[Diabetic thoracoabdominal neuropathy. Clinical and electrophysiological study with evaluation of the autonomic nervous system]

We report on eight patients with diabetic thoracoabdominal neuropathy in whom careful evaluation of peripheral and autonomic nervous system function was performed. All patients had non insulin-dependent diabetes mellitus of 10.5 +/- 6.7 years mean (+/- SD) known duration with poor glycemic control. Thoracic (n = 7) or abdominal (n = 1) pain of sudden onset involved several adjacent dermatomal segments and was bilateral and asymmetrical in 7/8 patients. Four patients had hypoesthesia in the painful zone and six presented with significant weight loss (6.2 +/- 4.3 kg) which reversed after the relief of pain. Truncal electromyogram was abnormal in 7/7 patients. Nerve damage was not limited to thoracic nerves since electrophysiological studies evidenced distal polyneuropathy in all patients. The autonomic nervous system was also involved. Sympathetic skin response was abnormal in 7/7 patients and autonomic cardiovascular function tests demonstrated cardiac denervation in 5/5 patients. In 4/4 patients a marked relief of pain was noted within one week with amitriptyline treatment. This report confirms the characteristic clinical presentation of diabetic thoracoabdominal neuropathy. Moreover, it suggests that this neuropathy is part of a diffuse damage that also involves peripheral nerves of the limbs and autonomic nervous system.

Regulation of somatostatin synthesis by GABAA receptor stimulation in mouse brain

Neuroanatomical data have documented the existence of synaptic contacts between gamma-aminobutyric acid (GABA) terminals and periventricular hypothalamic somatostatin (SRIF) neurons. In other brain regions, like the cortex or hippocampus, GABA and SRIF are colocalized in short interneurons. These observations suggest that GABA modulates SRIF neuronal activity. In order to test this hypothesis, we studied the effects of the in vivo stimulation of the GABAA receptor (muscimol, 0.75 mg/kg + diazepam, 2.5 mg/kg) on SRIF content and preproSRIF mRNA levels, in mouse brain. Chronic (7 days), but not acute, treatment induced a 38% decrease in hypothalamic SRIF content (as estimated by RIA), a 20% decrease in cortex and no effect in the striatum. The decrease in hypothalamic and cortical SRIF levels lasted until 24 h after cessation of the treatment. In the hypothalamus, prosomatostatin mRNA levels were estimated by Northern blot analysis using a 32P-labeled 45-mere oligoprobe. ProSR1F mRNA hypothalamic levels were equally (48%) decreased by the acute and chronic treatments and remained lower than controls 48 h after the last injection. Quantitative in situ hybridization was used to examine the regional distribution of GABA-induced acute inhibition of proSR1F mRNA densities, using the same oligomere labeled with 35S. ProSR1F mRNA levels were decreased by 35% in the periventricular hypothalamic nucleus. In contrast, no significant modification was observed in cortex, striatum and hilus of the dentate gyrus of the dorsal hippocampus. The present data demonstrate a regionally selective inhibitory action of GABA, mediated by GABAA receptors stimulation, on the biosynthetic mechanisms of the long projecting neuroendocrine SRIF neurons of the anterior periventricular nucleus of the hypothalamus.

Somatostatin receptors on thyrotropin-secreting pituitary adenomas: comparison with the inhibitory effects of octreotide upon in vivo and in vitro hormonal secretions

The in vivo and in vitro inhibitory effects of a somatostatin (SRIH) analog, octreotide, upon TSH, alpha-subunit, GH, and PRL have been studied, as well as SRIH receptors and their coupling to adenylate cyclase, in nine TSH-secreting pituitary adenomas. From in vivo and cell culture studies, the TSH- and alpha-subunit-secreting adenomas appeared heterogeneous, with four out of the nine tumors cosecreting GH and/or PRL. A single sc injection of octreotide (100 micrograms) lowered plasma concentration of TSH by 40 +/- 5% (mean +/- SE of 5), of alpha-subunit by 27 +/- 9% (n = 5), of GH by 60 +/- 5% (n = 4), and of PRL by 27 +/- 9% (n = 4). In cells cultures, octreotide (10(-8) mol/L) inhibited equally TSH, alpha-subunit, and GH release. 125I-Tyr0-DTrp8-SRIH binding sites were measurable in the nine TSH-secreting adenomas either on membrane preparations (n = 6; Bmax: 152 +/- 73 fmol/mg protein) or on frozen sections by radioautography (n = 3). Their density was variable among TSH adenomas and was lower than that measured in GH-secreting adenomas but higher than in nonfunctioning tumors. Two out of three TSH-secreting adenoma displayed an heterogeneous distribution of 125I-Tyr0-DTrp8-SRIH binding sites. 125I-Tyr0-DTrp8-SRIH specific binding was inhibited by guanosine triphosphate (GTP: 10(-4) mol/L). SRIH inhibited adenylate cyclase in 5/5 TSH-secreting adenomas and a good correlation (r = 0.92, P less than 0.02) was found between 125I-Tyr0-DTrp8-SRIH binding capacity (Bmax) and maximal adenylate cyclase inhibition by SRIH. These results demonstrate in vivo and in vitro inhibition of TSH, alpha-subunit, PRL, and GH secretion by octreotide in TSH-secreting pituitary adenomas. Functional SRIH receptors are present on these tumors and the effect of SRIH on hormonal secretion could be mediated, at least in part, by inhibition of adenylate cyclase. These findings support the medical treatment of this rare type of tumors by SRIH analogs.

Growth hormone-releasing hormone-synthesizing neurons are a subpopulation of somatostatin receptor-labelled cells in the rat arcuate nucleus: a combined in situ hybridization and receptor light-microscopic radioautographic study

Distribution of growth-hormone-releasing hormone (GHRH) cell bodies and somatostatin binding sites were compared in the mediobasal hypothalamus of the rat. GHRH-synthesizing neurons were visualized by in situ hybridization, using as 35S-labelled synthetic oligonucleotide (45 mere), and 125I-Tyr0-DTrp8-somatostatin (125I-SRIH) binding sites by light-microscopic radioautography on adjacent 20-microns-thick frozen mirror sections. GHRH mRNA hybridizing cells were detected mostly in the ventrolateral portion of the arcuate nucleus (ARC) and around the perimeter of the ventromedial nucleus (VMN). Comparison with the distribution of pericellular 125I-SRIH binding sites allowed to differentiate three types of cells: (1) GHRH perikarya not associated with pericellular 125I-SRIH binding sites around the perimeter of the VMN, (2) 125I-SRIH-labelled cells, not associated with GHRH perikarya in the periventricular zone along the dorsal part of the third ventricle, and (3) in the ventrolateral portion of the ARC, GHRH mRNA-labelled neurons had the same distribution as 125I-SRIH-labelled cells. Furthermore, on adjacent sections, the number of both labelled cells were correlated (r = 0.68; p less than 0.001). In this last population, the extent of colocalization of 125I-SRIH binding sites on GHRH mRNA-labelled neurons was further investigated in adjacent 5-microns-thick sections. The proportions of cells GHRH mRNA and 125I-SRIH allowed to differentiate three subdivisions of the arcuate: the periventricular (PV), ventrobasal (VB) and lateral portions. In the PV-ARC, 27% of GHRH-synthesizing cells were coidentified as 125I-labelled while only 6% of 125I-labelled cells contained GHRH mRNA. In the VB-ARC the proportion of double-labelled cells was equivalent (31 and 26%, respectively for GHRH mRNA and 125I-SRIH).(ABSTRACT TRUNCATED AT 250 WORDS)

Resistance to somatostatin (SRIH) analog therapy in acromegaly. Re-evaluation of the correlation between the SRIH receptor status of the pituitary tumor and the in vivo inhibition of GH secretion in response to SRIH analog

The development of a long-acting somatostatin (SRIH) analog (octreotide, Sandoz) has been a major breakthrough in the treatment of acromegaly. However, in 20-30% of the patients, growth hormone (GH) plasma levels remain elevated (> 10 micrograms/l) despite treatment with octreotide. This raised the concept of resistance to SRIH analog therapy in acromegaly. Indeed, in vivo response to SRIH analogs varies greatly among acromegalic patients. According to the reviews in the literature and our own autoradiographic data, no direct correlation can be established between the GH response to octreotide and the number or affinity of the SRIH receptors located on the tumor. In our series a greater density of SRIH receptors is present on tumors from patients very sensitive to the SRIH agonist. A subset of patients resistant to octreotide could result from a very low density of SRIH receptor although this type of GH-secreting tumor constitutes certainly a rare case. A subset of GH-secreting pituitary tumors can be characterized by a mutation on the alpha subunit of the guanine nucleotide-dependent protein coupled to the stimulation of adenylate cyclase (G alpha s). This mutation results in a high basal adenylate cyclase activity and a low GHRH-stimulated activity. However, when the adenomas are separated according to their basal adenylate cyclase activity, SRIH is able to decrease cAMP levels in both types of tumor. In addition, in our series no direct correlation is observed between the SRIH inhibition of adenylate cyclase and the amount of SRIH-binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Light microscopic radioautographic localization of somatostatin binding sites in the brainstem of the rat

The distribution of somatostatin binding sites was investigated by light microscopic radioautography in the brainstem of the rat following in vitro labeling with 125I-Tyr0-DTrp8-somatostatin14. Moderate to high labeling densities were detected within the superior colliculus, the locus coeruleus and subcoeruleus, the parabrachial complex, the nucleus of the solitary tract and the dorsal motor nucleus of the vagus. Most of the white matter was devoid of specific somatostatin binding except for fibers of the glossopharyngeal nerve and the spinal trigeminal tract. In most of the labeled areas, 125I-somatostatin binding was evenly distributed between neuropil and perikarya. In a few instances, however, the binding clearly predominated over nerve cell bodies: namely in the dorsal motor nucleus of the vagus and in the pontine and medullary tegmentum. In the latter two regions, the labeled neurons were identified in adjacent sections by tyrosine hydroxylase immunohistochemistry as belonging to the A5 and A1 catecholamine cell groups, respectively. These findings, together with the confirmed association of somatostatin binding sites with noradrenergic neurons in the locus coeruleus, suggest that interactions with catecholaminergic systems may represent a major mode of action for somatostatin in the brainstem.

Decreased bronchial response to methacholine in IDDM patients with autonomic neuropathy

This study was designed to evaluate the involvement of airways innervation during diabetic autonomic neuropathy. Bronchial response to methacholine was assessed by inhalation of serially doubling doses in 22 insulin-dependent diabetes mellitus (IDDM) patients and 11 nondiabetic control subjects selected for their nonsmoking habits. Cardiovascular autonomic control was studied by four standardized tests, i.e., blood pressure and heart-rate variations during orthostatism, heart-rate variation during Valsalva maneuver, and deep breathing. Magnitude and time-course of response to methacholine were similar in nondiabetic subjects and IDDM patients without any abnormal result on cardiovascular tests. Conversely, bronchial response to methacholine was markedly reduced in IDDM patients with one or more abnormal results by cardiovascular assessment of autonomic control. In the IDDM patients, bronchial response to methacholine was significantly correlated to indexes of cardiovascular autonomic control. These results suggest that, during diabetic neuropathy, innervation of the airways likewise involves cardiac autonomic control and leads to impairment of defense reflexes of the airways.

Somatostatin depletion by cysteamine increases somatostatin binding and growth hormone-releasing factor messenger ribonucleic Acid in the arcuate nucleus

We have previously described somatostatin (SRIF) pericellular binding sites in the vicinity of growth hormone-releasing factor (GRF)-containing cells in the ventrolateral part of the arcuate nucleus (ARC) of the male rat. To further assess the direct role of SRIF on GRF messenger ribonucleic acid (mRNA) levels in the mediobasal hypothalamus, we depleted endogenous SRIF by cysteamine (CS; 300 mg/kg body wt 6 h prior to sacrifice). In the ventrolateral part of the ARC, there was a 2-fold increase (P<0.05) in [(125)I]SRIF specific binding and GRF mRNA-labelled cell numbers in the CS-treated group as compared to control animals. Furthermore, there was a positive correlation between [(125)I]SRIF binding and the number of GRF mRNA-labelled cells (r = 0.89; P<0.01). In contrast, such effects were not observed along the base of the ventromedial nucleus where pericellular [(125)I]SRIF binding was not associated with GRF mRNA-labelled cells. These results provide functional evidence for a direct SRIF inhibition, through specific receptors, of GRF mRNA levels in ARC neurons.

A human TSH-secreting adenoma: endocrine, biochemical and morphological studies. Evidence of somatostatin receptors by using quantitative autoradiography. Clinical and biological improvement by SMS 201-995 treatment

An invasive TSH-secreting adenoma inducing mild hyperthyroidism was diagnosed in a 16-year-old male. Initial surgical treatment led to a temporary clinical and biological improvement. Recurrence of the thyrotoxicosis was treated with the somatostatin analogue, SMS 201-995 (octreotide) with normalization of the serum thyroid hormone levels with a dose of 200 micrograms per day. With immunoelectron microscopy, the tumour cells appeared poorly granulated with small secretory granules located at the periphery of the cells; only part of those were immunoreactive with an anti-TSH beta monoclonal antibody. No specific TRH binding site was found in a tumour membrane preparation. By quantitative autoradiography, somatostatin specific binding sites were as numerous in the TSH-secreting tumour as in control GH-secreting tumours. Binding kinetics and guanosine triphosphate dependency of the binding were equivalent in the TSH and GH tumours tested. Although all of the tumour cells displayed the same ultrastructural features, some were non-immunoreactive, suggesting that they could secrete an altered form of TSH. The absence of TRH receptors in the tumour cells is in accordance with previous reports on this type of tumour. We confirm the efficiency of octreotide treatment in this case of neoplastic TSH inappropriate secretion. The therapeutic effect of octreotide goes along with the presence of a high density of guanine nucleotide-dependent somatostatin binding sites in the tumour cells.

Characterization of pericellular [125I]Tyr0 DTrp8 somatostatin binding sites in the rat arcuate nucleus by a newly developed method: quantitative high-resolution light microscopic radioautography

In the present work we characterized the kinetic properties of [125I]somatostatin pericellular binding sites in the arcuate nucleus of the hypothalamus of the rat by quantitative high-resolution light microscopic radioautography. In order to determine whether these pericellular binding sites corresponded to functional receptors, their properties were compared with those of previously well-characterized [125I]somatostatin binding sites present on neuronal processes on the same sections in the stratum radiatum of the CA1 of the hippocampus. Radiolabelled sections were analysed by densitometry using a Biocom image analysis system coupled with a Leitz orthoplan microscope. The linear relationship between optical densities and radioactive standards allowed us to quantitate [125I]somatostatin-specific binding. Binding was time- and temperature-dependent, and saturable and specific in the arcuate nucleus as in the CA1 of the hippocampus. Saturation experiments indicated a single receptor population of binding sites with KD values of 0.2 +/- 0.1 nM in the arcuate nucleus and 0.6 +/- 0.4 nM in the CA1. In both structures, displacement curves obtained with somatostatin 14 and somatostatin 28 were monophasic, but shallow, while the somatostatin analogue SMS 201-995 induced a biphasic displacement, suggesting two populations of binding sites. In both regions binding was GTP-dependent. Desaturation procedures (in vivo by cysteamine and in vitro by preincubating with GTP) resulted in an increase in the number of measurable binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional distribution of somatostatin binding sites in the human hypothalamus: a quantitative autoradiographic study

Using in vitro quantitative autoradiography and [125I]Tyr0-D-Trp8SRIF 14 as radioligand, we characterized the detailed distribution of somatostatin binding sites in human hypothalamus of both infants and adults. Guanosine triphosphate pretreatment, before incubation, allowed us to detect higher [125I]Tyr0-D-Trp8SRIF 14 binding site densities in hypothalamic structures such as preoptic and anterior hypothalamic areas and ventromedial and dorsomedial nuclei. In contrast, guanosine triphosphate was without effect in the other hypothalamic regions. The regional effects of guanosine triphosphate pretreatment were not different in infant and adult hypothalamus. Scatchard analysis showed that in a guanosine triphosphate-sensitive region (preoptic area) and a guanosine triphosphate-insensitive area (infundibular nucleus), [125I]Tyr0-D-Trp8SRIF 14 bound to a single class of binding sites. Affinities were similar in both regions, not modified by guanosine triphosphate pretreatment and not different in the adult (1.5 +/- 1.2 nM vs 3.2 +/- 2.1 nM for preoptic area and infundibular nucleus, respectively) and infant (0.9 +/- 0.5 nM vs 2.4 +/- 1.7 nM for preoptic area and infundibular nucleus). [125I]Tyr0-D-Trp8SRIF 14 binding sites were widely distributed in the anterior, mediobasal and posterior hypothalamus. Somatostatin 28 was twice as potent as somatostatin 14 to displace [125I]Tyr0-D-Trp8SRIF 14 binding in the preoptic area and infundibular nucleus. However, IC50s were 30 times lower in the preoptic area as compared with the infundibular nucleus. In adult as well as in infant, high densities were found mainly in the diagonal band of Broca, preoptic area and infundibular nucleus. Intermediate densities were localized in the anterior hypothalamic area, ventromedial, dorsomedial and lateral mammillary nuclei. The dorsal hypothalamic area, the paraventricular and medial mammillary nuclei displayed low but measurable densities. The only marked difference in the distribution of [125I]Tyr0-D-Trp8SRIF 14 binding sites in adult vs infant was observed in the medial and tuberal nuclei where the concentrations were seven-fold higher in adult hypothalamus.

Effects of chronic growth hormone hypersecretion on intrinsic contractility, energetics, isomyosin pattern, and myosin adenosine triphosphatase activity of rat left ventricle

We studied papillary muscle mechanics and energetics, myosin phenotype, and ATPase activities in left ventricles from rats bearing a growth hormone (GH)--secreting tumor. 18 wk after tumor induction, animals exhibited a dramatic increase in body weight (+101% vs. controls) but no change in the ventricular weight/body weight ratio. The maximum isometric force of papillary muscles normalized per cross-sectional area rose markedly (+42%, P less than 0.05 vs. controls), whereas the maximum unloaded shortening velocity did not change. This was observed despite a marked isomyosin shift towards V3 (32 +/- 5% vs. 8 +/- 2% in controls, P less than 0.001). Increased curvature of the force-velocity relationship (+64%, P less than 0.05 vs. controls) indicated that the muscles contracted more economically, suggesting the involvement of V3 myosin. Total calcium- and actin-activated myosin ATPase activities assayed on quickly frozen left ventricular sections were similar in tumor-bearing rats and in controls. After alkaline preincubation, these activities only decreased in tumor-bearing rats, demonstrating that V3 enzymatic sites were involved in total ATPase activity. These data demonstrate that chronic GH hypersecretion in the rat leads to a unique pattern of myocardial adaptation which allows the muscle to improve its contractile performance and economy simultaneously, thanks to myosin phenoconversion and an increase in the number of active enzymatic sites.