Regulation of adenohypophyseal pyroglutamyl aminopeptidase II activity by thyrotropin-releasing hormone and phorbol esters

Thyrotropin-releasing hormone (TRH) is inactivated by a narrow specificity ectopeptidase, pyroglutamyl aminopeptidase II (PPII), in the proximity of target cells. In adenohypophysis, PPII is present on lactotrophs. Its activity is regulated by thyroid hormones and 17β-estradiol. Studies with female rat adenohypophyseal cell cultures treated with 3,3′,5′-triiodo-l-thyronine (T₃) showed that hypothalamic/paracrine factors, including TRH, can also regulate PPII activity. Some of the transduction pathways involve protein kinase C (PKC) and cyclic adenosine monophosphate (cAMP). The purpose of this study was to determine whether T₃ levels or gender of animals used to propagate the culture determine the effects of TRH or PKC. PPII activity was lower in cultures from male rats. In cultures from both sexes, T₃ induced the activity. The percentages of decrease due to TRH or PKC were independent of T₃ or gender; the percentage of decrease due to cAMP may also be independent of gender. These results suggest that T₃ and hypothalamic/paracrine factors may independently control PPII activity in adenohypophysis, in either male or female animals.     

Thyroxine-induced expression of pyroglutamyl peptidase II and inhibition of TSH release precedes suppression of TRH mRNA and requires type 2 deiodinase

Suppression of TSH release from the hypothyroid thyrotrophs is one of the most rapid effects of 3,3',5'-triiodothyronine (T(3)) or thyroxine (T(4)). It is initiated within an hour, precedes the decrease in TSHβ mRNA inhibition and is blocked by inhibitors of mRNA or protein synthesis. TSH elevation in primary hypothyroidism requires both the loss of feedback inhibition by thyroid hormone in the thyrotrophs and the positive effects of TRH. Another event in this feedback regulation may be the thyroid hormone-mediated induction of the TRH-inactivating pyroglutamyl peptidase II (PPII) in the hypothalamic tanycytes. This study compared the chronology of the acute effects of T(3) or T(4) on TSH suppression, TRH mRNA in the hypothalamic paraventricular nucleus (PVN), and the induction of tanycyte PPII. In wild-type mice, T(3) or T(4) caused a 50% decrease in serum TSH in hypothyroid mice by 5 h. There was no change in TRH mRNA in PVN over this interval, but there was a significant increase in PPII mRNA in the tanycytes. In mice with genetic inactivation of the type 2 iodothyronine deiodinase, T(3) decreased serum TSH and increased PPII mRNA levels, while T(4)-treatment was ineffective. We conclude that the rapid suppression of TSH in the hypothyroid mouse by T(3) occurs prior to a decrease in TRH mRNA though TRH inactivation may be occurring in the median eminence through the rapid induction of tanycyte PPII. The effect of T(4), but not T(3), requires the type 2 iodothyronine deiodinase.     

Some events of thyrotropin-releasing hormone metabolism are regulated in lactating and cycling rats.

Levels of thyrotropin-releasing hormone (TRH), TRH mRNA and pyroglutamyl peptidase II were analyzed in the hypothalamus-adenohypophyseal axis during lactation and estrous cycle. Mediobasal hypothalamic levels of TRH dropped 41% (p less than 0.01) from pregnancy levels (taken as 100%) on the first day of lactation, recovering until day 15 to the values observed at pregnancy. A sharp decrease was also observed during weaning (36%, p less than 0.01 compared to last day of lactation). TRH levels in the neurohypophysis increased during lactation and dropped at weaning. Highest TRH mRNA levels in the paraventricular nucleus were found at the end of pregnancy and beginning of lactation; they decreased 37% (p less than 0.05) at day 5 of lactation and stayed constant thereafter. Pyroglutamyl peptidase II adenohypophyseal activity was not modified during lactation but changed during estrous cycle. Relative to estrous values, activity diminished 58% (p less than 0.05) at 10.00 h (57% at 14.00 h) during diestrus 2 and 27% at 10.00 h (37% at 14.00 h) during proestrus. Hypothalamic TRH mRNA levels fluctuated in an opposite manner to adenohypophyseal pyroglutamyl peptidase II during the estrous cycle with a peak at diestrus 2: 183% of the estrous value (p less than 0.05). These data point to a regulation of TRH metabolism in conditions where prolactin (PRL) secretion fluctuates. They also suggest a sharp release of TRH between the end of pregnancy and the first day of lactation and that translational efficiency or post-translational processing of TRH precursor in the paraventricular neurons (projecting to the median eminence) increases during lactation and drops at weaning, concomitantly with PRL secretion.     

Thyroid-hypophyso-hypothalamic axis of the genetically hypoprolactinemic rats (IPL nude rats)

In order to evaluate thyrotropin function in the genetically hypoprolactinemic rat, (IPL nude), we measured by radioimmunoassay TRH hypothalamic content, pituitary TSH content and serum TSH, T3, T4, both in IPL nude and control rats at various times over the 24-hour period. Compared to normal rats, the hypothalamic TRH content in the IPL nude rat showed similar variations during the day, whereas a slight increase was observed during the night characterized by a significant difference at 20.00 h. Pituitary weight and TSH content were doubled in IPL nude rats; however, when expressed as micrograms TSH/micrograms protein or DNA, a significant increase was found only at 17.00 and 20.00 h. Serum TSH and total serum T3, T4 depicted similar variations although they were minute but nonetheless significant modifications, i.e. an increase of TSH at 17.00 and 23.00 h and a decrease of T4 at 11.00 h. However, only FT4 concentrations (and not-FT3) were slightly but significantly decreased in IPL rats over the experimental times. In conclusion, the slight increase in hypothalamic TRH and pituitary TSH contents and the absence of main associated variations of serum TSH, T3 and T4 do not lend support to the hypothesis that TRH could be the cause of the hypoprolactinemia of these rats. On the contrary, the observed thyrotropin axis variations might be rather interpreted as the consequence of it.     

Influences of hypothyroidism on TRH concentrations and preproTRH mRNA levels in rat hypothalamus: a simple and reliable method to detect preproTRH mRNA level.

To gain further insight into the regulation of hypothalamic TRH by thyroid hormones, we measured TRH concentration in specific hypothalamic nuclei and preproTRH mRNA levels in the anterior hypothalamus. Adult male rats were decapitated 1, 7, 14 days after thyroidectomy. Micropunches by the method of Palkovitz from seven hypothalamic nuclei and median eminence were used for measurement of TRH by radioimmunoassay. As compared with normal levels, TRH concentration significantly decreased in the median eminence and five hypothalamic nuclei including paraventricular nucleus (PVN), posterior nucleus, anterior nucleus, arcuate nucleus, and ventromedial nucleus pars lateralis, by 7 days after thyroidectomy. No significant changes were observed in dorsomedial nucleus or ventromedial nucleus pars medialis until 14 days after thyroidectomy. A rapid and simple method to detect specific mRNA for preproTRH was developed using the polymerase chain reaction and a single anterior hypothalamic section. PreproTRH mRNA levels in the anterior hypothalamus increased approximately twice 7 days after thyroidectomy. These data indicate that thyroidectomy caused a marked increase in preproTRH mRNA levels of the anterior hypothalamus, while it significantly reduced TRH concentrations not only in PVN and median eminence but also in other specific hypothalamic nuclei, suggesting that these nuclei might be involved in the thyrotropin regulation in the hypothalamus.     

Sexual differentiation of prolactin responsiveness to thyrotropin releasing hormone (TRH) in the rat. Effects of postnatal testosterone on adenohypophyseal TRH receptor ontogenesis in male rats

The influence of postnatal testosterone on thyrotropin releasing hormone (TRH)-induced prolactin (PRL) response was tested in male rats. Under urethane anesthesia following estradiol pretreatment, neonatally castrated males showed a female-like plasma PRL response 4-fold greater than in adult-castrated males. Substitution of testosterone reversed the NC effect. However, postnatal age-dependent difference was observed in the effect of testosterone. Testosterone produced a marked inhibition on PRL response when given at 2 or 4 weeks of life but not at earlier days. Determinations of adenohypophyseal PRL concentration and TRH receptor density revealed that testosterone inhibition occurred via its detrimental influence not on PRL concentration but on TRH receptor density. These results indicate that the sex-related difference in the rat PRL response to TRH ensues at least partially through inhibition by postnatal testosterone on the adenohypophyseal TRH receptor ontogenesis in male rats, and that there might be a functional dissociation in testosterone-dependent temporal development between two hypothalamic centers which independently regulate cyclic secretability and secretory reserve of PRL.     

Anterior pituitary type II thyroxine 5'-deiodinase activity is not affected by lesions of the hypothalamic paraventricular nucleus which profoundly depress pituitary thyrotropin secretion

Bilateral destruction of the hypothalamic paraventricular nuclei (PVN) produced a profound depression of plasma TSH and the median eminence TRH concentration in hypothyroid rats. Anterior pituitary type II iodothyronine 5'-deiodinase (5'-D) activity was consistently lower but not significantly different in sham- and PVN-lesioned rats. Treatment with suboptimal replacement doses of 0.15 and 0.75 micrograms T4/100 g BW.day produced a graded depression of plasma TSH in the PVN (P less than 0.02), but not in the sham (P greater than 0.8) groups. Adenohypophyseal 5'-D was depressed in both sham and PVN groups by the highest T4 dose. Plasma T4 was much lower in PVN than in sham rats given comparable doses of T4 (P less than 0.001), but plasma T3 was not significantly different. This suggests that an increase in peripheral T4 metabolism was produced by PVN lesions. Our data indicate that changes in adenohypophyseal 5'-D activity are not responsible for the decrease in plasma TSH in PVN-lesioned rats and that neither the PVN nor endogenous TRH plays a significant role in the regulation of anterior pituitary 5'-D activity.     

Ontogeny of nyctohemeral variations of thyrotropin-releasing hormone in rat hypothalamus

The ontogeny of nyctohemeral variations of hypothalamic TRH content was determined in male rats from 7-45 days after birth, exposed to a daily 12-h light, 12-h dark cycle (0600-1800 h light; 1800-0600 h dark) or maintained in complete darkness until 45 days. TRH was extracted from whole hypothalami with 90% methanol and assayed by specific RIA. Hypothalamic TRH extracted from rats at different ages showed immunological, chromatographic, and biological properties identical to those of synthetic TRH. No significant variations in hypothalamic TRH content during the day were observed in 7-, 10-, and 17-day-old rats; a significant change, with a maximal value at 1800 h, was observed in 23-day-old rats, while an adult pattern with a maximal value at 1200 h and a minimal value at 2400 h was found in rats of 31 days of age and became more evident in 45-day-old rats. In animals maintained in complete darkness for 45 days after birth, no significant changes in hypothalamic TRH content at 1200 and 2400 h were observed. These findings indicate that environmental cyclic light-dark exposure is required for the development of diurnal changes in hypothalamic TRH content. Furthermore, any study involving hypothalamic TRH determination should take into account the age of animals and the diurnal variations of TRH.     

Hypothalamic secretion of thyrotropin releasing hormone declines in aging rats

Young and aged male rats were used in experiments to investigate a possible decline in hypothalamic secretion of thyrotropin releasing hormone (TRH) to the anterior pituitary of aging mammals. We observed a 66% decrease in basal TRH release by incubated rat hypothalami with aging. Thyroid hormone-responsive hepatic alpha-glycerophosphate dehydrogenase (GPD) and malic enzyme (ME) levels in aged rats did not differ from 5-month-old controls in spite of a significant fall in serum thyroxine (T4) levels with aging. Other results suggest that these particular indicators of thyroidal status should not change in the aging rat because serum T3 is maintained in the normal range. Serum thyrotropin (TSH) levels, which normally rise when serum T4 levels decline, did not change with aging. These data suggest that gradual loss of the essential TRH stimulation of TSH release with aging may be compensated for by a decline in T4 inhibition of TSH release at the pituitary.     

Discordant effects of thyrotropin (TSH)-releasing hormone on pre- and posttranslational regulation of TSH biosynthesis in rat pituitary

To investigate whether TRH regulates TSH production through a pre- or posttranslational mechanism, we determined the pituitary levels of mRNAs for alpha-subunit and TSH beta in male Sprague-Dawley rats given TRH in the presence or absence of thyroid hormones, with or without hypothalamic influence. In normal rats, serum TSH increased 6-fold after a single sc injection of TRH (7 micrograms/kg BW), but the levels of mRNA for both TSH subunits did not differ from the control values. Infusion of TRH, achieved by osmotic minipumps that were implanted sc, increased serum TSH for 3 days. Conversely, the pituitary content of TSH dropped to and remained 35% of that in the controls. In these normal rats, throughout the TRH infusion, the pituitary levels of mRNA for the TSH subunits did not differ from those in the controls. Thyroidectomy increased, by 27 and 75 times, the normal levels of mRNAs for alpha and TSH beta, respectively. TRH, given either as a single injection or a 3-day infusion, did not further elevate these levels. We then studied thyroidectomized animals whose pituitaries were transplanted under their renal capsules. These pituitaries responded to TRH infusion by releasing TSH. T4 injection inhibited this response significantly, but not completely. In spite of this evidence of normal responsiveness to TRH, infusion of TRH for a week did not increase the level of mRNAs for either TSH subunit in transplanted pituitaries. We conclude that in the presence or absence of thyroid hormones, with or without concurrent hypothalamic influence, TRH did not affect rat pituitary level of mRNA for either TSH subunit despite persistent high levels of serum TSH. Therefore, TRH does not regulate TSH production through a pretranslational mechanism. Although a translational regulation cannot be completely excluded, the present data, in conjunction with previous findings, support the hypothesis that TRH regulates TSH production primarily by stimulating both posttranslational carbohydrate processing and secretion of this hormone.     

Impairment of hypothalamic-pituitary-thyroid function in rats treated with human recombinant tumor necrosis factor-alpha (cachectin)

Tumor necrosis factor-alpha (TNF; cachectin), a peptide secreted from stimulated macrophages, mediates some of the metabolic derangements in inflammatory and neoplastic disorders. To determine whether TNF is responsible for the changes in hypothalamic-pituitary-thyroid (HPT) function in nonthyroid illnesses, we administered synthetic human TNF to male Sprague-Dawley rats. The rats were given TNF or saline (control; both pair fed and nonpair fed) iv (six to eight per group). HPT function was tested 8 h after administration of 200 micrograms TNF/kg BW, 8 h after 5 days of 150 micrograms TNF/kg BW, and 8 h after a 3-day series of 50, 200, and 800 micrograms TNF/kg BW. The single injection of 200 micrograms TNF/kg significantly reduced (all P less than 0.05) serum TSH, T4, free T4, T3, and hypothalamic TRH compared to the corresponding hormone levels in saline-injected control rats. Serum TSH and hypothalamic TRH recovered to normal levels after 5 days of 150 micrograms/kg TNF treatment. With the increasing daily doses of TNF, serum TSH and hypothalamic TRH fell significantly. Hepatic 5'-deiodinase activity was reduced after 1 day of TNF treatment, but increased after the 3-day series of injections. TNF treatment reduced pituitary TSH beta mRNA, but did not affect alpha-subunit mRNA. TNF treatment also reduced thyroid 125I uptake and reduced thyroidal release of T4 and T3 in response to bovine TSH, but did not change the TSH response to TRH. TNF treatment reduced the binding of pituitary TSH to Concanavalin-A, indicating that it alters the glycosylation of TSH. The TSH with reduced affinity for this lectin had reduced biological activity when tested in cultured FRTL-5 rat thyroid cells. In vitro, TNF inhibited 125I uptake by cultured FRTL-5 rat thyroid cells and blocked the stimulation of [3H]thymidine uptake by these cells. The data indicate that TNF acts on the HPT axis at multiple levels and suggest that TNF is one of the mediators responsible for alterations in thyroid function tests in patients with nonthyroidal illnesses.     

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.     

Hypothalamic somatostatin mediates the suppression of growth hormone secretion by centrally administered thyrotropin-releasing hormone in conscious rats

The effect and mechanism of action of central TRH on the regulation of GH secretion was studied in conscious male rats with indwelling intraatrial and intracerebroventricular (icv) cannulae. Plasma GH was measured every 10-20 min from 1000 h-1400 h by repeated blood sampling. In animals that received saline iv or icv, GH secretion was pulsatile, with peak hormone levels occurring at 1120-1200 h. TRH (10 micrograms), injected icv at 1100 h, inhibited spontaneous GH secretion, and mean plasma GH levels remained suppressed (less than 20 ng/ml) for at least 3 h after injection. In contrast, an iv injection of the same dose of TRH at 1100 h did not significantly affect spontaneous GH secretion. Intravenous injection of human GH-releasing factor [1-40] (hGRF, 1 micrograms) at 1100 h in animals injected 5 min earlier with saline (10 microliters, icv) stimulated GH release, with peak values (748 +/- 63 ng/ml, mean +/- SE) observed 10 min after injection. However, animals injected icv with TRH (10 micrograms) 5 min before the iv injection of hGRF exhibited an attenuated GH response to hGRF (peak values, 115 +/- 28 ng/ml; P less than 0.001 vs. saline icv + hGRF). The inhibition of GH secretion by central TRH was abolished by pretreatment of animals with antisomatostatin serum (0.5 ml, iv) but not with normal serum (P less than 0.001). These results suggest an inhibitory role of central TRH in the regulation of spontaneous GH secretion in the rat that is mediated by stimulation of hypothalamic somatostatin.     

Differential effects of refeeding on melanocortin-responsive neurons in the hypothalamic paraventricular nucleus

To explore the effect of refeeding on recovery of TRH gene expression in the hypothalamic paraventricular nucleus (PVN) and its correlation with the feeding-related neuropeptides in the arcuate nucleus (ARC), c-fos immunoreactivity (IR) in the PVN and ARC 2 h after refeeding and hypothalamic TRH, neuropeptide Y (NPY) and agouti-related protein (AGRP) mRNA levels 4, 12, and 24 h after refeeding were studied in Sprague-Dawley rats subjected to prolonged fasting. Despite rapid reactivation of proopiomelanocortin neurons by refeeding as demonstrated by c-fos IR in ARC alpha-MSH-IR neurons and ventral parvocellular subdivision PVN neurons, c-fos IR was present in only 9.7 +/- 1.1% hypophysiotropic TRH neurons. Serum TSH levels remained suppressed 4 and 12 h after the start of refeeding, returning to fed levels after 24 h. Fasting reduced TRH mRNA compared with fed animals, and similar to TSH, remained suppressed at 4 and 12 h after refeeding, returning toward normal at 24 h. AGRP and NPY gene expression in the ARC were markedly elevated in fasting rats, AGRP mRNA returning to baseline levels 12 h after refeeding and NPY mRNA remaining persistently elevated even at 24 h. These data raise the possibility that refeeding-induced activation of melanocortin signaling exerts differential actions on its target neurons in the PVN, an early action directed at neurons that may be involved in satiety, and a later action on hypophysiotropic TRH neurons involved in energy expenditure, potentially mediated by sustained elevations in AGRP and NPY. This response may be an important homeostatic mechanism to allow replenishment of depleted energy stores associated with fasting.     

Human pituitary chronoendocrinology: repetitive stimulation with LRH/TRH at different times of the day

To determine whether human pituitary is characterized by a circadian periodicity in response to repetitive injection of hypothalamic hormones, 8 healthy subjects were challenged iv with a triple stimulation with 50 micrograms of LRH and 100 micrograms of TRH in a single bolus at 0, 90 and 180 min, receiving the first pulse of hypothalamic hormones either at 02.00 h (02.00 h test) or at 09.00 h (09.00 h test). In addition, a placebo was injected instead of LRH/TRH to evaluate the spontaneous hormonal changes during the 02.00 h test. The LH, FSH, Prl and TSH basal levels were similar in the two phases studied. The mean LH, FSH and TSH peaks after each injection of LRH/TRH were similar among them. The mean Prl peak responses to the third pulse of LRH/TRH, in both the 02.00 h and the 09.00 h tests, were lower (P less than 0.05) than those after the first pulse of LRH/TRH. Placebo did not significantly change circulating LH, FSH, Prl or TSH during nocturnal sampling. The mean LH, FSH and Prl levels after LRH/TRH during the 02.00 h test were similar to those during the 09.00 h test. The mean TSH levels 15 min after the second and third pulses of LRH/TRH during the 02.00 h test were higher (P less than 0.05) than those of the 09.00 h test. Thus, thyrotropes responsiveness to pulsatile stimulation with LRH/TRH is greater during the night than in the morning, while LH, FSH and Prl responses remain constant at the two phases studied.     

Site and mode of action of indomethacin on the hypothalamo-hypophyseal-adrenal axis: a temporal study in intact, hypothalamic-deafferentated, and hypothalamic-lesioned male rats

Adult male rats were given single sc injections of indomethacin (IM; 5 mg/100 g BW) and sacrificed 2-24 h later. IM effects upon serum ACTH and corticosterone (CS) levels, rectal temperature, and hypothalamic and adenohypophyseal prostaglandin E2 (PGE2) and cAMP contents were observed. Rectal temperature was normal for 5-10 h post injection and later decreased by approximately 2.5 C. Both hypothalamic and adenohypophyseal PGE2 concentrations were reduced from 2-24 h after IM administration; no changes in cAMP content were observed. Serum ACTH and CS levels were elevated 4- and 6-fold, respectively, over the entire period observed. In animals with complete hypothalamic deafferentations, the ACTH and CS responses to IM were as marked as they were in intact rats. In rats with hypothalamic lesions in which the ACTH and CS responses to ether stress were attenuated, marked ACTH and CS secretory responses to IM were seen. It is concluded: 1) that the main site of action of systemically administered IM on the hypothalamohypophyseal-adrenal axis, is within the adenohypophysis; 2) that this effect is mediated by PGE2, and cAMP is not involved; and 3) that central nervous system PGs may be involved in the maintenance of basal body temperature in the rat.     

Anterolateral hypothalamic deafferentation inhibits histamine-induced prolactin secretion and potentiates TRH-induced thyrotropin secretion in male rats

We studied the effect of histamine on serum prolactin and thyrotropin (TSH) levels in male rats with anterolateral hypothalamic deafferentation of hypothalamic connections or anterolateral cut (ALC). The success of ALC was confirmed by immunohistochemistry of somatostatin (SRIF) in the medial basal hypothalamus. ALC did not affect basal prolactin or TSH levels. Thyrotropin-releasing hormone (TRH, 200 ng/rat, i.p.) did not affect prolactin secretion either in sham-operated or ALC rats. In sham-operated rats intracerebroventricularly administered histamine increased significantly prolactin levels. Hypothalamic deafferentation abolished the effect of histamine on prolactin levels. TRH increased significantly serum TSH levels both in sham-operated controls and ALC rats. In the latter, however, the TSH-secretory response to TRH was significantly (p less than 0.05) larger compared to the controls. Intracerebroventricularly infused histamine (2 micrograms/rat) did not change the TRH-induced TSH secretion in either group of rats. These results show that (1) the effect of histamine on prolactin secretion is mediated through nerve tracts which are destroyed by ALC, and (2) cutting of afferent TRH (through sensitization) and SRIF fibers (through lacking inhibition) entering medial basal hypothalamus may both contribute to the enhanced TSH response to exogenous TRH.     

Thyrotropin and prolactin response to intraspinal TRH administration in man.

The effect of intraspinal (i.s.) TRH administration of Prolactin (Prl) and thyrotropin stimulating hormone (TSH) serum levels was studied in order to verify the existence of a ventricular route in man for releasing factor delivery to the anterior pituitary, which has been previously reported in rats. Ten young male subjects were given 200 microgram thyrotropin releasing hormone (TRH) i.s. injections and Prl and TSH were measured by radioimmunoassay (RIA) before and at various times after TRH administration. In the same subjects, an i.v. TRH test was also performed. After i.s. TRH, a prompt Prl increase (peak values at 10-30 min and return to baseline within 150 min) and a delayed increase (3-5 h following TRH injection) were observed in 7 and 5 subjects respectively, while an early elevation in serum TSH occurred in 6 subjects and a late one in other 6. In two subjects, a biphasic response of both tropins was present. Prl and TSH response to i.v. TRH was within the normal range in all cases; no late rise of the 2 hormones was observed. A kinetic experiment with 125I-TRH was also carried out to elucidate the mode of i.s. vs i.v. TRH action. These results confirm in man data reported in animals which suggest that TRH can be transported from the cerebrospinal fluid (CSF) to the portal system and the hypophysis.     

Thyroid function in patients with fibromyalgia syndrome.

Thyroid function was tested in 13 female patients with primary fibromyalgia syndrome (FS) and 10 healthy age matched controls by intravenous injection of 400 micrograms thyrotropin-releasing hormone (TRH). Basal thyroid hormone levels of both groups were in the normal range. However, patients with primary FS responded with a significantly lower secretion of thyrotropin and thyroid hormones to TRH, within an observation period of 2 h, and reacted with a significantly higher increase of prolactin. Total and free serum calcium and calcitonin levels were significantly lower in patients with primary FS, while both groups exhibited parathyroid hormone levels in the normal range.     

Hypothalamic thyrotropin-releasing hormone regulates pituitary thyrotropin beta- and alpha-subunit mRNA levels in the rat.

It has been controversial whether thyrotropin-releasing hormone (TRH) may be involved in the regulation of biosynthesis of anterior pituitary thyroid-stimulating hormone (TSH), whereas TRH is well known to control the secretion of TSH from anterior pituitaries. We therefore studied the effect of the destruction of paraventricular nuclei (PVN), containing TRH neuronal cell bodies, on anterior pituitary TSH beta- and alpha-subunit mRNA levels the thyroidectomized rat. Median eminence TRH contents and serum TSH levels significantly decreased even 1 day after PVN destruction, whereas anterior pituitary TSH beta- and alpha-subunit mRNA levels did not change. In contrast, these mRNA levels significantly decreased by 3 days after PVN destruction. Growth hormone mRNA levels were not affected during 7 days after PVN destruction. Although the involvement of other factors related to the PVN is not totally excluded, these results raise the strong possibility that hypothalamic TRH regulates anterior pituitary TSH mRNA levels.