THEROLESOFEXCESSIODINEANDGOITROGENICFOODSINTHYROID FUNCTIONANDGLUCOSEHOMEOSTASISINWISTARRATS

Abstract

Iodineisessentialforthyroidhormonesynthesis.Excessiveconsumptionof goitrogenicfoodslikesoybeans(GlycinemaxLinnaeus)andcassava(Manihot esculenta Crantz)which are staple foods in WestAfrica can resultin hypothyroidism.Increasediodineconsumptionwasproposedtoameliorate deleterious effects of goitrogenic foods on the thyroid but excessive consumptioncanleadtohyperthyroidism andhypothyroidism whichalters glucosehomeostasis.Thereishowever,limitedinformationontheeffectof excessiveiodineandgoitrogenicfoodcombinationonglucosehomeostasis. Therefore,thisstudywasdesignedtoinvestigatetherolesofexcessiodineand concurrentgoitrogenicfoodintakeonthyroidfunctionandglucosehomeostasis inrats. Cassavatuberswerepeeled,grated,fermentedandroasted.Soybeanseeds wereboiled,dehulledandsun-dried.Sixtymalerats(90-120g)weredivided intothreegroups(n=20);1(StandardRatFeed(SRF),2(30%soybeans)and3 (30%cassava).Eachofthethreegroupsconsistedoffoursubgroups(n=5);A (Non-diabeticwithoutiodine),B (Non-diabetic+iodine),C (Diabeticwithout iodine)andD(Diabetic+iodine).10mgofiodine/kgoffeedwasadministered. The rats were fed ad libitum according to theirgroups throughoutthe experiment.Diabetes mellitus was induced with intraperitonealalloxan monohydrate(150mg/kg)after6weeksoffeedingandtheratswerefedfor twomoreweeks.Onthelastdayoftheexperiment,oralglucose(1.75g/kg) wasadministeredandglucosetolerancewasassessedusingglucoseoxidase method.InsulinresistancewasmeasuredbyHomeostaticModelAssessment ofInsulinResistance(HOMA-IR).Serum triodothyronine(T3),thyroxine(T4), Thyroid Stimulating Hormone (TSH),thyroglobulin and thyroperoxidase antibodiesandfastinginsulinlevelswereassessedusingELISA.Datawere analysedusingdescriptivestatisticsandANOVAatα0.05. IndiabeticratsfedwithSRF,iodineintakeincreasedbloodglucoselevelsafter 30minutes(386.67±7.74vs496.83±5.73mg/dL),60minutes(332.00±3.47vs 495.83±4.27mg/dL),90minutes(352.17±3.51vs428.83±10.66mg/dL)and 120minutes(342.83±6.33vs447.00±4.66mg/dL)ofglucoseingestion.Innon -diabetic rats fed with 30% soybeans,iodine treatmentincreased blood glucose levels after120 minutes ofglucose ingestion (99.67±1.98 vs 114.00±3.41mg/dL).Iodineconsumptionincreasedfastingbloodglucose levelsindiabeticratsfedwith30% cassava(279.83±8.73vs304.50±5.38 mg/dL).Consumptionof30%soybeanscausedincreasedbloodglucoselevels indiabeticrats(342.83±6.35vs412.17±10.11mg/dL)butlowerbloodglucose vi levelswereobservedwithconsumptionof30% cassava(347.83±6.35vs 279.83±8.73mg/dL).Cassavaintakecausedinsulinresistance(4.8)indiabetic rats.Iodineintakeloweredinsulinlevelsinnon-diabeticratsfedwithSRF (1.48±0.16vs0.45±0.09IU/mL)andcassava(5.63±0.03vs0.43±0.17IU/mL). IndiabeticratsfedwithSRF,iodinetreatmentreducedT4andincreasedTSH concentrations(T4: 11.75±0.21 vs6.75±0.22 mg/dL,TSH:2.28±0.08 vs 3.08±0.15 IU/mL).Intake of30% soybeans increased serum T3 levels (2.98±0.26vs6.75±0.06ng/mL)andconcurrentiodinetreatmentloweredT3 levels(6.75±0.06vs2.90±0.91ng/mL)innon-diabeticrats.Thyroglobulinand thyroperoxidaseantibodieswereabsentinalltherats. Consumptionofgoitrogenicfoods;soybeansandcassavawithexcessiodine causedhyperglycaemiaandsuppressedthyroidfunctioninwistarrats.