Fine structures of nerve fibers with corticotropin-releasing factor-like immunoreactivity in the rat lateral septum

The fine structures of nerve fibers with corticotropin-releasing factor (CRF)-like immunoreactivity in the rat lateral septum were investigated by means preembedding immunoelectron microscopy. A number of CRF axon terminals formed synapses with cell bodies of non-immunoreactive septal neurons. They occasionally had broad terminal bulges whose subregions showed little or no immunoreactivity for CRF. CRF axon terminals were also in synaptic contact with non-immunoreactive dendrites or dendritic spines. Some dendrites with CRF were postsynaptic to non-immunoreactive axon terminals.

Ontogeny and afferent connections of corticotropin releasing factor-like immunoreactivity in the rat neocortex

The first set of the present experiments was designed to investigate the postnatal development of corticotropin releasing factor-like immunoreactivity (CRFI) in the rat cerebral cortex by means of cobalt-enhanced immunohistochemistry. Results showed the occurrence of CRFI fibres before cells in the developing rat cerebral cortex with and without colchicine treatment, suggesting that some CRFI cells in subcortical regions may project to the cerebral cortex. In the second set of experiments, ipsilateral double-labelled cells which contained both retrogradely transported horseradish peroxidase (HRP) and CRFI were observed in the zona incerta, subincertal nucleus, lateral hypothalamic area, perifornical hypothalamic area, and in the dorsal hypothalamic area after unilateral HRP injections into the cerebral cortex. These findings indicate the existence of corticopetal CRFI-containing projections arising from the above areas.

A reliable method combining horseradish peroxidase histochemistry with immuno-beta-galactosidase staining

A sensitive combination of horseradish peroxidase (HRP) tracing and immunohistochemistry was used by Rye et al. [J Histochem Cytochem (1984) 32:1145] in a search for the origins of neurotransmitter- and neuromodulator-containing nerve fibers in brain. In this combination, peroxidase as a marker in immunohistochemistry was thought to yield a homogeneous brown immunoreaction product of diaminobenzidine, different from the black granular reaction product of retrogradely transported HRP, which is visualized by the tetramethylbenzidine (TMB) reaction and subsequent stabilization. A neuron that exhibits both kinds of reaction products in its cytoplasm in sections subjected to combination staining is referred to as a double-labeled cell. With a combined HRP and corticotropin-releasing factor (CRF) immunoperoxidase-antiperoxidase (PAP) method, the first set of experiments showed "false" double-labeled cells in the pyramidal cell layer of rat cerebral cortex, but only rarely in the subcortical areas, possibly because of the use of one enzyme system in two different histochemical procedures. This limitation of the double-staining technique prompted us to demonstrate an alternate combination of HRP tracing and immunohistochemistry in the second set of experiments by employing two previously described independent enzyme systems: HRP as a retrograde tracer and beta-galactosidase as a marker for immunohistochemical demonstration of CRF. A homogeneous blue reaction product indicated immuno-beta-galactosidase staining, and a granular black or brown reaction product labeled retrogradely transported HRP in double-labeled cells in subcortical regions. Neither double labeling nor "false" double labeling was seen in pyramidal cells of cerebral cortex. These findings suggest that application of two independent enzyme systems in a combined HRP and immunohistochemical method may be useful for investigating in origins of peptidergic fibers in brain when the combination of HRP histochemistry and the PAP method appears to be inappropriate.

CRF-containing neuron systems in the rat hypothalamus: retrograde tracing and immunohistochemical studies

By employing a combination of the immunohistochemistry for rat corticotropin-releasing factor (rCRF) and retrograde tracing with biotinylated wheat germ agglutinin (b-WGA) injected into the posterior pituitary (group 1) or into the middle portion of the median eminence (group 2), functionally different populations of CRF neurons were identified in the rat hypothalamus. In the group 1 animals, WGA-labeling was seen not only in the posterior lobe but also in the intermediate lobe, in which CRF fibers exist. In these animals, WGA-labeling occurred for almost all large neurons in the anterior commissural, paraventricular (PV), and supraoptic (SO) nuclei, some of the neurons showing a slight immunoreactivity for anti-rCRF. Conversely, CRF positive neurons appeared in large numbers, some being labeled with WGA, in the caudal periventricular region (CPR), and in the dorsomedial to lateral hypothalamic area (DLH), especially in the latter. In the group 2 animals, WGA was disparsed throughout the subependymal, internal, and external layers of the medial portion of the median eminence, and was taken up by many small cells in the PV, almost half of the cells being immunoreactive for CRF. Slight WGA-labeling further occurred in some large neurons of the PV and SO, and in some cells of the DLH. It is concluded that hypophysiotropic CRF existing in the external layer of the median eminence originates from small neurons located in the PV, whereas CRF distributed in the posterior and intermediate pituitary originates from the magnocellular PV and SO, and from some neurons in the DLH and CPR.

Ontogeny of pituitary responsiveness to corticotropin-releasing hormone in rat

The ontogeny of the pituitary's responsiveness to synthetic rat corticotropin-releasing hormone (CRH) in the late prenatal and early postnatal periods of rats was studied by a superfusion system using whole pituitaries. A significant increase of immunoreactive beta-endorphin (IR-beta-Ep) secretion in response to 10(-10) M CRH but not to 10(-11) M CRH was observed in pituitaries from the 15th day of gestation, the earliest day that we tested, whereas 10(-11) M CRH stimulated IR-beta-Ep release from the pituitaries of 17.5-day-old fetuses. Dose-related IR-beta-Ep secretions induced by 10(-12) M to 10(-10) M CRH were observed in pituitaries of 19.5- and 21.5-day-old fetuses, and 1-, 3- and 9-day-old newborn pups. CRH stimulated not only IR-beta-Ep and IR-adrenocorticotropic hormone (ACTH) but also IR-alpha-melanocyte-stimulating hormone (IR-alpha-MSH) secretions from fetal pituitaries. The content of IR-CRH in the hypothalamic extract from 15-day-old fetus was 6.6 +/- 3.6 pg/hypothalamus (mean +/- S.E.M.) and it gradually increased to reach 212.7 +/- 20.3 pg/hypothalamus on the 21.5th day of gestation. However, the content of IR-CRH in the hypothalamus dramatically decreased just after birth and then rapidly increased again from the 5th day after birth. These data indicate that the responsiveness of corticotrophs to CRH is already present on the 15th day of gestation, when the content of IR-CRH in the hypothalamus is extremely low and that the amount of hypothalamic IR-CRH dramatically dropped for several days just after birth in rats.

Corticotropin releasing factor-containing afferents to the lateral septum of the rat brain

Corticotropin releasing factor (CRF)-containing afferents to the rat lateral septum (LS) have been determined by means of cobalt-enhanced immunohistochemistry, tracing of retrograde transport of horseradish peroxidase (HRP), and by lesioning experiments. When unilateral lesions included the rostral part of the hypothalamus, CRF-like immunoreactive (CRFI) ipsilateral fibers in the LS decreased in number. Lesions in other brain regions did not cause alterations in the septal CRFI fibers. These findings suggest that the septal CRFI fibers originate in the rostral part of the hypothalamus. Furthermore, combined HRP and immunohistochemical staining on the same sections demonstrated double-labeled cells in two discrete areas within the rostral hypothalamus: one was the perifornical hypothalamic area (PeF) at the level of the paraventricular hypothalamic nucleus, and the other was the most caudal part of the anterior hypothalamic nucleus (AHc). These findings show that a large proportion of the CRFI projections to the LS have their origins in the PeF and AHc.

Study on the mechanism of abnormal growth hormone (GH) secretion in anorexia nervosa: no evidence of involvement of a low somatomedin-C level in the abnormal GH secretion

The response of plasma growth hormone (GH) to an iv injection of synthetic human growth hormone-releasing factor (hGHRF-44) (2 micrograms/kg bw) was studied in 23 patients with anorexia nervosa. The basal plasma concentrations of somatomedin-C (Sm-C) in these patients were also measured. Basal plasma GH levels were above normal in 8 out of 23 patients and an exaggerated GH response to hGHRF-44 compared to that in age-matched normal females was found in 9 patients. Mean basal plasma Sm-C concentration in the patients was 0.41 +/- 0.04 U/ml (mean +/- SE), which was in the low normal limit. When 6 patients were reexamined after their weight gain of 4-18 kg as well as their normalization of basal plasma Sm-C levels, their elevation of basal plasma GH level was lowered and the responsiveness to hGHRF-44 improved. However, there was no significant correlation between the Sm-C concentration and basal plasma GH level as well as the integrated GH response to hGHRF-44 expressed as the area under the curve (OhGH). These findings, therefore, suggest that some factor(s) other than the lowered plasma Sm-C level are involved in the mechanism of abnormal GH secretion in patients with anorexia nervosa.

[Treatment of delayed brain injury after pituitary irradiation]

Treatment for delayed brain injury after pituitary irradiation is discussed. Six cases with delayed brain injury were treated with a combination of dexamethasone or betamethasone, with heparin, glycerol, dextran 40 and some vasodilators. Two cases with temporal lobe syndrome were treated in the early stages of brain injury for a period of over 12 months were almost completely cured, another two cases with chiasma syndrome were treated in the relatively late stages, showed a partial improvement. One case which was irradiated 120 GY during 13 years did not improve. The final case treated with steroids for a short period also resulted in failure and the patient underwent an operation for the removal of the necrotic mass three years after the radiotherapy. Steroid therapy started in the early stages of brain injury after irradiation for over the 12 months is thought to be effective. Heparin therapy was also effective in one out of three cases, but in one of the cases subarachnoid hemorrhage from a traumatic aneurysm occurred during the therapy. In an acute phase, showing edematous change of the injured brain, the administration of glycerol is also thought to be useful. But the effectiveness of the other medicines containing some vasodilators was obscure or doubtful. We propose the following: (1) A meticulous observation is essential for the patients who received high doses of irradiation to diagnose brain injury in the early reversible stage. (2) Steroids should be given immediately in this reversible stage of brain injury before the irreversible "necrosis" occurs. (3) Steroids should be maintained for a long period over 12 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonistic effect of somatostatin on corticotropin-releasing factor-induced anorexia in the rat

The effect of somatostatin on corticotropin-releasing factor (CRF)-induced anorexia was examined in rats. Intracerebroventricular (icv) administration of 0.11 nmol and 0.21 nmol ovine CRF significantly suppressed food intake of 24 h-starved rats. Icv administration of 0.31 nmol somatostatin 14 and somatostatin 28 partially reversed suppression of food intake induced by icv injection of 0.21 nmol CRF in 24 h-starved rats. These results suggest that somatostatin may counteract the suppressive effect of CRF on food intake within the central nervous system.

Cation-induced thermostability of yeast and Escherichia coli pyrophosphatases

Inorganic pyrophosphatases (PPiases) from both yeast and Escherichia coli were found to be stable against heat denaturation in the presence of Mg2+, as previously observed with the enzymes from thermophilic bacteria. No loss of activity was observed after 1 h of incubation at 50 degrees C and pHs between 6 and 9 in the yeast enzyme, and at 60 degrees C and pHs between 7.2 and 9.2 in the E. coli enzyme. Such an induced thermostability of the E. coli enzyme was detected when Mn2+, Co2+, Ca2+, Cd2+, and Zn2+ were added in place of Mg2+. On the other hand, the degree of induced thermostability of the yeast enzyme was dependent upon the divalent cations used, and Ni2+ and Cu2+ accelerated the heat inactivation. On adding the divalent cations, the difference spectra of the E. coli enzyme always showed negative peaks in the ultraviolet region, but those of the yeast enzyme changed again depending upon the divalent cations. The circular dichroism spectra in the near ultraviolet region of both enzymes greatly differed from each other, but both were not affected so much by adding the divalent cations unlike the thermophilic enzymes from Bacillus stearothermophilus and thermophilic bacterium PS-3. Yeast and E. coli PPiases did not cross-link with the anti-immunoglobulin G's from the thermophilic enzymes, but the thermophilic enzymes did with each other's antisera. The results in the present study indicated that the conformation of PPiase, in which the aromatic amino acid residues were buried in the interior of the protein molecule, was very important for the thermostability and also that the protein structures of PPiases from B. stearothermophilus and thermophilic bacterium PS-3 were very similar to each other, but were very different from those of the mesophilic enzymes.

Involvement of corticotropin-releasing factor in restraint stress-induced anorexia and reversion of the anorexia by somatostatin in the rat

The mechanism by which restraint stress induces suppression of food intake and the influence of intracerebroventricular (icv) administration of somatostatin on the anorexia induced by restraint stress were examined in the rat. Ninety minutes of restraint stress reduced food intake of rats to approximately 60% that of control. Anorexia induced by 90 min restraint stress was partially reversed by icv administration of alpha-helical CRF (9-41), a corticotropin-releasing factor (CRF) antagonist, and completely reversed by anti-CRF gamma-globulin. These results provide further evidence in support of the theory that CRF is involved in the inhibitory mechanism of food intake in restraint stress. ICV administration of somatostatin 14 and SMS 201-995, an analog of somatostatin, also reversed restraint stress-induced anorexia. It is, therefore, suggested that somatostatin may counteract the suppressive action of CRF on food intake in stress.

Corticotropin-releasing factor reverses the effect of pentobarbital through a beta-noradrenergic mechanism in rats

Corticotropin-releasing factor (CRF) has been shown to reverse effect of pentobarbital (PbNa) within the central nervous system. In this study, the mechanism of the antagonistic effect of CRF on PbNa-induced anesthesia and hypothermia in rats was examined. Intraventricular administration of CRF significantly shortened sleeping time and antagonized hypothermia induced by PbNa. Propranolol (148 micrograms, 0.5 mumol), a beta-blocker, completely reversed the CRF effect, although propranolol alone affected neither sleeping time nor rectal temperature. Phentolamine, an alpha-blocker, reversed the antagonistic effect of CRF on PbNa, though the same dose of phentolamine alone increased the sleeping time in the absence of CRF. Atropine, an anticholinergic agent, did not affect the ability of CRF to reverse the effects of PbNa. These results suggest that the ability of CRF to reduce some of the effects of PbNa may be mediated at least in part by brain beta-noradrenergic receptors.

Effect of sodium ion on atrial natriuretic factor release from rat hypothalamic fragments

The effects of Na ion and choline chloride on the release of atrial natriuretic factor (ANF) and growth hormone-releasing factor (GHRF) from rat hypothalamic fragments including the organum vasculosum of the lamina terminalis (OVLT) were examined in vitro. Although the release of ANF was stimulated by Na ion, choline chloride, and glucose in concentration-dependent manners, the release was more sensitive to a change in concentration of Na ion than to those of choline chloride and glucose. On the other hand, the change in Na ion concentration did not affect the release of GHRF. It can be therefore proposed that Na ion is the first candidate controlling ANF release from the brain tissue and that ANF in the hypothalamus and/or OVLT may play some role in the regulation of the Na ion and water balance in the central nervous system.

Effect of human growth hormone-releasing hormone on GH secretion in Cushing's syndrome and non-endocrine disease patients treated with glucocorticoids

The GH response to 100 micrograms human growth hormone-releasing hormone (hGRH) given intravenously was evaluated in eleven patients with Cushing's syndrome who had been ill for more than one year and in six patients with non-endocrine diseases who were treated with glucocorticoid for one to twelve weeks. Extremely low to no response of plasma GH to hGRH injection was noted in all seven patients with Cushing's disease and in four patients with Cushing's syndrome due to an adrenal adenoma or carcinoma. In contrast, all six patients with non-endocrine diseases who were treated with glucocorticoid showed normal GH responses to hGRH. These results suggest that the diminished hGRH-induced GH secretion in patients with Cushing's syndrome might be caused by the prolonged period of hypercortisolemia.

Corticotropin-releasing factor-like immunoreactive nerve fibers in the rat superior cervical ganglion and their fine structures

The existence of nerve fibers containing corticotropin-releasing factor (CRF)-like immunoreactivity (CRFI) in the rat superior cervical ganglion (SCG) was demonstrated by using immunocytochemistry. They were found to be extrinsic in origin, because no CRFI neurons were seen in the SCG and decentralization resulted in the disappearance of CRFI fibers in the SCG on the operated side. These findings were also confirmed by immunoelectron microscopic analysis; CRFI fibers contained a number of small clear synaptic vesicles but were devoid of large granular and agranular vesicles. These morphological characteristics are identical to those of the preganglionic fibers. The present immunoelectron microscopic analysis revealed that most of the CRFI fibers in the SCG make synaptic contact predominantly with the dendrites of the principal cells, partly with their somas and rarely with a non-CRFI terminal. Thus, the present study provides direct morphological evidence that CRF directly influences the function of the principal cells of the SCG and that CRFI fibers are preganglionic.

Desensitization of rat pituitary somatotrophs to growth hormone-releasing factor occurs in vitro

Desensitization of rat pituitary somatotrophs to human growth hormone-releasing factor (hGHRF) was investigated using cultured rat anterior pituitary cells. Growth hormone (GH) release decreased but the production of cAMP was still induced in response to subsequently added 10(-9) M hGHRF from cells pretreated with hGHRF at concentrations ranging from 10(-11) to 10(-7) M for 4 h. Desensitization to 10(-9) M hGHRF was also observed in cells pretreated with 10(-9) M hGHRF for 4 h in the presence of 2 mM EGTA, 10 ng/ml nifedipine or 10(-9) M somatostatin-28, which decreased GH release during pretreatment. Forskolin and A23187, at concentrations of 10(-6) M and 10(-4) M, respectively, stimulated GH release from cells pretreated with hGHRF to the same extent as that from the control cells. These results, therefore, suggest that desensitization to GHRF occurs regardless of the presence of releasable GH pool and that some changes such as uncoupling of GHRF receptors with adenylate cyclase and decreased sensitivity to cAMP of cAMP-dependent protein kinase of the secretory mechanism of GH, in addition to the decrease in releasable GH pool and down regulation of GHRF receptors, may be involved in the desensitization mechanism.

Effects of adrenergic blockers on corticotropin-releasing factor-induced behavioral changes in rats

The effects of adrenoreceptor blocking agents on corticotropin-releasing factor (CRF)-induced behavioral changes in rats were examined. The i.c.v. injection of 1 micrograms ovine CRF significantly increased the grooming frequency, number of occurrences of rearing and total distance moved. I.c.v. administered phentolamine at a dose of 10 nmol completely suppressed the increase in rearing and total distance moved induced by CRF without affecting the grooming frequency, whereas 100 nmol phentolamine significantly decreased the grooming frequency as well as the rearing and total distance moved. In contrast, propranolol reduced the increase in rearing induced by CRF only at a dose which induced ataxia in rats. The increases in rearing and total distance moved induced by CRF were reduced by 10 nmol of yohimbine and 100 nmol of prazosin. S.c. injection of caffeine (10 mg/kg) produced a significant increase in grooming frequency, rearing, and total movement. Administration of 10 nmol phentolamine and yohimbine did not affect these behavioral changes induced by caffeine, while 100 nmol prazosin suppressed them. Therefore, prazosin depressed the behavior of rats non-specifically. These results suggest that CRF-induced behavioral hyperactivity is mediated at least in part by alpha-noradrenergic, mainly alpha 2-noradrenergic, systems in the brain.

Intragranular colocalization of arginine vasopressin and methionine-enkephalin-octapeptide in CRF-axons in the rat median eminence

Ultrastructural appearances of axonal terminals containing corticoliberin (CRF) were examined in the rat median eminence prepared by a freeze-drying procedure. Immunolabeling was performed by using 5-, 8-, or 15-nm gold-antibody complexes for CRF, arginine vasopressin (VP) and methionine-enkephalin-octapeptide (Enk-8), singly or in combination. In intact animals, the CRF-containing secretory granules were only slightly labeled with gold-anti-VP or -Enk-8. In adrenalectomized rats, granules within single axons appeared to be labeled with all the immunogold complexes. This intragranular colocalization of the three antigens was confirmed by using three neighboring sections of the same axon terminals which were stained separately with each one of the antibodies and visualized with the avidin-biotin-peroxidase complex method. The granules labeled for CRF had decreased 9 days after adrenalectomy but had increased again by day 21, while those labeled for VP steadily increased after adrenalectomy. However, this did not correspond with the appearances of cell bodies in the paraventricular nucleus; the cell bodies labeled for both CRF and VP steadily increased in number and in stainability. By contrast, Enk-8 immunoreactivity in the axonal terminals and cell bodies was not affected by adrenalectomy. These findings suggest that although the three peptides could be released simultaneously from the axonal terminals, VP may play some special role in the expression of CRF activity.

Coronary hemodynamics and cardiac beating modulate atrial natriuretic factor release from isolated Langendorff-perfused rat hearts

The role of coronary hemodynamics and cardiac beating on atrial natriuretic factor (ANF) release was studied in the isolated Langendorff-perfused rat heart. ANF release was measured by radioimmunoassay. When the coronary flow rate was changed, ANF release decreased or increased in a flow-dependent manner. When the perfusion pressure was changed, ANF release also increased or decreased, respectively, with concomitant changes in coronary flow rate. Furthermore, perfusion with 50 mM potassium chloride showed immediate cardiac arrest and a decrease of ANF release to an undetectable level with a significant decrease in coronary flow. However, low but readily detectable amounts of ANF were released when coronary flow rate was maintained. These results may suggest that coronary hemodynamics and cardiac beating could be factors modulating ANF secretion from the atrium.

Corticotropin-releasing factor-containing afferents to the inferior colliculus of the rat brain

Using a modified cobalt-glucose oxidase-diaminobenzidine (Co-GOD) method in a combination of horseradish peroxidase (HRP) retrograde tracing and immunohistochemistry, a widespread localization of corticotropin releasing factor-like immunoreactive (CRFI) structures in the rat inferior colliculus (IC), and a CRFI-containing pathway from the subthalamus and the hypothalamus to the IC have been observed. By means of the modified Co-GOD method, CRFI cells were detected in almost all the subdivisions of the IC, including the dorsomedial part of the central nucleus, the ventrolateral part of the central nucleus, the pericentral nucleus and the external nucleus. Neural processes with CRFI were observed in all of the above areas. Following HRP injection into the IC, double-labeled cells which contained a homogeneous brown immunoreaction product of CRF and a granular black reaction product of retrogradely transported HRP were identified in the lateral hypothalamic area (LH), zona incerta (ZI) and perifornical hypothalamic area (PeF). These double-labeled cells provide direct evidence for CRFI projections from the LH, ZI and PeF to the IC. Thus, the present study supports the view that CRF may act as a neurotransmitter or neuromodulator in the brain.

Corticotropin releasing factor-like immunoreactivity in the rat brain as revealed by a modified cobalt-glucose oxidase-diaminobenzidine method

A cobalt-glucose-oxidase diaminobenzidine (Co-GOD) method, employing a specific antiserum against rat corticotropin releasing factor (CRF), was applied to determine immunohistochemically a widespread and detailed localization of corticotropin releasing factor-like immunoreactivity (CRFI) in the rat brain. Besides the CRFI cells in the paraventricular hypothalamic nucleus that project to the median eminence, CRFI cells were demonstrated in many brain regions, including the olfactory bulb, cerebral cortex, septal nuclei, hippocampus, amygdala, thalamic nuclei, medial hypothalamic nuclei, lateral hypothalamic area, perifornical area, central gray, cuneiform nucleus, inferior colliculus, raphe nuclei, mesencephalic reticular formation, laterodorsal tegmental nucleus, locus coeruleus, parabrachial nuclei, mesencephalic tract of the trigeminal nerve, pontine reticular formation, lateral superior olive, vestibular nuclei, prepositus hypoglossal nucleus, nucleus of the solitary tract, dorsal motor nucleus of the vagus, lateral reticular nucleus, nucleus of the spinal tract of the trigeminal nerve, external cuneate nucleus, inferior olive, and medullary reticular formation. CRFI-reacting neural processes were also detected in these same areas. In particular, the median eminence, lateral septum, bed nucleus of the stria terminalis, mesencephalic reticular formation, parabrachial nuclei, and nucleus of the solitary tract contained large numbers of CRFI fibres. The widespread localization of CRFI demonstrated in the present study strongly suggests that CRF, like many other neurohormones and peptides, may act as a neurotransmitter and/or neuromodulator in numerous extrahypothalamic circuits, as well as participate in neuroendocrine regulation.

Conductance and kinetics of delayed rectifier potassium channels in nodal cells of the rabbit heart

1. The delayed rectifier K+ current (IK) of single pace-maker cells from the sino-atrial node and the atrioventricular node of the rabbit heart was investigated using the whole-cell and cell-attached configurations of the patch-clamp technique. 2. The activation kinetics of the macroscopic IK were not altered by varying the extracellular K+ concentration ([K+]o) between 5.4 and 150 mM. The amplitude of the tail current of IK, however, was about 10-fold larger at a [K+]o of 150 mM than that at a [K+]o of 5.4 mM. 3. By using a high-[K+]o solution, inward single-channel currents were observed on repolarization from potentials positive to -40 mV. The current-voltage (I-V) relation was linear over the negative potential range and the reversal potential estimated by extrapolating the I-V curve was shifted by about 60 mV for a 10-fold increase in [K+]o, indicating that the channel was highly selective for K+. 4. The single-channel conductance was 11.1 pS at a [K+]o of 150 mM and varied in proportion to the square root of [K+]o. The total number of channels was estimated as approximately 1000 per cell (0.7/micron 2). On repolarization, the averaged single-channel current disappeared with a time constant similar to that of the macroscopic tail current of IK. 5. At potentials between -50 and -100 mV, the open and closed times of the single channel fitted well with single-exponential and biexponential distributions, respectively. As the membrane was progressively depolarized, the open time was shortened while the closed time was prolonged, suggesting a decrease of open probability. These changes were in the opposite direction to those expected from the delayed rectifier K+ current which progressively increases in magnitude at more positive potentials. 6. At the beginning of the macroscopic tail current, a transient increase of the inward current was found to precede the time-dependent decrease. This rapid initial change can be attributed to a quick removal of inactivation of IK which had occurred during the depolarizing pulse. This inactivation gate of the channel has very fast kinetics and could be responsible for the inward-going rectification observed in the 'fully activated' IK.

Traumatic giant aneurysm of the external carotid artery

Because the main trunks of the external carotid artery and maxillary artery are well protected from blunt trauma and superficial penetrating wounds through their course, traumatic aneurysms on these arteries are extremely rare. A 75-year-old woman had struck her occipital region against a door but there was no trauma to the mandibuloauricular region. After 1 month, she noticed a pulsatile mass below her right auricle. At operation an aneurysm was found to be located just distal to the origin of the maxillary artery.

Urotensin I-like immunoreactivity in amacrine cells of the goldfish retina

Urotensin I-like immunoreactivity (UILI), in different localization from that of corticotropin releasing factor-like immunoreactivity (CRFLI), in the goldfish retina has been demonstrated by means of radioimmunoassay, high-performance liquid chromatography (HPLC) and immunohistochemistry. Radioimmunoassay showed 350 +/- 40 pg/mg prot. of UILI in goldfish retina extracts. The immunoreactive material present in the retina was also characterized by reversed phase HPLC. Some of the UILI co-eluted with synthetic carp UI, though the HPLC experiments suggested the existence of other UILI substance(s) with less hydrophobicity than synthetic UI. By immunohistochemistry, UILI and CRFLI were seen in different amacrine cells of the goldfish retina. It is suggested that UI may be involved in the fish visual transmission system together with CRF and other neuropeptides.

Improved fixation and cobalt-glucose oxidase-diaminobenzidine intensification for immunohistochemical demonstration of corticotropin-releasing factor in rat brain

An optimal fixation method and intensification procedure may be required in brain immunohistochemistry to obtain intense and widespread staining for a specific antigen, in cases where ordinary fixation and conventional immunohistochemistry result in only partial demonstration of the antigen. In the present study of localization of corticotropin-releasing factor immunoreactivity (CRFI) in rat brain, the importance of such intensification is shown. We describe a fixation procedure in which perfusion of rat brain with Bouin's solution is followed by a PBS wash and a further perfusion with either Zamboni's fluid or 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4), for subsequent investigation of the detailed localization of CRFI in cerebral cortex and subcortical structures. The cobalt-glucose oxidase-diaminobenzidine (Co-GOD) intensification method has been modified to increase the sensitivity of immunostaining by reducing the concentration of glucose oxidase, which is added to the final incubation solution as a generator of hydrogen peroxide. The use of cobalt acetate instead of cobalt chloride appears to slightly suppress background staining in the Co-GOD method. Combination of the two modified procedures was applied to visualize intense and widespread CRFI in a variety of rat brain regions, including median eminence, cerebral cortex, and central amygdaloid nucleus.

Effect of a single administration of somatostatin analogue (SMS 201-995) on GH, TSH and insulin secretion in patients with acromegaly

The effect of a long-acting somatostatin analogue SMS 201-995 on GH secretion was investigated. Eleven acromegalic patients received a single dose of 50 micrograms SMS 201-995 administered subcutaneously, and plasma GH, IGF-I, GRF, TSH, IRI and blood glucose were determined at regular intervals. Nine of 11 patients had elevated basal plasma GH levels above 5 ng/ml. In all patients, plasma GH levels fell immediately from 39.5 +/- 17.3 ng/ml (mean +/- SEM) to 4.3 +/- 1.6 ng/ml (P less than 0.05) with a maximal inhibition of 82.9 +/- 3.3% of the basal levels and the suppression persisted for about 6 h of the observation period. IGF-I and GRF levels were not apparently altered. TSH and IRI levels also rapidly fell. Blood glucose levels fell slightly by 0.5 h. Ten of 11 patients had pain at injection sites. Except for this, no side effects were observed. Our results show that the new somatostatin analogue SMS 201-995 may inhibit GH hypersecretion in acromegalic patients for significant periods, suggesting that this agent can be a useful clinical tool for the treatment of acromegaly.

The antagonistic effect of corticotropin-releasing factor on pentobarbital in rats

The effects of corticotropin-releasing factor (CRF) on pentobarbital-induced sleeping time and hypothermia in rats were studied. Intraventricular administration of CRF significantly shortened the sleeping time induced by pentobarbital injection (50 mg/kg b.wt.) in a dose-dependent manner. CRF also attenuated the hypothermic effect of pentobarbital. However, peripheral administration of CRF did not affect the action of pentobarbital. alpha-Helical CRF9-41, CRF antagonist, reversed the effects of CRF. These results suggest that CRF antagonizes the effects of pentobarbital within the central nervous system.

Distribution and efferent projections of corticotropin-releasing factor-like immunoreactivity in the rat amygdaloid complex

Using cobalt-enhanced immunohistochemistry, the tracing of retrograde transport of horseradish peroxidase (HRP) and experimental manipulations, a widespread localization of corticotropin-releasing factor-like immunoreactive (CRFI) structures in the rat amygdaloid complex, and CRFI-containing pathways from the amygdala to the lower brainstem, bed nucleus of the stria terminalis (bst) and ventromedial nucleus of the hypothalamus (VMH) have been demonstrated. By means of cobalt-enhanced immunohistochemistry, CRFI cells were detected in almost all the regions of the amygdala, including the central amygdaloid nucleus (Ce), basolateral amygdaloid nucleus (B1), intra-amygdaloid bed nucleus of the stria terminalis (Abst), medial amygdaloid nucleus (Me), amygdalohippocampal area (Ahi), posterior cortical amygdaloid nucleus (Aco), lateral amygdaloid nucleus (La), anterior amygdaloid area (AAA) and basomedial amygdaloid nucleus (Bm). Neural processes with CRFI were found in all of the above areas. The greatest density of CRFI fibres was observed in the Ce, the Me and Ahi. Unilateral lesions located in the Ce and adjacent areas caused an ipsilateral decrease in CRFI fibre number in the lateral hypothalamic area (LH), mesencephalic reticular formation (RF), dorsal (Dpb) and ventral (Vpb) parabrachial nuclei, mesencephalic nucleus of the trigeminal nerve (MeV) and in the lateral division of the bst (bstl). In addition, ipsilateral CRFI fibres decreased in number in the core and shell of the VMH after unilateral lesions of the corticomedial amygdala (CoM) and ventral subiculum (S). These findings suggest that the CRFI cells in the Ce and adjacent areas innervate the Dpb, Vpb and MeV through the LH and RF; the CRFI fibres in the bstl are supplied by the Ce and adjacent areas; and the CoM and S give rise to the CRFI fibres to the VMH. The distribution of retrogradely transported HRP has confirmed these projections. Furthermore, combined HRP and immunohistochemical staining has demonstrated double labeled cells in the Ce following HRP injection into the Dpb, Vpb, MeV and bstl. This provides direct evidence for the amygdalofugal CRF-containing projections to the lower brainstem and bstl. Double-labeled cells were not seen in the CoM and S after HRP injection into the VMH.

Ontogeny of gamma-melanocyte-stimulating hormone in the brain and hypophysis of the rat: an immunohistochemical analysis

The ontogeny of gamma-melanocyte stimulating hormone (gamma-MSH)-like immunoreactive (gamma-MSHI) structures in the brain and hypophysis was investigated in the rat by means of indirect immunofluorescence. gamma-MSHI neurons in the arcuate nucleus appeared at Day 13 of gestation, in the anterior hypophysis at Day 16, in the intermediate lobe at Day 18, and in the nucleus commissuralis after birth. gamma-MSHI fibers first appeared at Day 15 of gestation in the hypothalamic area and extended dorsally to reach the surface of the diencephalon. At Day 16 of gestation, another gamma-MSHI fiber bundle was found that ran laterally along the ventral surface of the diencephalon. At Day 19, immunoreactive fibers first appeared in the forebrain, diencephalon, midbrain and upper pons, and thereafter they increased in number, reaching a maximum at postnatal Day 15. gamma-MSHI fibers in the lower pons and medulla oblongata first appeared after birth. They also increased in number with age and reached a maximum at postnatal Day 15. The present ontogenetical study has demonstrated the different times of first appearance of each of the 3 major gamma-MSHI structures-containing cell groups in the brain, i.e., the arcuate nucleus, hypophysis and nucleus commissuralis. These findings may reflect the different functions of 3 groups of cells.

In vitro release of growth hormone-releasing factor from rat hypothalamus: effect of insulin-like growth factor-1

The release of growth hormone-releasing factor (GHRF) from rat hypothalamus was investigated in vitro. After 60 min preincubation the released GHRF from sliced rat hypothalamic fragments during 60 min incubation was detected by a highly specific and sensitive radioimmunoassay for rat GHRF. The release of GHRF was Ca2+-dependent and enhanced by high concentration of K+. Insulin-like growth factor-1 (IGF-1) significantly decreased GHRF release to 65% and 84% of the control at concentrations of 10(-8) M and 10(-7) M, respectively. These results suggest that this in vitro system is useful for the investigation of the mechanism of GHRF release from the hypothalamus and that IGF-1 is probably involved in the feedback inhibition of growth hormone secretion by attenuating GHRF release from the hypothalamus besides countering the effect of GHRF on the pituitary.

Studies on the response of growth hormone (GH) secretion to GH-releasing hormone, thyrotropin-releasing hormone, gonadotropin-releasing hormone, and somatostatin in acromegaly

The plasma GH response to GH-releasing hormone (GHRH), TRH, or GnRH administration was examined in 25 acromegalic patients. Plasma GH levels increased in 21 patients after GHRH, in 19 after TRH, and in 4 after GnRH. The four GHRH nonresponders had had acromegaly longer than had the GHRH responders. No specific combination of GH responsiveness to these 3 releasing hormones was found among the patients. Infusion of 1 mg GHRH for 150 min gradually increased plasma GH levels, with some fluctuations, from the beginning to the end of infusion in normal subjects and in 7 patients who were GHRH responders, but a bolus injection of 100 micrograms GHRH at the end of the infusion did not further elevate plasma GH levels. These results suggest that desensitization to GHRH occurred in the normal subjects and acromegalic patients. However, in 5 acromegalic patients who responded to both GHRH and TRH, a bolus injection of 500 micrograms TRH given at the end of the 150-min infusion of 1 mg GHRH evoked a further plasma GH rise. In 5 normal subjects and 2 patients who were responders to GHRH but not TRH, a bolus injection of 500 micrograms TRH did not cause plasma GH elevation at the end of 150-min infusion of 1 mg GHRH. These results imply that TRH and GnRH stimulate GH secretion from the adenoma cells in vivo through receptors different from those for GHRH. In vitro studies using cultured pituitary adenoma cells from 2 patients revealed that the responses of GH secretion to GHRH were similar to those in vivo. These data, therefore, suggest that the responsiveness of GH secretion to stimuli is determined by the specificity of the receptors on adenoma cells. The action of somatostatin-28 was more potent than that of somatostatin-14 in the suppression of GH secretion from adenoma cells.

The effect of glucose and free fatty acids on growth hormone (GH)-releasing factor-mediated GH secretion in rats

We have examined the effect of glucose and FFA on GH-releasing factor (GHRF)-mediated GH secretion in rats under pentobarbital anesthesia. Hyperglycemia did not affect GH secretion induced by administration of 20, 100, and 200 ng GHRF/100 g body weight. In contrast, GH response to 50 ng GHRF/100 g body weight in lipid heparin-treated rats, which showed high plasma FFA levels, was significantly suppressed compared with the control group (plasma peak GH: control, 1526 +/- 263 ng/ml; lipid-heparin group, 377 +/- 69 ng/ml P less than 0.05, mean +/- SEM). This suppressive effect of FFA on GH secretion was abolished by pretreatment with antisomatostatin serum (ASS) (GH level at 4 min after GHRF administration: ASS-saline group, 1606 +/- 210 ng/ml; ASS-lipid-heparin group, 1531 +/- 174 ng/ml; mean +/- SEM). These results suggest that hyperglycemia does not change the GH response to GHRF and that elevation of plasma FFA suppresses GHRF-induced GH secretion by the stimulation of somatostatin secretion in rats.

Atrial natriuretic factor is released from rat hypothalamus in vitro

In vitro release of atrial natriuretic factor (ANF) from rat hypothalamic fragment during 60 min incubation was studied using a specific and sensitive radioimmunoassay (RIA). The Sephadex G-75 gel filtration profiles of the incubation medium revealed that the majority of released ANF-like immunoreactivity (LI) had a molecular weight same as alpha-atrial natriuretic polypeptide and a small amount of ANF-LI of larger molecular size was also released. The release of ANF was increased by addition of 50 mM KCl and the release by 50 mM KCl was completely suppressed in the presence of 2 mM EGTA, a chelating agent of Ca2+. A23187, a Ca2+ ionophore, at a concentration of 2 X 10(-4) M augmented the release of ANF-LI. These results indicate that hypothalamic ANF is released in a Ca2+-dependent manner like other hypothalamic peptides. This suggests that hypothalamic ANF acts as a neurotransmitter and/or neuromodulator in the hypothalamus and possesses some role in the regulation of pituitary hormone secretion.

Intragranular colocalization of CRF and Met-Enk-8 in nerve terminals in the rat median eminence

The ultrastructural localizations of rat corticoliberin (rCRF) and methionine-enkephalin octapeptide (Met-Enk-8) in the external layer of the rat median eminence were examined by double-immunogold labeling with anti-rCRF and anti-Met-Enk-8 sera labeled with small-sized (Gs) and medium-sized (Gm) gold particles, respectively. Two types of immunolabeled terminals were distinguished: one type with small granules (70 nm) labeled with Gs, and the other with large granules (100 nm) labeled with Gm. In both types, however, some granules were labeled with both Gs and Gm.

Rat atrial natriuretic factor suppresses proopiomelanocortin-derived peptides secretion from both anterior and intermediate lobe cells and growth hormone release from anterior lobe cells of rat pituitary in vitro

Synthetic rat atrial natriuretic factor (ANF) was found to attenuate, in a dose-dependent manner, basal and corticotropin-releasing factor-induced secretion of proopiomelanocortin-derived peptides from cultured anterior and intermediate lobe cells of rat pituitary. ANF was also found to suppress basal and growth hormone-releasing factor-stimulated secretion of growth hormone from anterior lobe cells of rat pituitary. These results, together with reports of the existence of ANF-positive neurons in the hypothalamus and ANF-positive fibers in the median eminence, suggest that hypothalamic ANF is probably involved in the regulation of pituitary hormone secretion, especially that of proopiomelanocortin-derived peptides and growth hormone.

A divergence of plasma growth hormone response between growth hormone-releasing factor and insulin-induced hypoglycaemia among middle-aged healthy male subjects

The capability of the anterior pituitary gland to secrete GH in response to an intravenous injection of growth hormone-releasing factor (GRF) and insulin-induced hypoglycaemia was evaluated in 9 healthy male subjects ranging in age between 37 and 52 years old. Plasma GH response to 100 micrograms human GRF showed considerable intersubject variation and the increment of the peak value from the basal did not exceed 5 ng/ml in four out of 9 subjects. In contrast, insulin-induced hypoglycaemia resulted in a consistent stimulation of GH that exceeded 21 ng/ml in all subjects. The mean peak GH response after insulin-induced hypoglycaemia was significantly higher than that after GRF (27.4 +/- 1.6 vs 10.6 +/- 1.9 ng/ml). These results demonstrate that a significant divergence exists in plasma GH responses between the two provocative tests in the middle-aged subjects and suggest that the stimulation of GH following insulin-induced hypoglycaemia is not mediated solely by endogenous GRF.

The responses of plasma adrenocorticotropin and cortisol to corticotropin-releasing hormone (CRH) and cerebrospinal fluid immunoreactive CRH in anorexia nervosa patients

Pituitary-adrenocortical responses to the iv injection of 100 micrograms synthetic ovine corticotropin-releasing hormone (CRH) were studied in 13 patients with anorexia nervosa, and the concentrations of immunoreactive CRH in cerebrospinal fluid were measured in 7 of them. Mean basal levels of plasma ACTH and cortisol were 32 +/- 5 pg/ml (+/- SEM) and 21.1 +/- 1.5 micrograms/dl, respectively. The latter value was significantly higher than that in age-matched normal women (P less than 0.005). The mean increments of plasma ACTH and cortisol in response to CRH injection in those 13 patients were 21 +/- 5 pg/ml and 5.3 +/- 1.7 micrograms/dl, respectively, significantly lower than those in normal women (58 +/- 6 pg/ml and 15.3 +/- 7.7 micrograms/dl, respectively; P less than 0.005). When 4 patients were reexamined after weight gains of between 3 and 22 kg, their responses to the CRH injection increased. The mean concentration of immunoreactive CRH in the cerebrospinal fluid of seven patients was 30.8 +/- 3.9 pg/ml (+/- SEM), which was higher than the value of 18.4 +/- 1.1 pg/ml (P less than 0.005) in control subjects with cervical spondylosis. These findings suggest the possibility that hypersecretion of CRH may occur in patients with anorexia nervosa.

Concentrations of glycine and serine in cerebrospinal fluid during disturbed consciousness; a study of the therapeutic effect of thyrotropin-releasing hormone on the consciousness level

The concentrations of aliphatic amino acids (glycine, serine, valine, threonine, alanine, leucine, isoleucine) in lumbar cerebrospinal fluid from patients with consciousness disturbances and normal controls were measured. Thyrotropin-releasing hormone (TRH) was administered to patients and the changes of levels of consciousness and amino acid concentrations were followed before and after TRH administration. The concentrations of glycine and serine from patients were significantly higher than those from controls; they returned to the control values with improvement of consciousness disturbances. The influence of TRH upon these amino acid concentrations was not observed. These results suggest that within the central nervous system, an alteration of the level of consciousness is associated with a distortion of glycine and serine metabolism and that TRH itself has no influence upon these amino acid concentrations.

Ontogenetic appearance of immunoreactive GRF-containing neurons in the rat hypothalamus

Ontogenetic development of GRF-containing neurons in the rat hypothalamus was studied employing antisera which were generated against hpGRF (1-44)NH2 and rhGRF(1-43)OH: anti-hpGRF-C and -rhGRF sera recognize the species-specific C-terminal portions of the peptides, and anti-hpGRF-MC and -N sera recognize hpGRF(27-44)NH2 and the N-terminal portion of hpGRF(1-44)NH2, respectively. The anti-hpGRF-C and -rhGRF sera stained different neuronal cell bodies, which were localized in distinct hypothalamic areas. The former serum did not stain the axonal terminals in the median eminence, but the latter stained them strongly. The anti-hpGRF-MC and -N sera stained neuronal cell bodies, some of which corresponded to those immunolabelled with anti-hpGRF-C or -rhGRF serum. The anti-rhGRF serum first demonstrated immunoreactive perikarya in the ventral-lateral border of the arcuate nucleus of 19.5-day-old fetuses that had received an intraventricular colchicine administration 24 h previously. The immunoreactive fibers were recognized first in the external layer of the median eminence of untreated fetuses on day 19.5 of gestation, and then they increased in amount with development. No immunoreactive fibers, however, were found in the median eminence of colchicine-treated animals during the fetal period. It is concluded that in rats GRF may be synthesized in the perikarya on day 18.5 of gestation and conveyed to the median eminence without delay via axonal flow.

Effect of hypothalamic ventromedial lesions on plasma growth hormone response to growth hormone-releasing factor in rats

The effect of ventromedial-arcuate (VMH-ARC) nuclei lesions on plasma growth hormone (GH) response to human growth hormone-releasing factor (GRF, 1 microgram/kg b.wt., i.v.) was studied in conscious rats after they had received chlorpromazine (CPZ) or CPZ plus antiserum against somatostatin (ASS). When rats were pretreated with CPZ alone, there was no difference in basal plasma GH level between VMH-ARC lesioned rats and controls. The magnitude of plasma GH response to GRF in 5 out of 6 VMH-ARC lesioned rats exceeded that of controls. When the same observation was repeated using the same rats after they had received ASS and CPZ, basal plasma GH levels of controls were significantly higher than those of VMH-ARC lesioned rats, and the magnitude of the plasma GH response to GRF was augmented in both groups of rats. The plasma GH response to GRF was comparable between two groups, though the peak plasma GH response to GRF was slightly but significantly lower in VMH-ARC lesioned rats as compared to controls. Pituitary GH content was reduced significantly in VMH-ARC lesioned rats as compared to controls. The results demonstrate that the pituitary responsiveness to GRF does not appear to be altered significantly in rats bearing bilateral VMH-ARC lesions. In addition, the placement of electrolytic lesions in VMH-ARC regions causes reduced SS secretion into the hypophyseal portal vessels and leads to an augmentation of plasma GH response to GRF.

Plasma growth hormone response to human growth hormone releasing factor in rats administered with chlorpromazine and antiserum against somatostatin. Effects of hypo- and hyperthyroidism

The effect of hypo- and hyperthyroidism on the plasma growth hormone (GH) response to synthetic human growth hormone releasing factor (GRF) was determined in conscious, freely moving rats pretreated with chlorpromazine and antiserum against somatostatin. Chlorpromazine plus somatostatin antiserum pretreated rats gave consistent response to GRF which was not observed in untreated rats. Chlorpromazine alone has no effect on GH secretion induced by GRF in rat pituitary monolayer culture. In rats made hypothyroid by thyroidectomy, both basal and peak plasma GH responses to a small (0.25 microgram/kg bw) and a moderate dose of GRF (1 microgram/kg bw) were significantly reduced as compared to controls. In rats made hyperthyroid by the administration of thyroxine, basal and peak plasma GH responses to a small but not to a moderate dose of GRF were significantly reduced as compared to controls. A reduced plasma GH response to a small dose of GRF was observed 8 days after the cessation of thyroxine administration. The pituitary GH reserve was markedly reduced in hypothyroid but not in hyperthyroid rats as compared to their respective controls. These results indicate that plasma GH response to GRF is reduced both in hypo- and hyperthyroidism. The mechanism involved in the phenomenon appears to be different between the two conditions.

The inter- and intra-subject variabilities of plasma GH response to human growth hormone-releasing hormone (1-44) NH2 in men

The effects of intravenously given human growth hormone-releasing hormone (1-44) NH2 (hGRH-44) on growth hormone (GH) secretion were studied in normal men. A wide variability of intersubject GH response to hGRH-44 was observed. The peak plasma GH levels in response to 50, 100 and 200 micrograms hGRH-44 in 7 normal men were 9.1 +/- 3.2 ng/ml (Mean + SEM), 19.3 +/- 3.3 ng/ml and 22.4 +/- 4.0 ng/ml, respectively. Both the mean peak values for plasma GH response to 100 and 200 micrograms were significantly greater than that for 50 micrograms hGRH-44 injection (p less than 0.01), although there was no significant difference of the mean peak plasma GH values and mean concentrations at each time point, except for those at 120 min, when 100 or 200 micrograms hGRH-44 was administered. A significant difference in the mean amount of plasma GH secreted in response to hGRH-44 was observed only between 50 and 200 micrograms hGRH-44 injection (p less than 0.01). Furthermore, a dose-related plasma GH increase in response to hGRH-44 was not always observed in each subject. In contrast to the wide intersubject variability, the difference among responses of plasma GH to 100 micrograms or 200 micrograms of hGRH-44 given at multiple times separated by intervals of at least 1 week in each individual was relatively small.(ABSTRACT TRUNCATED AT 400 WORDS)

The satiety effect of growth hormone-releasing factor in rats

The effect of growth hormone-releasing factor (GRF) on feeding behavior in rats was examined. Starvation-induced feeding was suppressed by intraventricular administration of 1 nmol and 4 nmol of synthetic human GRF (hGRF). Food intake was not affected when the peptide was administered by intraperitoneal injection. Furthermore, centrally administered hGRF also suppressed feeding in hypophysectomized rats. These results suggest that GRF suppression of food intake is mediated through the central nervous system independent of its effect on pituitary growth hormone secretion.