulse widths or in the interpeak valley mean GH concentrations were found among the groups. Multiple regression of each pulse parameter against serum concentrations of testosterone, 17 beta-oestradiol and progesterone revealed a significant (P = 0.045) positive correlation between maximum GH pulse amplitude and oestradiol and a significant (P = 0.04) negative correlation between maximal GH pulse amplitude and progesterone (r = 0.41). CONCLUSION: These results suggest that late follicular phase concentrations of oestradiol may enhance circulating GH via an amplitude-modulated rather than a frequency-modulated effect on the endogenous GH pulse. Progesterone may blunt this oestrogen-associated effect, thus resulting in the observed mid-luteal phase concentrations of GH. Whether these gonadal hormones act primarily at the hypothalamus and/or anterior pituitary gland remains to be clarified, but the present observations indicate that pulsatile GH release throughout the normal menstrual cycle is significantly amplitude regulated.     

Changes in plasma LRH during the normal menstrual cycle in women

The plasma concentration of immunoreactive LRH, LS, FSH, oestradiol and progesterone were measured dialy by a sensitive double antibody radioimmunoassay during 12 cycles of 8 normal cyclic women. The mean (+/- SE) immunoreactive LRH levels in the follicular and luteal phase except the immunoreactive LRH peaks during normal cycles were 4.18 +/- 0.38 pg/ml and 4.50 +/- 0.45 mg/ml, respectively. The immunoreactive LRH peaks were observed in 11 of 12 cycles, appearing on day -4 to -1 from the LH surge in 9 cycles and on day +1 and +2 in 2 cycles. The mean value of immunoreactice LRH peaks was 42.0 +/- 11.4 pg/ml with range of 12 to 154 pg/ml. The immunoreactive LRH peak lasted for one day in 10 cycles and for 4 days in one cycle. The immunoreactive LRH peaks in different cycles of the same women did not occur on the same day relative to the LH peak. The plasma immunoreactive LRH levels measured every 10 min for 40 min periods every day in normal cyclic women during the ovulatory phase showed slight, but not significant fluctuations. Plasma oestradiol levels began to increase on day -6, reaching a peak on day -1, and were followed by peaks of LH and FSH. These data indicate that increase in serum oestradiol was followed by release of LRH from the hypothalamus and pre-ovulatory discharge of gonadotrophins from the pituitary.     

The relationship of changes in serum estradiol and progesterone during the menstrual cycle to the thyrotropin and prolactin responses to thyrotropin-releasing hormone.

The responses of serum TSH and PRL to TRH (500 microgram) were studied in normal young women in the early follicular, periovulatory, and midluteal phases of the menstrual cycle in order to examine the relationship of these responses to the levels of estradiol relationship of these responses to the levels of estradiol (E2) and progesterone. Each woman was studied twice in each phase in order to assess intraindividual variability. There was no significant difference in either the TSH or PRL responses among the phases of the menstrual cycle nor was either response affected by the periovulatory rise in E2 or by the luteal rise in both E2 and progesterone. Thus, the interpretation of the TSH and PRL responses to TRH in normal women is not affected by the menstrual cycle although both responses are greater in women that in men. Both the peak TSH and peak PRL after TRH were highly correlated with the basal levels of TSH (r = 0.85; P less than 0.01) and PRL (r = 0.67; P less than 0.01), respectively, indicating that the TSH and PRL responses to TRH in women are directly proportionate to the basal levels of the respective hormones, as previously shown for the TSH response in men. The mean intraindividual variability (coefficient of variation) of the TSH response to TRH was 18%, but ranged as high as 56%, while that of the PRL response was 16% and ranged up to 31%; variability was not affected by the phase of the menstrual cycle. The normal range of the peak TSH after TRH in women is 7-33 microU/ml (mean +/- 2 SD); however, because of the variability, a normal woman may sometimes have a peak TSH after TRH as low as 4 microU/ml. Repeating the test will result in a normal value if the woman is truly normal. Similarly, the normal peak PRL after TRH in women is 22-111 ng/ml (mean +/- 2 SD); usually, however, the lower limit is 30 ng/ml with lower values due to intraindividual variation. The data suggest that the higher average level of E2 in women compared to women, but that the cyclic changes in serum E2 or progesterone in women have little or no additional effect.     

Statistical evaluation of coincident prolactin and luteinizing hormone pulses during the normal menstrual cycle

The purpose of this work was 2-fold. First, we sought to develop statistical criteria by which it could be established that the coincident occurrence of pulses of two different hormones exceeds that which would occur by chance alone, thereby suggesting that secretion of the two hormones is either coupled or controlled from a single source generator. Using computer simulations of uncoupled pulse generators operating at different frequencies, we were able to derive the appropriate statistical criteria and to apply them to achieve our second objective, to determine whether the occasional coincidence of plasma LH and serum PRL pulses that occurs throughout the menstrual cycle in normal women exceeds that which would happen by chance. The results of the computer simulations indicated that pulses emanating from two completely independent oscillators will occur coincidently at a predictable rate, despite the fact that the generator sources are not coupled; moreover, the rate of coincidence is increased when the pulse frequency of one of the source generators is increased. Using this knowledge and the statistical criteria we derived, we analyzed the coincidence of LH and PRL pulses in five normal women during their early follicular, late follicular, and midluteal phases and in another five women during their late luteal phase. We found that the number of PRL pulses that occurred coincidently with LH pulses consistently exceeded that which would be predicted if the two pulse generators were operating completely independently of one another; however, only during the late follicular and late luteal phases was the coincidence level between LH and PRL pulses sufficiently high in a sufficient number of women to conclude that there was coupling between the pulse sources. These studies suggest, first, that stringent and rigorous statistical criteria must be applied to the analysis of spontaneously coincident secretory phenomena before it can be deduced that two pulse generators are indeed coupled, and second, that the pulse generators governing the secretion of PRL and LH are probably coupled, at least during certain phases of the menstrual cycle.     

Insulin receptors during the menstrual cycle in normal women.

Specific binding of 125I-insulin to circulating monocytes from eight normal menstruating women, four postmenopausal women and four men were studied four times during a 28-day period (one sample at 7-day intervals). Data indicate the presence of a higher specific cell binding fraction in the follicular phase compared to the luteal phase due to changes in insulin receptor concentration. No changes were observed in men or postmenopausal women during the same period of time suggesting that sex hormones should be included among the factors influencing insulin receptors.     

The pattern of growth hormone secretion during the menstrual cycle in normal and depressed women

OBJECTIVE: Major depression is associated to altered hypothalamic-pituitary function. Stress is linked to elevated cortisol as well as menstrual cycle disturbance; however, there is no known relationship between depression and menstrual cycle disruption. The aim of this study was to investigate changes of growth hormone (GH) secretion during the menstrual cycle in normal and depressed women. DESIGN: Case-control study. PATIENTS AND METHODS: Nineteen women affected with depression and 24 normal controls were included. The two groups had comparable body mass index (BMI), and age (29.4 +/- 9.8 vs. 28.6 +/- 9.7 years). Nine depressed and 10 controls were studied in the follicular phase, while 10 depressed and 14 controls were studied in the luteal phase of the cycle. GH was sampled every 10 min for 24 h, and the data were analysed by the cluster pulse detection method. RESULTS: There was no difference in 24-h mean GH concentrations between depressed and control subjects (P = 0.93), even after accounting for menstrual cycle phase (P = 0.38). GH pulse frequency was higher during the follicular phase of the cycle (P = 0.032), and nocturnal GH was higher in the follicular phase of the cycle (P = 0.05, and after adjusting for 24-h GH, P = 0.0138) regardless of whether the subjects were depressed or healthy. CONCLUSIONS: In studies of GH secretion in women with or without depression, it is necessary to control for the phase of menstrual cycle.     

Cysteamine decreases prolactin responsiveness to thyrotropin-releasing hormone in normal men

Cysteamine depletes pituitary and plasma prolactin in rats. It acts through a nondopaminergic mechanism to alter both immunoactive and bioactive prolactin. The effect of cysteamine on prolactin secretion is reported in normal men. Six normal subjects received a control thyrotropin-releasing hormone (TRH) test at 0900 using 200 micrograms TRH intravenously; serum prolactin and TSH were measured at -10, 0, 10, 20, 30, 60, and 90 min after administration of TRH. Serum calcium and parathyroid hormones levels were measured at -10 min. Seven or more days later, they received cysteamine hydrochloride 15 mg/kg body weight orally every 6 hours for 5 doses. One hour after the last dose, the TRH test was repeated. Peak serum prolactin levels following TRH, prolactin levels at the 10-min time point, and total area from 0 to 30 min under the prolactin secretory curve were significantly decreased by cysteamine administration. TSH levels were unchanged. Serum calcium levels were significantly decreased by cysteamine administration, but parathyroid hormone levels were unchanged. It was concluded that cysteamine reduced TRH-stimulated prolactin secretion. Cysteamine also decreases serum calcium levels and suppresses the anticipated rise in serum parathyroid hormone levels. These effects on serum calcium and parathyroid hormone are similar to those previously shown for WR2721, another sulfhydryl compound. Cysteamine should be further considered as an alternative drug in the treatment of hyperprolactinemia and as a therapeutic agent for hypercalcemia.     

Inappropriate growth-hormone (GH) response to thyrotropin-releasing hormone (TRH) occurs infrequently in well-regulated diabetes mellitus

Summary We randomly administered thyrotropin-releasing hormone (200 μg, as an i.v. bolus) or control saline (in isovolumic amount) to 30 male diabetic subjects (23 IDDM, 7 NIDDM) in fair metabolic control (HbA₁ 9.7±0.3%, ) and to 12 healthy male controls on two different mornings. While GH in the basal state was similar in IDDM, NIDDM and normal subjects, TRH administration evoked a significant GH release only in a single IDDM individual. The only GH-responder to TRH was a newly-diagnosed (two weeks) IDDM patient, still with a high glycated hemoglobin level (HbA₁ 11.1%), despite normal plasma glucose levels. Saline infusion did not affect GH concentrations either in normals or in diabetics. Exaggerated GH responses to TRH are uncommon in diabetic patients in good metabolic conditions. This study was performed in the context of theRicerca Finalizzata della Regione Toscana, and supported in part by a grant (87.00381.56) from the Italian National Research Council (CNR) and by a grant from theMinistero della Pubblica Istruzione (Ricerca Scientifica 1987).     

Hypothalamic hypothyroidism due to isolated thyrotropin-releasing hormone (TRH) deficiency

Cold intolerance and secondary amenorrhea developed in a patient who had meningoencephalitis 4 yr prior to study. A clinical diagnosis of hypothalamic hypothyroidism was made on the basis of low serum thyroxine and triiodothyronine levels, and low plasma thyrotropin concentrations, which were responsive to thyrotropin-releasing hormone (TRH). The secretion of the remaining pituitary hormones (growth hormone, prolactin, adrenocorticotropin and gonadotropins) was intact. Not only was thyroid function normalized by oral administration of TRH, but also menses resumed after adequate replacement therapy with thyroid hormone. These results imply that hypothyroidism in this patient was due to isolated dysfunction of hypothalamic TRH release.     

Serum thyrotrophin, prolactin and growth hormone, response to TRH during oestrogen treatment.

The serum levels of thyrotrophin (TSH), prolactin (PRL) and growth hormone (GH) and the response of these hormones to 500 mug thyrotrophin-releasing hormone (TRH) iv were studied in menstruating women, in post-menopausal women before and after 2 mg oestradiol valerate for 5 consecutive days, and in men on long term oestrogen treatment. Oestrogen treatment had no effect on basal serum TSH levels, which were within the normal range in all groups. The TSH response to TRH was not different in menstruating and post-menopausal women and was not changed in the latter group after oestrogen treatment. In men treated chronically with oestrogens, the TSH response to TRH was similar to that found in normal male subjects.     

Increased thyroid-stimulating hormone response to thyrotropin-releasing hormone in hyperprolactinemic women

The TSH response to TRH and basal thyroid function were studied in 21 unselected women with hyperprolactinemia. The mean serum free T4 (FT4) concentration was significantly lower in hyperprolactinemic women than in normal women. The mean basal TSH concentrations were similar, but the incremental TSH response to TRH was significantly greater in hyperprolactinemic women than in normal women. Increased dopaminergic inhibition of TSH release has been reported in hyperprolactinemic women. The low serum FT4 concentration in hyperprolactinemic women may be the result of increased dopaminergic inhibition of TSH release, and the increased pituitary TSH reserve may reflect increased TSH storage due to dopaminergic inhibition of basal TSH release. Alternatively, though less likely, the low serum FT4 concentration may be the result of direct action of PRL on the thyroid, and the low FT4 concentration may, in turn, lead to the increased pituitary TSH reserve.     

Changes of prolactin response to dopamine during the rat estrous cycle

The effects of dopamine (DA) on prolactin (PRL) secretion in anterior pituitary tissue from rats selected during various stages of the estrous cycle were analyzed under in vitro conditions. The results were examined in relation to plasma PRL, estradiol and progesterone levels. During the estrous cycle there was a marked variation in the responsiveness of the lactotrophs to the inhibitory action of DA. Rapid changes occurred during proestrus: pituitary lactotrophs were not sensitive to the inhibitory action of 10 nM DA at 15.00 and 17.00 h and were less sensitive to 1 microM DA compared to 09.00 h (p less than 0.01), 12.00 h (p less than 0.05) and 19.00 h (p less than 0.05). This lowest PRL response to DA was associated with the preovulatory PRL surge. The recovery of a higher PRL response at 19.00 h coincided with the decrease of plasma PRL levels. During the remainder of the cycle, plasma PRL levels remained low in estrus, diestrus 1 and diestrus 2. Lactotrophs were sensitive to 1 microM and 10 nM DA during estrus and diestrus 2 but a significant lower PRL response to 1 microM DA (p less than 0.05) and no PRL response to 10 nM DA was observed in diestrus 1. These data show that alterations in the sensitivity of the lactotrophs' responsiveness to DA occur in the anterior pituitary gland during the rat estrous cycle and can lead to the removal of DA inhibition in the presence of physiological DA concentrations. This phenomenon is consistent with the fact that DA could be involved in the preovulatory PRL surge during the estrous cycle.     

Effect of thyroid hormones on the prolactin response to thyrotropin-releasing hormone in normal persons and euthyroid goitrous patients.

In nine euthyroid goitrous patients, increasing doses of T4 caused a significant decrease in the PRL response to TRH; the PRL response fell significantly at a dose of T4 of 100 micrograms/day for 1 month (P less than 0.02) and fell further with increasing doses so that at 300 micrograms T4/day, the PRL response was 40% of that in the untreated state. T4 treatment also blunted the PRL response to chlorpromazine (P less than 0.05) in a separate group of euthyroid goitrous patients. In contrast, there was only a small drop of the PRL response to TRH in normal subjects treated with T4 (n = 9) and none at all with T3 (n = 7). These data, together with previously published reports, suggest that thyroid hormone may affect PRL secretion in the presence of thyroid disease (hyperthyroidism, hypothyroidism, or euthyroid goiter), but that physiological amounts of thyroid hormone have little or no modulating effect on PRL secretion in normal persons.