Effects of tablet and effervescent formulations of ranitidine 75 mg and cimetidine 200 mg on gastric acidity and oesophageal acid exposure in healthy humans

BACKGROUND

Because of their tolerance and safety, low doses of H2-receptor antagonists are now increasingly used in some countries for self-care medication of gastro-oesophageal reflux symptoms.

AIM

The purpose of this randomized, double-blind, placebo-controlled, five-way crossover study was to determine and to compare the effects of low doses of ranitidine and cimetidine both on gastric pH and on oesophageal acid exposure.

METHODS

Gastric and oesophageal pH were simultaneously monitored in 20 healthy subjects using two glass pH electrodes, after placebo and single doses of ranitidine 75 mg and cimetidine 200 mg (effervescent and tablet forms), for 4 h before and after a meal.

RESULTS

During the fasting period, median gastric pH rose significantly with both drugs, but more rapidly with the effervescent forms; the oesophageal acid exposure was significantly decreased by all drug regimens. After the meal, although there was no significant difference in gastric pH values, oesophageal acid exposure was significantly decreased in comparison with placebo with both forms of ranitidine (P < 0.05), and also for ranitidine tablets in comparison with cimetidine tablets (P < 0.05).

CONCLUSIONS

Low doses of ranitidine and cimetidine increase gastric pH, with a more pronounced effect for ranitidine. Effervescent formulations of both drugs induce a slightly more rapid initial increase in pH than tablets. Ranitidine demonstrates a more prolonged effect than cimetidine and decreases oesophageal acid exposure monitored after a meal ingested 4 h after the drug intake.

On-demand treatment of gastro-oesophageal reflux symptoms: a comparison of ranitidine 75 mg with cimetidine 200 mg or placebo

AIM

To compare the effects of ranitidine 75 mg with those of either cimetidine 200 mg or placebo given on demand for relief of typical symptoms of gastro-oesophageal reflux disease during a 15-day period.

METHODS

A total of 1336 patients (aged > or = 18 years) with heartburn episodes were recruited and randomly assigned to a ranitidine 75 mg, cimetidine 200 mg or placebo group. Depending on the occurrence or persistence of heartburn, treatment was administered as required up to three times daily, with at least 2 h between drug doses. Antacids were allowed as rescue medication if symptoms persisted for at least 2 h after the third medication on any given day. The primary end-point was defined as the proportion of patients with relief of at least 75% of heartburn episodes during the study period (i.e. relief occurring within 2 h after drug ingestion and lasting for at least 5 h).

RESULTS

Analysis was performed in an intention-to-treat population comprising 504 subjects in the ranitidine group, 515 in the cimetidine group and 270 in the placebo group. Primary end-point success rates were 41, 38 and 28%, respectively, for the three groups (P < 0.001 for ranitidine vs. placebo, P = 0.274 for ranitidine vs. cimetidine). Ranitidine 75 mg was significantly more effective than placebo in providing overall heartburn relief (P < 0.001). The differences between the ranitidine and cimetidine groups were not significant, except for a greater reduction in heartburn frequency in the ranitidine group at the end of the study period (P < 0.05). Drug dose was lower and less rescue medication was used in the ranitidine group than the placebo group. The three treatment groups did not differ in terms of tolerability.

CONCLUSION

On-demand ranitidine 75 mg or cimetidine 200 mg are safe and effective treatment for reflux-related symptoms.

Species differences between male rat and ram pituitary somatostatin receptors involved in the inhibition of growth hormone secretion

The sheep is a valuable model in which to study GH neuroregulation as its pattern of GH secretion is very close to that in humans. Furthermore, important differences in somatostatin (SRIH) action between rats and sheep have been found previously. Our goal was to compare in male rat and ram pituitaries the binding characteristics of somatostatin receptors and the effect of SRIH and 17 analogues on GH release. Using radioautography, SRIH binding was seen to be evenly distributed over the anterior pituitary of both species. In the binding assay, binding sites were three times more concentrated in rats than in sheep. Important interspecies differences in the action of SRIH and its analogues were found: they inhibited GH at lower concentrations in rats than in sheep. Seven peptides displayed greater inhibitory ability in sheep than in rats while three were more potent in rats. Agonistic potencies to inhibit GH release in rats were correlated with somatostatin receptors subtype 2 (sst2) affinities. Our data confirm and extend the quantitative differences between rat and sheep in SRIH inhibitory action on GH secretion and confirm that ligand-binding properties of a given receptor subtype cannot be extrapolated across species.

Distribution and pharmacological characterization of somatostatin receptor binding sites in the sheep brain

Somatostatin binding sites have been localized and quantified in the sheep brain using 125I-Tyr0-DTrp8-somatostatin, by quantitative high resolution light microscopic autoradiography. Sections were analyzed by densitometry on radioautographic film, and subsequently on slides coated with photoemulsion. Specific somatostatin binding sites were concentrated in the medial habenula, superior colliculus, dorsal motor nucleus of the vagus nerve, inferior olive, spinal trigeminal nucleus, and cerebellum. In competition experiments, octreotide, a sst2/sst3/sst5 selective agonist only partially displaced 125I-Tyr0-DTrp8-somatostatin in the three cerebellar layers while it was fully active as compared to somatostatin 14 and 28 in the deeper layers of the parietal cortex. Moderate to low somatostatin receptor densities were present in the mesencephalic periaqueductal gray, dorsal raphe, thalamic paraventricular nucleus, interpeduncular nucleus, pineal gland, dorsal tegmental, dorsolateral tegmental and parabrachial nuclei, nucleus of the solitary tract. The distribution of somatostatin binding sites generally correlates with the data obtained on slides dipped in photoemulsion which provided better resolution and more precise localization. In most of the labeled areas, 125I-Tyr0-DTrp8-somatostatin receptor binding was distributed between both neuropil and perikarya. Perikarya bearing 125I-Tyr0-DTrp8-somatostatin receptors were observed in areas which did not display detectable binding sites on film such as the preoptic-anterior hypothalamic complex and arcuate nucleus and in the locus coeruleus. In conclusion, the distribution of 125I-Tyr0-DTrp8-somatostatin binding sites in sheep brain is very reminiscent of other mammals being closer to the human than to rodents.

Complementation analysis of carnitine palmitoyltransferase I and II defects

Carnitine palmitoyltransferase (CPT) consists of two activities located in the outer (CPT I) and the inner (CPT II) mitochondrial membranes. CPT II deficiency in the adult as well as in the infantile form of the disease has been shown to result from mutations in the CPT II cDNA. Nothing is known regarding the genetic defect in CPT I deficiency. We carried out complementation experiments between CPT I- and infantile CPT II-deficient cell lines. Restoration of 3H2O release from [9,10(n)-3H]-palmitate was chosen as criterion of complementation. As expected, no complementation was observed in heteropolykaryons resulting from fusions between CPT II-deficient cells. Similar results were obtained in fusions between CPT I-deficient cells, suggesting that the enzymatic defect in these cell lines results from mutations in the same gene. Conversely, complementation was observed in fusions between CPT I- and CPT II-deficient cells. These data support that CPT I and CPT II defects result from mutations in distinct genes. Palmitate oxidation by control or CPT I-deficient cell lines was decreased when cocultured with infantile CPT II-deficient cell lines. This effect, not observed in coculture including an adult CPT II-deficient cell line, was carnitine-dependent. The possible mechanism of this effect, suppressed by a high carnitine concentration, is discussed.

[Antacid activity of citrate-bicarbonate complex of effervescent formulations of ranitidine. In vitro analysis using 'artificial stomach-duodenum' model]

Antacid activity supported by citrate-bicarbonate complex of four effervescent ranitidine forms has been assessed in vitro using an 'artificial stomach-duodenum' model controlled by microcomputer. This model allows (i) maintenance of constant the rates of the fluxes throughout the experiments or (ii) simulation of gastroduodenal flux regulation, in the normal subject (NS) or in the duodenal ulcer patient (DU) situation. The four forms developed a theoretical maximal antacid capacity between 61 and 81 mmol with a maximum intragastric pH between 3.2 and 4.8. In the gastroduodenal flux regulation simulation, antacid activity duration was rapid and included between 85 and 118 min in NS situation (50 to 56 mmol H+ consumed) and between 75 and 93 min in DU situation (43 to 47 mmol H+ consumed). The reduction of acid load penetrating into the duodenum was contained between 36 and 50 per cent. Effervescent compounds exerted a neutralising activity and a buffering capacity close to pH 6.0 (5 per cent of total antacid capacity), related to antacid potency.

Correlations between water maze performance and cortical somatostatin mRNA and high-affinity binding sites during ageing in rats

Somatostatin levels and high-affinity (somatostatin-1) binding sites are decreased in post-mortem cortical samples of Alzheimer's disease patients but the relationships between such modifications and the cognitive deficits remain to be established. We investigated these relationships in the ageing rat. Three age groups (3-4, 14-15 and 26-27 months) were tested in a modified version of the Morris water maze. Somatostatin mRNA levels were quantified by in situ hybridization and somatostatin binding sites by radioautography using the selective agonist octreotide (SMS 201995) as a competing drug to evaluate high-affinity (somatostatin-1) and low-affinity (somatostatin-2) binding sites. The number of somatostatin mRNA-containing cells was not modified with age or memory performance in cortical, hippocampal and hypothalamic regions, but somatostatin mRNA densities were significantly decreased with age and with memory performance in the frontal and parietal cortex. In the frontal cortex somatostatin mRNA densities were already decreased in 14- to 15-month-old rats, whereas the decrease was observed only in 26- to 27-month-old rats in the parietal cortex. A decrease in somatostatin-1 binding was observed with memory performance, independently of age, in the basolateral amygdala only, while somatostatin-2 binding sites were not affected. In the frontal and parietal cortex, a significant correlation occurred between the latency to find the invisible platform in the water maze and somatostatin mRNA (r = -0.54 and 0.59 respectively, P < 0.02). These results indicate that ageing rats with memory impairments display some of the features of the somatostatinergic deficits observed in Alzheimer's disease.

Effects of neonatal administration of octreotide, a long-lasting somatostatin analogue, on growth hormone regulation in the adult rat

The pulsatile pattern of GH secretion slowly develop in the postnatal period concomitantly with the dual network of GHRH and somatostatin (SRIH) hypothalamic neurons. We investigated whether an early postnatal treatment with a long acting SRIH analogue, octreotide, could affect maturation and subsequent operation of those networks in the adult rat. Octreotide administration (5 mu g/rat SC) every other day during the first 10 days of life resulted in growth retardation in the adult. In parallel, the amplitude of plasma GH secretory episodes in free moving unanesthetized animals was markedly reduced. The numbers of arcuate GHRH mRNA-containing and periventricular SRIH-mRNA containing neurons were not affected by the treatment. GHRH mRNA levels per neuron however was decreased by 30%, and median eminence GHRH stores by 50%. SRIH expression in the arcuate nucleus was also diminished, as was the number of 125I-SRIH labeled neurons in that nucleus. The effects of octreotide were compared to the hyposomatotropinemia induced by administration of monosodium glutamate (MSG), every other day during the first 10 days of life. Growth retardation and inhibition of GH secretory episodes in adult rats neonatally treated with MSG were slightly more pronounced than after octreotide. In contrast to octreotide, MSG induced a massive loss of GHRH neurons and a concomitant decrease in 125I-SRIH binding. Somatostatin did not protect GHRH neurons against the neurotoxic action of MSG since octreotide treatment did not further affect any of the parameters impaired by MSG. In conclusion, these experiments demonstrate that neonatally injected octreotide cannot counteract the toxic effect of MSG on arcuate neurons. However, a neonatal treatment with the SRIH agonist affects permanently growth rate and GH pulsatility. This effect is mediated in the hypothalamus by permanently impairing the neural networks that control GH secretion.

The increase in growth hormone secretion in experimentally induced arthritic rats is an adaptive process involved in the regulation of inflammation

In Sprague-Dawley rats, Freund-adjuvant-induced arthritis (AIA) results in an increase in the amplitude of ultradian growth-hormone (GH)-secretory episodes without modification of their frequency. This is most apparent at the time of maximal inflammation, i.e. 14-21 days after inoculation of the adjuvant. GH responsiveness to a maximal dose of clonidine (10 micrograms/100 g body weight, BW), a secretagogue known to act at the hypothalamic level, is comparable in AIA and control rats. In contrast, GH response to a maximal dose of GH-releasing hormone (GHRH, 1 microgram/100 g BW), a peptide acting directly on pituitary somatotropes, is greater in AIA than in control rats. Furthermore AIA affects significantly neither hypothalamic somatostatin and GHRH mRNA levels nor pituitary GH content. In adult rats treated neonatally with monosodium glutamate (MSG), a neurotoxin which destroys the majority of GHRH neurons of the arcuate nucleus and reduces considerably plasma GH levels, clinical symptoms observed 14 days after inoculation of the Freund adjuvant are more marked than in AIA. The MSG-treated rats exhibit in particular a significantly higher increase in hindpaw diameter. Pulsatile administration of GH (40 micrograms/day/rat, with successive periods of 2 h of GH and 4 h of mineral oil) restoring the endogenous GH-secretory pattern throughout the 15-day period of arthritis development prevents hindpaw diameter increase. These results indicate that the impact of AIA on GH regulation occurs at the pituitary but not the hypothalamic level and suggest that increased GH secretion observed in AIA rats is an adaptive mechanism involved in the regulation of the inflammatory process.

Neonatal hyperammonemia caused by a defect of carnitine-acylcarnitine translocase

Carnitine-acylcarnitine translocase deficiency is a newly recognized inborn error of metabolism that involves transport of long-chain fatty acids into mitochondria, which in turn impairs mitochondrial beta-oxidation, and ketogenesis. We report a new familial example; the affected twins had neonatal distress, hyperammonemia, and transient intracardiac conduction defects. Clinical and biochemical analysis of both our patients and the two previously reported patients revealed that this inherited defect could be manifested during the neonatal period without any of the signs classically associated with fatty oxidation defects. In contrast, all four patients had sustained and "isolated" hyperammonemia, which could be misinterpreted as being caused by urea cycle defects. We conclude that carnitine-acylcarnitine translocase deficiency is a potential differential diagnosis in neonates with unexplained neonatal hyperammonemia. Cardiac and muscle involvement may represent further early pivotal symptoms.

Pain and quality of life in patients with acute duodenal ulcer treated with ranitidine

BACKGROUND

The various components of pain and quality of life in duodenal ulcer patients receiving antisecretory drugs have not been studied to date.

METHODS

Ninety-five patients with epigastric pain and duodenal ulcer at endoscopy completed this prospective, multicenter, open-study. All were treated with effervescent ranitidine 300 mg daily for 4 weeks. The following parameters were assessed: (a) disappearance of duodenal ulcer pain by self-evaluation and on a weekly visual analogue scale (VAS) from 0 to 100; (b) evolution of sensory and affective components of ulcer pain by the Validated French Version of the McGill Pain Questionnaire (Questionnaire Douleur de Saint-Antoine, QDSA); (c) quality of life by the Nottingham Health Profile (NHP) which includes six criteria: pain, mobility, energy, emotions, sleep and social isolation.

RESULTS

Forty-nine, 66 and 87% of the patients were pain-free during the day-time after 7, 14 and 28 days, respectively. Corresponding figures for the night-time were 80%, 88% and 97% respectively. Median time to disappearance of ulcer pain was 8 days. VAS self-assessment showed a significant decrease each week throughout the treatment period (P = 0.001). Sensory and affective QDSA scores were significantly improved after the second day and at each assessment during the 28 days of treatment (P = 0.001). Physical as well as affective aspects of quality of life were significantly improved after 28 days for each of the six criteria explored (P = 0.001). The duodenal ulcer healing rate was 86% after 4 weeks of treatment.

CONCLUSIONS

Using complementary scales measuring different aspects of ulcer pain, sensory and affective components improved significantly from the second day of treatment with ranitidine 300 mg. A significant improvement in quality of life is observed after a 4-week treatment. QDSA and NHP appear to be useful evaluation tools of duodenal ulcer pain and quality of life.

Molecular pharmacology of somatostatin receptors

Somatostatin was discovered for its ability to inhibit growth hormone (GH) secretion. Later, it was found to be widely distributed in other brain regions, in which it fulfills a neuromodulatory role, and in several organs of the gastrointestinal tract where it can act as a paracrine factor or as a true circulating factor. In mammals, two molecules of 14 (somatostatin 14) and 28 (somatostatin 28) amino acids are the only biologically active members of the family. They originate from a single gene which gives rise to a single propeptide alternately cleaved in different tissues. In 1992, a major breakthrough in our understanding of somatostatin functions was made with the cloning of five different receptor genes (sstr1 to sstr5) which belong to the seven transmembrane domain receptor family. Their closer relatives are opioid receptors. In first approximation, the tissular expression of the sstrs matches quite well with the distribution of somatostatin binding sites in the "classical" targets of the peptide ie brain, pituitary pancreatic islets and adrenals. The pharmacology of GH inhibition is very close to sstr2 binding but other actions of somatostatins have not yet been attributed clearly to a single receptor subtype. All clinically relevant agonists tested so far (octreotide, lanreotide and vapreotide) are selective of sstr2 being less potent on sstr3 and inactive for sstr1 and sstr4. Surprisingly, rat sstr5 displays nanomolar affinities for octreotide and vapreotide while these agonists are only active at much higher concentrations on human sstr5. All five receptors can be more or less efficiently coupled to inhibition of adenylate cyclase activity in transfected cell systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid diagnosis of long chain and medium chain fatty acid oxidation disorders using lymphocytes

A method based on the release of tritiated water from [9,10(n)-3H] palmitic and myristic acids previously described for fibroblasts, was adapted for lymphocytes for the rapid diagnosis of fatty acid oxidation disorders. Optimal concentrations for both substrates and linearity of the assay were established. Normal values were established in control subjects of different age groups (58 children and 117 adults) and 16 patients with known fatty acid oxidation disorders were tested. Tritiated water production from patients' lymphocytes was expressed as a ratio between residual oxidations of palmitate and myristate and the results show that this method allows good differentiation between long chain and medium chain fatty acid oxidation defects.

Developmental patterns of somatostatin-receptors and somatostatin-immunoreactivity during early neurogenesis in the rat

The temporal pattern of distribution of somatostatin receptor was investigated using the somatostatin analogue [125I]Tyr0-DTrp8-somatostatin14 as a ligand and compared with that of somatostatin immunoreactivity during early developmental stages in the spinal cord and the sensory derivatives in rat fetuses. Qualitative and quantitative analysis showed that somatostatin receptors were detected in a transient manner. In the neural tube, they were clearly associated with immature premigratory cells and with the developing white matter. During the time-period examined (from day 10.5 to 16.5), the disappearance of somatostatin receptors followed a ventro to dorsal gradient probably linked to the regression of the ventricular zone. In sensory derivatives, they were expressed in the forming ganglia and their central and peripheral nerves from embryonic day 12.5 to 16.5 inclusive, with a peak around day 14.5 and low levels observed at day 16.5. Competition experiments performed at embryonic day 14.5 demonstrated that somatostatin1-14, somatostatin1-28, and Octreotide displaced specific binding with nanomolar affinities while CGP 23996 was only active at micromalar doses. Such displacements are compatible with the SSTR2 and/or SSTR4 pharmacology. During the time period examined, some transient somatostatin immunoreactive cell bodies and fibers were detected in the neural tube and in the sensory derivatives. These results demonstrate the existence, in neuronal derivatives, of a complex temporal and anatomical pattern of expression of somatostatin receptors, from the SSTR2/SSTR4 subtype(s), and somatostatin immunoreactivity. It appears that the transient expression of somatostatin receptors and/or somatostatin immunoreactivity characterizes critical episodes in the development of a cohort of neurons; a fact that unequivocally reinforces the notion that somatostatin plays a fundamental role during neurogenesis in vertebrates.

Immunocytochemical and in vitro autoradiographic evidence for a direct somatostatinergic modulation of the enkephalinergic hypothalamoseptal tract of the guinea-pig

The present study was undertaken to determine whether the enkephalinergic hypothalamoseptal tract originating in the magnocellular dorsal nucleus in the guinea-pig brain is under the influence of somatostatin. In the first step, double immunocytochemical labeling of enkephalinergic cells and somatostatinergic fibers was combined at the light and electron microscopic levels in the magnocellular dorsal nucleus. As a second step, an in vitro radioautography was used to determine whether somatostatin receptors are present in the same area. A close relationship between somatostatin nerve endings and enkephalin perikarya was observed at both the light and electron microscopic levels. Contracts were more numerous in the ventral part of the magnocellular dorsal nucleus. Whenever synaptic images were clearly observable, they appeared symmetrical. In the same area, a moderate concentration of G-protein-coupled somatostatin binding sites was also visualized. These results suggest that somatostatin has a regulator role on the enkephalinergic hypothalamoseptal tract, directly at the level of the magnocellular dorsal nucleus.

Two year maintenance treatment of duodenal ulcer disease with ranitidine 150 mg: a prospective multicentre randomised study. GEMUD (Groupe d'Etude de la Maladie Ulcéreuse Duodénale)

Maintenance treatment of duodenal ulcer (DU) with ranitidine 150 mg/day was compared with placebo in a two year prospective multicentre randomised study. Three hundred and ninety nine patients were included (mean age: 44.7 years, M/F ratio = 2.47/1; 37.6% of smokers) in placebo (n = 202) and ranitidine (n = 197) groups. Efficacy was assessed by the length of time to the first ulcer pain attack (with or without endoscopic confirmation) or DU complication. One hundred and fourteen patients of 399 (28.6%) had incomplete follow up. Actuarial survival curves of patients without ulcer pain (26 and 53% at two years in placebo and ranitidine groups, respectively) were significantly different (p < 0.0001). Endoscopies were performed depending on physicians' decision (mainly where there was severe pain or complication). Patients without relapses from endoscopy were more frequent in the ranitidine group (83%) than in the placebo group (47%, p < 0.0001). A greater incidence of complications, mainly bleeding, was also seen in the placebo group (13 complications v two in the ranitidine group, p < 0.002). No factor predicting DU relapse was identified. No important side effect was encountered. Ranitidine 150 mg/day is effective and well tolerated in preventing ulcer pain attacks and DU complications for up to two years.

125I-somatostatin-labeled cells in the anterior arcuate nucleus mediate somatostatin effects on growth hormone but not prolactin secretion

The regional brain distribution of 125I-somatostatin (SRIH) binding sites was determined by quantitative radioautography in neonatally monosodium glutamate (MSG) treated adult male rats, a procedure which selectively destroys most neurons of the arcuate nucleus. Neonatal MSG treatment did not modify the extrahypothalamic distribution of 125I-SRIH-binding sites. In contrast, the number of 125I-SRIH-labeled cells in the ventrolateral part of the arcuate nucleus was strongly reduced in MSG-treated animals. The effect was selective for the anterior part of the arcuate nucleus and was not found in its posterior part or in the cells located more dorsally, beneath the ependymal zone of the periventricular nucleus. Intracerebroventricular SRIH injections, which increased growth hormone levels in control rats, were totally ineffective in MSG-treated animals. In contrast, the prolactin levels were equally stimulated by intracerebroventricular injections in control and MSG-treated animals. These results demonstrate that extrahypothalamic SRIH-binding sites are not located on neurons originating in the anterior arcuate nucleus neurons. In addition, 125I-SRIH-labeled cells in the ventrolateral part of the arcuate nucleus are necessary for the paradoxical stimulation of growth hormone secretion induced by intracerebroventricular SRIH injection, but do not seem to be essential for the increased prolactin secretion observed under these conditions.

Carnitine-acylcarnitine translocase deficiency with severe hypoglycemia and auriculo ventricular block. Translocase assay in permeabilized fibroblasts

Deficiency of the enzymes of mitochondrial fatty acid oxidation and related carnitine dependent steps have been shown to be one of the causes of the fasting-induced hypoketotic hypoglycemia. We describe here carnitine-acylcarnitine translocase deficiency in a neonate who died eight days after birth. The proband showed severe fasting-induced hypoketotic hypoglycemia, high plasma creatine kinase, heartbeat disorder, hypothermia, and hyperammonemia. The plasma-free carnitine on day three was only 3 microM, and 92% of the total carnitine (37 microM) was present as acylcarnitine. Treatments with intravenous glucose, carnitine, and medium-chain triglycerides had been tried without improvements. Measurements in fibroblasts confirmed deficient oxidation of palmitate and showed normal activities of the carnitine palmitoyltransferases I and II and of the three acyl-CoA dehydrogenases. A total deficiency of the carnitine-acyl-carnitine translocase was found in fibroblasts using the carnitine acetylation assay (1986. Biochem. J. 236:143-148). This assay has been further simplified by seeking conditions permitting application to permeabilized fibroblasts and lymphocytes.

ATP-modulated K+ channels sensitive to antidiabetic sulfonylureas are present in adenohypophysis and are involved in growth hormone release

The adenohypophysis contains high-affinity binding sites for antidiabetic sulfonylureas that are specific blockers of ATP-sensitive K+ channels. The binding protein has a M(r) of 145,000 +/- 5000. The presence of ATP-sensitive K+ channels (26 pS) has been demonstrated by electrophysiological techniques. Intracellular perfusion of adenohypophysis cells with an ATP-free medium to activate ATP-sensitive K+ channels induces a large hyperpolarization (approximately 30 mV) that is antagonized by antidiabetic sulfonylureas. Diazoxide opens ATP-sensitive K+ channels in adenohypophysis cells as it does in pancreatic beta cells and also induces a hyperpolarization (approximately 30 mV) that is also suppressed by antidiabetic sulfonylureas. As in pancreatic beta cells, glucose and antidiabetic sulfonylureas depolarize the adenohypophysis cells and thereby indirectly increase Ca2+ influx through L-type Ca2+ channels. The K+ channel opener diazoxide has an opposite effect. Opening ATP-sensitive K+ channels inhibits growth hormone secretion and this inhibition is eliminated by antidiabetic sulfonylureas.

Estradiol regulation of somatostatin receptors in the arcuate nucleus of the female rat

Somatostatin receptors on lactotroph cells of the anterior pituitary are positively regulated by estradiol. In the present work, we investigated whether estradiol regulation of somatostatin receptors also occurred in the female rat brain. 125I-Tyr0-DTrp8-somatostatin (125I-SRIF: 780 Ci/mM) was used as a ligand. Female adult rats were ovariectomized and treated or not with estradiol benzoate (20 micrograms/day for 1 or 8 days). In female brains, 125I-SRIF binding, as assessed by film radioautography, was high in the basolateral amygdala, CA1 field and dentate gyrus of the hippocampus and locus coeruleus, moderate in the median habenula and deep layers all through the cortex. Castration or estradiol treatment did not modify 125I-SRIF binding in these regions. By light-microscopic radioautography, a subpopulation of 125I-SRIF-labeled cells was localized in the ventrolateral portion of the arcuate nucleus. Ovariectomy alone did not significantly affect the number and binding density of 125I-SRIF-labeled cells in the arcuate nucleus. However, estradiol treatment in ovariectomized animals significantly increased both parameters. Along the estrus cycle, the number of 125I-SRIF-labeled cells was not significantly modified but 125I-SRIF binding density was significantly higher in proestrus as compared to diestrus I, diestrus II and estrus. These results demonstrate that brain 125I-SRIF binding sites are positively regulated by estradiol only in the arcuate nucleus of the hypothalamus.

Comparative effects of diabetes and monensin on the lectin asialoglycoprotein receptor: biosynthesis, structure and function in rats

The hepatic asialoglycoprotein receptor is the first studied mammalian lectin. Modulations in vivo by diabetes and in vitro by the carboxylic ionophore monensin gave rise to similar apparent alterations on its biosynthesis, structure and ligand binding capacity. In normal rats, the receptor (whether purified by ligand or antibody-affinity chromatography) presented a similar pattern in SDS-PAGE analysis, with a major 42-kDa band and two minor ones (49 and 52-54 kDa). In diabetic rats, a new 38-kDa band appeared, but only after antibody-affinity purification. In vitro biosynthesis of the receptor by normal hepatocytes in the presence of 35S-methionine showed that this 38-kDa band was present at the end of a 30-min pulse but decreased during a 180-min chase, in association with an increase in the major 42-kDa band. In diabetic cells, this evolution was retarded. Using a 30-min pulse followed by a 120-min chase in the presence of 100 microM monensin, we showed that this carboxylic ionophore had similar effects on diabetes, leading to a delay in the maturation process of the 42-kDa band and the persistent emergence of the 38-kDa species. Allowing incubation in the presence of 25 or 100 microM monensin, we observed a decrease in the number of ligand binding sites both at the surface (40%) and within the cell (28%). In hepatocytes from diabetic rats, monensin showed no additional effect on the partial diabetes-induced inactivation.