Influence of Long-Term Simmondsin Administration on Thyroid Hormone Levels in Adult Rats

Abstract

Treatment of adult rats for 28 days with 0.50% of simmondsin induced a reduction of food intake of about 40%. The degree of emaciation was the same in simmondsin treated rats (SM) and pair-fed controls (PF). Diurnal variation of plasma thyroid hormone concentrations was determined. The reduction in food intake induced a decrease of mean 24 h plasma T₃, T₄ and TSH concentrations. Plasma T₄ concentrations were decreased more in SM than in PF at almost all times of the day. No difference was seen between SM and PF for plasma T₃ and TSH concentrations. Liver outer ring deiodinating activity (type I) remained unchanged compared to controls in PF and SM, but liver inner ring deiodinating activity (type III) was increased 4 fold in both SM and PF. It was concluded that the food intake reduction induced by simmondsin produced a decrease in plasma TSH concentrations which in turn reduced plasma T₄ concentrations. Decreased plasma T₄ concentrations together with an increased degradation of plasma T₃ resulted in lower plasma T₃ concentrations.

Key words

Rat - Simmondsin - Jojoba - T₄ - T₃ - TSH - Food Restriction - Liver Outer Ring Deiodinating Activity - Liver Inner Ring Deiodinating Activity