René Maier

[Structure-activity relationship of human calcitonin. III. Biological activity of synthetic analogues with shortened or terminally modified peptide chains (author's transl)].

Assays of 8 synthetic analogues of human calcitonin in rats showed that their hypocalcaemic activity was drastically reduced by deletion of the C-terminal amide group, chain-shortening or opening of the disulphide ring, but unaffected or enhanced by modification of the N-terminal amino group.Assays of 8 synthetic analogues of human calcitonin in rats showed that their hypocalcaemic activity was drastically reduced by deletion of the C-terminal amide group, chain-shortening or opening of the disulphide ring, but unaffected or enhanced by modification of the N-terminal amino group.

P2Y RECEPTOR SUBTYPES DIFFERENTIALLY COUPLE TO INWARDLY-RECTIFYING POTASSIUM CHANNELS

Subtypes of P2Y receptors are well characterized with respect to their agonist profile but little is known about differences in their intracellular signalling properties. When expressed in Xenopus oocytes, both P2Y2 and P2Y6 receptors effectively couple to endogenous Ca2+‐dependent Cl−‐channels. However, only P2Y2 receptors increased currents mediated by inward‐rectifier K+ channels of the Kir3.0 subfamily. This incrase in Kir‐current was sensitive to pertussis toxin, while activation of Ca2+‐dependent Cl−‐channels was not. In contrast, suramin, a P2 receptor antagonist, inhibited activation of both channels. These observations suggest that, in contrast to P2Y6, P2Y2 receptors couple to two different classes of G proteins.

Identity of calcitonin extracted from normal human thyroid glands with synthetic human calcitonin-(1–32)

Calcitonin in human thyroid glands obtained at autopsy from normal subjects were extracted with 2 M acetic acid. The extracts were additionally purified by adsorption to Sep-Pak C18 cartridges, and calcitonin was identified after gel filtration analysis, reverse-phase high-performance liquid chromatography (HPLC), thin-layer chromatography and isoelectric focusing. The purification steps were monitored by radioimmunoassay, and partially purified calcitonin was used for biological and physicochemical comparison with synthetic human calcitonin-(1-32) and its Met8-sulfoxide form. On gel filtration analysis a predominant peak coeluted with the synthetic hormone, and on HPLC two discrete peaks with the retention times of monomeric and dimeric human calcitonin were found. Thin-layer chromatography allowed the detection of two peaks with the Rf of human calcitonin-(1-32) and of its sulfoxide, respectively. The pI (7.9) of the predominant peaks of synthetic calcitonin were identical. Our findings provide strong evidence that the predominant forms of human calcitonin extracted from normal thyroid glands correspond to synthetic calcitonin-(1-32) and to dimeric calcitonin.

ANALOGUES OF HUMAN CALCITONIN: IV. INFLUENCE OF LEUCINE SUBSTITUTIOS IN POSITIONS 12, 16 AND 19 ON HYPOCALCAEMIC ACTIVITY IN THE RAT

The replacement of the three aromatic amino acids in positions 12, 16 and 19 of human calcitonin (HCT) leucine residues, which occupy the corresponding positions in ultimobranchial, e.g. salmon and eel, calcitonins, increased the hypocalcaemic potency of the peptide, as determined by bioassay on the rat, about 10‐fold. The individual substitutions were not all equally augmentative: leucine (12) enhanced the activity of HCT about 4‐5 times, but leucine (16) and (19) afforded no increase at all. Combination of leucine (12) with a deamino cysteine at the N‐terminmus yielded an analogue 10 times more potnet than HCT. Another analogue containing valine in position 8 in place of methionine as well as the three leucine substituents in position 12, 16 and 19 proved more active than the tri‐leucine analogue, but the additional introduction of tyrosine (22) nearly doubled the hypocalcaemic potency of the latter. The duration of the hypocalcaemic effects of the substituted peptides closely followed the changes in potency.

Analogues of human calcitonin I. Influence of modifications in amino acid positions 29 and 31 on hypocalcaemic activity in the rat

The principal sites of calcitonin biosynthesis are the C-cells of the thyroid gland in mammals and the ultimobranchial body in birds, reptiles and fish. The amino acid sequences of the thyrogenic calcitonins from four species are known and two, the human [l] and the porcine [2] hormones, have been synthesized [3,4,5]. Attempts to elucidate the sequence of and synthesize ultimobranchial peptides, on the other hand, have up to now only succeeded in the case of salmon calcitonin [6,7], though others have been isolated in highly purified form. The calcitonins so far obtained from ultimobranchial glands exhibit greater biological activity in rat assays than dhose of thyroid origin [8]. This must be attributable to some particular amino acids, since the sequential differences between the thyroid hormones, which are all roughly equal in activity, are as great or even greater than the differences between them and the ultimobranchial peptides.

Steroidogenic and lipolytic effects of cannabinols in the rat and the rabbit.

Abstract † 9 - Tetrahydrocannabinol (Δ9-THC), Δ8-tetrahydrocannabinol (Δ8-THC) and dimethylheptyl- Δ6a–10a-tetrahydrocannabinol (dimethylheptylpyran, DMHP) deplete the adrenals of cholesterol ester and ascorbic acid and increase the plasma concentrations of corticosterone and unesterified fatty acids in intact rats. These effects are similar to those evoked by adrenocorticotropic hormone (ACTH) and are abolished after hypophysectomy. In rabbits, however, the cannabinols increase neither unesterified fatty acids nor plasma cortisol levels, although responsiveness to exogenous ACTH was well established. It is suggested that the apparent discrepancy between the results obtained in the two species might be due (a) to the greater handling stress in the rabbit, and (b) to the fact that cortisol exerts a stronger inhibitory effect than corticosterone on the hypothalamic feed-back mechanism regulating the secretion of ACTH.

Effects of Various Hypolipidemic Drugs on Fatty Acid Composition of Liver and Serum Lipids

1. Treatment of rats with hypolipidemic drugs elicited an increase in oleic and a decrease in linoleic acid content in cholesterol esters, triglycerides and phospholipids of serum and liver lipids. 2. The change was most pronounced in triglycerides followed by cholesterol esters and phospholipids. 3. The shift was dose-dependent, starting with doses eliciting hypolipidemic effects. 4. The shift became obvious immediately after beginning of treatment and reached after 4 days a new steady state. 5. This effect was shared by both drugs of aryloxy fatty acid structure, but was not seen with either L-thyroxine or nicotinic acid. 6. The mechanism underlying this phenomenon is thus far unknown, but in our view it merits further attention.

Effect of al-chlorophenoxyisobutyrate (alufibrate) on pyruvate metabolism and on the fate of very low density lipoprotein lipids in hyperlipidemic patients

Abstract he exhalation of total CO2 and 14 CQ2 after an intravenous injection of either [1-14C]- or [2-14C]pyruvate was measured in six male patients with type IV hyperlipidemia who had previously been receiving treatment with alufibrate or placebo. Considerably more 14 CO2 was exhaled after the injection of [1-14C]pyruvate than after the injection of [2-14C] pyruvate. Treatment with alufibrate only slightly diminished the oxidation of [1-14C]-pyruvate, but increased the oxidation of [2-14C] pyruvate to 14CO2 by 25%. The total concentrations of [2-14C] pyruvate and its incorporation into the lipids of lipoprotein fractions were measured over 24 h. Alufibrate treatment decreased the serum concentration of VLDL by 53%, by reducing the turnover rate by 25% and increasing the net removal rate by about 30%. No effects on LDL and HDL lipid fractions were detected.