A B S T R A C T To better understand why plasma immunoreactive insulin (IRI) concentration is high in the rat fetus during the last 3 d of gestation and why fetal hyperinsulinemia abruptly subsides after birth, insulin secretion and metabolic clearance rates were estimated in fetuses and nursed pups.Intravenously injected ['251]monoiodoinsulin was cleared from the plasma of prematurely delivered pups at least as rapidly as from that of 7-to 10-d-old pups, suggesting that fetal hyperinsulinemia is not a result of slow clearance of the hormone. The fetal liver bound 35% of the injected label within 3 min, and binding was saturable. The uptake of radioactivity by *the fetal kidney was nonsaturable and much lower than that of adult rat kidney.Isolated fetal islets were already reactive to glucose on the 19th d of gestation. Pancreatic insulin secretory capacity was estimated by measuring (a) the insulin release of isolated islets incubated in the presence of 2.8 mM glucose, (b) the insulin content of the same islets, and (c) the total insulin extracted from the pancreas, using the formula (a x c)lb. 2 d before birth, the pancreatic insulin secretory capacity was high, accounting for fetal hyperinsulinemia. It was even higher after birth, not accounting for the postnatal decrease in plasma IRI concentration.Pups delivered by caesarian section 1 d before term exhibited a brisk decrease in plasma IRI concentration when the cord was cut. By contrast, if the feto-placental unit was removed from the dam, maintaining fetal Parts of this work were presented at The 13th Annual

Purified carrier-free 125I-insulin was injected into the vitelline vein of rat fetuses in utero after 17, 19 or 21 days of a 22-day gestation. Three minutes later, the weight and radioactivity of various organs and the remaining carcass were measured. A radioactivity concentration index was calculated by dividing the specific activity of each organ by that of the whole feto-placental unit. In each of the three age groups studied, the gastrointestinal tract radioactivity concentration indices were 1.7, 2 and 1.9 respectively, indicating that the gastrointestinal tract concentrated the labelled hormone. Three, 9 and 15 min after 125I-insulin injection, the gastrointestinal tract was removed, homogenized and chromatographed on a G-50 fine Sephadex column. At 3 min, 91.4% of gastrointestinal tract radioactivity co-eluted with a standard of 125I-insulin. At the later time intervals studied, the percentage of 125I-insulin decreased while that of low molecular weight degradation products increased. Quantitative autoradiographic study of the fetal gastrointestinal tract indicated that epithelial cells bound 125I-insulin and that this binding was inhibited by co-injection of large amounts of unlabelled insulin. 125I-insulin binding was highest in the proximal small bowel and lowest in the colon. Insulin binding did not appear to depend upon degree of cell maturation or cell type. These results indicate that the epithelium of the gastrointestinal tract is characterized by the presence of numerous insulin receptors and is a potentially important insulin target.

Summary1. The drug HA-966 (1-hydroxy-3-amino-pyrrolidone-2), which chemically resembles the cyclic form of GABA, has been studied for neuro-pharmacological properties and for effects on the catecholamine content of the corpus striatum. 2. The acute effects on spontaneous behaviour of rodents included flaccid catalepsy and reversible tranquillization in doses which were 5% or less of the lethal dose. Long lasting depression of the CNS, followed by complete recovery, was produced in the cat and the dog. In the monkey HA-966 caused periodical sleeping episodes. 3. The exploratory behaviour and the amphetamine-induced motor activity in mice were blocked by HA-966. The toxicity of amphetamine in aggregated mice was only moderately reduced, suggesting that HA-966 differs from neuroleptics. 4. Tremors induced by chemical agents (nicotine, zinc and tremorine) were markedly inhibited by HA-966. The muscarinic effects of tremorine were not reduced by HA-966, indicating a selective central antitremor effect. 5. HA-966 elevated the threshold to strychnine convulsions and abolished the ipsilateral flexor reflex, while not having motor endplate blocking properties. It is suggested that HA-966 depresses central internuncial neurones. 6. In rats and rabbits HA-966 produced synchronous EEG and inhibited the sensory arousal in doses not causing sedation. In the monkey the drug caused a periodical dissociation between 'sleep-EEG' and behaviour. 7. In rat brain, HA-966 selectively elevated the dopamine content in the corpus striatum, while no changes in noradrenaline and 5-hydroxytryptamine contents could be demonstrated. The effect was still present when dopa synthesis was inhibited with a-methyl-p-tyrosine. 8. Several effects of intravenously administered HA-966 became manifest after an appreciable delay and in hepatectomized mice the effects were much reduced. It is postulated that HA-966 is converted to a pharmacologically active metabolite.HA -966, drug for extrapyramidal diseases 9. The results are discussed in the light of current views on drug therapy in extrapyramidal conditions and a GABA-related hypothesis as to the mode of action of HA-966 is presented.

Summary. Insulin, biosynthetic human proinsulin and 2 human proinsulin conversion intermediates, des (64, 65) human proinsulin and des (31, 32) human proinsulin, were labelled with 123 I and the derivatives monosubstituted on Tyr A14 were purified by reverse phase high performance liquid chromatography. The four tracers were injected into anaesthetized rats via a jugular or a portal vein and time activity curves were generated for the liver and kidneys using a gamma camera and an online computer. Liver extraction coefficients varied in the order insulin (38%), des (64, 65) human proinsulin (11.7%), des (31, 32) human proinsulin (3.2%), human proinsulin (1.6%); whereas half-life of hepatic activity varied in the reverse order, from 6 rain for insulin, to 45 min for human proinsulin. As expected for a non-receptor mediated process, kidney extraction varied conversely to liver extraction, being highest for human proinsulin and lowest for insulin. It is concluded that the kinetics of human proinsulin conversion intermediates depends upon the site of cleavage and deletion and is intermediate between those of insulin and intact human proinsulin.Key words: Biosynthetic human proinsulin, conversion intermediates, 123-I-labelling, scintillation scanning.Most of proinsulin is converted to insulin inside the B cells of the pancreas, a process resulting from the interplay of several endopeptidases, different from trypsin itself [1][2][3]. Recently, two distinct site-specific endopeptidases regulated by calcium concentration and pH were identified in a B granule fraction of rat insulinoma [4]. During proinsulin processing, conversion intermediates are formed, in particular the split products des (64, 65) human proinsulin (HPI) and des (31, 32) HPI. These intermediates and intact HPI have been found in human sera [5], in insulin producing islet cell tumours [6-81 and in familial hyperproinsulinaemia [9-111. Conversion to intermediates or insulin does not seem to occur after proinsulin enters the blood stream; partial conversion to intermediates might occur in the skin after subcutaneous injection [121.From the standpoint of biological activity, proinsulin has remarkable characteristics. Compared to insulin, HPI has a low biological potency, a low avidity for insulin receptors and a prolonged half-life [13][14][15][16][17]. Moreover, the proinsulin conversion intermediates have been shown to exhibit greater biological activity than proinsulin itself, and this is particularly true for the conversion intermediate in which the C peptide/A chain bond has been cleaved. Peavy et al. demonstrated that cleavage and/or dibasic amino acid deletions in the connecting peptide region of proinsulin enhance the receptor binding and hypoglycaemic activities of these compounds. In these studies, C peptide/A chain split products exhibited greater receptor affinity and hypoglycaemic activity than B chain C peptide split intermediates [18]. These observations prompted us to investigate the hepatic extraction and processing of HPI and its conver...

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