Immunoreactive Somatostatin Content Research Articles

Immunoreactive somatostatin content in the pineal gland increases after lesion of the hypothalamic periventricular nucleus in male rats

Immunoreactive somatostatin (IRS) content in the pineal gland increased about two-fold when the hypothalamic periventricular nucleus (Pe) of male rats, which contains many tuberoinfundibular somatostatin (SRIF) neuron cell bodies, was lesioned. However, the mechanism by which this increase takes place remains to be elucidated. Using 125I-Tyr11-SRIF-14 as a ligand and autoradiography, specific binding was detected in several brain areas. However, we were unable to detect specific SRIF binding sites either in the pineals of control or lesioned animals. This undetectable binding of SRIF-14 could be due to the localization of low-affinity receptors that were not demonstrated by the present method. Another possibility for the undetectable binding of the radioligand to the pineal could be due to the fact that the majority of IRS may be within the nerve terminals and the receptors in a different location.

Role of locally produced growth hormone-releasing factor in somatostatin regulation by fetal rat brain cells in culture.

To determine the possible physiological role of endogenous growth hormone-releasing factor (GRF) in the neuronal content and release of cerebral somatostatin (SS), we studied the effect of endogenous GRF blockade on the immunoreactive SS (IR-SS) content of cells and media in fetal rat cerebral cortical and hypothalamic cells in culture. Cells were cultured in minimum essential medium (MEM) with 10% fetal calf serum and 10% horse serum. After 7-10 days in vitro, media were replaced with MEM without sera containing anti-GRF immunoglobulins G (IgG) for 1, 5 or 24 h. Controls were incubated with equal amounts of IgG from normal rabbit serum (NRS). In another group of experiments, cells were incubated with GRF (10(-11) to 10(-7) M) for 1 or 24 h. Long-term exposure (24 h) to anti-GRF IgG resulted in decreased media and intracellular IR-SS content, in both cerebral cortical and hypothalamic cells. 24 h treatment with GRF caused a dose-dependent increase in the IR-SS content of cells and media, the stimulatory action being abolished by the addition of anti-GRF to plates containing 10(-7) M GRF. On the contrary, when cells were exposed to anti-GRF IgG for 1 h, IR-SS increased in the media as compared to the control group. Short-term incubation (1 h) with GRF (10(-9) to 10(-7) M) resulted in a dose-dependent inhibition of IR-SS content in the cells and media. This inhibitory action was partially prevented by the addition of anti-GRF to plates containing 10(-7) M GRF.(ABSTRACT TRUNCATED AT 250 WORDS)

Dexamethasone-Induced Accumulation of Neuropeptide-Y by Aggregating Fetal Brain Cells in Culture: A Process Dependent on the Developmental Age of the Aggregates*

Neuropeptide-Y (NPY) and glucocorticoid receptors are coexpressed in many neurons in the brain. We addressed the question: Do glucocorticoids regulate the accumulation and/or secretion of immunoreactive (IR) NPY by fetal rat brain cells in culture, and if so, is the effect developmental stage dependent? Aggregates, formed from dissociated cells obtained from the hypothalamus-olfactory tubercle of 17-day-old fetuses, were cultured in serum-free medium for 23 days. On day 23, the aggregate NPY content was 6 ng/flask, and secretion (last 2 days) was approximately 12 ng/24 h. Exposure to dexamethasone (Dex; 20 nM) between days 0-23 led to a 1.9-fold increase in the aggregate content of NPY, whereas NPY secretion was not altered. When Dex exposure was limited to days 12-23, 16-23, 19-23, or 21-23, only a 12- to 23-day exposure induced NPY accumulation, and it was as effective as a 0- to 23-day exposure. The Dex-induced increase in NPY content was evident after a lag period of 4 days or more. When Dex exposure occurred on days 0-12, the aggregate NPY content on day 12 or 23 was not altered. None of these treatments altered the aggregate/medium content of immunoreactive somatostatin (SRIF) or the response to a 48-h exposure to forskolin (10 microM). Dex induction of NPY accumulation was a saturable function of the Dex concentration (maximal at 20 nM), and it was completely inhibited by RU486, a glucocorticoid/progesterone receptor antagonist; neither progesterone, 17 beta-estradiol, nor testosterone altered aggregate/medium NPY contents. Protein/DNA contents of the aggregates were either unaffected or slightly reduced by Dex. Thus, 1) Dex stimulates the accumulation of immunoreactive NPY, but not SRIF, by cultured fetal brain cells; 2) this effect requires a continuous 8-12 days of exposure to Dex during a late developmental stage in culture; 3) Dex does not potentiate or attenuate forskolin action on the NPY neuron; and 4) Dex action appears to be mediated by the glucocorticoid receptor. These results are consistent with glucocorticoid induction of production and/or decreased intracellular degradation of NPY, and with glucocorticoids regulating the NPY neuron in the perinatal brain in a developmental age-dependent manner.

Plasma and tissue concentrations and molecular forms of somatostatin in calves infected with Sarcocystis cruzi

The effects of parasitic infection on plasma and tissue content of immunoreactive somatostatin (SRIF) were studied in 4-mo old male calves inoculated with the protozoan Sarcocystis cruzi. Because feed intake significantly decreased (70%) in infected calves around day 28 postinfection (pi), concomitant with the asexual replication of S. cruzi and outward expression of clinical signs, the relative contributions of infection and associated reduction in nutrition on plasma SRIF were evaluated. Treatment groups were: noninfected ad libitum fed (C), infected (250,000 S. cruzi oocysts per os) ad libitum fed (I) and noninfected calves pairfed to the level of intake of each infected calf (PF). Mean plasma concentrations of SRIF (pg/ml) on day 30 pi were: C, 224 ± 22; I, 742 ± 150; PF, 246 ± 31 (effect of infection P<.05). In another study, SRIF was measured in plasma and in pancreatic, duodenal, jejunal and ileal tissue extracts from normal and S. cruzi infected calves. Plasma and tissue samples were collected on day 42 pi. Mean plasma SRIF were 2.5 times higher in infected than control calves. Plasma insulin and insulin-like growth factor 1 was lower in infected v control calves (P<.02). Plasma glucagon was similar between groups. Duodenal (P<.05) and jejunal (P<.02) SRIF content was higher in infected than control calves. Chromatography of tissue extracts on Sephadex G-50 revealed that the increase in SRIF was accounted for, in part, by molecular forms larger than cyclic SRIF-14. Data suggest that peripheral SRIF is increased in calves during S. cruzi infection. The increase in SRIF is not solely related to plane of nutrition. Altered levels of gut SRIF(s) may be associated with perturbed metabolic regulation in parasitized animals through direct effects on the gut.

Somatostatin is increased in the dorsal root ganglia of adjuvant-inflamed rat

To determine whether biosynthesis of somatostatin is enhanced in the primary sensory neurons by inflammatory pain, we examined the effects of adjuvant inoculation on the content of immunoreactive somatostatin, mainly composed of somatostatin-14 and somatostatin-28, in the dorsal root ganglia and the spinal cord of the rat. The adjuvant inoculation, which produced long-lasting inflammation and hyperalgesia, increased the content of immunoreactive somatostatin, especially somatostatin-14, in the dorsal root ganglia at L4–L6 levels with no change in the dorsal and ventral horns of lumbar enlargement. Such an increase was enhanced by an intrathecal injection of colchicine (0.2 mg) that inhibits axonal flow of somatostatin. Chronic administration of the anti-inflammatory analgesic, sodium diclofenac (3 mg·kg −1·d −1), abolished an adjuvant-induced increase in the content of immunoreactive somatostatin in the dorsal root ganglia. These results suggest that the turnover (biosynthesis and axonal flow) of somatostatin in the primary sensory neurons is enhanced in the presence of persisting inflammatory pain, and support the idea that somatostatin-containing primary afferents are involved in the transmission of pain in the spinal dorsal horn.

Immunoreactive somatostatin diurnal rhythms in rat pineal, retina and Harderian gland: Effects of sex, season, continuous darkness and estrous cycle

Diurnal profiles of the content of immunoreactive somatostatin (IRS) in the male and female rat pineal, Harderian gland and retina have been studied. Supplementary experiments have been performed to elucidate a possible effect of infradian cycles, namely estrous and seasonal cycles, and continuous dark on IRS concentration. Results demonstrate that the IRS content in the rat pineal gland, Harderian gland and retina is submitted to diurnal variations, but not under all studied conditions. A sexual dimorphism exists between male and female animals: male rats showed higher IRS content in pineal (103.8 +/- 4.7 vs 32.3 +/- 1.8 pg IRS/gland), but lower in retina (1,362.1 +/- 82.7 vs 2,176 +/- 102.2 +/- pg IRS/mg of protein) and Harderian gland (10.3 +/- 0.8 vs 30.6 +/- 3.5 pg IRS/mg of protein). Additionally, seasonal differences appeared: in male and female animals pineal IRS content was lower in spring than in November. This decrease also appeared in female retina IRS concentration. Estrous cycle did not seem to change IRS content in the three studied tissues. Finally, pineal IRS rhythm persisted after continuous dark for a week. These results demonstrate, in the rat, sexual differences in the IRS content of the various tissues studied and suggest a physiological role for somatostatin, possibly related to seasonal adaptation.

Relationship between serum growth hormone levels and the brain and pituitary content of immunoreactive somatostatin in the goldfish, Carassius auratus L

In this study, the relationships between endogenous brain and pituitary immunoreactive somatostatin (irSRIF) and circulating growth hormone (GH) levels in the goldfish were examined using two approaches. First, the amount of irSRIF in extracts of the pituitary gland and various brain regions was measured by radioimmunoassay several times throughout the year and was compared to serum GH levels at each time. The amounts of irSRIF in extracts of the pituitary gland, hypothalamus, and telencephalon were found to be inversely related to seasonal changes in serum GH levels, such that irSRIF was highest in these regions when serum GH levels were lowest (November and February). Conversely, irSRIF in these regions was lower in May, June, and July when serum GH levels were highest. These results suggest that endogenous irSRIF in the pituitary and forebrain may participate in the regulation of seasonal changes in serum GH levels in the goldfish. In extracts from other brain regions (thalamus + midbrain and cerebellum + medulla), some changes in the amount of irSRIF were observed among the various sample times, but these variations were not related to changes in serum GH levels. In a second set of experiments, the origin of irSRIF fibers innervating the goldfish pituitary gland was examined by using brain lesioning techniques to destroy regions of the forebrain known to contain irSRIF perikarya and fibers, and subsequently measuring the amount of irSRIF in the pituitary gland. Lesions in the preoptic area of the forebrain resulted in increased serum GH levels concomitant with a decrease in pituitary irSRIF content. This provides direct evidence that the preoptic area is the origin of a somatostatinergic projection inhibiting GH secretion from the goldfish pituitary. Lesions centered in the nucleus lateral tuberis (NLT) pars anterioris did not influence serum GH levels or the pituitary content of irSRIF. In contrast, more posterior lesions centered in the NLT pars posterioris (NLTp) resulted in a dramatic reduction in the amount of irSRIF in the pituitary. This suggests that the majority of irSRIF projections to the goldfish pituitary pass through the area destroyed by the lesion centered in the NLTp; it is also possible that perikarya within this area may be the origin of at least some of the irSRIF-containing fibers in the goldfish pituitary. Together, results from the present study provide evidence of a functional relationship between circulating levels of GH and endogenous brain and pituitary irSRIF in the goldfish.

Regional distribution of immunoreactive somatostatin in the bovine pineal gland.

Regional distribution of immunoreactive somatostatin (IRS) and melatonin were investigated in the bovine pineal gland. The total IRS and melatonin content ranged from 0.26 to 2.28 pmol, and from 19.4 to 42.7 pmol, respectively, per bovine pineal. Reverse phase liquid chromatography of pineal extracts demonstrated that more than 90% of IRS coeluted with synthetic somatostatin-14 and somatostatin-28. While the IRS content was shown to vary considerably throughout the gland, with a constant and marked maximal concentration at the proximal end of the pineal, the maximal melatonin concentration appeared in the central part of the gland, coinciding with the total protein distribution. The existence of the highest levels of pineal IRS near the habenular commissure, where the afferent fibers of the central pinealopetal innervation enter the gland, suggests that pineal somatostatin may be, at least in part, of neural origin.

Rhythms in pineal immunoreactive somatostatin in the Syrian hamster, mouse, and gerbil.

Immunoreactive somatostatin (IRS) has been previously demonstrated in the pineal gland of different rodent species, and we observed a 24-hr rhythm in rats. Recent data suggest that the peptide may represent a neurotransmitter in the so-called peptidergic nerves of the central, pinealopetal innervation of the epiphysis, which may modulate the activity and secretion of the gland. We investigated whether 24-hr changes of pineal IRS content occurred in Syrian hamsters, gerbils, and mice. Adult males, kept in a 14:10 LD photoperiod, were decapitated at 4-hr intervals throughout a 24-hr period. Pineals and median eminences were analyzed for IRS by radioimmunoassay. No significant changes in the median eminence content of IRS with time was observed. As previously described in rats, a statistically significant rhythm of IRS was observed in the pineal of hamsters and mice, with a peak at 2000 hr (mice 51.7 +/- 5 pg/pineal; hamsters 26.3 +/- 4.6) and a nadir at 2400 hr (mice 30.8 +/- 1.4) or 0400 hr (hamsters 8.6 +/- 1). However, in the gerbil pineal IRS content remained unchanged throughout the period of study. Since the three species examined have very different melatonin cycles, it is suggested that the melatonin and IRS rhythms are unrelated and independently regulated events within the pineal gland.

The effect of cysteamine on the somatostatin content of guinea-pig islets.

Cysteamine is known to deplete the immunoreactive somatostatin content in different organs from rat and mouse. The aim of the present work was to test if cysteamine also affects the somatostatin content in guinea-pig islets, since guinea-pigs have a carbohydrate metabolism different from that of other laboratory animals. Cysteamine was injected to guinea-pigs and the pancreatic islets were isolated four hours later. Cysteamine was also incubated in vitro with isolated pancreatic islets from untreated guinea-pigs. Cysteamine depleted the somatostatin content in the pancreatic islets in both the in vivo and in vitro studies.

Characterization of forms of immunoreactive somatostatin in sensory neuron and normal and deafferented spinal cord

In order to determine the contribution made by primary sensory afferents and supraspinal projections to the immunoreactive somatostatin (IRS) content of the spinal cord, measurements were made of the concentration of IRS in the dorsal and ventral halves of the cord in cats subjected to unilateral lumbosacral dorsal rhizotomy (L1-S3) alone or combined with spinal cord transection. The molecular forms of IRS (characterized by gel chromatography) in L7 lumbar spinal cord, L6-S1 dorsal roots, ventral roots and dorsal root ganglia, and sciatic nerve were also determined. S14 was the predominant form in all tissues examined, but two additional molecular forms corresponding to S28 and S11.5 kdalton were present in dorsal root ganglia and spinal cord; S28 but not S11.5 kdalton was detected in both dorsal roots and sciatic nerves. These results indicate that S14 and S28 and S28 are transported along the central and peripheral processes of dorsal root ganglia, but that spinal cord S11.5 kdalton originates in the central nervous system. IRS in the dorsal horn was reduced by ca. 40% following dorsal root section. Neither disruption of descending pathways by spinal transection nor surgical isolation of the lumbar segements lowered cord somatostatin content below that produced by dorsal root section, indicating that most of the somatostatin within the cord arises from the dorsal root and from neurons in local spinal segments. Although the total content of IRS in the dorsal horn was reduced by ca. 40% following dorsal rhizotomy, the pattern of molecular forms was not changed accordingly. Since S14 and S28 but not S11.5 kdalton are transported via the dorsal root, the dorsal root section would be predicted to produce a relatively greater decrease in S14 and S28 than in S11.5 kdalton. Therefore, failure to find a selective loss of S14 and S28 suggests that dorsal rhizotomy affects dorsal horn IRS content not only by removing afferent input but possibly also by modifyinh the processing of IRS by the remaining somatostatinergic neurons.

The effects of growth hormone, prolactin, corticotropin, and thyrotropin on the production and secretion of somatostatin by hypothalamic cells in vitro.

The influence of GH and several other pituitary hormones on the secretion and intracellular content of immunoreactive somatostatin (IRS) in cultured hypothalamic cells was examined. Hypothalamic cells prepared from 17-day-old rat embryos and maintained as reaggregate monolayers for 12 days in vitro were used. Short term release of IRS from these cultures was found to be stable and relatively constant. IRS release was enhanced by 60 mM K+ in a calcium-dependent fashion and by dopamine at concentrations as low as 1 nM. GH (1 microM) increased medium IRS content above baseline 12, 24, and 48 h after the incubation was begun, but had no effect after only 4 h. Hypothalamic cell content of IRS was increased by a 24-h incubation in 0.3 and 1.0 microM GH, but not by 0.1 microM GH. TSH (1 microM) induced an increase in IRS release comparable to 1 microM GH. However, intracellular IRS content was decreased after exposure to TSH. Cosyntropin, an ACTH analog, inhibited both IRS release and cell content, whereas PRL had no effect on either medium or cellular IRS content. Our results demonstrate that developing somatostatinergic neurons in the hypothalamus have the capacity to respond to pituitary hormones, indicating that short-loop feedback pathways may exist in perinatal hypothalamic cells.

Deficiency of immunoreactive somatostatin in the median eminence of snell dwarf mice

Snell dwarf mice (dw/dw) are characterized by a genetically determined, congenital lack of pituitary GH, TSH and prolactin. Given that hypothalamic somatostatin is involved in the regulation of pituitary GH and TSH release, it was decided to investigate the content of immunoreactive somatostatin (IRS) in the median eminence of dw/dw and phenotypically normal mice of the same strain. The content of IRS in the pyloric antrum and pineal gland of these animals was also examined. The effects of ovariectomy and of hyperprolactinemia (induced by a pituitary graft under the kidney capsule) on the median eminence content of IRS were also studied in both normal and dwarf mice. Median eminence IRS content was significantly lower in the dw/dw (23.6 ± 1.8 ng) than in normal mice (57.4 ± 7.1 ng); no difference was found in the pyloric IRS content of dw/dw (16.9 ± 1.6 ng/mg of protein) and normal animals (13.8 ± 1.9 ng/mg of protein), nor in the pineal content of IRS (639.4 ± 64.4 pg/gland in the dw/dw; 732 ± 265 pg/gland in normals). Neither ovariectomy nor hyperprolactinemia were found to affect the IRS content in the tissues studied in normal or dwarf mice. Treatment of an additional group of 9 dwarf mice with L-thyroxine (L-T 4 2 μg/48 h. s.c. for 2 weeks) significantly increased the animals weight (10.2 ± 0.4 g versus 7.4 ± 0.3 g) and produced maturation of facial features; however, it did not change the IRS content in any of the tissues studied. It is concluded that the content of IRS in the median eminence of mice with a congenital lack of GH, TSH and prolactin is significantly reduced and that this is unlikely to be related to the deficiency of thyroid hormones in these animals.

Effect of dopamine, bombesin and cysteamine hydrochloride on plasma growth hormone response to synthetic growth hormone-releasing factor in rats

In urethane anesthetized rats, an intracerebroventricular (icv) injection of 2 μg bombesin 5 min prior to the administration of synthetic human growth hormone-releasing factor (GRF) (1 μg/kg, iv) inhibited plasma growth hormone (GH) response, while cysteamine hydrochloride (90 mg/kg, sc) administered 150 min beforehand depleted immunoreactive somatostatin content in the pituitary-stalk median eminence and consequently potentiated the response to GRF. Under the same experimental conditions, central injection of 1.89 μg (10 −8M) dopamine hydrochloride or iv administration of L-DOPA (10 mg/kg) did not influence the subsequent plasma GH response to GRF. Results suggest indirectly that bombesin and cysteamine, but not dopamine, predominantly modulate somatostatin release from the hypothalamus.

Nighttime immunoreactive somatostatin content of the median eminence in hypo-and hyperthyroid rats

1. 1. The median eminence content of immunoreactive somatostatin (IRS) was measured by radioimmunoassay in 107 male albino rats, who were either hypothyroid after surgical thyroidectomy ( N = 38), hyperthyroid following a subcutaneous implant of 5 mg of l-thyroxine ( N = 36), or otherwise untreated ( N = 33). 2. 2. Thyroid function was assessed by determining plasma levels of T 4 and TSH from trunk blood obtained at the time of decapitation. Subgroups of animals from the 3 groups were killed either before (1800 hr), during (2200, 0200, 0400 hr), or after the dark portion of their 14:10LD photoperiod. 3. 3. Although no changes in median eminence IRS content were found throughout the period of study within any of the 3 groups, hypothyroid animals (297.23 ± 13.47 ng per ME; 620.41 ±58 ngIRS/mg protein) had a significantly lower median eminence IRS concentration than untreated rats (355.86 ± 16.55 ng of IRS per ME, P < 0.01; 906.86 ± 96.38 ng IRS/mg protein, P <0.05) and hyperthyroid animals (384.12 ± 14.67 ng per ME, P < 0.001; 874.1 ± 104.5 ng IRS//mg protein, P < 0.05). 4. 4. It is concluded, that the feedback of thyroid hormones on the hypothalamic-pituitary axis during thyroid hormone excess in vivo, contrary to what occurs in hypothyroidism, is probably independent of hypothalamic somatostatin.

Changes in immunoreactive somatostatin in brain following lidocaine-induced kindling in rat

The kindling phenomenon has become a useful model for studying epileptogenesis. The present authors have previously reported increased levels of immunoreactive somatostatin (IR-SRIF) in various regions of the brain of electrically-amygdaloid kindled (EAK) rats. In this study, an examination was made of immunoreactive somatostatin in pharmacologically-kindled (PK) rats. Sixteen male Sprague-Dawley rats were injected intraperitoneally (i.p.) with a subthreshold dose of lidocaine (60 mg/kg), once daily. Once the kindling phenomenon was established, kindled rats (7), non-kindled rats (9) and controls (6) were sacrificed by microwave irradiation. Another group of 5 rats was injected with a single suprathreshold dose of lidocaine (110 mg/kg) and killed 10 min after the resultant seizure. Various brain areas were removed and assayed for immunoreactive somatostatin in kindled rats. Immunoreactive somatostatin was significantly greater than in controls in the amygdala (56%; P < 0.02), entorhinal + piriform cortex (50%; P < 0.05) and hypothalamus (29%; P < 0.02). In non-kindled rats, immunoreactive somatostatin increased only in the amygdala (58%; P < 0.02). No difference was found in the immunoreactive somatostatin content of rats injected with an suprathreshold dose of lidocaine compared to controls. The alteration of immunoreactive somatostatin, in both lidocaine-kindled and electrically-amygdaloid kindled rats suggests a possible role of this neuropeptide in kindling.

Studies of the axoplasmic transport of somatostatin in the vagus nerve of the rat.

These studies were performed to examine the axoplasmic transport of somatostatin (SS) in the cervical vagus nerve of the rat. As a preliminary step, the immunoreactive SS (IR-SS) obtained from extracts of the vagal nodose ganglion and the vagus nerve was subjected to chromatographic analysis. On a Bio-Gel P-10 column, 92% of the nodose ganglion IR-SS and 98% of the vagal IR-SS coeluted with synthetic SS-14. The remaining immunoreactivity in both areas coeluted with synthetic SS-28. Vagal IR-SS demonstrated migratory characteristics identical to those of synthetic SS-14 on high performance liquid chromatography. A larger molecular weight form of IR-SS, which may correspond to prosomatostatin, was not identified in either site. When the vagus nerve was ligated distal to the nodose ganglion, the content of IR-SS increased in a time-dependent manner in the 3-mm segment of nerve proximal to the ligature. No increase in IR-SS was observed in an equal segment of nerve distal to the ligation or in the unligated contralateral nerve. Twenty-four hours after the ligation, the content of IR-SS (picograms per 3 mm; mean +/- SD) was: proximal segment, 33.9 +/- 9.6; distal segment, 3.4 +/- 3.0; and contralateral nerve, 1.7 +/- 0.7. The apparent transport velocity of IR-SS was estimated to be 2.1 +/- 1.5 mm/h. A variety of experimental approaches were used to characterize the mechanisms underlying the transport process and to define the anatomical sites of origin of the transported peptide. The application of colchicine to the vagus nerve resulted in an accumulation of IR-SS above the area which was not significantly different from that obtained after nerve ligation. When the vagus nerve was crushed above the nodose ganglion, the accumulation of IR-SS in the proximal segment was reduced by 50%, although the IR-SS content in the nodose ganglion and in the intervening nerve segments was unchanged by this procedure. The induction of a chemical sympathectomy with guanethidine had no effect on the accumulation of IR-SS. The administration of capsaicin during the neonatal period or in adult life had no effect on the transport of IR-SS, but greatly decreased the transport of substance P.(ABSTRACT TRUNCATED AT 400 WORDS)

Profound suppression of kindled seizures by cysteamine: possible role of somatostatin to kindled seizures

Recently we reported significant increase in immunoreactive somatostatin content in various brain regions of amygdaloid-kindled rats. We report here that acute intraperitoneal administration of cysteamine, an agent reported to deplete brain and gastrointestinal immunoreactive somatostatin content in kindled rats, led to profound suppression of kindled seizures. Purified anti-somatostatin antibody injected intracerebroventricularly also blocked the kindled seizures. The results show that endogenous immunoreactive somatostatin has a role in the development of seizures in amygdaloid kindled rats.

Distribution and characterisation of immunoreactive somatostatin in human gastrointestinal tract.

Immunoreactive somatostatin (IRS) was measured in acid extracts of human gastrointestinal tissue. The highest levels were found in the duodenum, pancreas, jejunum and stomach with lower levels in the ileum and colon. In the antrum, pylorus, duodenum and pancreas the main peak of IRS (1.6K IRS) coeluted with synthetic somatostatin-14 on both gel filtration chromatography and HPLC. In the body of stomach, jejunum, ileum and colon, a large peak coeluting with synthetic somatostatin-28 (3.5K IRS) on both chromatographic systems was also identified, while minor peaks of IRS assigned molecular weights of 6000 (6K) and greater than 15 000 (15K) were seen in some extracts. The total IRS content and pattern of molecular forms were similar in tissues obtained from adults at surgery or rapid post mortem, and in tissue taken from human fetuses after prostaglandin termination of pregnancy. When tissues were divided into mucosal and muscle layers, greater than 90% of the IRS was in the mucosa with less than 10% in the muscle layer. In the muscle layer the IRS was almost entirely the 1.6K form in all tissues. Immunohistochemical studies showed the IRS in the mucosa to be localised in endocrine-type cells, while in the muscle layer the IRS is present in nerve fibres and neurones of the myenteric plexus. It is suggested that (1) different mechanisms may control the biosynthesis of somatostatin-14 and somatostatin-28 in mucosal cells in different parts of the gut, (2) different biosynthetic controls may operate in endocrine-like and neuronal cells in the same region of the gut.

Somatostatin biosynthesis by cerebral cortical cells in monolayer culture.

We examined the ability of isolated rat cerebral cortical cells to synthesize and secrete immunoreactive somatostatin (IRS). Dispersed telencephalic cells (10(7] from rat embryos contain approximately 24 pg IRS. The IRS content of 10(7) cultured cells increased steadily to a level of 2800 pg by 20 days in vitro. The IRS content in the medium followed a parallel production curve and was, in general, 10% of the cellular content. The nature of this IRS was characterized by gel filtration. Bio-Gel P-10 chromatography resolved four discrete IRS peaks. The first peak had an apparent molecular weight of 11,500. The second peak, which comigrated with synthetic Somatostatin-28, had a molecular weight of 7,000. The third peak had a molecular weight of 1,800, and the fourth peak, which comigrated with Somatostatin-14, had a molecular weight less than 1,800. Incubation with [3H]phenylalanine (Phe) revealed that 3H was incorporated into each peak. Isolation of 3H-labeled peak 4 was carried out by double affinity column purification. Sequential automated Edman degradation of this material revealed [3H] Phe in the positions that Phe occupies in Somatostatin-14. These studies document the ability of isolated rat cerebral cortical tissue to synthesize several forms of IRS, establishing them as endogenous cortical peptides.