[Adipogenic function and other biologic effects of insulin].

Studies on experimental animals with knockout of the insulin receptor gene Insr (in the whole body or in certain tissues) and/or related genes encoding proteins involved in realization of insulin signal transduction in target cells, have made an important contribution to the elucidation of insulin regulation of metabolism, particularly fat metabolism. Since the whole insulin secreted by b-cells, together with the products of gastrointestinal tract digestion of proteins, fats, and carbohydrates reach the liver, the latter is the first organ on which this hormone acts. The liver employs released amino acids for synthesis of proteins, including apoproteins for various lipoproteins. Glucose is used for synthesis of glycogen, fatty acids, and triglycerides, which enter all the organs in very low density lipoproteins (VLDL). The LIRKO mice with knockout of the Insr gene in the liver demonstrated inhibition of synthesis of macromolecular compounds from amino acids, glucose, and fatty acids. Low molecular weight substances demonstrated increased entry to circulation, and together with other disorders induced hyperglycemia. In LIRKO mice blood glucose levels and glucose tolerance demonstrated time-dependent normalization and at later stages the increase in glucose levels was replaced by hypoglycemia. These changes can be well explained if we take into consideration that one of the main functions of insulin consists in stimulation of energy accumulation by means of activation of triglyceride deposition in adipose tissue. FIRKO mice with selective knockout of adipose tissue Insr were characterized by decreased uptake of glucose in adipocytes, and its transformation into lipids. However, the level of body fat in animals remained normal, possibly due to preserved insulin receptor in the liver and insulin-induced activation of triglyceride production which maintained normal levels of body fat stores, the effective functioning of adipose tissue and secretion of leptin by adipocytes during inhibition of glucose transformation into triglyceride in adipose tissue. Knockout of the Insr gene in muscles blocked glucose uptake by myocytes, but it did not induce hyperglycemia, probably due to the increase in glucose uptake by other organs, which retained the insulin receptor, and induced some increase in fat resources in adipose tissue. Similar results were obtained in mice with knockout the glucose transporter 4 GLUT4 in muscle and/or adipose tissue. Insulin microinjections in the brain, in the cerebral ventricle 4 (ICV) and mediobasal hypothalamus (MBH) did not affect the insulin levels in the general circulation, but effectively activated lipogenesis and inhibited lipolysis in adipose tissue. They induced obesity, similar to conventional obesity when the insulin levels increased. These results may serve as additional evidence for importance of the adipogenic insulin function in mechanisms of regulation of general metabolism.

Antibodies to pituitary surface antigens during various pituitary disease states.

Autoantibodies to cell surface antigens of human somatotropinoma (ASAS), human prolactinoma (ASAP) and rat adenohypophysis (ASARA) were assayed in the serum of patients with pituitary diseases associated with GH deficiency (GHD), such as pituitary dwarfism and primary empty sella syndrome (ESS), and in the serum of patients with hyperprolactinaemia of different etiologies: idiopathic hyperprolactinaemia, prolactinoma and ESS. The investigation was carried out with a cellular variant of an ELISA. Among children with GHD, the highest percentage of antibody-positive patients was found in the group with idiopathic isolated GHD (89% of ASAS(+) patients and 30% of ASARA(+) patients vs 33.3% and 0% respectively in the group with idiopathic combined pituitary hormone deficiency, and 33.3% and 9% in patients with pituitary hypoplasia associated with isolated GHD or combined pituitary hormone deficiency). Among hyperprolactinaemic patients, the highest ASAP and ASARA frequency was observed in patients with idiopathic hyperprolactinaemia (67.7% and 41.9% respectively) where it was twice as high as in the group of patients with prolactinoma. The proportion of ASAS(+) and ASARA(+) did not differ significantly between the groups of patients with ess with or without GHD. Similarly, there was no significant difference between the number of ESS ASAP(+) and ASARA(+) patients with or without hyperprolactinaemia. The data obtained suggested that autoimmune disorders may be primary, and responsible, at least in part, for pituitary dysfunction in the cases of idiopathic isolated GHD and idiopathic hyperprolactinaemia. At the same time, the autoimmune disorders in the patients with prolactinoma or ESS are probably secondary to the organic pituitary lesion and their significance in the development of the pituitary dysfunction is obscure.

Adipose tissue as an endocrine organ regulating growth, puberty, and other physiological functions.

There are reports on some patients with clearly manifested specific features of genotype and phenotype similar to those of ob/ob and db/db mice. Three patients from Turkey were described who had a homozygous mutation in the gene of leptin identical to the mutation in C57BL6J ob/ob mice. This mutation is a C --> T substitution in codon 105 of the amino acid sequence of leptin. In mice this mutation generates a stop-codon; in humans it substitutes Arg-105 with Trp. The mutant human leptin cannot be secreted by the cells and thus has no effect on the hypothalamus. Patients with a homozygous mutation of the leptin receptor resulting in the G --> T substitution in the splice donor site of exon 16 were studied in a family of Kabilian origin. Exon 16 was not included in the mature mRNA molecule, and a truncated leptin receptor was synthesized which lacked the transmembrane and intracellular domains; this receptor was unable to transduce the hormonal signal. Both groups of patients suffered from obesity, delayed linear growth, infertility, increased blood insulin level, and other disorders. Leptin influences lipid metabolism by stimulating the expression of the proopiomelanocortin (POMC) gene in melanocortinergic neurons of the hypothalamus. POMC is the precursor of alpha-melanocyte-stimulating hormone (alpha-MSH), which binds to the melanocortin receptor MC4-R in the brain, decreases appetite, and activates lipid metabolism. Patients with mutations in MC4-R suffered only from obesity, but their growth and puberty were not affected. Thus, leptin apparently stimulates growth and puberty not through its binding to the receptors on melanocortinergic neurons, but through its binding to receptors on other hypothalamic neurons; this effect of leptin is not affected by mutations in the MC4-R gene.

Molecular studies of diabetes reported at the Fourth European Congress of endocrinology.

In his lecture at the Fourth European Congress of Endocrinology, C.R. Kahn considered the effects of knock-out of genes encoding the proteins involved into insulin signal transduction on the development of insulin-resistance and non-insulin-dependent diabetes mellitus. The latter were induced in animals by knockout of genes encoding insulin receptors and intracellular substrate proteins of the insulin receptor. Using special technology, the authors achieved selective knock-out of the insulin receptor gene in muscles and pancreatic beta-cells of mice. Non-insulin-dependent diabetes mellitus developed only after the knock-out of the insulin receptor gene in beta-cells and resulted from the inability of glucose to penetrate into beta-cells and stimulate insulin secretion. The insensitivity of muscles to insulin due to the lack of its receptor did not result in diabetes. In these animals insulin and glucose blood level did not differ from the control values, but blood lipid concentration was increased. For the cases of the reduction in the insulin-dependent penetration of glucose into muscles, these data may indirectly indicate a transition of energy metabolism in muscles from carbohydrate utilization to increased fat consumption as an energy source.

Growth hormone and a partial mediator of its biological action, insulin-like growth factor I.

This review summarizes data on two hormones, growth hormone (GH) and insulin-like growth factor I (IGF-I). Genes encoding these hormones are actively expressed in various tissues which can synthesize and secrete the corresponding hormones into the intracellular space and blood. Apart from the pituitary, GH gene is also expressed in mammary gland, thymus, spleen, lymph nodes, and blood cells. GH activates expression of the gene of IGF-I and stimulates its secretion by the liver, adipose tissue, thymus, and other tissues. The growth-stimulating effect of GH is mediated (at least partially) by IGF-I, but direct (IGF-I-independent) influence on target tissues is also possible. Genes encoding GH and IGF-I receptors are expressed in all organs and tissues, including various cells of the immune system. GH and IGF-I regulate the function of the immune system via endocrine, paracrine, and autocrine mechanisms.

Hormones as life regulators in the current molecular endocrinology.

This review considers results of studies on six hormones-- leptin, adrenomedullin, parathyroid hormone-related protein, vascular endothelium growth factor, fibroblast growth factor 2, and prolactin. Genes of these hormones are markedly expressed in various tissues which can synthesize and release the corresponding hormones into the intercellular space and blood. The structure of hormone receptor genes and their expression in various tissues which are target organs of the hormones are discussed. All organs, tissues, and cells of the body are concluded to be endocrine and releasing their specific hormones into blood. Hormones regulate vital processes, provide communications between organs and tissues, and integrate them into a united entity. All hormones are multifunctional compounds of wide spectrum of biological activities. The regulation of gene expression via various mechanisms is a common property of all hormones. Many tissue-specific hormones are yet to be discovered.

The effect of RU486 on progesterone and oestrogen receptor concentration in human decidua on early pregnancy.

Concentrations of progesterone receptor (PR) and oestrogen receptor (ER) were measured by radioligand assay in decidual tissue of women undergoing termination of early pregnancy (amenorrhoea up to 49 days). Pregnancies were terminated by vacuum aspiration at 12 or 36 h after oral administration of placebo or antiprogestin RU486 in different doses. Treatment with RU486 decreased decidual PR content, the effect being observed at 12 h as well as at 36 h after 600 mg RU486 and at 36 h after 3 x 25 mg RU486 given at 12 h intervals. PR concentration 12 h after a single dose of 25 mg RU486 was not affected. ER content was unchanged at 12 h after RU486 but increased 36 h after 600 mg and 3 x 25 mg RU486. Our data suggest that apart from blocking progesterone action, RU486 may exert its abortifacient effect through decreasing the PR concentration. The simultaneous decrease of PR concentration and an increase of ER concentration changes the balance between them in favour of ER, which might also play a role in the abortifacient effect of RU486.

Isolation, primary structure, and biological and immunological properties of pink and chum salmon insulins.

1. Insulins have been isolated from islet tissue of pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon. The primary structure of chum and pink salmon insulins was found to be identical. Compared to the amino acid sequence of human insulin, the salmon insulins under study differed at 14 positions. 2. Biological activity of pink salmon insulin was 83% of that of standard porcine insulin. 3. The immunological properties of fish insulins were investigated in specific radioimmunoassay (RIA) systems, based on porcine and pink salmon insulins. 4. A significant difference in the antigenic determinants of these fish and mammalian hormones was revealed.

Islet cell transplantation in type I diabetes mellitus: evaluation of humoral immune response.

Four males and three females ranging in age from 20 to 35 years and afflicted with complicated Type 1-diabetes for more than 8 years underwent islet cell allotransplantation (ATx, 6 cases) and xenotransplantation (XTx, 1 case). Precultured islet cells derived from human or bovine fetal pancreata were injected into the m. rectus abdominis. Immunosuppression was not applied. Plasma C-peptide and islet cell surface antibodies (ICSA) were continually measured both before and until the twentienth week following islet cell transplantation. All recipients were subdivided as "responsive" (RR, 3 males) or "non-responsive" (NRR, 1 male and 3 females), according to the dynamics of their ICSA levels. All 3 RR (1XTx and 2 ATx) showed a peak of ICSA two weeks after cell injection. Subsequent ICSA levels had the tendency to either diminish or increase. Heterogeneity of preoperative antibody level, especially in NRR, was also observed. No associations between ICSA and ATx or XTx, age at diabetes onset, or duration of the disease was found. Only one RR with XTx had a reduced daily insulin requirement and a significant C-peptide response similar to the dynamics of ICSA levels. A greater mass of available bovine islet cells might be responsible for this effect.

The effects of sera obtained from children with insulin-dependent diabetes mellitus on cultivated islet cells: cytotoxicity and insulin release.

Sera were obtained from 24 patients with newly-diagnosed insulin-dependent diabetes mellitus (IDDM) and 14 children with a high risk of diabetes. The influence of the decomplementated sera on basal and stimulated insulin secretion was studied in a mixed culture of newborn rat islet cells. In addition, complement-dependent antibody-mediated cytotoxicity (C'AMC) was measured by 51Cr-release from pre-labelled islet cells. Incubation of the islet cells with sera from ten IDDM patients did not affect the basal insulin release. Sera from other children with IDDM (n = 14) either significantly increased (n = 7) or inhibited (n = 7) basal IRI secretion was compared with the sera of control donors. Nearly half of the sera from the high-risk children was found to be insulin-stimulating. Preincubation of islet cells with sera from IDDM children caused a significant decrease of insulin response to 16.5 mM glucose plus 5 mM theophylline (P less than 0.001). Sera from the high-risk children did influence the response of pancreatic cells to secretagogues. C'AMC was found in 45% of the patients with IDDM and in 33% of the high-risk children, however, there was no correlation between C'AMC and serum effect upon basal insulin secretion. These results suggest the presence of B-cytotropic factors in serum from children with IDDM or with a risk of diabetes. Opposite effects of different sera on insulin secretion may reflect the variety of pathogenetic mechanisms involved in islet cell destruction.

Involvement of proteolytic enzymes in the lipotropic effect of the pituitary polypeptide hormones.

The influence of proteinase inhibitors on the lipolytic effect of the pituitary polypeptide hormones and epinephrine in an isolated adipose tissue of rabbits and rats has been studied. Neither of proteinase inhibitors changed the basal rate of lipolysis. Trasylol, a serine proteinase inhibitor, suppressed completely growth hormone (GH) effect and partially reduced the effect of adrenocorticotropin (ACTH) and beta-lipotropin (beta-LPH) but did not change the effect of epinephrine. Bacitracin proved ineffective with regard to the effect of polypeptide hormones. Pepstatin, an acid proteinase inhibitor, partially blocked the stimulation of lipolysis by ACTH without affecting the effect of GH and beta-LPH. The influence of proteinase inhibitors on the ACTH effect in rat adipose tissue was similar to that found in rabbit tissue. The Trasylol-induced inhibition of the hormone-stimulated lipolysis decreased to a considerable extent after GH or ACTH incubation with rabbit plasma or partial GH digestion with pepsin. This decrease was not observed when plasma serine proteinases were blocked during GH incubation with plasma. The results demonstrate an involvement of some proteolytic enzymes in the realization of the polypeptide hormone lipolytic effect and permit to suppose the requirement of preliminary activation of the hormones by means of proteolytic modification.