[Diagnosis of adult-onset Still's disease: contribution of biology]. / Apport du laboratoire dans le diagnostic de la maladie de Still.

We report one case of adult-onset Still's disease. The diagnosis of this disease currently requires application of Yamaguchi's criteria and then exclusion of infectious, haematological, autoimmune and neoplasic disorders. The place of biology is enhanced with the use of new markers like ferritin and glycosylated ferritin. Low percentage of glycosylated ferritin (<20%) in presence of very high level of ferritin, unexplained prolonged fever with leukocytosis can help to diagnosis. However, glycosylated ferritin is not yet of in routine use.

Glutamate stimulates somatostatin release from diencephalic neurons in primary culture.

The action of excitatory amino acid agonists on endogenous somatostatin release was examined in primary cultures of rat diencephalic neurons. Increasing concentrations of glutamate stimulated somatostatin release in a dose-dependent manner. Since this effect was decreased by Mg2+, all experiments were performed in Mg2+-free media. We found that excitatory amino acid agonists evoked somatostatin release in the following order of potency: quisqualate greater than glutamate = N-methyl-D-aspartate (NMDA) greater than kainate, as calculated from the dose-response curves. The increase in somatostatin release elicited by glutamate or NMDA was selectively antagonized by DL-2-amino-5-phosphonovaleric acid and by thyenyl-phencyclidine, two specific antagonists of NMDA receptors. The NMDA effect was strongly inhibited: in a competitive manner by APV and in a noncompetitive manner by TCP with IC50 of 90 microM and 0.2 microM, respectively. Glutamate-induced somatostatin release was not blocked by tetrodotoxin (1 microM) suggesting that tetrodotoxin-sensitive sodium-dependent action potentials are not involved in this effect. Our data suggest the presence of functionally active excitatory amino acid receptors in somatostatinergic neurons. Glutamate seems to exert its stimulatory action on somatostatin release essentially through NMDA type receptor sites.

Benzodiazepines inhibit thyrotropin (TSH)-releasing hormone-induced TSH and growth hormone release from perifused rat pituitaries.

The perifusion technique was used to investigate the action of diazepam (DZ), a benzodiazepine molecule known to compete for TRH receptor binding in rat pituitary, on TRH-induced TSH and GH release. The release kinetics for the two hormones from quartered pituitaries were measured in response to a 6-min pulse of TRH (10 nM), without or with DZ addition for a period of 30 min before and during the TRH pulse, plus an additional 15-min period. The dynamic patterns of TSH and GH release in response to TRH were characterized by a rapid increase in hormone release, declining slowly over the next 20 min. The rate of release represented 2.98 +/- 0.02 (+/- SE) and 1.75 +/- 0.06 times the corresponding basal level for TSH and GH, respectively, when evaluated over the first 15 min of the response to TRH. Addition of increasing doses of DZ suppressed the stimulatory effect of TRH in a dose-related manner, with an ID50 of 3 nM for both TSH and GH. The maximal effect of DZ was obtained with a concentration of 10 nM for both hormones. Ro 15-1788 (100 nM), a selective antagonist of the central type of benzodiazepine-binding sites (added to the perifusion system 30 min before DZ and then during the whole period of DZ perifusion), completely abolished (P less than 0.01) the inhibitory effect of DZ (10 nM) on the TRH-induced TSH and GH responses. When added alone before the TRH pulse, Ro 15-1788 had no effect on the TSH response to TRH. In contrast, PK 11,195 (100 nM), a selective antagonist of the nonneuronal benzodiazepine-binding sites, was unable to abolish the inhibitory action of DZ on TRH-stimulated TSH release. In addition, the effects of four other types of benzodiazepine (flurazepam, chlordiazepoxide, midazolam, and medazepam), all tested at a 10-nM concentration, corroborated these findings. Furthermore, DZ inhibition of the TSH response was nullified by picrotoxin (1 microM), but not by bicuculline (1 microM), two gamma-aminobutyric acid antagonists that had no effect, by themselves, on this response. For comparison, the effect of DZ (10 nM) was also tested on the release of GH in response to human GH-releasing factor-(1-44)-NH2 (10 nM) and was found to be ineffective.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for alpha 1-adrenergic stimulatory control of in vitro release of immunoreactive thyrotropin-releasing hormone from rat median eminence: in vivo corroboration.

The aim of this study was to investigate whether the alpha-adrenergic stimulation of TSH secretion may occur directly at the median eminence (ME) level by modulating the release of TRH. The effects of pharmacological manipulations of the two subtypes of central alpha-adrenergic receptors, alpha 1 and alpha 2, were tested on in vitro TRH release from medial basal hypothalami containing mainly the ME. Hypothalamic fragments were superfused with a modified Locke medium, and TRH was measured by RIA in samples collected every 10 min. After a preliminary period of 40 min to test TRH release during basal conditions, drug effects were checked for 20 min. Superfusion with norepinephrine (NE) (10(-10), 10(-8), 10(-6) M) induced a rapid and dose-dependent rise of TRH release; epinephrine (10(-8) M) induced an effect similar to that of NE 10(-8) M. Phentolamine (10(-7) M), an alpha-adrenergic antagonist, completely blocked the NE (10(-8) M)-induced release of TRH, which was not modified by the beta-adrenergic antagonist propranolol (10(-7) M). Neither antagonist had an effect on basal TRH release when added alone to the medium. The NE-induced release of TRH was completely suppressed by prazosin (10(-7) M), whereas yohimbine had no effect. Superfusion with clonidine (10(-9), 10(-8), 10(-7), 10(-6) M), an alpha 2-receptor agonist, did not alter basal TRH release. In contrast, phenylephrine (10(-8) and 10(-6) M), an alpha 1-receptor agonist, induced a significant (P less than 0.01) rise in TRH release. These results were corroborated in vivo in several unanesthetized rats bearing a push-pull cannula previously and stereotaxically implanted into the ME. Perfusion with artificial cerebrospinal fluid containing NE (10(-7), 10(-6) M) or phenylephrine (10(-7) M) elicited a rapid rise in TRH release, within 15 min after the onset of drug perfusion. Clonidine (10(-5) M), similarly perfused for 15 min, had no effect. Our data suggest a direct stimulatory influence of catecholamines on TRH release at the ME level that is mediated through alpha 1-adrenergic receptors.

Evidence for a dual effect of gamma-aminobutyric acid on thyrotropin (TSH)-releasing hormone-induced TSH release from perifused rat pituitaries.

The effects of gamma-aminobutyric acid (GABA) on the spontaneous and TRH-induced TSH release were investigated in vitro on perifused rat pituitaries. The dynamic pattern of TSH release was measured in response to a 6-min pulse of TRH (10 nM) with or without GABA addition. GABA had no effect on spontaneous TSH release but exhibited a dual effect on TSH-stimulated release according to the dose (as calculated by the induced-basal ratio): a potentiation of the TSH response to TRH at the lowest concentrations tested (less than or equal to 10 nM) and an inhibition for GABA concentrations equal or higher than 100 nM. The GABA potentiation was mimicked by muscimol (10 microM) and isoguvacine (10 nM) but not by baclofen (1 microM). Bicucullin (1 microM) or picrotoxin (1 microM) added 15 min before GABA was unable to reverse the GABA potentiation of the TSH response, although SR 95103 (1 and 10 microM), a specific GABA A antagonist, partially or totally antagonized this response. Diazepam (7 nM) was able to potentiate the TSH response by 216% when GABA was added to the system at a concentration (60 nM) which does not modify by itself the TSH response. The inhibitory effect of GABA (100 nM) was completely abolished by bicucullin (1 microM), by picrotoxin (1 microM), and by SR 95103 (1 microM). Picrotoxin not only blocked the inhibitory action of GABA but significantly (P less than 0.05) potentiated the TSH response to TRH. Our data suggest a dual GABA-ergic control of TRH-stimulated TSH release directly on the pituitary, probably mediated by two different kinds of GABA receptors: a GABA A receptor site mediating the inhibitory effect and a nonclassical GABA A receptor site of higher affinity for its stimulatory action.

Somatostatin blocks the potentiation of TRH-induced TSH secretion from perifused pituitary fragments and the change in intracellular calcium concentrations from dispersed pituitary cells elicited by prepro-TRH (PS4) or by tri-iodothyronine.

TRH and somatostatin (SRIH) are well known to stimulate and to inhibit TSH secretion respectively. However, the mechanisms underlying the effect of SRIH on thyrotrophs are still not understood. We have previously shown in vitro that the TSH response to TRH is potentiated in a Ca(2+)-dependent fashion through the activation of dihydropyridine (DHP)-sensitive Ca2+ channels by the prepro-TRH (160-169) cryptic peptide (PS4) and tri-iodo-L-thyronine (T3), when the hormone was added shortly before a TRH pulse in order to avoid its genomic effect. Using perifused rat pituitary fragments, the present study has shown that SRIH inhibits, in a dose-dependent manner, the TSH response to physiological concentration of TRH (10 nM) and reverses the Ca(2+)-dependent potentiation of that response induced either by PS4 or by T3. We have also demonstrated that the inhibition by SRIH of the T3 potentiation of TRH-induced TSH secretion is pertussis toxin-sensitive. Our data suggest that SRIH inhibits the PS4 and T3 potentiation of TRH-induced TSH secretion through the inactivation of DHP-sensitive Ca2+ channels. Using primary cultures of rat anterior pituitary cells and videomicroscopy, we have already demonstrated that TRH, as well as PS4 and T3, are able to increase intracellular Ca2+ concentration ([Ca2+]i) rapidly, in 15 s. Our study has shown that SRIH is able to abolish the acute rise in [Ca2+]i induced either by PS4 or by T3. Since [Ca2+]i responses to PS4 and T3 are also abolished by the DHP nifedipine, our results suggest that [Ca2+]i changes in PS4- or T3-sensitive pituitary cells depend directly or indirectly on the activation of DHP-sensitive Ca2+ channels and that the inhibitory effect of SRIH may be mediated by inactivation of this type of channel.

Age-related decreases in the thyrotropin (TSH) responsiveness to thyrotropin-releasing-hormone (TRH) stimulation and to the inhibitory effect of triiodothyronine (T3); in vitro study on superfused rat pituitaries.

The effect of age on the thyrotropic function was investigated in vitro by superfusing pituitary fragments obtained from 2-3-month- and 24-month-old male Wistar rats with medium 199 (GIBCO) and by measuring basal TSH secretion and TSH response to a 6-min pulse of TRH (10 nM): a/ in the absence and b/ in the presence of T3 (100 nM). TSH was measured by RIA in 3-min fractions with rat TSH materials from the NIADDK. The TRH-induced TSH release elicited by pituitary fragments from the old rats was decreased in comparison to that found in young animals. Addition of T3 to the superfusion medium did not alter basal TSH release but significantly decreased the TSH secretory response to TRH in the young rats. This response was not modified in the old animals. Our results suggest that aging induces not only a TSH hyporesponsiveness to TRH stimulation but also a decrease of this responsiveness to the inhibitory effect of T3 which could be related to a decreased TSH synthesis and to an age-related impairment of T3 action on the thyrotrophs.

Dihydropyridine-like effects of amiodarone and desethylamiodarone on thyrotropin secretion and intracellular calcium concentration in rat pituitary.

Amiodarone (AM) and its major metabolite desethylamiodarone (DEA) are structurally similar to biologically active thyroid hormones. Amiodarone therapy is frequently associated with impairment of thyrotropic function, whose mechanisms are still controversial. Besides its effect on nuclear thyroid hormone binding. AM is able to displace dihydropyridine (DH) binding on membrane preparations from several tissues. By perifusing rat pituitary fragments and measuring thyrotropin (TSH) release we examined: the effect of AM on Ca(2+)-dependent and DHP-sensitive potentiation of the TSH response to thyrotropin-releasing hormone (TRH) induced by either triiodothyronine (T3, perifused for only 30 min before a TRH pulse) or by the prepro-TRH peptide 160-169 (PS4); and the effect of DEA on TRH-induced TSH response in the presence or absence of the DHP nifedipine. We show that AM reverses T3 or PS4 potentiation of the TSH response to TRH; this effect is specific because AM does not modify ionomycin potentiation of that response. In contrast, DEA significantly potentiates the TSH response to TRH and the DHP nifedipine reverses that potentiation. We also tested whether AM would change the acute T3-induced increase in intracellular Ca2+ concentration by measuring intracellular Ca2+ ([Ca2+])i with fura-2 imaging on primary cultures of pituitary cells. We show that AM reverses the effect of T3 on [Ca2+]i as well as the PS4-induced increase in [Ca2+]i. In contrast, DEA increases [Ca2+]i and nifedipine reverses this effect. Our results suggest that AM and DEA display DHP-like effects on TRH-induced TSH release, behaving either as a Ca2+ channel blocker (AM) or as a Ca2+ channel agonist (DEA).

Adenylate cyclase activation is not sufficient to stimulate somatostatin release from dispersed cerebral cortical and diencephalic cells in glia-free cultures.

Under conditions in which vasoactive intestinal peptide (VIP) induces somatostatin release from cortical and diencephalic neuronal cultures, VIP causes large increases in intracellular cyclic AMP. Both the release of somatostatin and the increase in cyclic AMP elicited by VIP require exogenous calcium, can be blocked by cobalt ion, and can be qualitatively mimicked by depolarizating concentrations of exogenous potassium ion. Direct activation of adenylate cyclase by forskolin causes large increases in cyclic AMP content but does not induce somatostatin release. In the absence of VIP, the calcium ionophore, ionomycin, and the phorbol ester, phorbol 12-myristate-13-acetate, also stimulate somatostatin release. These results indicate that VIP-stimulation of cyclic AMP formation and VIP-stimulation of somatostatin release are calcium-dependent and that the two phenomena are dissociatable. Cyclic AMP formation is not a necessary condition for VIP-induced somatostatin release. Nucleotide formation may be a sufficient condition for release or, possibly in association with calcium influx, it may be an event unrelated to the release process.

The presence of non-neuronal cells influences somatostatin release from cultured cerebral cortical cells.

We examined the effect of non-neuronal cells on somatostatin release from cultured cerebral cortical cells. Three culture models were used: (1) neuron-enriched cultures obtained from cortex of 17-day-old rat embryos and exposed to 10 microM cytosine arabinoside (Ara C) for 48 h between days 3 and 5 after plating; (2) whole cell cultures obtained by using the same protocol but untreated with Ara C; (3) glial primary cultures obtained from newborn rats. We studied: (i) the cellular composition of the cultures by using two astroglial markers: vimentin and glial fibrillary acidic protein (GFAP); (ii) the spontaneous and forskolin-stimulated somatostatin release. In 8-day-old cultures morphological data revealed that Ara C treatment reduced glial cells to 6%. At 7 and 10 days of culture somatostatin spontaneously released from Ara C-treated cells was higher than that measured from untreated cells. On the 17th day of culture, neuron-enriched cultures contained a lower amount of somatostatin than whole cell cultures. Forskolin elicited a dose-dependent release of somatostatin from whole cell cultures, but had no effect on neuron-enriched cultures. Astroglial released media (ARM) from glial primary cultures exposed to forskolin for 20 min induced somatostatin release from neuron-enriched cultures. HPLC analysis of endogenous amino acids of ARM showed that glutamate, glutamine, glycine and alanine were significantly increased after forskolin stimulation. Our results suggest a functional interaction between glial cells and neurons secreting somatostatin.

Ontogeny of the metencephalic, mesencephalic and diencephalic content of catecholamines as measured by high performance liquid chromatography with electrochemical detection.

Developmental changes in norepinephrine (NE), dopamine (DA) and epinephrine (E) contents of the rat metencephalon, mesencephalon and diencephalon, have been measured by high performance liquid chromatography with electrochemical detection, from fetal stages (E15 or E17 to E21) to postnatal days (P0 to P30) and compared to the adult levels. The data show a biphasic pattern in NE changes of the three brain areas, with a first increase in the late prenatal period, followed by a further development from P0 to P18, thus reaching the adult levels. A similar pattern of development is found for the mesencephalic and diencephalic DA contents. The E levels of the diencephalon are very low in comparison to the NE and DA concentrations, but present a gradual increase from E17 to P18. The results correlate with the development of catecholamine systems in brain area as measured by other methodological approaches.

Pharmacological properties of the NMDA receptor involved in somatostatin release from cortical neurons.

Glutamate increases somatostatin release from cultured cerebral cortical neurons, presumably through a N-methyl-D-aspartate (NMDA) receptor type. We report here that the NMDA response was potentiated by D-serine (10 microM) and that this potentiation was blocked by kynurenic acid (4-hydroxyquinoline-2-carboxylic acid; KYN). A higher concentration of D-serine (100 microM) reduced the antagonistic effect of KYN. Furthermore, the NMDA response exhibited another characteristic property of the NMDA receptor: it was decreased by low concentrations of Zn2+ (50 microM). In contrast, Zn2+ slightly but significantly potentiated the quisqualate (QA)- and kainate (KA)-induced responses.

Involvement of dihydropyridine-sensitive calcium channels in the GABAA potentiation of TRH-induced TSH release.

The effects of gamma-aminobutyric acid (GABA) and isoguvacine on the thyrotropin (TSH) secretion stimulated by thyrotropin releasing hormone (TRH), were investigated in vitro with perifused rat pituitaries. At nanomolar concentrations the two agonists induced potentiation of the TRH-induced TSH release. The potentiation was blocked by SR 95531 a specific GABAA antagonist. The isoguvacine potentiation of the TSH response to TRH failed to occur when cobalt (Co2+) was added to the perifused medium. Nifedipine completely blocked the GABA or isoguvacine potentiation of the TSH response while omega-conotoxin did not modify it. Pre-perifusion of the pituitaries with pertussis toxin did not change the TSH response to TRH but completely inhibited the isoguvacine potentiation of the response. Our results demonstrate that the GABA potentiation of TRH-induced TSH release occurring through the stimulation of GABAA receptor sites is a calcium (Ca2+)-dependent phenomenon, probably mediated by activation of dihydropyridine (DHP)-sensitive, omega-conotoxin-insensitive Ca2+ channels involving a pertussis toxin-sensitive G protein.

Somatostatin inhibition of VIP-induced somatostatin release, cyclic AMP accumulation and 45Ca2+ uptake in diencephalic cells.

The effect of somatostatin (SRIF) on VIP induction of SRIF secretion, cyclic AMP accumulation and 45Ca2+ influx was investigated in cultured diencephalic cells. [D-Trp8]SRIF suppressed VIP-stimulated SRIF release and decreased VIP-stimulated cyclic AMP accumulation in a dose-dependent manner. SRIF-14 blocked basal and VIP-stimulated 45Ca2+ entry into cells. The data suggest that the inhibitory effect of SRIF on VIP-induced SRIF release is partly due to a decrease in Ca2+ entry into cells.

Triiodo-L-thyronine enhances TRH-induced TSH release from perifused rat pituitaries and intracellular Ca2+ levels from dispersed pituitary cells.

There is now increasing evidence that Ca2+ serves as the first messenger for the prompt and non-genomic effects of 3,5,3' triiodo-L-thyronine (T3) in several tissues. We have previously shown that the first phase of thyroid stimulating hormone (TSH) release in response to thyrotropin-releasing hormone (TRH) can be potentiated by messengers of hypothalamic origin, by a Ca(2+)-dependent phenomenon involving the activation of dihydropyridine-sensitive Ca2+ channels. By perifusing rat pituitary fragments, we have investigated whether T3 would modify TSH release when the hormone is applied for a short time (i.e. 30 min) before a 6 min pulse of physiological concentration of TRH, thus excluding the genomic effect of T3. We show that: (1) increasing concentrations of T3 (100 nM-10 microM) in the perifused medium potentiates the TRH-induced TSH release in a dose-dependent manner; (2) the T3 potentiation is not reproduced by diiodothyronine and T3 does not potentiate the increase if TSH release induced by a depolarizing concentration of KCl; (3) the protein synthesis inhibitor cycloheximide, does not significantly modify the effect of T3; (4) addition of Co2+, nifedipine, verapamil, or omega-conotoxin in the medium, at a concentration which does not modify the TSH response to TRH, reverses the T3 potentiation of that response. We also tested whether T3 would change intracellular concentrations of Ca2+, by measuring [Ca2+]i with fura-2 imaging on primary cultures of dispersed pituitary cells, either in basal conditions or after stimulation by TRH or/and T3. Both substances induced a fast increase of [Ca2+]i, with a peak at 15 s, followed by a subsequent progressive decay with TRH and a rapid return with T3. Our data suggest that T3 enhances TRH-induced TSH release by a protein synthesis-independent and Ca(2+)-dependent phenomenon, probably due to an increase in Ca2+ entry through the activation of dihydropyridine- and omega-conotoxin-sensitive Ca2+ channels. They also show that T3 may acutely enhance [Ca2+]i in pituitary cells. These findings support the idea of the occurrence of a prompt and stimulatory role of T3 at the plasma membrane level in normal rat pituitary gland.

K+-induced thyrotropin-releasing hormone release from superfused mediobasal hypothalami in rats. Inhibition by somatostatin.

Somatostatin (SRIF), in concentration of 10(-6) M, significantly inhibited the depolarization-induced release of immunoreactive thyrotropin-releasing hormone (IR-TRH) from superfused mediobasal hypothalami (MBH) containing mainly the median eminence (ME), without affecting the basal release of TRH. The total amount of K+-induced TRH release was 0.24 +/- 0.02 and 0.61 +/- 0.08 pg/MBH/min, respectively, in the presence and absence of SRIF in the medium. The data are consistent with a role of SRIF as a neuromodulator on TRH release from the ME. In contrast, superfusion with Locke medium containing triiodothyronine (10(-6) M) had no effect on basal and K+-induced IR-TRH release in our system.

Evidence for a role of central type benzodiazepine receptors in the inhibition of the thyrotropin-releasing hormone-induced thyrotropin release from rat perifused pituitaries.

Several centrally active benzodiazepines (BZ) were tested for their ability to inhibit the TRH-induced secretion of TSH in vitro from perifused pituitaries. Diazepam, flurazepam, chlordiazepoxide (CDZ) and midazolam (10 nM) inhibited the TSH response to TRH (10 nM) by 33-50%, while medazepam, a prodrug having virtually no affinity for central BZ sites, did not. CDZ inhibition was reversed by Ro 15-1788, antagonist of the central type BZ binding sites, but not by PK 11195, antagonist of the peripheral type. The data are consistent with an involvement of central type BZ receptor sites in the TSH-lowering effects of BZ in rats.

Physiological evidence for alpha 1-adrenergic facilitatory control of the cold-induced TRH release in the rat, obtained by push-pull cannulation of the median eminence.

The alpha-adrenergic antagonists phentolamine and prazosin were administered to male rats to explore their effects on cold-induced TRH release, measured by a chronic push-pull cannula stereotaxically implanted in the median eminence (ME). Phentolamine was given either i.p. (24 or 40 mg/kg), or locally (10(-5) M) in the ME, whereas prazosin was only applied locally (10(-5) M). Phentolamine significantly decreased the cold response (5 +/- 1 pg/15 min vs 21 +/- 5 pg/15 min; P less than 0.02), whatever the administration mode. Moreover, the blocking effect of prazosin directly perfused into the ME (11 +/- 3 pg/15 min vs 26 +/- 9 pg/15 min; P less than 0.05), indicates the specific involvement of alpha 1-adrenergic receptors in the cold-induced TRH response, and points to the ME as a possible site of facilitatory adrenergic control.

The inhibitory effect of picrotoxin on basal and cold-induced thyrotropin secretion involves somatostatin mediation.

This work was undertaken to investigate whether the inhibitory tone exerted by GABA on somatostatin (SRIH) release operates in the control of thyrotropin (TSH) secretion in both basal and cold-stimulated conditions. In a first group of animals (G1) undergoing both carotid and third ventricle push-pull cannulation, i.vt. injection of picrotoxin (10(-5) M) induces a significant decrease in plasma TSH level under basal conditions (0.09 +/- 0.02 versus 0.27 +/- 0.4 ng/100 microliters; P < 0.03, n = 5). In a median eminence (ME) push-pull cannulated group of rats (G2), picrotoxin, peripherally administered, blocks cold-induced inhibition of SRIH release (35.0 +/- 1.8 versus 7.4 +/- 3.3 pg/15 min; P < 0.005; n = 5). In a third group of intact rats (G3), peripheral administration of picrotoxin (2 mg/kg i.p.) blunts the cold-induced TSH release (0.17 +/- 0.03 versus 0.46 +/- 0.04 ng/100 microliters; P < 0.001; n = 5). Our results strongly suggest that a decrease in SRIH release is involved in the GABAergic control of basal and cold-induced TSH secretion.

Chronic stress affects in vivo hypothalamic somatostatin release but not in vitro GH responsiveness to somatostatin in rats.

One week after stereotaxical implantation of a push-pull cannula into the median eminence (ME), rats were stressed by immobilization for 2 h daily for 7 days. Thereafter, ME was perfused for 1 h in basal, stress and recovery conditions, respectively, and somatostatin (SRIH) was measured in perfusate fractions. Pituitaries were in vitro perifused to assess GH responsiveness to SRIH. In the stressed group, basal SRIH release was significantly higher than in the control group and stress caused a significant sharp peak in neurohormone release. GH responsiveness to SRIH was not affected in pituitaries obtained from stressed donors. High SRIH levels secreted under chronic stress thus did not impair the GH pituitary response to SRIH.