Riassunto
La produzione giornaliera di insulina da parte delle cellule beta delle isole diLangerhans corrisponde approssimativamente a 50 U di insulina. Lo stimolo per questa produzione di insulina è costituito dal glucosio che permea nelle isole. Viene preso in considerazione il ruolo degli altri esosi e dei metaboliti del glucosio nella stimolazione dell'insulinopoiesi pancreatica. Altre sostanze hanno un effetto sulla formazione di insulina da parte delle betacellule, come le sulfoniluree e un aminoacido, la leucina.
Vengono riassunti inoltre gli aspetti istologici e ultramicroscopici che si accompagnano alla sintesi ed alla secrezione di insulina da parte delle betacellule.
Sebbene la concentrazione di glucosio che penetra entro le cellule costituisca, secondo le vedute comuni, lo stimolo principale della secrezione insulinica, certamente non sono ancora note le tappe biochimiche di tale controllo. L'assimilazione glucidica da parte di preparati di tumori insulari non è eccessivamente abbondante. Vi sono motivi fondati per ritenere che nel tessuto insulare siano contemporaneamente presenti ambedue le vie metaboliche del ricambio glucidico e cioè la via diEmbden-Meyerhof e loshunt degli esoso-monofosfati. Studi istiochimici e dosaggi diretti degli enzimi hanno già dimostrato la presenza degli enzimi che sono interessati nell'una e nell'altra di queste vie metaboliche. Studi metabolici ed enzimaticiin vitro hanno messo in evidenza la presenza, nel tessuto insulare, del ciclo degli acidi tricarbossilici. Sono stati determinati inoltre, nel tessuto delle cellule insulari, parecchi enzimi interessati nel metabolismo degli aminoacidi.
Altre ricerche, attuate sull'apparato insulare di alcuni pesci, hanno dimostrato l'incorporazione della radioattività proveniente dal glucosio negli aminoacidi di una proteina che possiede molte caratteristiche dell'insulina. Allorchè la concentrazione di glucosio nel mezzo di incubazione di isole di pesce viene progressivamente aumentata, si verifica un aumento dell'ossidazione del glucosio e della incorporazione del glucosio in una proteina estraibile con etanolo acido.
Vengono presi in considerazione infine gli effetti dei vari fattori che presumibilmente influenzano la secrezione e la liberazione di insulina sotto i vari parametri metabolici del tessuto insulare. Sebbene alcuni dei processi metabolici delle betacellule siano stati ben studiati, le attuali conoscenze non permettono di chiarire le tappe attraverso le quali i vari fattori influenzano la sintesi o la liberazione dell'insulina.
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Titolo originale: FACTORS CONCERNED WITH INSULIN SYNTHESIS AND RELEASE pubblicato in METABOLISM13, 407, 1964 e tradotto integralmente per gentile concessione dell'Autore e dell'Editore.
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Field, J.B. Fattori aventi rapporto con la sintesi e la liberazione di insulina. Acta diabet. lat 1, 283–297 (1964). https://doi.org/10.1007/BF01458420
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DOI: https://doi.org/10.1007/BF01458420