[The synthesis of secretin. VI. Purification of synthetic secretin]

Identification of secretin diastereoisomers produced during synthesis

The byproducts P-1 and P-2, which were produced during the synthesis of porcine secretin, were isolated in pure form from the crude secretin by HPLC. These were identified by a combination of amino acid analysis, enzymatic digestion, and isocratic or linear gradient reversed-phase (RP)-HPLC. The amino acid compositions of P1 and P2, determined by amino acid analysis after acid hydrolysis, were found to be the same as those of porcine secretin without distinction between L-and D-amino acids. But, HPLC of their digestive fragments with trypsin and alpha-chymotrypsin differed from that of secretin. The fragments, S7-12 of P-1 and S13-21 of P-2 were determined to be different from the corresponding fragments obtained from secretin by HPLC analysis of their digestive fragments. The amino acid composition of each acid hydrolysate, following digestion with D-amino acid oxidase, was found to have less leucine or alanine content than secretin. The HPLC analysis of the fragments from P-1 and P-2 by tryptic and alpha-chymotryptic digestion showed that they are the same as those from synthetic D-Leu10 secretin or D-Ala17 secretin, respectively. Consequently, P-1 and P-2 are concluded to be the secretin diastereoisomers, D-Leu10 and D-Ala17 secretin, respectively.

Improvements in the synthesis of secretin by the repetitive excess mixed anhydride (REMA) method

Protected secretin, a 27-peptide amide, was synthesized by the all-repetitive excess mixed anhydride (REMA) method and purified by preparative reverse-phase high-performance liquid chromatography. Highly potent secretin was obtained after deprotection with the aid of HF/anisole and purification by ion-exchange chromatography. The scope of the REMA-strategy is discussed in comparison with other strategies.

Secretin-induced histamine release in duodenal-ulcer patients

Because a majority of duodenal-ulcer patients responded locally to intradermal secretin, skin samples from 7 patients with duodenal ulceration and 6 patients with goitre or cholelithiasis were incubated with "tris" buffer alone and with tris buffer containing 20 C.U./ml synthetic secretin or 100 microng/ml compound 48/80. Skin from duodenal-ulcer patients released significantly more histamine than did that of controls (p less 0-01). Histological examination of skin samples from these patients showed that the number of histamine-containing mast-cells averaged 5-7 per field and dropped to 1-2 per field after incubation with secretin. It is concluded that in a certain type of duodenal ulceration intradermal secretin releases histamine from mast-cells and thus induces a local anaphylactic reaction. This might prove suitable for preclinical ulcer diagnosis and/or for detection of patients at risk of acquiring that disease.

Comparison of pancreatic responses to portal and systemic secretin and VIP in cats

This study was designed to compare pancreatic bicarbonate responses to secretin and vasoactive intestinal peptide (VIP) administered either by peripheral or portal route in 24 anesthetized cats. Continuous intravenous infusion of graded doses of secretin (rang from 0.04 to 0.68 nmol/kg per h), stimulated pancreatic volume flow and bicarbonate outputs dose dependently and not statistically differently when given into the peripheral or portal vein. VIP infused in graded doses (range from 0.60 to 9.62 nmol/kg per h) into the peripheral vein produced pancreatic volume flow and bicarbonate outputs not statistically different from those obtained with secretin. In contrast, the biological activity of VIP administered intraportally was reduced by 60% at lower VIP doses (0.60 and 1.20 nmol/kg per h) and by 40% at 2.40 nmol/kg per h, whereas at higher doses it was not significantly changed. This study provides evidence that VIP in the cat is a secretin-like full agonist of pancreatic bicarbonate secretion and that it is only partially inactivated by the liver.

The solid phase synthesis of porcine secretin with full biological activity

The solid phase synthesis of procine secretin is described. The C-terminal residue was attached to a polymeric amino support and all the Boc-amino acids, including Boc-glutamine, were coupled by a modified carbodiimide method. A preliminary test synthesis showed that the couplings of several amino acids of the N-terminal section were unsatisfactory. This problem was overcome in the main synthesis by executing all the major reactions twice. Cleavage of the peptide fromthe resin as well as the removal of all the side chain protecting groups was achieved with liquid HF. The product was purified by ion-exchange chromatography on SP-Sephadex to obtain a highly purified heptacosapeptide amide with full biological activity.

Preparation of 125I-labeled synthetic porcine secretin for radioimmunoassay

Synthetic porcine secretion was labelled by the conjugation-labelling method of Bolton & Hunter, the lactoperoxidase method, the gaseous diffusion method, and the chloramine-T method. The chloramine-T technique was adapted as routine method. Ten mug (3.27 nmol) peptide was reacted with 5 mCi of Na125I at a concentration of chloramine-T of 1.3 mmol/l. Synthetic secretin was suitable for labelling for at least eight months when stored as dry matter in nitrogen-filled glass ampoules. Purification and separation of labelled from unlabelled hormone was carried out by gel-permeation chromatography on Sephadex G-50 superfine. The labelled preparation had a specific radioactivity of 405 +/- 33 muCi/nmol (mean +/- SEM., n = 9) and was unable for six days. 6-tyrosyl-secretin took more iodine compared to porcine synthetic secretin but had lower immunoreactivity with all antisera tested.

Effects of 13-nle-motilin on salivary, gastric, and pancreatic secretions in man

Salivary, gastric, and pancreatic secretory responses to intravenous 13-norleucine-motilin (13-nle-motilin), a synthetic analog of motilin and biologically equivalent to the natural polypeptide, were studied in healthy volunteers. 13-nle-Motilin in doses of 100 ng/kg body wt/hr significantly stimulated gastric pepsin output, while H + secretion and serum gastrin levels remained unchanged. Enhanced pepsin secretion was not accompanied by an increase in gastric secretion of cyclic 3', 5'-adenosine monophosphate, nor did gastric mucosal levels of the cyclic nucleotide rise. A dose of 13-nle-motilin, which stimulated gastric pepsin output, did not exert any significant effect on salivary and pancreatic secretions.

[Pancreatic response to graded doses of synthetic secretion: comparison between intravenous and pernasal administration in man]

The response of the human pancreas to varying doses of pure synthetic secretin administered intravenously and, for comparison, 8 days later in the form of snuff was examined, intraindividually, in 10 healthy test subjects. After intubation of the stomach and duodenum and continuous instillation of radioactive vitamin B12, the recovery rate of the marker substance was measured in duodenal aspirates and employed to compute the pancreatic bicarbonate and enzyme outputs. The dose-response relationship between pancreatic bicarbonate production and varying doses of synthetic secretin administered intravenously and in the form of snuff, was good. The pancreatic response to a dose of secretin snuff was only about 1/25 of the response obtained with the same dose of secretin injected intravenously. The level of the pancreatic enzyme output remained relatively uninfluenced by varying doses of synthetic secretin.

[The effect of natural and synthetic secretin on insulin secretion (author's transl)]

The effect of natural secretin (G.I.H.) and synthetic secretin (Wünsch) on the secretion of insulin was investigated. Natural as well as synthetic secretin causes a short uniphasic release of insulin without influence on the concentration of glucose in the serum. Since the insulin releasing effect on synthetic secretin was demonstrated, it is clear, that the release of insulin by preparations of natural secretin mentioned in medical literature is not due to contamination by other peptides.