Porcine Glucagon Research Articles

Activation of insect anti-oxidative mechanisms by mammalian glucagon

Resembling the main function of insect adipokinetic hormones (AKHs), the vertebrate hormone glucagon mobilizes energy reserves and participates in the control of glucose level in the blood. Considering the similarities, the effect of porcine glucagon was evaluated in an insect model species, the firebug Pyrrhocoris apterus. Using the mouse anti-glucagon antibody, presence of immunoreactive material was demonstrated for the first time in the firebug CNS and gut by ELISA. Mammalian (porcine) glucagon injected into the adult bugs showed no effect on hemolymph lipid level or on the level of AKH in CNS and hemolymph, however, it activated an antioxidant response when oxidative stress was elicited by paraquat, a diquaternary derivative of 4, 4'-bipyridyl. Glucagon elicited the antioxidant response by increasing glutathione and decreasing protein carbonyl levels in hemolymph, decreasing both protein carbonyl and protein nitrotyrosine levels in CNS. Additionally, when co-injected with paraquat, glucagon partially eliminated oxidative stress markers elicited by this redox cycling agent and oxidative stressor. This indicates that glucagon might induce an antioxidant defense in insects, as recently described for AKH. Failure of glucagon to alter AKH level in the bug's body indicates employment of an independent pathway without involving the native AKH.

Ontogeny of the endocrine pancreatic cells of the gilthead sea bream, Sparus aurata (Teleost)

The development of the gilthead sea bream, Sparus aurata, endocrine pancreas was studied from hatching to 114 days, using immunocytochemical techniques. Bonito insulin (INS)-, synthetic somatostatin-14 (SS-14)-, salmon somatostatin-25 (SS-25)-, mammalian somatostatin-28 (1–12) (SS-28)-, porcine glucagon (GLU)-, glucagon-like peptide-1 (1–19) (GLP-1)-, synthetic porcine peptide tyrosine tyrosine (PYY)-, and neuropeptide Y (NPY)-like immunoreactivities were demonstrated. The different types of endocrine cells appear at distinct stages of development and differ in their arrangement. The coexistence of INS and SS-25 immunoreactivities was demonstrated in the cells of one strand or primordial cord and a primordial islet that appeared close to the dorsal epithelium of the anterior region of the undifferentiated gut or next to the gut at hatching and one day after hatching, respectively. INS- and SS-25- immunoreactive (ir) cells were located in the core and at the periphery of the single islet found in 2-day-old larvae, while SS-28-ir cells were found in the single islet in 4- to 11-day-old larvae. GLU/GLP-1-ir cells were located next to the outer SS-25-ir cells in the single islet of 12- and 16-day-old larvae. SS-14/SS-25- and SS-14/SS-28-ir cells were detected in the outer region and in the inner area of the single islet, respectively, in 17- to 23-day-old larvae. One big islet and several small islets and isolated or clustered cells next to the pancreatic duct were present in 24- and 25-day-old larvae. The islets were similar in cell composition to the single islet seen in the previous stage, while the isolated and grouped cells showed the coexistence of INS and diverse SSs immunoreactivities. Nerve fibers showing PYY immunoreactivity were identified in the islets from 17 days onwards. In 30- to 44-day-old larvae, GLU and NPY immunoreactivities coexisted in a few cells at the periphery of some small islets. PYY-ir cells were first detected at day 51. One big islet, several intermediate islets and numerous small islets were present from 51-day-old-larvae to juveniles. GLU was colocalized with PYY and NPY in a few cells in a small peripheral area in the big islet and a few intermediate islets. The outer region of small islets and other intermediate islets showed the complete coexistence of GLU, PYY, and NPY.

Glucagon Receptor Agonists and Antagonists Affect the Growth of the Chick Eye: A Role for Glucagonergic Regulation of Emmetropization?

In chicks, plus defocus retards eye growth, thickens the choroid, and activates glucagonergic amacrine cells, probably releasing glucagon. Glucagon receptor antagonists (expected to inhibit compensation to plus defocus) and agonists (expected to block myopia induction by form deprivation) were administered to eyes of chicks, to test the hypothesis that glucagon mediates the induction of changes in eye growth by plus defocus. Seven-day-old (P7) chick eyes were injected intravitreally with peptides at concentrations of approximately 10(-9) to 10(-5) M in 20 microL (injection volume). The glucagon-receptor antagonists [des-His(1),des- Phe(6),Glu(9)]-glucagon-NH(2) (des- Phe(6)-antagonist) and [des-His(1),Glu(9)]-glucagon-NH(2) (Phe(6)-antagonist) were administered daily for 4 to 5 days to plus-defocused eyes. Agonists (porcine glucagon-[1-29] and [Lys(17,18),Glu(21)]-glucagon-NH(2)) were monocularly administered daily for 5 days to form-deprived eyes. The contralateral eye remained open and received saline. After treatment, eyes were refracted, measured, and examined for histologic changes. The Phe(6)-antagonist at 10(-5) M (in the syringe) inhibited changes in both refractive error and axial length compensation induced by +7-D lens wear; however, des-Phe(6)-antagonist (10(-5) M) had weak, inconsistent effects and did not antagonize the action of exogenous glucagon. Glucagon prevented ocular elongation and myopia and induced choroidal thickening in form-deprived eyes. [Lys(17,18),Glu(21)]-glucagon-NH(2) had little effect at 10(-7) M, but at 10(-6) to 10(-5) M altered rod structure and inhibited eye growth. Exogenous glucagon inhibited the growth of form-deprived eyes, whereas Phe(6)-antagonist inhibited compensation to plus defocus, as might be expected if glucagon is an endogenous mediator of emmetropization. The reason for the failure of des-Phe(6)-antagonist to counteract the effects of exogenous glucagon requires further investigation.

Properties of amidinated glucagons.

Porcine glucagon has been reacted with a series of alkyl imidates. The epsilon-amino group and both the alpha and epsilon-amino groups were modified and the subsequent glucagon derivatives were purified by ion-exchange chromatography and characterized. The modified glucagons were compared with native glucagon in their ability to activate hepatic adenylate cyclase and to compete with 125I-glucagon for binding to sites specific for glucagon in hepatic plasma membranes. N epsilon-acetamidino-glucagon was as biologically potent, in both activity and binding, as native glucagon, whereas N epsilon-4-hydroxyphenylamidinoglucagon required a twofold higher concentration to obtain similar levels. These findings suggest that modification through the epsilon-amino group with alkyl imidates possessing reporter groups should result in glucagon derivatives with significant biological potency, thus providing a new approach to the study of this peptide hormone. Amidination of both epsilon and alpha-amino groups resulted in glucagon derivatives which were agonists with respect to adenylate cyclase activation and which displayed unexpected anomylous behavior on chromatography.

Effects of glucagon and insulin on plasma glucose, triglyceride, and triglyceride-rich lipoprotein concentrations in laying hens fed diets containing different types of fats

The influence of dietary fat supplementations differing in the ratio of n-6 to n-3 polyunsaturated fatty acids (PUFA) on the effects of glucagon and insulin on plasma glucose, triglyceride (TG), and TG-rich lipoprotein concentrations was investigated in laying hens. Birds were fed either a low-fat control diet (LF) or diets supplemented with 4% pumpkin seed oil (PO; rich in n-6 PUFA) or 4% cod liver oil (CO; rich in n-3 PUFA). After 4 wk feeding of the experimental diets, hens were implanted with wing vein catheters and injected with porcine glucagon (20 microg/kg BW) and porcine insulin (0.5 IU/kg BW), 2 to 5 h after oviposition. Plasma glucose, TG, and TG-rich lipoprotein concentrations were determined from 10 min pre-injection to 60 min post-injection. PO diet resulted in a prolonged plasma glucose response to glucagon administration and altered hypoglycemic response to insulin. However, CO diet did not influence plasma glucose response to either glucagon or insulin administration compared to LF diet. The effects of glucagon and insulin on plasma TG and TG-rich lipoproteins were similar for all diets regardless of the amount or type of fat. The results suggest that feeding dietary fats with high n-6 to n-3 PUFA ratio alters the glucagon and insulin sensitivity of plasma glucose in laying hens. Fats rich in n-3 PUFA seem to have no influence on the plasma glucose response to glucagon and insulin.

Immunocytochemical demonstration of glucagon-like peptides in Mytilus edulis cerebral ganglia and an in vitro effect of vertebrate glucagon on glycogen metabolism

Immunological detection of glucagon-like peptides was performed in the cerebral ganglia of the mussel Mytilus edulis using an anti-vertebrate glucagon antibody. Two clusters of positive neurosecretory cells were observed, as well as stained nervous fibers. The effect of vertebrate glucagon on glucose incorporation into glycogen of reserve cells was tested using an in vitro microplate bioassay. Optimal incubation conditions were previously defined and an inhibitory effect of porcine glucagon was obtained for concentrations ranging from 10 −6 to 10 −9 M. It is postulated that the glucagon-like peptide may be implicated in the regulation of glucose metabolism in bivalves.

Glucagon- and NPY-Related Peptide-Immunoreactive Cells in the Gut of Sea Bass (Dicentrarchus labraxL.): A Light and Electron Microscopic Study

Glucagon and peptide of the neuropeptide Y (NPY) family immunoreactivities were studied in the gut of sea bass (Dicentrarchus labrax) using antisera against bovine/porcine glucagon, porcine glucagon, glicentin (10–30), bovine pancreatic polypeptide (PP), peptide tyrosine tyrosine (PYY), salmon PYY (sPYY), and NPY. Glucagon-, glicentin-, PYY-, and NPY-immunoreactive (ir) cells were detected in the stomach, and glucagon-, PP-, PYY-, sPYY-, and NPY-ir cells in the intestine. PP, PYY, and NPY immunoreactivities coexisted in intestinal endocrine cells (NPY-like peptide containing cells), in some of which there was also glucagon immunoreactivity. Preabsorption tests indicated that different products of the glucagon gene(s) are probably expressed in the stomach and intestine of sea bass and that the peptides belonging to the NPY family in the endocrine cells of the intestine are more similar to NPY than to other peptides of this family. Glucagon-ir cells in the stomach, and glucagon/NPY-like containing cells in the intestine, were characterized by conventional and immunogold electron-microscopic techniques. The glucagon cells had secretory granules with a clotted content, the gold particles being observed in both the core and the halo. Glucagon/NPY-like cells showed two types of secretory granules differing in size, both of which were immunogold labeled with anti-NPY and anti-sPYY; the smaller granules were weakly immunogold labeled with anti-glucagon.

Metabolic responses of the turkey hen ( Meleagris gallopavo) to an intravenous injection of chicken or porcine glucagon

The purpose of this study was to compare the metabolism of chicken and porcine glucagon in the turkey hen. Six hens each were infused with either porcine or chicken glucagon (16.6 μg/kg body weight). Blood samples were obtained at intervals pre- and post-infusion and analyzed for glucagon, glucose, insulin, free fatty acids, thyroxine (T 4) and triiodothyronine (T 3). The half-life (T 1 2 ) of porcine (4.5 min) and chicken glucagon (5.5 min) were similar. A 13% increase in glucose concentrations occurred within 10 min and remained elevated (22%) for 2 hr. A concomitant increase in insulin was noted, though not significant from pre-injection levels. A 50% increase in free fatty acids occurred in 2 min, reaching a zenith at 10–15 min post-treatment, and returned to baseline by 2 hr. Significant ( P < 0.05) decreases in the circulating concentrations of both T 3 and T 4 hormones were observed within 5–10 min post-glucagon treatment and remained suppressed for the duration of sampling. These data indicate that the hormonal and metabolic responses of female turkeys to mammalian and avian glucagon are similar.

Glucagon binding to receptors on the surface of chicken adipocytes.

Adipocytes isolated from abdominal fat of chickens were used 1) to demonstrate that [125I]-tyr10-glucagon binds with all the characteristics of a hormone-receptor interaction and 2) to determine whether glucagon binds to one or more receptor sites. Binding of [125I]-tyr10-glucagon was characterized at 12 degrees C, a temperature found to completely inhibit internalization of the radioligand. Culturing adipocytes increased radioligand binding by 60 to 100% and, therefore, fat cells were incubated for 72 h before characterizing binding. Binding of [125I]-tyr10-glucagon to chicken adipocytes reached steady-state, was reversible, was specific for glucagon, was saturable, and increased linearly as a function of fat cell concentration. Both kinetic and steady-state experiments indicated that [125I]-tyr10-glucagon bound to two sites on chicken adipocytes. Equilibrium dissociation constants (Kd) of 54 +/- 16 pM and 3.3 +/- 1.3 nM were obtained for [125I]-tyr10-glucagon, whereas Kd of .49 and 81 nM were calculated for mammalian glucagon. There were 4,831 +/- 1,057 high-affinity receptors and 200,780 +/- 63,404 low-affinity receptors per adipocyte. Thus, only 2.3% of the glucagon binding sites were of high affinity. In addition to higher binding affinity, [125I]-tyr10-glucagon stimulated glycerol release from chicken adipocytes with greater potency than porcine glucagon. Therefore, it was concluded that [125I]-tyr10-glucagon was a supra-agonist that bound to high- and low-affinity receptors on the surface of chicken adipocytes with all the characteristics of a hormone-receptor interaction.

Parathyroid hormone and glucagon compete for binding to low affinity sites on human skin fibroblasts

We have studied the binding sites for parathyroid hormone (PTH) present on normal human fibroblasts by studying these receptors with respect to (1) affinity and specificity towards various peptide hormones including human PTH(1–34) and porcine glucagon(1–29); (2) ability to mediate stimulation of cAMP production in response to these hormones; and (3) molecular size. Binding assays using 125I-labelled human PTH(1–34) and 125I-labelled porcine glucagon(1–29), and hormone stimulations of cAMP production were performed on confluent fibroblasts grown in 24-well dishes (passage 4–10). The molecular sizes of the binding sites for PTH and glucagon were assessed after cross-linking to the corresponding 125I-labelled ligand using the heterobifunctional reagent 1, 4-difluoro-2, 5-dinitrobenzene (DFDNB), by sodium dodecyl sulphate gel electrophoresis and autoradiography. The results demonstrate: (1) Biologically active PTH and glucagon, but not other peptide hormones tested, are equipotent competitors for binding on human fibroblasts to sites which have a relatively low affinity for these ligands ( K d ≈ 0.8−2.4 × 10 −7M); these sites have an apparent molecular weight of 95 kDa and are not linked to stimulation of cAMP production by PTH. (2) A distinct class of receptors for PTH with an apparent molecular weight of 60 kDa and which probably are linked to stimulation of cAMP production by PTH is also expressed by these cells; glucagon cannot compete with PTH for binding to these sites, and does not interfere with the stimulation of cAMP production by PTH. (3) Glucagon does not stimulate cAMP production in human fibroblasts. The demonstration that PTH and glucagon compete for binding to low affinity sites on human fibroblasts should be helpful in further studies aimed at defining the functional role of these sites.

Characterization of insulin receptors in the bovine adrenal cortex and medulla.

In order to identify insulin receptors in the bovine adrenal cortex and medulla, we have studied 125I-porcine insulin binding to the membrane preparations from the bovine adrenal cortex and medulla. 125I-porcine insulin bound not only to the bovine adrenal cortex but to the medulla in time-, temperature-, and pH-dependent manners. The maximum levels of 125I-porcine insulin binding in the two tissues were observed at 4 degrees C for 24 h of incubation, and its optimum pH ranged from 7.6 to 8.0. Under these conditions, at tracer concentration of porcine insulin (200 pg/ml), 10.4% and 6.6% of 125I-porcine insulin added to each reaction tube bound specifically to 10(5) x g-pellet fractions (microsomal membrane) from the cortical tissue (0.3 mg of protein) and from the medullary tissue (2 mg of protein), respectively. 125I-porcine insulin binding was observed predominantly in the microsomal membrane from the bovine adrenal cortex, and in a 15,000 x g- pellet fraction (synaptosomal membrane) from the bovine adrenal medulla. Scatchard analysis of binding data yielded curvilinear plots in each tissue. Analysis of curvilinear plots based on two sites model revealed similar affinity constant between the cortex and medulla. Receptor concentration of the cortex was several times higher than that of the medulla. In the two bovine adrenal tissues, human proinsulin and insulin-like growth factor I (IGF-I) had about 1/100 potency compared to porcine insulin in displacing 125I-porcine insulin binding. Porcine glucagon added with concentration up to 10(-6) M did not inhibit 125I-porcine insulin binding to both the cortex and the medulla.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurohormonal peptides in the gut of the Atlantic hagfish ( Myxine glutinosa) detected using antisera raised against mammalian regulatory peptides

Concentrations of regulatory peptides in an extract of the intestine of the cyclostome, Myxine glutinosa (Atlantic hagfish), were measured by radioimmunoassay using 12 antisera of defined regional specificity that were raised against mammalian gastrointestinal peptides. The hagfish gut contained somatostatin-, cholecystokinin/gastrin-, C-terminal substance P-, and neurokinin A-like immunoreactivity in concentrations that were 10 to 100 times less than the corresponding concentrations in the rat intestine. The hagfish gut also contained glucagon-like immunoreactivity, measured with both C- and N-terminally directed antisera, but the immunoreactivity did not dilute in parallel with the porcine glucagon standard in radioimmunoassay. No immunoreactivity was detected using antisera to calcitonin gene-related peptide, gastrin-releasing peptide, neuromedin U, neurotensin, N-terminal substance P, and vasoactive intestinal polypeptide. The somatostatin-like immunoreactivity in the hagfish gut was resolved by HPLC into components with the retention times of somatostatin-34 and somatostatin-14, previously isolated from the hagfish islet organ (relative abundance 2:1). The retention times of hagfish glucagon and of the multiple molecular forms of the tachykinin-like peptides were appreciably different from the retention times of the corresponding mammalian peptides.

Effect of glicentin-related peptides upon the secretion of insulin and glucagon in the canine pancreas.

In order to clarify responses of the endocrine pancreas to glicentin, four glicentin-related peptides were investigated in a local circulation preparation of the canine pancreas. These peptides were administered in a dosage of 200 pmole for 10 min into the pancreaticoduodenal artery under the continuous infusion of 0.5% arginine solution. In a group of six dogs, the administration of glicentin-related pancreatic peptide (GRPP) and glicentin 1-16 resulted in an increase in plasma insulin (IRI) and a decrease in plasma glucagon (IRG). In the other group of six dogs, the administration of glicentin 62-69 induced an increase in plasma IRI and a decrease in plasma IRG. Following the successive infusion of oxyntomodulin, both plasma IRI and IRG increased slightly. Porcine glucagon administered at the end of each experiment exerted a rise in blood glucose and plasma IRI in addition to an increase in plasma IRG. In comparison of the maximal responses of plasma IRI and IRG to these glicentin-related peptides, the administration of glicentin 1-16, 62-69 or GRPP elicited an increase in plasma IRI and a decrease in plasma IRG. In contrast, oxyntomodulin and glucagon increased both plasma IRI and IRG. The present study indicates that glicentin-related peptides, both the N- and C-terminal portions, affect the endocrine function of the pancreas and suggests that glicentin released by nutrient ingestion plays an important role in the enteroinsular axis.

Membrane currents elicited by porcine vasoactive intestinal peptide (VIP) in follicle-enclosed Xenopus oocytes

Membrane currents were recorded from voltage-clamped Xenopus laevis oocytes, surrounded by their enveloping follicular and epithelial cells. Porcine vasoactive intestinal peptide (VIP) generated a membrane current due to an increase in membrane conductance to K+. The VIP current was mimicked by the adenylate cyclase activator forskolin and was potentiated by phosphodiesterase inhibitors, suggesting that adenosine 3',5'-cyclic monophosphate (cyclic AMP) plays a role in mediating the response. Though resembling the follicle's responses to catecholamines and adenosine in ionic basis and apparent mechanism, the response to VIP was not blocked by catecholaminergic or purinergic antagonists, indicating the presence of a specific VIP receptor in the follicle. Among the VIP related peptides, PHM-27 generated similar but smaller K+ currents and porcine secretin and glucagon neither elicited a response nor blocked that to VIP. After treating follicles with collagenase to remove the epithelial and follicular cells the responses to VIP were either substantially reduced or abolished, suggesting that the VIP receptors and K+ channels are both located in the follicular cells.

Insulin resistance and delayed clearance of peptide hormones in cirrhotic rat liver.

Clearance of porcine insulin, glucagon, and human growth hormone was measured in intact perfused cirrhotic and normal rat livers. Binding and degradation of 125I-insulin by hepatocytes isolated from cirrhotic and normal livers were also studied. The half-lives (t1/2) of immunoreactive insulin and glucagon were 14.0 +/- 3.1 and 9.6 +/- 2.1 min in normal livers and 26.0 +/- 6.1 and 25.0 +/- 7.1 min in cirrhotic livers (P less than 0.001). Insulin binding and degradation by hepatocytes from control and cirrhotic livers showed no significant differences. Intraportal insulin infusion in perfusion studies suppressed glucagon-stimulated increases in glucose output from control livers but failed to suppress glucose production by cirrhotic livers, suggesting the presence of hepatic insulin resistance in cirrhosis. Impaired clearance of insulin and glucagon by the intact cirrhotic liver and normal binding and degradation of insulin by isolated hepatocytes suggest that factors such as intrahepatic fibrosis and shunting and postbinding defects may be responsible for the impaired hormone clearance and hepatic insulin resistance.

Mitochondrial function after acute alteration of the endogenous insulin-to-glucagon ratio

Mannoheptulose (2g/kg i.p.) increases serum glucagon and decreases serum insulin via its effect on pancreatic islet cells. These changes in endogenous hormone status had effects on rat liver mitochondria that were comparable to the effects of injecting porcine glucagon (0.5 mg/kg i.p.). Mitochondrial adenine nucleotide content was increased 38 or 39% by mannoheptulose or glucagon respectively, citrulline synthesis by 165 or 193%, pyruvate carboxylation by 113 or 135%, coupled respiration by 34 or 42%, and uncoupled respiration by 40 or 54%. We conclude that the reciprocal changes in endogenous insulin and glucagon brought about by mannoheptulose offer a useful and interesting alternative to glucagon injection for studying the effects of these pancreatic hormones on liver mitochondria.

Guinea pig glucagon differs from other mammalian glucagons.

Mammalian glucagon is thought to be highly conserved. Glucagons from pig, cow, human, rat, and hamster have identical amino acid sequences, whereas the amino acid contents of rabbit and camel glucagons are consistent with this 29-amino acid sequence. It had earlier been reported that guinea pig (GP) glucagon contains 40 amino acids. In the current study, glucagon was purified from two GP pancreata by a series of three HPLC steps after acid-alcohol extraction and acetone precipitation. GP glucagon is a 29-amino acid peptide that differs from other mammalian glucagons by substitution of Gln for Asp in position 21, Leu for Val in position 23, Lys for Gln in position 24, Leu for Met in position 27, and Val for Thr in position 29. In view of the marked changes in the COOH-terminal of GP glucagon, receptor binding studies were performed using both rat and GP liver membranes. Labeled synthetic porcine glucagon has similar binding in the two systems and its binding is inhibited to a similar degree by synthetic porcine glucagon, whereas GP glucagon is 10-fold less potent at inhibiting binding in both systems. This suggests that glucagon receptor binding sites in the GP are evolutionarily more conserved than is GP glucagon.

Isolation and structures of coho salmon ( Oncorhynchus kisutch) glucagon and glucagon-like peptide

Glucagon and a glucagon-like peptide (GLP) containing 31 amino acids have been isolated from the principal islet of coho salmon ( Oncorhynchus kisutch) by gel filtration of acid alcohol extracts followed by HPLC, and the complete amino acid sequence of both peptides has been determined. Salmon glucagon is a simple 29 residue peptide differing at 3 positions when compared to catfish glucagon and at 8 positions when compared to porcine glucagon. Salmon GLP differs at 6 positions when compared with the N-terminal 31 amino acids of the 34 amino acid catfish GLP. Both coho salmon glucagon and GLP cross-react weakly in our mammalian glucagon radioimmunoassay and therefore this technique could not be used to determine tissue content. Glucagon and GLP isolated amounted to 156 μg/g and 350 μg/g wet tissue, respectively.

Primary structure of glucagon from an elasmobranchian fish, Torpedo marmorata

Glucagon has been isolated from the pancreas of Torpedo marmorata, an elasmobranchian cartilaginous fish, and purified to homogeneity using only reverse-phase high-performance liquid chromatography. Amino acid sequence analysis indicates that the molecule differs from mammalian glucagon at position 3 (glutamic acid for glutamine), position 16 (asparagine for serine), and position 20 (lysine for glutamine). Extracts of T. marmorata intestine and brain were associated with glucagon-like immunoreactivity determined by radioimmunoassay using antisera directed against the C-terminal and N-terminal to central regions of porcine glucagon. Although elasmobranchian and teleostean fish are believed to have diverged from the main line of vertebrate evolution at about the same time, the structure of two glucagons from the teleost, Lophius americanus (anglerfish) differ from mammalian glucagon by seven and nine residues. This study supports the assertion that the structure of glucagon has been highly conserved during evolution and suggests that the considerable morphological development of the pancreas is teleosts was associated with an accelerated rate of molecular evolution.

Structure-function relationships in glucagon. Re-evaluation of glucagon-(1-21).

Glucagon-(1-21) was prepared fully synthetically as well as by carboxypeptidase A digestion of natural porcine glucagon. Neither of the two preparations had glucagon agonistic effects with regard to receptor binding or adenylate cyclase activation in purified rat liver plasma membranes. Nor did these preparations contain lipolytic activity in isolated free fat cells. A preliminary batch of glucagon-(1-21) prepared by carboxypeptidase A digestion did, however, contain 1-2% glucagon bioactivity. This activity was separated from glucagon-(1-21) by high-performance liquid chromatography and quantitatively recovered in four minor hind peaks which eluted close to but not in a position identical to the elution position of native glucagon.