Failure of naloxone to modify anterior pituitary secretory pattern in insulin-dependent diabetics

Arabidopsis, tobacco, nightshade and elm take insect eggs as herbivore alarm and show similar transcriptomic alarm responses

Plants respond to insect eggs with transcriptional changes, resulting in enhanced defence against hatching larvae. However, it is unknown whether phylogenetically distant plant species show conserved transcriptomic responses to insect eggs and subsequent larval feeding. We used Generally Applicable Gene set Enrichment (GAGE) on gene ontology terms to answer this question and analysed transcriptome data from Arabidopsis thaliana, wild tobacco (Nicotiana attenuata), bittersweet nightshade (Solanum dulcamara) and elm trees (Ulmus minor) infested by different insect species. The different plant-insect species combinations showed considerable overlap in their transcriptomic responses to both eggs and larval feeding. Within these conformable responses across the plant-insect combinations, the responses to eggs and feeding were largely analogous, and about one-fifth of these analogous responses were further enhanced when egg deposition preceded larval feeding. This conserved transcriptomic response to eggs and larval feeding comprised gene sets related to several phytohormones and to the phenylpropanoid biosynthesis pathway, of which specific branches were activated in different plant-insect combinations. Since insect eggs and larval feeding activate conserved sets of biological processes in different plant species, we conclude that plants with different lifestyles share common transcriptomic alarm responses to insect eggs, which likely enhance their defence against hatching larvae.

Alanine and hyperosmolarity are responsible for the stimulation of cardiomyocyte glucose transport by samples containing a glucose tolerance factor

Low-molecular-weight, cationic samples, that were previously reported to contain a glucose tolerance factor, were obtained by partial purification from yeast extract. These samples increased the rate of glucose transport in isolated cardiomyocytes 2.0- to 2.5-fold. A further purification by gel filtration led to the separation of two active components that were identified as (i) L-alanine and (ii) an elevated osmolarity. Moreover, the effect of partially purified fractions (before gel filtration) (i) was decreased upon alanine depletion with alanine dehydrogenase and (ii) was mimicked by the additive action of alanine and of a hyperosmolar medium. These findings indicate that the effect of this partially purified material is not accounted for by a putative glucose tolerance factor. Interestingly, alanine elicited its effect at concentrations that correspond to physiological plasma values, which suggests that this amino acid might be involved in the regulation of glucose transport in cardiomyocytes. Furthermore, the effect of alanine was prevented by DL-cycloserine (1 mM) or aminooxyacetate (1 mM), but not by cycloheximide (35 microM), indicating that (a) transamination reaction(s), but not protein synthesis, is required.

Clinical and pharmacological characterization of anomalous metoclopramide-induced growth hormone secretion in insulin-dependent diabetes mellitus

An abnormal growth hormone (GH) increase after non-specific stimuli (such as TRH, LHRH and, in a few cases, metoclopramide), has been described in insulin-dependent diabetes. Sixty-nine non-hypogonadic male insulin-dependent diabetic patients (mean age 38.6 years, range 18-54; mean duration of diabetes 11.1 years, range 1.3-28, in different degree of metabolic control, some of them with retinopathy, nephropathy and peripheral and/or autonomic neuropathy) were tested twice with 10 mg i.v. metoclopramide (MCP), an antidopaminergic agent with weak serotoninergic activity. Anomalous GH response (i.e. GH increment equal to or higher than 5 ng/ml from basal level) occurred in 33 patients (47.8%). Mean (+/- SE) MCP-induced GH release in these 'responder' patients peaked up to 17.2 +/- 1.7 ng/ml in comparison with no variation found in 'non-responders' and in 25 healthy control men. Abnormal GH secretion appeared to be unrelated to age, metabolic control, basal GH values and duration of diabetes. Moreover, it remained unmodified by pretreatments with placebo, cimetidine, meclastine, propranolol, acetylsalicylic acid and naloxone, while it was enhanced by metergoline, significantly reduced by bromocriptine and almost completely blunted by pirenzepine, a cholinergic muscarinic receptor antagonist. Neuropathy and nephropathy were equally distributed in the two groups, while retinopathy was more frequent in 'responders'. In conclusion, the exact mechanism(s) by which MCP may induce a paradoxical GH release in many insulin-dependent diabetic patients, is still unclear; it might be dependent, at least in part, on the activation of cholinergic pathways. Indeed, it seems to indicate the presence, in diabetes, of a rather complex derangement in the regulatory mechanisms of GH secretion.

Hypogonadotropic secondary amenorrhea in diabetes: effects of central opiate blockade and improved metabolic control

The effect of improving diabetic control on secondary hypogonadotropic amenorrhea was investigated in patients with insulin-dependent diabetes mellitus (IDDM). Second, the hypothesis that increased central (hypothalamic) opiate inhibition may have been responsible for the suppression of gonadotropin-releasing hormone (GnRH) was tested by observing the effect of a four-hour naloxone infusion (1.4 mg/hour) on serum gonadotropin levels. All known causes of secondary amenorrhea were excluded before patients were eligible for the study. The median duration of amenorrhea was six years, and median body weight was 101 percent of ideal. After six months of improved metabolic control (n = 5) using intensified conventional therapy or continuous subcutaneous insulin infusion, the level of glycosylated hemoglobin dropped from 11.8 +/- 0.9 percent to 8.5 +/- 0.5 percent (p less than 0.005), and body weight increased from 60.5 +/- 1.8 kg to 64.7 +/- 1.4 kg (p less than 0.02). Menses did not, however, return in any patient. There was no significant change in serum levels of estradiol, progesterone, dihydroxyepiandrosterone, testosterone, prolactin, basal or GnRH-stimulated luteinizing hormone, or follicle-stimulating hormone. There was no change in the levels of luteinizing hormone or follicle-stimulating hormone during the naloxone infusion either during poor metabolic control or after six months of improved metabolic control. In conclusion, a form of secondary hypogonadotropic amenorrhea was identified in patients with IDDM that did not remit with sustained improvements in metabolic control. It did not appear to be mediated through increased central opiate tone.

Insulin-like activity of chromium-binding fractions from brewer's yeast

51CrCl3 was added to the incubation medium of Saccharomyces cerevisiae for up to 48 hr. After repeated freezing and thawing, lysing in 9 M urea with 1% NP-40 detergent, and dialysis against water, the lower molecular weight (Mr less than 3500) dialysate was retained on a SE53 cationic exchange column, eluted with 0.25 M NH4OH and fractionated on a Bio-gel P-2 column. The insulin-like biological activity of the fractions was measured by the 14C-glucose oxidation in isolated rat adipocytes. The biological activity that was found in two of nine fractions did not correspond to their chromium content. Moreover, identical findings were obtained when chromium was added not to the live yeast but to the yeast extract, which showed that its binding was a chemical process not requiring cellular activity. No fraction demonstrated insulin-potentiating activity on rat adipocytes.

The GABAergic control of prolactin release is not affected by insulin-dependent diabetes mellitus: evidence from studies with sodium valproate

In order to evaluate the influence of the GABAergic system in the regulation of PRL secretion in patients with IDDM, serum PRL levels were measured in 7 diabetics and in 7 normal men with sodium valproate (400 mg per os), a drug capable of increasing cerebral GABA concentrations. A significant decrease of serum PRL concentrations was observed between 30 and 120 min after sodium valproate administration in both control and diabetic subjects. The time course and magnitude of the sodium valproate effect were similar in all subjects. These data confirm the inhibitory control of the GABAergic system on PRL secretion in man as evidenced by the GABAergic drug sodium valproate. It is suggested that this system is not altered in diabetic patients.