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We have used the polymerase chain reaction with mixed sequence primers to generate a probe for rat amylin and have used this to detect expression in various rat tissues. Amylin mRNA is found in greatest concentrations in the pancreas where a single mRNA species can be detected giving a hybridisation signal intensity approximately 10% that of insulin mRNA. When the beta cell population was depleted with streptozotocin, both amylin and insulin mRNAs were reduced to a similar extent. Consistent with its supposed role in the control of carbohydrate metabolism, amylin mRNA was also found in the stomach. Unlike the related peptide, CGRP, amylin mRNA is not present in the thyroid and is not widely distributed in the central nervous system. The only nervous tissue in which it could be detected was the dorsal root ganglion. Surprisingly, amylin mRNA was also found in the lung though only at very low levels.

Summary. The response of the islet amyloid polypeptide gene to chronic dexamethasone treatment in adult rats was investigated. After 12 daily injections, rats were severely underweight and fasting blood glucose levels were elevated. When pancreatic mRNA was analysed, a 16-fold elevation in islet amyloid polypeptide mRNA was observed with only a fourfold increase in insulin mRNA levels. Pancreatic islet amyloid polypeptide and insulin mRNA levels were also determined 12 days after streptozotocin treatment. In these rats, which were not severely diabetic, the reduction in islet amyloid polypeptide mRNA levels was sixfold less than the reduction in insulin mRNA levels. In both these models of diabetes the ratio of islet amyloid polypeptide to insulin mRNA levels was raised. This would not be expected if the physiological role of islet amyloid polypeptide is as a simple hyperglycaemic agent opposing insulin action or release.Key words: Islet amyloid polypeptide, amylin, Type 2 (noninsulin-dependent) diabetes mellitus, mRNA, streptozotocin, dexamethasone, rat.A 37 amino acid peptide with homology to calcitonin gene related peptide (CGRP) has recently been characterised from the pancreatic amyloid deposits of a Type 2 (non-insulin-dependent) diabetic patient [1] and from an insulinoma [2]. This peptide is now known as islet amyloid polypeptide (IAPP) [2], or amylin [3]. IAPP opposes the action of insulin on isolated muscle preparations [3] and inhibits insulin release from rat islets in vitro [4]. Using a cloned DNA probe representing the rat IAPP coding sequence, we have recently found IAPP to be present in the stomach as well as the pancreas [5]. A variety of evidence thus suggests that this peptide may play an important role in the control of carbohydrate metabolism. We therefore decided to study the expression of the IAPP gene in the rat pancreas after treatment with agents known to affect carbohydrate metabolism. In particular, we wanted to know whether IAPP and insulin levels could be regulated independently and whether induced peripheral insulin resistance would lead to changes in the pancreas which might have relevance to amyloid deposition in man. Materials and methods Drug treatmentsAdult male Wistar rats of 125-150g were divided into 3 groups: (1) controls (n = 5) fed ad libitum on standard rat chow, (2) dexamethasone (n = 5) 2 mg/kg injected i.p. each day for 12 days, and (3) streptozotocin treatment (n =24) 60 mg/kg injected i.v. 12 days prior to analysis. After treatment, rats were starved overnight and killed by cervical dislocation after ether anaesthesia. Blood was taken for glucose measurements and the pancreas was dissected and frozen under liquid nitrogen for RNA extraction. RNA analysisTotal RNA was prepared from the frozen tissues and analysed by Northern blotting with rat IAPP and insulin probes as previously [5]. However, to minimise handling, polyadenylated RNA was not purified in the present experiments and 30 ~g of total RNA was loaded onto each track of these gels. Stringent washing conditi...

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